Chemistry, 8th Edition Jill Robinson Instructors Manual

Instructor’s Resource Manual

LABORATORY MANUAL Sandra Chimon Rogers National University of Health Sciences With Contributions by Stephanie Dillon, Florida State University Barbara Mowery, York College of Pennsylvania

CHEMISTRY Eighth Edition Jill K. Robinson John E. McMurry Robert C. Fay

Table of Contents To the Instructor

v

1)

Measurement and Expression of Experimental Data

1

2)

A Submarine Adventure: Density Saves the Day

13

3)

Conservation of Matter

21

4)

Plop, Plop, Fizz, Fizz: The Mass Percent of NaHCO3

28

5)

Proof of Alcohol

35

6)

Empirical Formula of a Compound

42

7)

Pancake Mix as a Limiting Reactant?

48

8)

Redox Reactions in Voltaic Cells: Construction of a Potential Series

56

9)

Reactions in Aqueous Solutions: Strong Acids and Bases

62

10)

The Copper Cycle

68

11)

Atomic Spectra

75

12)

Colligative Properties of Solutions

82

13)

Building Molecular Models

92

14)

Calorimetry and Hess’s Law

99

15)

Gas Laws and Airbags

107

16)

Intermolecular Forces and the Triple Point of CO2

113

17)

The Purification of Water

120

18)

Kinetics: The Iodine Clock

129

19)

Photometric Determination of an Equilibrium Constant

136

20)

Analysis of Vitamin C in Fruit Juices By Titration

143

21)

Murder Solved by the Analysis of a Kiss

148

iii

22)

Entropy, Free Energy, and Chemical Equilibrium

153

23)

Electrochemistry: The Nernst Equation

160

24)

Qualitative Analysis: Anions

167

25)

Qualitative Analysis: Cations

173

26)

Qualitative Analysis: Cations, Anions, and Complex Ions

179

27)

Whodunit? A Forensic Investigation

186

28)

Chemical Structure and Smell

193

29)

Proteins, Carbohydrates, and Fats: Analysis of a Peanut

202

iv

To the Instructor: This manual is for you, the instructor. It was designed in a way that you are able to get insight into the labs and have a clear sense of purpose catered and designed for your students without you having to do an obscene amount of prep-work. I have included a section of notes, some insight, a great background, and solutions and also a rubric to ease every instructor’s troubles. The rubric will not only allow you to grade with ease and confidence but also allow you to quantitatively and qualitatively compare your students’ results with fellow colleagues from around the nation, if they are using the same lab manual.

Another wonderful thing about this manual is if you have no assistance for grading your lab worksheets or if you do what I do and that is utilize the help of my dear husband, who knows nothing about chemistry, this manual and its solutions make it easy for someone to assist you in grading. In addition to ease of grading, the labs are designed in a way that you can easily transit from a worksheet format to a lab report. The manual is designed in a way that they if the students need the crutches, they are there.

I wanted to show you that the students can learn without realizing that you are learning. The emphasis here is that chemistry experiments are not just your stereotypical beaker and Bunsen burner experiments. They can be fun, real-life based, and educational. The experiments are based on such topics from air bags to a murder investigation.

There are real-life situations which utilize chemistry as a way to ask a question and solve it.

Reemphasizing that the focus is you, the instructor, not only are these experiments more fun, the lab manual is designed to help you get through the experiment and the lab write-up. The lab manual is designed to have a well thought out, articulate an introduction to capture the interest of our students along with the instructors, a step-by-step list of instructions on what to do and why you are doing the experiments, to a nice follow-up which ensures critical thinking. The questions at the end of the experiment are designed to help you collect, interpret, and analyze the data.

Not only will the students be questioning the data but they are also starting the means to writing up a thought-provoking chemistry lab report by simply following the format of the questions at the end of the experiment.

Let’s not look at chemistry labs as that dreaded class everyone has to take, but get it out of its rut and let this manual be your guide to show the students that chemistry can be fun! Chemistry should be fun because without chemistry, we couldn’t have fireworks, electric cars, and makeup.

Now let the fun begin. Let’s take what we are learning in the classroom and apply it in the lab.

Warmest regards, Dr. Sandra Chimon Rogers Associate Professor of Physical and Natural Sciences Dean of College of Professional Studies National University of Health Sciences

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v

Experiment 1: Measurement and Expression of the Experimental Data Instructor Notes and Lab Preparation Each fall and spring semester a week after school starts, things are hectic, students are still registering for classes, and some sort of holiday interrupts the first week of labs. This allows the instructors only to check in the labs but then have an off week before the students are able to start performing experiments. Rather than allow the students to waste a full week of lab time, assigning this math and graphing review as the first experiment of the semester is a great way to refresh their minds and get them back into the swing of things. Part A is designed for the first semester, and Part B is designed for the second semester of general chemistry.

As the check-in process is generally quick, at the end of the check-in day, I have each of my teaching assistants give a short lecture on the math involved.

Particular Points to Stress Scientific or exponential notation is used so often in scientific literature and calculation; it seems we sometimes forget how confusing it can be to someone dealing with it for the first time. I always stress that students should look at the values they calculate to make sure they make sense. For example, one of the most common mistakes students make when dealing with exponents is when they must change an exponent to add or subtract two exponential values. The process requires students “move the decimal” in the correct direction to “match up” the exponents. The most common mistake is the movement of the decimal in the wrong direction. So ask the students to check and make sure that the number resulting after the move still makes sense, that is, does it have the same value it did before the move? Simply plugging it into a calculator should do the trick.

Another sticky point with many students is an overall lack of graphing skills. I have placed a brief Excel® tutorial at the end of the manual to encourage students to use this program or one similar to it to complete the graphing exercises. If you choose to have your students complete the graphs by hand, I understand the reasoning, but I would encourage you to consider asking for the graphs in both styles. The reality of the world today is that computers are everywhere. Skillful use of technical programs like Excel® is a must for scientific analysis.

The most common mistakes that should be discussed with respect to graphing are (1) attempts to fit straight lines to data that do not fit y = mx + b and (2) irregular spacing of values on an axis. I often see graphs with axes that are marked at regular intervals with the values given as part of the problem. Markings of this sort always generate perfectly straight lines, which thrill the students, but give me migraines.

Last but not least, the discussion we have about logarithms and the proper use of significant figures in logarithms is generally the first exposure students will have to the subject. Special attention should be paid to the introduction of this material.

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1

Lab Report Key Exercises 1A 1) Indicate how many significant figures are present in each of the following: (a) 01.501 × 103 4 (b) 700.01 5 (c) 193005 6 –4 (d) 6.010 × 10 4 (e) 0.070 2 2) Round the following to three significant figures (put in scientific notation where necessary): (a) 151626 1.52e + 05 (b) 0.00844 8.44e – 03 (c) 0.000010350 1.04e – 05 (d) 1255 1.26e + 03 (e) 33.353 33.4 3) Perform the following mathematical operations: (a) (6.49 × 105/2) – 45.38 = 3e + 05 (b) 5.32 × 10–15 × 2.447 × 1016 = 1.30e + 02 (c) (3.15 × 10–1 – 9.7 × 10–3) × [(4.7 × 10–2)/(2.33 × 10–3)] = 6.2 (d) 1.62 × 10–3 + 8.1 × 10–4 = 2.43e – 03 (e) (0.45 + 167.6)/1.6 × 10–2 = 1.1e + 04 4) Express the following using scientific notation: (a) The Bohr radius: 0.0000000000529189379 m 5.29189379e – 11 m (b) The speed of light: 29979245.8 m/s 2.99792458e + 08 m/s (c) Charge of a proton: 0.0000000000000000001602176487C 1.602176487e – 19 C (d) Rydberg constant: 10973731 m–1 1.0973731 e+ 07 m–1 5) Calculate the following and round to the proper number of significant figures: (a) Antilog 0.485 = 3.05 (b) Ln 60 = 4.09 (c) e–1.41 = 2.4E–01 –2 (d) Log 3.975 × 10 = –1.4007 (e) Antilog 6.86 = 7.2e + 06 (f) Log 8.74 = 0.942 6) Calculate the average and standard deviation for the following set of calibration data: 3.8842, 3.8611, 3.8263, 3.8191, 3.8945, 3.8916, 3.8511, 3.8651 average = 3.8616 STDev = 0.0285

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2

7) Graph the following data and answer the questions about the resulting line.

Temperature (K) 273 283 293 303 313 323 333 343 353 363 373

Pressure (atm) 1.10 1.14 1.18 1.22 1.26 1.30 1.34 1.38 1.42 1.46 1.50

Q1: According to the graph, how would you describe the relationship between temperature and pressure (linear or nonlinear)? linear 8) Create a graph of the absorbance (optical density) versus molar concentration and answer the questions about the resulting line.

.

Concentration (M)

Optical Density (AU)

0.13

0.19

0.28

0.38

0.43

0.56

0.58

0.72

0.73

0.85

0.88

0.96

1.03

1.06

1.18

1.13

1.33

1.18

1.48

1.21

3

NOTE: The absorbance, or optical density, of a solution for a particular wavelength of light is given by log(Io/I), where Io is the incident light on a sample and I is the transmitted light. Beer’s law states that the optical density of a substance in solution is directly proportional to its concentration (i.e., it has a linear relationship). Not all substances follow Beer’s law, but a calibration graph of optical density versus concentration can still be used to measure concentrations of unknown solutions. Because optical density is a ratio, it does not have any units; the expression absorbance units is sometimes used.

Q1: Does the solution in your graph follow Beer’s law? no Q2: What is the concentration of a solution that has an optical density of 0.28? 0.20 M Q3: What is the concentration of a solution that has an optical density of 1.01? 0.95 M

9) Using the same data as problem 8, calculate the logarithm of the volume. Graph the pressure versus the log10 volume and answer the questions about the resulting line.

Q1: If this graph is a straight line, then it is of the form P = mLog10V + b, in which m is the slope, and b is the y-intercept. Is the graph a straight line or a curved line (nonlinear variation)? straight line with some slight deviation; see fit below Q2: If possible, calculate the equation of the line for the graph. Show your work.

P = –2507.3LogV + 3361.7 R² = 0.9903 Q3: Using the resulting equation from question 2, what would be the volume of a system that had a pressure of 5.4 atm?

0.51 mL

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4

10) Robert Boyle used an open-end barometer (similar to that in the figure) for the experiments, which led to the discovery of Boyle’s law, which describes mathematically the effect of pressure on the volume of a gas. He determined the nature of the law by graphing his data.

The law states that PV = constant, where P is the total pressure, which is the sum of Patm + PHg. The pressure can be measured in torr, which corresponds to the height of the mercury column in millimeters.

The following table contains some data in an experiment similar to that of Boyle’s, though the open-end manometer is considerably larger. The volume of the gas in the closed end of the tube is measured in milliliters, and the pressure recorded is PHg, the height of the column, not the total pressure.

Pressure (torr) 45 149 226 303 372 455 523 607 720

Volume (mL) 21.7 19.1 17.6 16.3 15.3 14.2 13.5 12.6 11.7

You are to analyze this data by graphing it, discovering that a direct graph (V vs. P) gives a curved line. Scientists often try manipulating data to give a straight line, and when the data is regraphed as P vs 1/V, you will see that a straight line is produced, revealing the nature of Boyle’s law (that pressure and volume are reciprocally related). Further analysis of this straight line will also reveal the atmospheric pressure at which the measurement is made.

Since PtotalV = constant Ptotal = constant(1/V) Patm + PHg = constant(1/V) PHg = constant(1/V) – Patm the graph is of the form y = mx + b, where the slope, m, gives the value of the constant, and the P-intercept is the negative of the atmospheric pressure.

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5

Q1: What is the slope of the line (i.e., the constant in the Boyle’s law equation)? Give units in your answer. 1.70E + 04 torr•mL Q2: What is Patm (i.e., the negative of the P-intercept)? Give units in your answer. 7.40e + 02 torr 11) The following data was used to calibrate a spectrometer. Graph the data and answer the questions regarding the resulting line.

Known Wavelength (nm) 388.9 488.6 501.6 587.6 667.8 706.5

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Spectrometer Reading (absorbance units) 3.47 4.43 4.56 5.38 6.15 6.52

6

Q1: Add a best-fit line and calculate the equation for that line. y = 0.0096x – 0.2596 R² = 1 Q2: You have collected some more data using the above spectrometer. Use either the graph or the equation of the line to “correct” the data you have collected.

Experimental Spectrometer Reading (absorbance units) 5.82 4.27 4.00 6.18

Corrected Wavelength (nm) 633 472 444 671

Exercises 1B 1) Consider the following experiment in which you wish to determine the molarity of the concentrated HCl in your new bottle of reagent. You carefully measure out 100.0 mL of the concentrated acid and dilute it to 1.000 L (in a 1 L volumetric flask). You then use a 5.00 mL volumetric pipette to remove 7 aliquots for titration with 0.1045 M sodium hydroxide solution.

The following are the volumes of base needed for each sample.

59.0 mL, 58.8 mL, 59.2 mL, 58.9 mL, 58.9 mL, 59.1 mL, 57.9 mL Calculate Qexp for both the maximum and minimum values in this data. (a) QCalculated for 59.2 mL = 0.077 (b) QCalculated for 57.9 mL = 0.692 (c) Can you reject 59.2 mL with 90% confidence? no (d) Can you reject 59.2 mL with 95% confidence? no (e) Can you reject 59.2 mL with 99% confidence? no (f) Can you reject 57.9 mL with 90% confidence? yes (g) Can you reject 57.9 mL with 95% confidence? yes (h) Can you reject 57.9 mL with 99% confidence? yes Average your measurements (throwing out the outlier if justified with 90% confidence) and calculate the molarity of the original concentrated HCl solution. 12.3 M 2) You are asked to calibrate a 10 mL volumetric pipette by weighing to the nearest 0.1 mg the mass of water delivered by the pipette. You weigh six samples of water delivered by the pipette and convert the mass of each to volume by dividing by the density of water at 25 ºC (0.997048 g/mL). Following are your measurements: 9.9690 mL, 9.9700 mL, 10.0360 mL, 9.9650 mL, 10.0150 mL, 10.0200 mL

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Calculate the following statistical measures for this data: Mean (x) = 9.9958

Standard deviation (s) = 0.03131

Variance (s2) = 9.9958 Standard error of the mean (smean) = 0.01278 90% confidence interval = 9.9958 ± 0.0258 (The “true value” of the volume will lie within this interval 90% of the time.)

95% confidence interval = 9.9958 ± 0.0329 (The “true value” of the volume will lie within this interval 95% of the time.)

99% confidence interval = 9.9958 ± 0.0515 (The “true value” of the volume will lie within this interval 99% of the time.)

3) The table below shows some data in which the peak height of triplicate samples of a substance is listed as a function of the quantity of material injected. You would like to know first how good the precision of the method is by determining the standard deviations and confidence intervals of each set of triplicate samples. Then you would like to know whether the means of the triplicate samples show a linear relationship with sample size, and the equation for this relationship.

Gas Chromatograph Calibration Sample Peak Height (cm) Mass Trial 1 Trial 2 Trial 3 μg

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10

2.6

2.3

2.4

20

3.8

4.2

4.8

30

6.2

6.5

5.9

40

9.0

8.7

8.4

50

11.3

10.9

11.4

60

13.7

13.0

13.7

8

Q1. Using Excel or another similar spreadsheet program, graph the average peak height versus sample mass. Apply a best-fit line to the resulting graph.

Q2. Again using the spreadsheet program, calculate sample mean, variance, standard deviation, standard error of the mean, and confidence intervals for the data above.

Q3. Answer the following questions: a. For the 60 μg sample, what is the sample standard deviation and 90% confidence interval of the three peak height measurements? standard deviation = 0.404; confidence interval = 0.681 b. Excel gives the best straight line fit to the data as an equation y = mx + b. What are the slope and intercepts of this line? (Be sure to include units.) m = 0.224 g/cm; b = –0.1356 g

4) The table below contains data that were collected to create a calibration curve in which the absorbance of a substance is plotted versus samples of known concentration. Graph this data.

Known Concentration Absorbance (M) (AU) 0.10

0.115

0.20

0.260

0.30

0.485

0.40

0.790

0.50

1.175

0.60

1.640

Determine from your graph the concentrations of the following unknown solutions. (Give units.)

Solution A: 0.163 AU: 0.14 M Solution B: 0.658 AU: 0.36 M Solution C: 1.444 AU: 0.56 M

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5) The table below contains some initial reaction rate data for reaction of substances A and B at the indicated initial concentrations. The rate law for this reaction follows the form rate = k[A]a[B]b, where a and b are the reaction orders for A and B, respectively.

Experiment

Initial Conc.

(M)

Initial Conc.

(M)

[A]

[B]

Initial Rate (M/s)

Trial 1

2.0 × 10–2 4.3 × 10–3

2.2 × 10–3

Trial 2

4.0 × 10–2 4.3 × 10–3

8.9 × 10–3

Trial 3

6.0 × 10–2 4.3 × 10–3

2.0 × 10–2

Trial 4

2.0 × 10–2 8.6 × 10–3

4.5 × 10–3

Trial 5

2.0 × 10–2 1.3 × 10–2

6.7 × 10–3

Q1. Plotting log rate versus log [A] at constant [B] will give a as the slope, and plotting log rate versus log [B] at constant [A] will give b as the slope. Use a spreadsheet to determine these values. Calculate the logarithm of the concentration and rate data to enter in the spreadsheet. Use trials 1, 2, and 3 for the log rate versus log [A] plot, and trials 1, 4, and 5 for the log rate versus log [B] plot. Add trend lines to the resulting graphs and determine the slopes of the lines.

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(a) What is the reaction order for reactant A?

2

(b) What is the reaction order for reactant B?

1

Q2. The reaction rate constant (k) can be determined from the rearranged rate equation k = [(rate)/([A]a[B]b)] using data from any of the trials. The units of k will depend on the overall order of the reaction, which in this case will be a + b. (The units of k must be such that the units of the rate become M/s.) The following table gives the units for different overall orders.

Overall Reaction Order Units of k (a + b) 0

Ms–1

1

s–1

2

M–1s–1

3

M–2s–1

4

M–3s–1

What is the rate constant for the above reaction? (Include units.) 1.3E + 03 m–2s–1

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Experiment 1: Measurement and Expression of Experimental Data Section Points Points Worth Earned

Experiment 1: Measurement and Expression of Experimental Data Section Points Points Worth Earned

Title page for 1A and 1B

Title page for 1A and 1B

(name, title, date, TA, course, section, partner’s name) Purpose for 1A and 1B (at least three points) Graph for part 1A (axis, data points, labeling, title, best line fit, equation of a line, etc. )

(name, title, date, TA, course, section, partner’s name) Purpose for 1A and 1B (at least three points) Graph for part 1A (axis, data points, labeling, title, best line fit, equation of a line, etc. )

Exercises 1–11 for part 1A

Exercises 1–11 for part 1A

(show all work, graphs, tables, label the graphs properly and answer the questions in each exercise, etc.)

(show all work, graphs, tables, label the graphs properly and answer the questions in each exercise, etc.)

Exercises 1–5 for part 1B

Exercises 1–5 for part 1B

(show work for all the calculations of Qexp, mean, standard deviation, variance, standard error of the mean, confidence interval, graph with proper labels, best line fit, line of an equation, standard deviation, standard error of the mean, confidence intervals, sample mean, variance, rate of the reactions, rate constant, etc. )

(show work for all the calculations of Qexp, mean, standard deviation, variance, standard error of the mean, confidence interval, graph with proper labels, best line fit, line of an equation, standard deviation, standard error of the mean, confidence intervals, sample mean, variance, rate of the reactions, rate constant, etc. )

Total Grade

100 /

%

Total Grade

100 /

%

Experiment 1: Measurement and Expression of Experimental Data Section Points Points Worth Earned

Experiment 1: Measurement and Expression of Experimental Data Section Points Points Worth Earned

Title page for 1A and 1B

Title page for 1A and 1B

(name, title, date, TA, course, section, partner’s name) Purpose for 1A and 1B (at least three points) Graph for part 1A (axis, data points, labeling, title, best line fit, equation of a line, etc. )

(name, title, date, TA, course, section, partner’s name) Purpose for 1A and 1B (at least three points) Graph for part 1A (axis, data points, labeling, title, best line fit, equation of a line, etc. )

Exercises 1–11 for part 1A

Exercises 1–11 for part 1A

(show all work, graphs, tables, label the graphs properly and answer the questions in each exercise, etc.)

(show all work, graphs, tables, label the graphs properly and answer the questions in each exercise, etc.)

Exercises 1–5 for part 1B

Exercises 1–5 for part 1B

(show work for all the calculations of Qexp, mean, standard deviation, variance, standard error of the mean, confidence interval, graph with proper labels, best line fit, line of an equation, standard deviation, standard error of the mean, confidence intervals, sample mean, variance, rate of the reactions, rate constant, etc. )

(show work for all the calculations of Qexp, mean, standard deviation, variance, standard error of the mean, confidence interval, graph with proper labels, best line fit, line of an equation, standard deviation, standard error of the mean, confidence intervals, sample mean, variance, rate of the reactions, rate constant, etc. )

Total Grade

.

100 /

%

Total Grade

100 /

%

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Experiment 2: A Submarine Adventure: Density Saves the Day Instructor Notes and Lab Preparation Chemicals and Equipment Various metal shapes of copper, nickel, lead, aluminum, brass, iron, and magnesium 10 mL graduated cylinder 100 mL graduated cylinder Large tub of salt water (NaCl) Round balloons Disposable pipettes and bulbs ¼ ounce fishing weight egg pellets Vernier calipers Analytical balance

Preparation There is very little preparation for this lab. The glassware and equipment above should be available to each student.

I have left the shape of the unknown metal objects up to the discretion of the instructor. I have most commonly used cylinders, but even balled up wire will work. The metal unknowns should be constructed such that each metal either has a different dimension or shape or is stamped with a code to differentiate them. Some of the metals should be either too large or too oddly shaped to measure by use of the calipers so that each student must calculate the volume by difference at least once.

The concentration of the salt in the ocean water is also up to the discretion of the instructor. I would suggest a density of about 1.2 g/mL. To save money, table salt or rock salt can be used instead of reagent-grade NaCl. For the reservoir, you can use a 5 L beaker or a plastic tub.

Simply dissolve the desired amount of NaCl in distilled water to create the “ocean.” I generally have the prep person take a sample of the prepared “ocean” and calculate the density so that I have a relative value to expect from the students.

Instruction Notes This lab experiment normally takes about 2 hours for the students to complete both parts.

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Part 1 For the best results in part 1, you should separate the metal unknowns into two groups: those whose volume can be determined by calculation and those whose volume must be determined by displacement. I generally have the students take one of each for investigation. The prelab determines the possible identities of the metal unknowns. If you would like to use other metals, the densities of those metals would simply need to be made available to the students.

A key teaching point in this part of the experiment is a discussion regarding which method of volume determination is more accurate. The metals over time tend to become scratched and dented so that the volume by displacement is more accurate. But students often think that the more numbers they collect, the more accurate their data become.

Another key point is the discussion of observation to assist in the identification of the metals.

Obviously, copper and brass unknowns could probably be identified by their color alone. A discussion about how a scientist uses all of his or her senses to investigate a subject can be incorporated into the experiment.

Potential Problems The greatest difficulty can arise when the students forget the difference between diameter and radius in their calculations. A reminder at the beginning of the lab session generally keeps the students straight on this point. Also, the prelaboratory exercise should be checked to make sure that the values the students transfer into their lab notebooks are accurate enough to use for their conclusions.

Part 2 The creation of the submarine, while silly, seems to really firm up the concept of density in the minds of the students in my labs. One of the main teaching points is the relationship between the mass and volume and how a change in either can cause a shift in the density. A good discussion point is which change has a greater impact. Even though the weight of 20 quarter-ounce lead pellets is well over 100 g, the total volume of the balloon and thus its diameter is still pretty small. Because they often must adjust their sub’s volume to get a good submarine, students start to get a feel for how a very small adjustment in the volume can lead to big changes in density. A good submarine will very seldom end up floating exactly in the middle of the beaker/tub of water. A good submarine is a balloon that is completely below the water line with just the knot of the balloon touching the surface.

Potential Problems Although we use round balloons, when they are blown up, they are still fairly small and thus not quite round in shape. The best way to get a good balloon volume is to set the calipers to the measured balloon diameter desired and lay it flat on the counter or table top. Then blow the balloon up as close as possible to that diameter while pressing the balloon into as round a shape as possible. Only once the correct diameter is achieved should the balloon be tied off.

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The egg weights we use are quarter-ounce lead egg sinkers. The company we use is http://www.bulletweights.com/Products/Lead/eggsinkers.aspx. You can also use marbles to represent the passengers on the sub, but the number required to get a sufficient weight is often difficult to get into the balloon.

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Experiment 2 Prelaboratory Assignment KEY Name: ___________________________ Date: _________________ Instructor: ____________________________ Sec. #: ___________

Show all work for full credit.

1) A pycnometer with a mass of 56.96 g when empty, has a mass of 108.22 g when filled with water (density = 1.000 g/mL), and a mass of 97.56 g when filled with liquid C.

(a) What is the volume of the pycnometer? 51.26 mL (b) What is the density of liquid C? 0.7920 g/mL 2) Finding the density of solids requires a method of measuring the volume of the solid. If the solid has a regular geometric shape, the volume can be calculated from a measurement of the dimensions of the shape. Examples of three simple shapes are shown here, with the formulas for calculating their volumes.

Rectangular Block

.

Sphere

Cylinder

16

V = L W  H

4 D V =   3 2

3

2

D V =   L 2

You measure the following dimensions of a rectangular metal block of metal A: length = 10.89 cm; width = 6.49 cm; height = 1.57 cm. It has a mass of 193.07 g.

What is the density of metal A? 1.74 g/cm3 A sphere of metal B has a mass of 298.15 g and a diameter of 3.09 cm.

What is the density of metal B? 19.3 g/cm3 You measure the following dimensions of a cylinder of metal C: length = 9.49 cm; diameter = 2.35 cm. It has a mass of 469.24 g.

What is the density of metal C? 11.4 g/cm3 Metal Nickel Lead Aluminum Gold Brass Copper Iron Magnesium

Density (g/cm3)* 8.90 11.4 2.70 19.3 8.51 8.92 7.86 1.74

Based on the densities in the table, identify the unknown metals A, B, and C: Metal A = magnesium Metal B = gold Metal C = lead

3) You determine that the salt water in the tank has a density of 1.02 g/mL. The balloon weighs 2.0 g, and your weights have a mass of 30.0 g each. If you put six weights in your balloon, you must inflate the balloon to what diameter for it to have a density equal to the salt water, and therefore float in the middle of the tank?

6.98 cm

Lab Report Key The title page should include: Student’s full name Date of experiment Complete title of lab report Name of partner(s)

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Instructor’s name Lab and section number The purpose should include: This experiment deals with several subjects, including density, balance use, caliper use, and measurements of volumes and masses using balances and graduated cylinders. The purpose should include references to most of these topics and should not be a copy of what is given in the manual. Full credit can be given if at least three of the aforementioned topics are discussed.

Procedure: This should be an MLA form reference to the lab manual with any changes in the procedure noted.

Data: The data section should include all observations made during the lab of the cylinders, balloons, and anything else involved in the experiment. A data table for determining the density of a metal cylinder should also be included with the following information a) measurements of the cylinders, b) volume of both cylinders, c) mass of the cylinders d) density of the cylinders, and e) identity of unknown metals.

A second data table with the submarine data should be included. Be sure that the table includes the following information: a) mass of graduated cylinder, b) volume of ocean water, c) mass of water, d) weight of balloon with weights, e) density of ocean water, f) volume of balloon needed to match salt water density, g) final volume of submarine design, and h) final density of submarine design.

Calculations: The calculations section should have example calculations of the following: a) volume of the cylinders, b) mass of water, c) density of ocean water, d) volume of balloon needed to match salt water density, e) final volume of submarine, and f) final density of submarine. Units must be used correctly in all tables and calculations.

Conclusions: The conclusion section should be in paragraph format. This section should summarize the information in the data section. For the density of the metal cylinder section, there should be a report of the density and identity of the unknown metals. There should be a discussion of any differences in the known and unknown density and the percent error. Also any experimental errors that might have led to these differences should be discussed.

For the submarine data, a report of the density of the ocean water, the ideal volume of the submarine, and the final volume and density of the submarine should be present. A description of

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the trial and error portion of making the submarine and the differences in the ideal volume of the submarine and the final volume of the submarine should be presented. Finally, a discussion of any errors in the submarine design and the experiment should be included.

Questions: 1) Give an example of the use of density (other than submarines) that you have observed in your own life.

This could be salad dressing, hot air balloons, etc. Anything reasonable can apply.

2) What is third-person writing, and why is it used in the writing of scientific papers?

When writing, “person” refers to the point of view of the author. First person is written from the “I” point of view, second person is written from the “we” point of view, and third person is written from the “it” point of view. Because much of science is collaborative in nature, most all papers are written without personalization of the text, i.e., from the third person neutral point of view. Writing from the first or second person implies that none of the information in the paper was contingent on any research/work done previously, which is seldom true.

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Experiment 2: A Submarine Adventure: Density Saves the Day Section Points Points Worth Earned

Experiment 2: A Submarine Adventure: Density Saves the Day Section Points Points Worth Earned

Title page (name, title, date, TA,

Title page (name, title, date, TA,

course, section, partner’s name) Purpose (at least three points)

course, section, partner’s name) Purpose (at least three points)

Procedure (cited/changes) Data (observations) Table I (measurements, volumes,

Procedure (cited/changes) Data (observations) Table I (measurements, volumes,

mass, density, metal #, ID) Table II (m ass graduated cylinder, volume water, mass water, density water, mass of balloon, volume of balloon, final volume and density) Calculations (volume by displacement and measurement, density, mass of water, density of water, balloon volume needed, final volume and density of submarine) Conclusions (ID and density, differences in known and unknown values, density of ocean water, ideal volume, final volume and density, trial and error discussions, errors)

mass, density, metal #, ID) Table II (mass graduated cylinder, volume water, mass water, density water, mass of balloon, volume of balloon, final volume and density) Calculations (volume by displacement and measurement, density, mass of water, density of water, balloon volume needed, final volume and density of submarine) Conclusions (ID and density, differences in known and unknown values, density of ocean water, ideal volume, final volume and density, trial and error discussions, errors)

Questions Total Grade

Questions Total Grade

100 /

%

100 /

%

Experiment 2: A Submarine Adventure: Density Saves the Day Section Points Points Worth Earned

Experiment 2: A Submarine Adventure: Density Saves the Day Section Points Points Worth Earned

Title page (name, title, date, TA,

Title page (name, title, date, TA,

course, section, partner’s name) Purpose (at least three points)

course, section, partner’s name) Purpose (at least three points)

Procedure (cited/changes) Data (observations) Table I (measurements, volumes,

Procedure (cited/changes) Data (observations) Table I (measurements, volumes,

mass, density, metal #, ID) Table II (mass graduated cylinder, volume water, mass water, density water, mass of balloon, volume of balloon, final volume and density) Calculations (volume by displacement and measurement, density, mass of water, density of water, balloon volume needed, final volume and density of submarine) Conclusions (ID and density, differences in known and unknown values, density of ocean water, ideal volume, final volume and density, trial and error discussions, errors)

mass, density, metal #, ID) Table II (mass graduated cylinder, volume water, mass water, density water, mass of balloon, volume of balloon, final volume and density) Calculations (volume by displacement and measurement, density, mass of water, density of water, balloon volume needed, final volume and density of submarine) Conclusions (ID and density, differences in known and unknown values, density of ocean water, ideal volume, final volume and density, trial and error discussions, errors)

Questions Total Grade

.

100 /

%

Questions Total Grade

100 /

% 20

Experiment 3: Conservation of Matter Instructor Notes and Lab Preparation Chemicals and Equipment 3.0 M HCl in 1 L bottles with pour spout Bottle of anhydrous copper(II) sulfate Weighing boats Bottle of zinc metal (mossy) 50 mL volumetric flasks with stopper 125 mL flasks with side arm #4 black rubber stoppers *** DO NOT USE CORK *** 1 bag of 7 inch balloons 1 box of calipers Long tweezers Disposable pipets Parafilm 1 box of baking soda for acid spills Setup • • • •

Make sure there are Kimwipes near the balance(s).

Set out equipment and chemicals.

Place 1 bottle of HCl on each lab bench.

Place 50 mL volumetric flasks on each lab bench.

Preparation 3.0 M HCl Use 247.93 mL of concentrated HCl per 1 L of solution.

Prepare a large carboy: To prepare 12 L of 3.0 M HCl: Fill a carboy with approximately 5 L of water. Add 2.98 L of concentrated HCl (IN THE HOOD). Then dilute to 12 L with DI water (supply for 20 class sections @ 24 students). Mix well.

To prepare 6 L of 3.0 M HCl: Fill a carboy with approximately 3 L of water. Add 1.49 L of concentrated HCl (IN THE HOOD). Then dilute to 6 L with DI water (supply for 10 class sections @ 24 students). Mix well.

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Instruction Notes The conservation of matter experiment was originally developed for our nonmajors course. For that course, we prepare the copper(II) sulfate solution for the students. When we adapted the experiment for majors, we decided to have them prepare their own solution and introduce the use of volumetric glassware. If you feel your students are not ready to mix their own solution, this is an easy change that both shortens and simplifies the experiment. The experiment is very visual, as the color of the solution changes dramatically in a short period of time and the balloon is inflated to a large size. This leaves no doubt that a reaction has taken place.

Points to Stress Students are working with 3.0 M HCl. This is strong acid, and it should be stressed repeatedly that all safety precautions must be taken to avoid burns. All spills of any size should be cleaned up by lab personnel, not the students. I provide my teaching assistants with baking soda and gloves to handle the clean-up.

When the students are preparing the solution, they should weigh the CuSO4 in a weigh boat and then use a small amount of HCl to assist in transferring the salt to the volumetric flask. CuSO4 is a sticky, wet salt and thus clumps making dry transfer difficult (the neck of the 50 mL volumetric flask is small). You can also use paper funnels, but the “stickiness” of the salt may cause a loss of mass there as well. We have found that using the HCl to aid in the transfer best reduces the loss of mass and also keeps the lab benches much cleaner.

Potential Problems As mentioned above, the necks of the volumetric flasks are fairly small, so students should be shown the proper way to transfer the salt so that they don’t make a huge mess on the benches and more importantly don’t lose mass of salt.

The only other problem that sometimes occurs is a hole in a balloon or a balloon that is not securely fastened to the side-arm of the flask. Have your students blow the balloon up once before attaching it to the side-arm. This will allow them to determine if the balloon is airtight, and it also stretches the balloon so that the resistance is lowered when the reaction starts to fill it with hydrogen gas.

You might note tweezers in the list of items needed for this lab. Because our lab balances are capable of weighing only up to ~100 g of material, at the end of the lab we have to remove the pellets from the solution and weigh them separately using a tared weigh boat. If you have the same difficulty, tweezers work well as long as the students are gentle. The removal and separate measurement also reinforces the notion that the total mass of the products is what is important; not that they all remain in the same state or container.

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Experiment 3 Prelaboratory Assignment KEY Name: ___________________________ Date: _________________ Instructor: ____________________________ Sec. #: ___________

Show all work for full credit.

Prelaboratory

1) Calculate the number of moles or grams in each of the following quantities of salt.

8.745 g of Cu(NO3)2·6H2O = 3.545 g of zinc nitrate trihydrate =

0.029580 mol 0.014563 mol

2.516 × 10–2 mol of Na2SO4·10H2O = 8.105 g –2 1.198 × 10 mol of zinc nitrate hexahydrate = 3.565 g 2) You would like to make up 745 mL of a 0.23 M solution of ZnSO4·7H2O. How many moles of the salt do you need? How many grams of the salt do you need?

0.171 mol; 49.3 g You have a 0.43 M solution of Na2SO4·10H2O. What volume of the solution (in milliliters) must you measure in order to have 0.20 moles of the salt?

465 mL You have a 0.57 M solution of Cu(NO3)2·6H2O. What volume of the solution (in milliliters) must you measure in order to have 98.6 grams of the salt?

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585 mL 3) Zinc metal reacts with acid solution to produce hydrogen gas and zinc ion as follows: Zn(s) + 2H+(aq) → Zn2+(aq) + H2(g) You add 6.825 g of Zn metal to 29.0 mL of 1.70 M HCl, and set up the flask to catch the hydrogen in a balloon as in the following picture.

How many moles of Zn have you added to the flask?

0.104 mol How many moles of H+ are in the solution?

0.0493 mol How many moles of Zn will have reacted with the H+ when the reaction is complete?

0.0246 mol How many moles of Zn will remain unreacted?

0.0797 mol What mass of Zn will remain unreacted?

5.312 g How many moles of H2 gas will be produced?

0.0246 mol What mass of H2 gas will be produced?

0.0497 g Assuming that one mole of H2 gas would occupy a volume of 22 L at the temperature and pressure in the balloon, what would be the volume of the balloon?

0.542 L

Lab Report Key The title page should include: Student’s full name Date of experiment Complete title of lab report Name of partner(s) Instructor’s name Lab and section number (e.g., CHM1045L-02)

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The purpose should include: This experiment deals with several subjects including but not limited to conservation of mass, balance use, preparation of solutions, volumetric flasks, stoichiometry, balancing equations, etc.

The purpose should include references to most of these topics and should not be a copy of what is given in the manual. It should also mention how success will be determined. Full credit can be given if at least three of the aforementioned topics are discussed.

Procedure: This should be an MLA form reference to the lab manual with any changes in the procedure noted.

Data: The data section should include a table with the following information in some type of organized format. The data section should also include all observations made during the experiment and the exact concentration or molarity of CuSO4 solution. For before the reaction takes place, include a) mass of 250 mL side-arm flask, b) mass of 4 or 5 pieces of solid zinc metal, c) mass of 250 mL side-arm flask with CuSO4 acidic solution, d) mass of CuSO4 acidic solution alone, e) mass of Zn metal alone, and f) total mass before the reaction. For after the reaction takes place, include a) mass of metal pieces if removed from reaction mixture, b) mass of 250 mL side-arm flask with CuSO4 acidic solution, c) mass of solution alone, d) total mass after the reaction, e) volume of the balloon, and g) calculated mass of H2 gas alone.

Calculations: The values that need to be calculated should include one of each of the following: mass of CuSO4 acidic solution alone = (mass of 125 mL side-arm flask with CuSO4 acidic solution) – (mass of 125 mL side-arm flask) mass of Zn metal alone = (mass of 4 or 5 pieces of solid zinc metal on weigh boat) – (mass of 1 weigh boat) total mass of reactants before = (mass of CuSO4 solution alone) + (mass of Zn metal alone) volume of balloon = 4/3 r3 for a sphere or r2h for a cylinder (recall that 1 cm3 = 1 mL = 0.001 L) calculated mass of H2 gas alone (g) = 8.244 × 10–2 × (volume in L) total mass of products after = (mass of CuSO4 solution alone) + (mass of Zn metal alone) + (mass of H2)

Mass% recovered after the Reaction =

.

Total Mass after Reaction 100 Total Mass before Reaction

25

Conclusions: The conclusion for this experiment should be in paragraph format. A statement of the total mass before the reaction and the total mass after the reaction, and a discussion of the mass percent recovered should be present. Whether the mass recovered supports the law of conservation of mass should be included in the discussion. An explanation of whatever conclusion was reached should be presented with plenty of support for the conclusion provided. Further discussion regarding the amount of H2 that the reaction produced should be presented. Finally, inclusion of a discussion of possible errors in the experiment and how they might have affected the results is required.

Questions: 1) Why is the acid in the reaction necessary? Why can the solution of copper(II) sulfate simply be made with water?

As we learn in Chapter 4, an acid when combined with a metal creates hydrogen gas.

Since one of the products we wish to produce in this reaction is hydrogen gas, the acid was a necessary ingredient. Water plus zinc would not produce the hydrogen gas we need.

2) Explain how the law of conservation of mass is the basis for all of stoichiometry.

All of stoichiometry is based on the concept that the number of moles of an element that is reactant will equal the number of moles of an element that is a product in a reaction in a closed system. The law of conservation of mass states this as a rule that matter (moles of an element) can be neither created nor destroyed during the process of a reaction. If this were not true, then stoichiometry would not exist, since we could not make mathematical predictions of product amounts.

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Experiment 3: Conservation of Matter Points Points Section Worth

Experiment 3: Conservation of Matter Points Points Section

Earned

Title page (name, title, date, TA, course,

Title page (name, title, date, TA, course,

section, partner’s name) Purpose (at least three points)

section, partner’s name) Purpose (at least three points)

Procedure (cited/changes) Data (% mass, [Concentration],

Procedure (cited/changes) Data (% mass, [Concentration],

observations) Table I (mass of side-arm flask, mass of zinc, mass of side-arm flask with CuSO4 acidic solution, mass of CuSO4 acidic solution, Zn total mass before the reaction, after reaction mass of metal pieces on Kimwipe, mass of flask with CuSO4, mass of solution, mass of metal, total mass after, volume of the balloon, mass of H2 gas alone) Calculations (mass of solution alone, mass of Zn, total mass before, volume of balloon, calculated mass of gas, total mass of reaction after, % recovery, molarity) Conclusions (total mass of reaction before and after, discuss mass% recovered, discuss how mass recovered supports the law of conservation of mass or not, discuss amount of gas produced, errors, and effect of errors)

observations) Table I (mass of side-arm flask, mass of zinc, mass of side-arm flask with CuSO4 acidic solution, mass of CuSO4 acidic solution, Zn total mass before the reaction, after reaction mass of metal pieces on Kimwipe, mass of flask with CuSO4, mass of solution, mass of metal, total mass after, volume of the balloon, mass of H2 gas alone) Calculations (mass of solution alone, mass of Zn, total mass before, volume of balloon, calculated mass of gas, total mass of reaction after, % recovery, molarity) Conclusions (total mass of reaction before and after, discuss mass% recovered, discuss how mass recovered supports the law of conservation of mass or not, discuss amount of gas produced, errors, and effect of errors)

Questions Total Grade

Questions Total Grade

100 /

%

Experiment 3: Conservation of Matter Points Points Section Worth

Earned Title page (name, title, date, TA, course,

section, partner’s name) Purpose (at least three points)

section, partner’s name) Purpose (at least three points)

Procedure (cited/changes) Data (% mass, [Concentration],

Procedure (cited/changes) Data (% mass, [Concentration],

observations) Table I (mass of side-arm flask, mass of zinc, mass of side-arm flask with CuSO4 acidic solution, mass of CuSO4 acidic solution, Zn total mass before the reaction, after reaction mass of metal pieces on Kimwipe, mass of flask with CuSO4, mass of solution, mass of metal, total mass after, volume of the balloon, mass of H2 gas alone) Calculations (mass of solution alone, mass of Zn, total mass before, volume of balloon, calculated mass of gas, total mass of reaction after, % recovery, molarity) Conclusions (total mass of reaction before and after, discuss mass% recovered, discuss how mass recovered supports the law of conservation of mass or not, discuss amount of gas produced, errors, and effect of errors)

observations) Table I (mass of side-arm flask, mass of zinc, mass of side-arm flask with CuSO4 acidic solution, mass of CuSO4 acidic solution, Zn total mass before the reaction, after reaction mass of metal pieces on Kimwipe, mass of flask with CuSO4, mass of solution, mass of metal, total mass after, volume of the balloon, mass of H2 gas alone) Calculations (mass of solution alone, mass of Zn, total mass before, volume of balloon, calculated mass of gas, total mass of reaction after, % recovery, molarity) Conclusions (total mass of reaction before and after, discuss mass% recovered, discuss how mass recovered supports the law of conservation of mass or not, discuss amount of gas produced, errors, and effect of errors)

Questions Total Grade

Questions Total Grade

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Earned

100 /

%

Experiment 3: Conservation of Matter Points Points Section

Title page (name, title, date, TA, course,

100 /

Worth

%

Worth

Earned

100 /

% 27

Experiment 4: Plop, Plop, Fizz, Fizz: The Mass Percent of NaHCO3 Instructor Notes and Lab Preparation Chemicals and Equipment Alka-Seltzer tablets; be sure to purchase only original formula; if you use a store brand, be sure the ingredients are the same as the brand-name product 0.3 M acetic acid—may be labeled as vinegar Distilled water Small weighing boats or weighing papers

Preparation We run 40 sections of labs with an average enrollment of 22 students each. We prepare 16 L of solution to last the week.

Volume 16 L 8L 4L 2L

mL Concentrated Acetic Acid 275.86 mL 137.93 mL 68.97 mL 34.48 mL

Prepare a carboy of 16 L of 0.3 M acetic acid: Fill carboy partially with DI water and place in hood. Add 275.86 mL of concentrated acetic acid. Then dilute to 16 L with DI water.

Instruction Notes This is another lab that is easy to set up. To cut down on cost, issue each student only one AlkaSeltzer tablet. Although the lab procedure and background use vinegar as the acid source, we prepare 0.3 M acetic acid to cut cost and also to control the concentration of acid. Each student is assigned two of the four runs outlined in the table. The 0.3 M concentration was selected because it yields a graph that levels out at around 15 to 20 mL of acid, giving a nice centered line.

Points to Stress At the point in the semester when we perform this lab, the students have often not reached the limiting and excess reagent section of the text and thus are not ready to do that kind of

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calculation. Since this is a one-to-one mole relationship, there is not a great deal of difficulty with the students understanding the calculations, but it should be pointed out how the process would differ if the mole ratio were not one-to-one.

As with earlier labs, there is a gas being generated in this experiment. Most freshman think of gases as being weightless, and this experiment provides another example of the fallacy of that thinking, which should be pointed out again to the students.

Potential Problems One of the problems that we have with the lab is that our analytical balances are capable of weighing only up to ~100 g of mass. This means that we have to weigh each item separately.

This is generally not a problem except for when weighing the watch glass. If you also have this problem, it is important to instruct your students to place the watch glass onto the beaker in a convex (dome side up) orientation so that when it is removed, it can be flipped over to catch any liquid in its center. If it is placed on the beaker in a concave manner, the liquid will roll off and be lost when taken off to weigh it.

The other main error that can occur is not allowing the reaction to run to completion. It is somewhat like watching water boil; the process can take up to 30 min. It should be stressed that if the reaction is finished, no bubbles should form when the beaker is swirled. If bubbles still form or there is noticeable tablet residue in the bottom of beaker, then the reaction is incomplete.

You can allow the students to use hotplates on low heat to speed the reaction, but they must allow the solution to return to room temperature before trying to weigh it and it should not be boiled, since this would create a loss of mass through evaporation.

Finally, with respect to the graph, it is rarely a perfectly formed curve. Student data tends to jump around, often because of the errors mentioned above. Just like real experimental data, the students will need to assess the data to see if a trend can be found. They will probably not have done this type of trend line previously and should be given a rough example in class when the lab report is discussed.

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Experiment 4 Prelaboratory Assignment KEY Name: ___________________________ Date: _________________ Instructor: ____________________________ Sec. #: ___________

Show all work for full credit.

1) Acidification of sodium bicarbonate (NaHCO3) produces carbon dioxide in a two-step process. The first step produces carbonic acid (H2CO3). Write and balance the molecular equation for the first step of the reaction of sodium bicarbonate with HF.

NaHCO3 + HF → H2CO3 + NaF The second step is the decomposition of carbonic acid to carbon dioxide. Write and balance the molecular equation for the second step.

H2CO3 → H2O + CO2 Now, write the overall net ionic equation for the acidification of NaHCO3 to produce CO2.

HCO3− + H+ → H2O + CO2 What is the molar ratio of CO2 produced to NaHCO3 decomposed?

1:1 What mass of CO2 will be produced by the complete decomposition of 1346 mg of NaHCO3?

705 mg

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2) Two enterprising chemistry students decide to develop an alternative to Alka-Seltzer tablets, replacing the aspirin (acetylsalicylic acid) with vitamin C (ascorbic acid). The following table shows one of the formulations they tried for a 5 g tablet.

Ingredient Sodium bicarbonate Citric acid Vitamin C Inert binder Total mass:

Formula NaHCO3 H3C6H5O7 HC6H7O6

Quantity (mg) 1991 886 370 1753 5000

When the tablet dissolves in water, it “fizzes” as the bicarbonate reacts with the citric acid and the vitamin C. What mass of the NaHCO3 reacts with the vitamin C?

176 mg Citric acid is triprotic and reacts with base to form the citrate ion (C6H5O73−).

Write the overall net ionic reaction for the acidification of NaHCO3 by citric acid, giving CO2 as the product. Citric acid should be written as H3C6H5O7 in the net ionic equation, as weak acids are written in the molecular form even though they slightly ionize.

3HCO3− + H3C6H5O7 → 3H2O + 3CO2 + C6H5O73− What mass of the NaHCO3 reacts with the citric acid?

1163 mg What is the mass of CO2 released in this reaction?

701 mg The remaining NaHCO3 is available to neutralize stomach acid. What mass of stomach HCl could be neutralized by one tablet?

279 mg

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Lab Report Key The title page should include: Student’s full name Date of experiment Complete title of lab report Name of partner(s) Instructor’s name Lab and section number The purpose should include: This experiment deals with several subjects, including to mass percent, limiting and excess reagents, stoichiometry, balance use, and gas production. The purpose should include references to most of these topics and should not be a copy of what is given in the manual. Full credit can be given if at least three of the aforementioned topics are discussed.

Procedure: This should be an MLA reference to the lab manual. Students should note any changes that were made in the procedure.

Data: A completed table such as the following should be included.

Trial

1 2 3 4 5 6 7 8

Volume (mL) V W i a n t e e g r a r 0 35 5 30 10 25 15 20 20 15 25 10 30 5 35 0

Mass before Reaction (g) ½ T a b l e t

B e a k e r

Beaker and Solution

Watch Glass

Mass after Reaction (g) Total Mass

Beaker and Solution

Watch Glass

Mass Total

CO2 G r a m s

NaHCO3 M o l e s

M o l e s

G r a m s

M a s s %

Calculations: For the calculation section, a sample calculation for each calculation done to complete the data table should be presented. This section should also include the calculation for the percent error in the mass percent for each run.

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A graph of the mass percent of NaHCO3 and milliliters of vinegar should be included. The mass percent of NaHCO3 goes on the y-axis, and the volume of vinegar goes on the x-axis. Remember that all graphing guidelines apply here. The total amount of NaHCO3 in a tablet from where the graph begins to level out should be shown and/or described.

Conclusions: The conclusion section should be several paragraphs in length and include a discussion of the trends in mass of CO2, mass of NaHCO3, and mass percent found in the data table. Values should be included in the discussion. This section should also state the minimum volume of vinegar required to react with all of the NaHCO3 present in an Alka-Seltzer tablet. The minimum volume should be supported and explained using the data presented. A statement and explanation of the total amount of NaHCO3 in an Alka-Seltzer tablet is required. A discussion of the percent error in each run should be included, as well as any errors in the experiment that may have led to the discrepancies in values.

Questions: 1) Explain why the mass percent in a half-tablet is the same as the mass percent in a whole tablet of Alka-Seltzer.

Since we assume that the distribution of each component in the tablet is consistent, this means that the mass percent is the same and uniform throughout the tablet. Also, students could mention that mass percent is an intensive property.

2) Explain how the graph of mass percent of NaHCO3 versus milliliters of acetic acid helps you determine the amount of NaHCO3 in an Alka-Seltzer tablet.

The graph curves upward until the amount of acid neutralized remains constant. The point at which the graph levels out equals the point at which there is no more NaHCO3 available to neutralize acid.

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Experiment 4: Plop, Plop, Fizz, Fizz: The Mass Percent of NaHCO3 Section Points Points Worth Earned

Experiment 4: Plop, Plop, Fizz, Fizz: The Mass Percent of NaHCO3 Section Points Points Worth Earned

Title page (name, title, date, TA,

Title page (name, title, date, TA,

course, section, partner’s name) Purpose (at least three points)

course, section, partner’s name) Purpose (at least three points)

Procedure (cited/changes) Data (balanced chemical equation,

Procedure (cited/changes) Data (balanced chemical equation,

observations) Table I (mass before and after reaction data recorded in lab; grams and moles of CO2; moles, grams, and mass% NaHCO3: for all eight test with correct sig. figs.)

Calculations (total mass before and after, grams and moles CO2 , grams and moles NaHCO3, mass%, and %error) Graph (mass% vs. mL of vinegar)

observations) Table I (mass before and after reaction data recorded in lab; grams and moles of CO2; moles, grams, and mass% NaHCO3: for all eight test with correct sig. figs.)

Calculations (total mass before and after, grams and moles CO2 , grams and moles NaHCO3, mass%, and %error) Graph (mass% vs. mL of vinegar)

Conclusions (discussion of trends in

Conclusions (discussion of trends in

mass of CO2, mass of NaHCO3 and mass% with values, the minimum volume of vinegar required with support, value and explanation of the total amount of NaHCO3 in an Alka-Seltzer tablet, discussion of %error in each run, errors)

mass of CO2, mass of NaHCO3 and mass% with values, the minimum volume of vinegar required with support, value and explanation of the total amount of NaHCO3 in an Alka-Seltzer tablet, discussion of %error in each run, errors)

Questions Total Grade

Questions Total Grade

100 /

%

100 /

%

Experiment 4: Plop, Plop, Fizz, Fizz: The Mass Percent of NaHCO3 Section Points Points Worth Earned

Experiment 4: Plop, Plop, Fizz, Fizz: The Mass Percent of NaHCO3 Section Points Points Worth Earned

Title page (name, title, date, TA,

Title page (name, title, date, TA,

course, section, partner’s name) Purpose (at least three points)

course, section, partner’s name) Purpose (at least three points)

Procedure (cited/changes) Data (balanced chemical equation,

Procedure (cited/changes) Data (balanced chemical equation,

observations) Table I (mass before and after reaction data recorded in lab; grams and moles of CO2; moles, grams, and mass% NaHCO3: for all eight test with correct sig. figs.)

Calculations (total mass before and after, grams and moles CO2 , grams and moles NaHCO3, mass%, and %error) Graph (mass% vs. mL of vinegar)

observations) Table I (mass before and after reaction data recorded in lab; grams and moles of CO2; moles, grams, and mass% NaHCO3: for all eight test with correct sig. figs.)

Calculations (total mass before and after, grams and moles CO2 , grams and moles NaHCO3, mass%, and %error) Graph (mass% vs. mL of vinegar)

Conclusions (discussion of trends in

Conclusions (discussion of trends in

mass of CO2, mass of NaHCO3 and mass% with values, the minimum volume of vinegar required with support, value and explanation of the total amount of NaHCO3 in an Alka-Seltzer tablet, discussion of %error in each run, errors)

mass of CO2, mass of NaHCO3 and mass% with values, the minimum volume of vinegar required with support, value and explanation of the total amount of NaHCO3 in an Alka-Seltzer tablet, discussion of %error in each run, errors)

Questions Total Grade

Questions Total Grade

.

100 /

%

100 /

% 34

Experiment 5: Proof of Alcohol Instructor Notes and Lab Preparation Chemicals and Equipment Separatory funnels Gloves NaCl Diethyl ether Ethyl acetate Ethanol Organic waste jar (IN HOOD) Analytical balances Yellow/red food color

Setup • • •

• • •

Diethyl ether in dropper bottle dispenser set to 10 mL (kept in hood) Ethyl acetate in dropper bottle dispenser set to 10 mL (kept in hood) 2 L alcohol solution of unknown percentage (38%, which is 40% by volume using 95% ethanol works well) dyed with only red/yellow food dye; blue/green will separate and make phases indistinguishable NaCl in container(s) at front of lab Separatory funnels at the front of the lab Red organic waste container in hood for organic phase; aqueous phase can go down sink

Note: ALL diethyl ether must be tracked with the ether log. Note the amount placed in the labs, the amount retrieved, and the amount used.

Preparation of Reagents Unknown Alcohol Use the following graphic to make the unknown solution at the volume percentage you desire: For example: For 1 L of 40% ethanol solution, add 400 mL of ethanol to 634 mL of DI water.

Add a few drops of yellow food color to mimic the color of beer and to make the separatory line more visible.

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35

Instruction Notes This laboratory was created at Florida State University as an alternative to all of the “dehydration of hydrate” labs that are generally used for mass percent experiments. A couple of bonuses to the use of this process to teach mass percent is that you can also cover volume percent, revisit density, and introduce the concept of efficiency. So often in first year chemistry, we give students the impression that reactions are always 100%. This is—of course—very seldom the case, and it is nice to introduce the reality of chemical processing at this point. After completing 20 trials of the experiment, we determined the process when run one time was 85% efficient.

Because we want to limit the amount of contact the students have with the organic solvents, we use preset pump dispensers for the diethyl ether and ethyl acetate. In the process of the experiment, the solvents are transferred from pump to separatory funnel to waste jar, so if the experiment is conducted properly, the students are never exposed.

Potential Problems We have had relatively few problems with this experiment despite it being fairly new. Most of the error we have had is in regards to the students’ understanding of which layer in the funnel is aqueous and which is organic. The first term we ran the experiment, a student took it upon themselves to email the entire class and let them know that since we discarded the clear water layer without weighing it, there was no way to complete the calculations for the report. The misunderstanding arose because the student believed that all aqueous solutions are clear.

Obviously this was incorrect, and we have added some color description to the procedure to make sure the students know which layer is aqueous.

A second issue is that to run this lab, the instructor or lab manager will need to obtain an ether license if they do not already have one. Diethyl ether is a restricted chemical and needs to be audited annually. Your Environmental Health and Safety Department should be able to provide you with the permit and monitoring.

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Experiment 5 Prelaboratory Assignment KEY Name: ___________________________ Date: _________________ Instructor: ____________________________ Sec. #: ___________

Show all work for full credit.

1) You have a beer labeled as 7.3% alcohol. What is the molar concentration of ethanol?

2.4×10–3 M 2) It is more complicated to convert volume percent ethanol to mass percent ethanol because you must know the density of the solution. The graph below plots the density of aqueous ethanol solutions versus the volume percent ethanol.

What is the density of a 7.3% ethanol solution? (Note the actual density of beer will be a bit different because of other components in the solution.)

0.988 g/mL What is the mass of ethanol dissolved in 1 L of a 7.3% ethanol solution?

57.6 g What is the mass of water dissolved in 1 Lof a 7.3% ethanol solution?

930.4 g What is the mass percent of ethanol (also known as ABW, alcohol by weight) in this solution?

5.8 % 3) In your laboratory experiment, you will determine the quantity of ethanol in an ethanol–water mixture indirectly by extracting the ethanol from the mixture and measuring the mass of the water remaining. Of necessity, such a procedure will give you the mass percent of ethanol in the mixture.

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To determine the proof of the alcohol, you must convert the mass percent ethanol to a volume percent, as the proof value in the United States is defined as twice the volume percent.

Your 50 mL graduate cylinder has a mass of 63.288 g. You measure approximately 31 mL of the unknown mixture in it and find that the total mass of the cylinder and the unknown is 92.244 g.

What is the mass of your unknown solution? 28.956 g You place this unknown sample into your separatory funnel and add 1.026 g NaCl and 10 mL each of ethyl ether and ethyl acetate. After extraction, you remove the bottom layer and find it has a mass of 22.057 g.

What mass of ethanol was removed by the extraction? 7.952 g

Complete extraction of the ethanol would require several extraction steps. To simplify the laboratory and to cut down on errors and losses involved in transferring liquids, you will only do a single extraction. Assuming that prior experiments have shown that the singlestep extraction removes only 70% of the ethanol, what is the mass of ethanol in your original unknown? 11.322 g What is the mass percent ethanol in the original unknown? 39.1% Now, calculate the volume percent and the proof of the ethanol in the unknown solution based on this mass percent. Use the graph from the background information that plots the density of ethanol solutions from 20 to 60 mass percent to answer the following questions: Given a density of 0.789 g/mL, what would the volume of the ethanol in the original unknown have been? 14.35 mL Using the density from the graph, calculate the volume of your original unknown solution. (The calculated volume should be more precise than the volume you could measure with your graduate cylinder.) 30.90 mL What would the volume percent of ethanol be in the original unknown? 46.4% What is the ethanol proof value of this unknown? 92.8 proof

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38

Lab Report Key They should know this by now. I generally do not give point for the title page, but rather take away points if something is missing.

The title page should include: Student’s full name Date of experiment Complete title of lab report Name of partner(s) Instructor’s name Lab and section number (e.g., CHM1045L-02)

The purpose should include: This experiment deals with several subjects, including mass percent, volume percent, density, proof, balance use, efficiency, and extraction methods. The purpose should include references to most of these topics and should not be a copy of what is given in the manual. Full credit can be given if at least three of the aforementioned topics are discussed.

Procedure: This should be an MLA form reference to the lab manual with any changes in the procedure noted.

Data: The data section should include two tables. For parts I and II, the table should include the following for both the ethanol and water: a) mass of graduated cylinder, b) volume of liquid, c) mass of liquid, and d) density of liquid.

For part III, the table should include the following: a) mass of graduated cylinder, b) mass of graduated cylinder with solution, c) mass of solution, d) volume of solution, e) density of solution, f) mass of salt, g) mass of water layer, h) mass of alcohol layer, i) volume of water layer, j) volume of alcohol layer, k) density of water layer, l) percent alcohol by mass, m) percent alcohol based on a 85% efficiency, n) percent alcohol by volume, and o) proof of the alcohol. Also any and all observations made during the extraction process.

Calculations: The calculation section should include example calculations of everything in the data section that was not collected during the actual experiment. That would include the following: a) mass of liquid, b) density of liquid, c) mass of water layer, d) mass of alcohol layer, e) volume of alcohol

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39

layer, f) percent alcohol based on mass, g) percent alcohol based on volume, h) percent alcohol based on a 85% efficiency, and i) proof of the alcohol solution.

Conclusions: The conclusion section should be several paragraphs in length and include the following information: a discussion for part I, which includes the densities of the two liquids and a complete discussion for part II, which includes a comparison and explanation of the densities, volumes, and masses before and after the extraction. Also included should be a detailed explanation of the percent alcohol values by mass and volume and how the 85% efficiency plays a role in the actual alcohol content of the unknown solution. Students should be sure to clearly state the percent alcohol content and proof of your solution. Finally, they should state any errors.

Questions: 1) Name another product (other than drinking alcohol) that is sold as a percentage by weight or volume. bleach, rubbing alcohol, peroxide, etc.

2) Draw a diagram of the separatory funnel you used and label the two layers of liquid in the funnel. Explain why the two layers are where they are. For example, what physical properties determine which liquid is on top?

Should be a picture of the sep funnel with the water layer on the bottom and the alcohol/organic layer on top. The property of density and polarity should be discussed as the reasons for the separation.

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40

Experiment 5: Proof of Alcohol

Experiment 5: Proof of Alcohol Section

Points Worth

Points Earned

Section

section, partner’s name)

section, partner’s name)

Purpose Procedure (cited & changes) Data

Purpose Procedure (cited & changes) Data

Table I (mass of graduated cylinder, volume of liquid, mass of liquid, density of liquid, molarity) Table II (mass of graduated cylinder, mass of graduated cylinder with solution, mass of solution, volume of solution, density of solution, mass of salt, mass of water layer, mass of alcohol layer, volume of water layer, volume of alcohol layer, density of water layer, percent alcohol by volume, percent alcohol based on an 85% efficiency, percent alcohol by mass)

Table I (mass of graduated cylinder, volume of liquid, mass of liquid, density of liquid, molarity) Table II (mass of graduated cylinder, mass of graduated cylinder with solution, mass of solution, volume of solution, density of solution, mass of salt, mass of water layer, mass of alcohol layer, volume of water layer, volume of alcohol layer, density of water layer, percent alcohol by volume, percent alcohol based on an 85% efficiency, percent alcohol by mass)

Calculations (mass of liquid, density of liquid,

Calculations (mass of liquid, density of liquid,

molarity of salt water only, mass of water layer, mass of alcohol layer, volume of alcohol layer, percent alcohol based on mass, percent alcohol based on volume, percent alcohol based on an 85% efficiency)

molarity of salt water only, mass of water layer, mass of alcohol layer, volume of alcohol layer, percent alcohol based on mass, percent alcohol based on volume, percent alcohol based on an 85% efficiency)

Conclusions (discussion on the densities of the

Conclusions (discussion on the densities of the

two liquids, comparison and explanation of the densities, volumes and masses before and after the extraction, explanation of the percent alcohol values by mass and volume and how the 85% efficiency plays a role in the actual alcohol content of the unknown solution, clearly stated the percent alcohol content of your solution and errors)

two liquids, comparison and explanation of the densities, volumes and masses before and after the extraction, explanation of the percent alcohol values by mass and volume and how the 85% efficiency plays a role in the actual alcohol content of the unknown solution, clearly stated the percent alcohol content of your solution and errors)

Questions Total Grade

Questions Total Grade

100 /

%

100 /

%

Experiment 5: Proof of Alcohol

Experiment 5: Proof of Alcohol Points Worth

Points Earned

Section

Points Worth

Points Earned

Title page (name, title, date, TA, course,

Title page (name, title, date, TA, course, section, partner’s name)

section, partner’s name)

Purpose Procedure (cited & changes) Data

Purpose Procedure (cited & changes) Data

Table I (mass of graduated cylinder, volume of liquid, mass of liquid, density of liquid, molarity) Table II (mass of graduated cylinder, mass of graduated cylinder with solution, mass of solution, volume of solution, density of solution, mass of salt, mass of water layer, mass of alcohol layer, volume of water layer, volume of alcohol layer, density of water layer, percent alcohol by volume, percent alcohol based on an 85% efficiency, percent alcohol by mass)

Table I (mass of graduated cylinder, volume of liquid, mass of liquid, density of liquid, molarity) Table II (mass of graduated cylinder, mass of graduated cylinder with solution, mass of solution, volume of solution, density of solution, mass of salt, mass of water layer, mass of alcohol layer, volume of water layer, volume of alcohol layer, density of water layer, percent alcohol by volume, percent alcohol based on an 85% efficiency, percent alcohol by mass)

Calculations (mass of liquid, density of liquid,

Calculations (mass of liquid, density of liquid,

molarity of salt water only, mass of water layer, mass of alcohol layer, volume of alcohol layer, percent alcohol based on mass, percent alcohol based on volume, percent alcohol based on an 85% efficiency)

molarity of salt water only, mass of water layer, mass of alcohol layer, volume of alcohol layer, percent alcohol based on mass, percent alcohol based on volume, percent alcohol based on an 85% efficiency)

Conclusions (discussion on the densities of the

Conclusions (discussion on the densities of the

two liquids, comparison and explanation of the densities, volumes and masses before and after the extraction, explanation of the percent alcohol values by mass and volume and how the 85% efficiency plays a role in the actual alcohol content of the unknown solution, clearly stated the percent alcohol content of your solution and errors)

two liquids, comparison and explanation of the densities, volumes and masses before and after the extraction, explanation of the percent alcohol values by mass and volume and how the 85% efficiency plays a role in the actual alcohol content of the unknown solution, clearly stated the percent alcohol content of your solution and errors)

Questions Total Grade

Questions Total Grade

.

Points Earned

Title page (name, title, date, TA, course,

Title page (name, title, date, TA, course,

Section

Points Worth

100 /

%

100 /

%

41

Experiment 6: Empirical Formula of a Compound Instructor Notes and Lab Preparation Chemicals and Equipment Bunsen burners Striker Crucibles Magnesium strips Waste container Balance Water

Empirical Formula of a Compound •

• • •

•

Each instructor should describe the proper use of this equipment in lab (e.g., Bunsen burners). Be sure to instruct the students to keep the crucibles in the hottest part of the flame, or the magnesium will never ignite. They should also coil the Mg so that it is at the bottom of the crucible.

It is the case that some Mg samples never ignite. If time is running short, make sure that each student has one good trial. They can explain the bad trial in the lab report.

The students should complete the calculations in lab (if they have time).

The lab instructor/lab assistant will put out a separate waste container for the solid waste.

Please remind the students to place the solid waste in this container and the waste from rinsing the crucible in a liquid waste container.

This lab (including the calculations) will take most students the entire lab time.

This week in lab, you will be carrying out a reaction between magnesium and oxygen: Mg(s) + O2(g) → MgxOy(s). Your goal is to determine the empirical formula of the generated compound. The values the student determine in lab may or may not be equal to x and y in the chemical equation as written, depending on whether the empirical and molecular formulas for this compound are identical.

Step 1: Crucible Preparation Obtain two crucibles and lids (check for cracks, etc.). Find the masses of the crucibles and lids separately in case disaster strikes (i.e., the lid breaks) later in the lab. The crucibles and lids available in the lab have already been fired once to drive off any contaminants. You will fire the crucibles (and lids) to ensure that all contaminants have been removed. To do so, you will use a Bunsen burner. Before starting the Bunsen burner, check the tubing to make sure that there are no cracks that could lead to gas leaks. There are two adjustments on the Bunsen burner: one for the gas flow and one for oxygen intake. Be sure to have the gas flow turned fairly low (shut

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42

valve all the way, open a quarter to a half turn so that a huge flame is not produced at the outset.

With the gas on, use a striker to start the flame—you will need to grind the striker to get a spark.

Once you have a flame, adjust the gas flow as necessary. If the flame glows yellow, you should reduce the flow of oxygen until a blue flame is observed. The blue inner cone of the flame is the hottest portion, and you should use this portion to fire the crucible for about 5 min. After heating, let the crucible cool to room temperature before finding the mass. To carry the crucible to and from the balance, use both tongs and the “hot hands” in your drawer. Repeat this process a second time. If the mass after the last heating agrees with the previous mass value (i.e., the change in mass is no more than 0.0100 g), then you are done. If there is a large mass change, continue heating until the change in mass is less than 0.0100 g.

Step 2: Reaction Once the mass of the crucible is known, obtain a sample of Mg. The Mg will already be cut up into small strips. Choose a strip that looks shiny (i.e., no white powder on it). If there is white powder on the wire, attempt to remove it by cleaning or get a new piece of Mg. Once a clean piece of Mg is in hand, coil the Mg ribbon in the crucible (don’t touch anything with your bare hands; make sure the Mg is at the bottom of the crucible) and find the initial mass of this system.

Heat the magnesium sample with the cover ajar—if the sample smokes, stop the experiment until the smoking ceases (cover) and then heat the sample for another several minutes. Make sure that the crucible is in the hottest part of the flame for the majority of the heating. Mg is called the little sun because it glows so brightly when it is heated strongly—look for this glow and wait until the metal is no longer glowing (brightly or red) before stopping the reaction. Generally, the reaction will be completed in about 15 to 20 min if you use the hottest part of the flame.

It is possible that Mg3N2 will form during the course of the reaction. To convert this compound to magnesium oxide, add 3 to 4 drops of water and then heat again (continue heat cycles until no mass change occurs). You may smell the ammonia generated in this reaction.

You need to perform two trials for this experiment. Be sure that you do not leave an open flame at your area unless a neighbor has kindly agreed to keep an eye on your flame.

Step 3: Calculations The calculations are described in your lab manual. The calculations will be briefly explained by the lab instructor/lab assistant. As we are trying to find an empirical formula, what is the goal?

Mole ratio. Find the masses of Mg and O, and convert these values to moles. Then compute the mole ratio. Recall that the ratio of the moles should be a small whole number. You may need to round your results.

Step 4: Cleanup Put the solid waste in the solid waste container. Rinse the crucible with acetone and put this waste in the liquid waste container in the hood. Make sure that the area you worked at is clean and that everything is put back into your drawer. Be sure to lock your drawers!

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Lab Report Key Purpose: This experiment had two overall goals: (1) to facilitate a successful reaction between magnesium and oxygen and produce magnesium oxide, and in doing so (2) the empirical formula of magnesium oxide could be determined.

Two staggered trials were run in which a strip of magnesium metal was melted down inside of a crucible, and when allowed to react with the oxygen in the air, magnesium oxide was produced.

The initial mass (g) of the magnesium used in each trial was recorded and was then compared to the final recorded mass (g) of magnesium oxide, respectively. The final mass in grams of the magnesium oxide produced was then used to determine the empirical formula of magnesium oxide.

Procedure: ChemXXX lab general chemistry. Lab manual. Semester 20XX. XXXXX University.

Deviations: • The crucible used in trial 1 broke after the second firing, and the trial could not be continued.

Data and Results: After multiple firings, a constant mass (g) was determined for each of the respective crucibles.

Once a Mg strip was added to each of the respective crucibles, the crucibles were massed, and the mass of the magnesium (g) was determined, respectively. Based on these values, the mass of the crucible and magnesium (g) was subtracted from the final mass of the crucible and magnesium oxide (g) to determine the mass of oxygen absorbed (g). These values then lead to the determination of the moles of each of the reactants, respectively. Keep track of the data acquired, as shown in Table 1.

Table 1: Reactant and Product Masses Trial 1

Trial 2

Empty crucible + lid/constant mass (g) Crucible + lid and magnesium (g) Magnesium (g) Crucible + lid after first firing (g) Crucible + lid after second firing (g) Crucible + lid after third firing with added ddH2O (g) Magnesium oxide (g) Oxygen (g) Moles of magnesium Moles of oxygen After determining the molar ratio of magnesium to oxygen, the empirical formula for magnesium oxide was determined to be MgO.

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Calculations: The constant mass of the crucible (g) was determined by finding the difference in the masses (g) before and after each firing, respectively. If the difference is no more than ± 0.01 g, then the constant mass had been achieved: mass before firing (g) – mass after firing (g) = difference (g) 41.0949 g – 41.0941 g = difference (g) 0.0008 g = difference (g) The initial mass of magnesium (g) was determined by subtracting the constant mass of the crucible (g) from the mass of the crucible and magnesium metal (g): initial mass of magnesium (g) = mass of crucible and magnesium metal (g) – constant mass (g) initial mass of magnesium (g) = 41.2161 g – 41.0941 g initial mass of magnesium (g) = 0.1220 g The moles of magnesium for each trial were determined by dividing the mass of magnesium (g) by the molar mass of magnesium (g/mol): Mass of Magnesium ( g ) moles of magnesium = g Molor mass of Magnesium mol

( )

moles of magnesium =

0.1220 g

( )

g 24.3050 mol

moles of magnesium = 0.005020 mol

The mass of oxygen absorbed (g) by the conversion was determined by subtracting the mass of the crucible and magnesium metal (g) from the mass of the crucible and magnesium oxide (g): mass of oxygen (g) = mass of crucible and magnesium oxide (g) – mass of crucible and magnesium (g)

mass of oxygen (g) = 41.2726 g – 41.2161 g mass of oxygen = 0.0565 g The molar ratio of magnesium to oxygen was determined by dividing the moles of magnesium by the moles of oxygen: moles of magnesium Mg:O = moles of oxygen 0.005020 mol Mg:O = .003531 Mg:O = 1:1 Discussion: During the initial stages of the reaction, it is possible that the magnesium bonded with nitrogen in the air to form magnesium nitride. It is for this reason that deionized water was added to the reaction and the crucible was then fired, producing magnesium hydroxide and releasing ammonia. The crucible was fired once more, producing the final products of water and magnesium oxide. This process is displayed in the two following balanced equations: Mg3N2 + 6H2O → 3Mg(OH)2 + 2NH3 Mg(OH)2 → MgO + H2O

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If this experiment were carried out again and at the end some of the magnesium metal were still left within the crucible, the empirical formula ratio would be too high for magnesium. This is because oxygen could bind the magnesium only after the crucible was fired and it was changed from its metal form. However, if not all of the metal were melted down, then the mass of magnesium would still be the same, but the mass of oxygen would be lower than it should be, causing an empirical formula ratio that is too high in magnesium.

If the experimental formula for magnesium oxide were Mg2O3, then the implied charge on the magnesium would be a 3+ charge, and the implied charge on the oxygen would be a 2– charge. However, these values do not entirely agree with the trend observed in the periodic table.

According to the periodic table, the charge on oxygen would be correct, but the charge on magnesium should be a 2+, not a 3+. A 3+ charge corresponds to elements in column 3A, but magnesium is found in column 2A that has elements with a 2+ charge.

At the end of the experiment, and after the molar ratio of magnesium to oxygen was calculated, the empirical formula of magnesium oxide was determined to be MgO. This translates to there being one magnesium atom present for every one oxygen atom. As stated before, magnesium has a 2+ charge based on the periodic table, and oxygen has a 2– charge based on the periodic table. When put together, these charges would cancel out; when written out, they would look like MgO. Therefore, the calculated experimental empirical formula of magnesium oxide does correspond with the expected empirical formula based on the periodic table.

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Experiment 6: Empirical Formula of a Compound Section Points Points Worth Earned Title page (name, title, date, TA,

Experiment 6: Empirical Formula of a Compound Section Points Points Worth Earned Title page (name, title, date, TA,

course, section, partner’s name)

course, section, partner’s name)

Purpose (at least three

Purpose (at least three

discussion points)

discussion points)

Data and Results Table Sample Calc. Calculation is

Data and Results Table Sample Calc. Calculation is

complete, correct, and reported with the correct number of significant figures.

complete, correct, and reported with the correct number of significant figures.

Average Empirical Formula Question 1 Question 2 Question 3 Question 4

Average Empirical Formula Question 1 Question 2 Question 3 Question 4

Total Grade

100 /

%

Total Grade

100 /

%

Experiment 6: Empirical Formula of a Compound Section Points Points Worth Earned Title page (name, title, date, TA,

Experiment 6: Empirical Formula of a Compound Section Points Points Worth Earned Title page (name, title, date, TA,

course, section, partner’s name)

course, section, partner’s name)

Purpose (at least three

Purpose (at least three

discussion points)

discussion points)

Data and Results Table Sample Calc. Calculation is

Data and Results Table Sample Calc. Calculation is

complete, correct, and reported with the correct number of significant figures.

complete, correct, and reported with the correct number of significant figures.

Average Empirical Formula Question 1 Question 2 Question 3 Question 4

Average Empirical Formula Question 1 Question 2 Question 3 Question 4

Total Grade

.

100 /

%

Total Grade

100 /

%

47

Experiment 7: Pancake Mix as a Limiting Reactant?

Instructor Notes and Lab Preparation Chemicals and Equipment Table 1: Equipment and Chemicals for Limiting Reactant Equipment

Quantity

Beaker, 250 mL

2

Beaker, 400 mL

2

Filter paper, Whatman 42 or Fisher Q2

2

Funnel, long stem

2

Funnel support

1

Hot plate

1

Stirring rod

2

Test tubes, any size

4

Chemicals

Quantity

0.5 M BaCl2

As needed

0.5 M Na3PO4

As needed

Sample (2  1.5–2.0 g)

1 vial

Water, deionized

As needed

Preparation and Notes: •

Please emphasize to the students that they need to vigorously shake the unknowns before massing out a sample, as the heavier component could settle to the bottom of the vial, leading to very different results for their two trials.

•

The students should be reminded to start the water heating before they mass their samples.

Suggesting that they use their 600 mL beaker is a good idea, as they need over 400 mL of hot water.

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•

While the students are heating the water, they should label everything and set up the filtration apparatus (using the ring stand attached to the hot plate they are using). You may want to demonstrate the proper folding of the filter paper to the students.

•

The students should determine the limiting reactant and set up the calculations in lab, if time permits.

A summary of the prelab lecture I gave to the students appears below.

This week in lab, you will examine a sample that is a mixture of two hydrated compounds: sodium phosphate dodecahydrate (Na3PO4∙12H2O) and barium chloride dihydrate (BaCl2∙2H2O).

When water is added to these compounds, they dissolve, separating into the component ions: Na+, Cl−, Ba2+, and PO43−. Looking at these ions, you know that NaCl is a soluble solid; many ionic compounds are not soluble in water. One of these insoluble compounds is Ba3(PO4)2 (ask students to predict formula based on charges). The reaction to form barium phosphate is as given below: 2Na3PO4∙12H2O (aq) + 3BaCl2∙2H2O (aq) → Ba3(PO4)2 (s) + 6NaCl (aq) + 30H2O(l) As the reaction that actually occurs involves just Ba2+ and PO43−, the reaction can be written more simply as: 6Na+(aq) + 2PO43– (aq) + 3Ba2+ (aq) + 6Cl– (aq) → Ba3(PO4)2 (s) + 6 Na+ (aq) + 6Cl– (aq) Removing the ions that are unchanged as a result of the reaction gives the net ionic equation: 2PO43– (aq) + 3Ba2+ (aq) → Ba3(PO4)2 (s) The sample you will examine will be a mixture of Na3PO4∙12H2O and BaCl2∙2H2O in some unknown mass proportions. BE SURE TO RECORD THE UNKNOWN NUMBER IN YOUR NOTEBOOK! As the compounds are not present in perfect stoichiometric amounts, one of the compounds will be the limiting reagent in the reaction. The goals of this lab are to determine the limiting reagent and the percent by mass composition of the sample.

You will have enough of the sample to perform two simultaneous trials. It is critical to the success of your lab experiment that you vigorously shake the sample to make sure it is mixed well. If you do not, you may have different mass percents for the two trials you perform, making your results difficult to interpret. It is not crucial that your sample be divided exactly 50:50; approximately in half is fine. It will also be important to carefully label everything.

When you carry out the reaction, you will use boiling water, as this will result in larger particulate formation, making it easier to isolate the precipitate via filtration. While you are digesting the samples, you should set up your filtration systems (funnels in iron rings, filter paper) on the ring stand on your hot plate. Your lab instructors will discuss this set up more thoroughly in the lab. You will mass your product with the filter paper, so it is very important to find the mass of the filter paper.

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49

Once the reaction is completed, you will filter the samples. The next step will be to determine the limiting reagent. This can be accomplished by examining the filtrate, or the solution that passed through the filter. Consider again the net ionic equation for the reaction: 2PO43– (aq) + 3Ba2+ (aq) → Ba3(PO4)2 (s). This equation makes it more straightforward to consider the limiting reagent. If the compound containing Ba2+ is the limiting reagent, the solution above the precipitate will contain Na+, Cl–, and PO43– ions. After the solid sample is removed by filtration, the solution, or filtrate, can be examined. When some amount of a solution of BaCl2∙2H2O is added to the filtrate, Ba2+ will be introduced. This will result in the formation of the Ba3(PO4)2 precipitate. If Ba2+ ions are introduced and no reaction occurs, then PO43– must have been the limiting reagent.

How would you confirm that PO43– was the limiting reagent? Add some of a solution of Na3PO4∙12H2O to a new sample of the filtrate.

Once the limiting reactant is known, you can use the moles of the product to determine the moles of the limiting reactant present in the original sample. You can then find the mass of the limiting reactant in the original sample—remember to include the waters of hydration when calculating the mass (the molar masses are provided in the lab manual). If the mass of the limiting reagent is known, and the mass of the original sample is known, then the mass percent of the limiting reactant (and the nonlimiting reactant) can be determined. All of these calculations hinge on the correct determination of the mass of the product. As the product will be wet after the filtration process, the product must be dried before its mass can be determined. As this will take several hours, you must return to the lab in order to determine this mass. A list of possible times to return to lab to mass your samples will be available in the lab. If you do not find the mass of your product before next lab period, your samples will be thrown away, and your lab report score will be severely diminished. When you have completed all of the steps of the lab, and your two samples are in properly labeled beakers (your name, the date, your section number, and sample A/B, 1/2), put these beakers in the oven at the front of the lab.

As you will need to perform the calculations outside of lab, be sure to set up the calculations in your notebook before you leave lab and make sure that you understand how to perform all of the calculations.

Please be sure to clean up your area thoroughly and to properly dispose of your waste solutions.

Barium is very bad for the environment, so be extremely diligent when disposing of your filtrates and your solid waste samples.

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Experiment 7 PreLaboratory Preparation KEY Name: ___________________________ Date: _____________ Instructor: ____________________________ Sec. #: ________

1) What does the dot mean in the formula of the hydrated salt Na3PO4 • 12H2O (1 Points)?

The sodium compound is a hydrated salt. When it crystallizes from aqueous solution, water molecules are trapped in fixed positions in its crystal structures. There are no chemical bonds between the water molecules and the ions in the hydrated compound. This condition is indicated in chemical formula by placing a dot after the ion portion of the formula and just before the number of waters of hydration. The molar mass for such compounds must account for the waters of hydration. Separately, each component of this mixture is soluble in water.

2) Based on the net ionic equation for the formation of Ba3(PO4)2 included in the lab instructions, if 5 moles of barium phosphate, Ba3(PO4)2 are formed, how many moles of phosphate ion, PO43−, must have reacted with Ba2+, assuming that PO43– is the limiting reactant? (1 Points)

moles of PO43− = 5 moles Ba 3 ( PO4 )2 *

2 mol PO43− = 10 mol PO43− 1mol Ba 3 ( PO4 )2

3) A sample containing 3.9421 g of a mixture of Na3PO4 and BaCl2 • 2H2O is added to water.

After the sample is filtered, 0.1882 g of Ba3(PO4)2 are recovered and Ba2+ is identified as the limiting reagent.

MW (g mol–1)

.

Ba3(PO4)2

601.9

Na3PO4

163.9

BaCl2 • 2H2O

244.3

51

a) How many moles of barium ion reacted, and what is the mass of the original barium chloride hydrate (2 Points)?

moles of Ba 2+ = 0.1882 g Ba 3 ( PO4 )2 *

1mol Ba 3 ( PO4 )2 601.9 g

Mass of BaCl2 • 2H 2O = 9.380*10−4 mol Ba 2+ *

*

3mol Ba 2+ = 9.380 *10−4 mol 1mol Ba 3 ( PO4 )2

1mol BaCl2 • 2H 2O 244.3 g * = 0.2292 g 2+ 1 mol Ba 1mol BaCl2 • 2H 2O

b) What is the mass percent of BaCl2 • 2H2O in the original sample mixture (1 Points)?

Mass percent of BaCl2 • 2H 2O =

0.2292 g BaCl2 • 2H 2O *100% = 5.813% 3.9421 g mixture

Laboratory Report Key The title page should include: They should know this by now. Only take away points if incorrect!

Student’s full name Date of experiment Complete title of lab report Name of partner(s) Instructor’s name Lab and section number (e.g., CHM1045L-02) The purpose should include: There are several topics covered in this lab, including pigmentation, calculation of Rf values, color components, mobile phase, stationary phase, chromatography, and TLC sheets.

Procedure: This should be an MLA form reference to the lab manual with any changes in the procedure noted.

Data and results table: Create two tables, each with three columns. The first table should show the preparation of the sample and the result of the mass-by-difference calculation for the unreacted sample (see Table 2 below). The results from each calculation, including intermediate results such as the masses of the excess and limiting reactants, should be added as rows to the bottom of the second table (see Table 3 below). As usual, make sure that all of your numeric values have the proper number of significant figures.

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Table 2: Suggested Data Organization for the Sample Preparation Unknown #: Trial 1 2+

Trial 2

3−

Limiting reactant (Ba or PO4 ) Mass of initial sample and vial (g) Mass of final sample and vial (g) Mass of sample (g) Table 3: Suggested Data Organization for Percent Composition Determination Trial 1

Trial 2

Mass of filter and product (g) Mass of filter (g) Mass of product (g) Moles of Ba3(PO4)2 product (mol) Moles of limiting reactant (mol) Mass of limiting reactant (g) Percent by mass BaCl2·2H2O Percent by mass Na3PO4 Sample calculations In a step-by-step fashion, show an example of each calculation step for the lab. Each step should result in values that are rounded to the correct number of significant figures and with the correct units of measure. Provide a brief description of each step in your own words. Equations should be centered on the page. The sample calculations may either be typewritten or handwritten. In either case, the work must be well-organized and neat. If the instructor cannot read or follow the sample calculations, no credit will be awarded for this section of the report.

Identification of Limiting Reactant and Percent Composition In a separate section, clearly, state your unknown number and the limiting reactant. Then state the final average composition in terms of percentage by mass of each component in your unknown sample.

Questions: 1) Explain why washing the precipitate once it is in the filter should increase the accuracy of this experiment. What is being removed? What effect would this have on the percent by mass of the limiting reagent?

Washing will remove any excess and increase the purity of the limiting reactant. This would provide a more accurate reading in the percent by mass and even though it may be less, it would not be over 100%, which seems to be the trend especially when working with excess products.

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2) Calculate the amount of excess reagent in the sample (before the reaction) for Trial 1.

1. Figure out which of the reactants is the limiting reactant or limiting reagent.

2. See how much product can be formed by using the maximum amount of the limiting reactant or limiting reagent.

3. The excess reactant is what is left over after all of the limiting reactant has been used up.

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Experiment 7: Pancake Mix as a Limiting Reactant?

Section Points Points Worth Earned

Experiment 7: Pancake Mix as a Limiting Reactant?

Section Points Points Worth Earned

Title page (name, title, date, TA,

Title page (name, title, date, TA,

course, section, partner’s name) (you lose points for not having these from now on) Purpose (at least three points)

course, section, partner’s name) (you lose points for not having these from now on) Purpose (at least three points)

Procedure (cited/changes)

Procedure (cited/changes)

Data (observation, all tables, calculations, and figures. There should be a narrative that accompanies the presentation of the data) Table I (data organization for the sample prep. Two trials including masses and limiting reactant) Table II (data organization for the percent composition determination, mass, moles, limiting reactant, percent mass)

Data (observation, all tables, calculations, and figures. There should be a narrative that accompanies the presentation of the data) Table I (data organization for the sample prep. Two trials including masses and limiting reactant) Table II (data organization for the percent composition determination, mass, moles, limiting reactant, percent mass)

Calculations (step by step sample

Calculations (step by step sample

calculation of the entire process for a trial. Mass of initial sample and barium phosphate, moles of barium phosphate, identification, mass, moles, and percentage of limiting reactant)

calculation of the entire process for a trial. Mass of initial sample and barium phosphate, moles of barium phosphate, identification, mass, moles, and percentage of limiting reactant)

Questions Total Grade

100 /

%

Experiment 7: Pancake Mix as a Limiting Reactant?

Section Points Points Worth Earned Title page (name, title, date, TA,

Questions Total Grade

100 /

%

Experiment 7: Limiting and Excess Reagents Section Points Points Earned Experiment 7: Pancake Mix as aWorth Limiting Reactant?

Title page (name, title, date, TA, Section Points Points course, section, partner’s name) (you lose Worth Earned points for not having these from now on) Title page(at(name, title,points) date, TA, Purpose least three course, section, partner’s name) (you lose Procedure (cited/changes) points for not having these from now on) Data (observation, balanced equation) Purpose (at least three points) Table I (personal data: masses, + or –) Procedure (cited/changes) Data (observation, all tables, calculations, Table II (class data: masses, + or –)

course, section, partner’s name) (you lose points for not having these from now on) Purpose (at least three points)

Procedure (cited/changes) Data (observation, all tables, calculations, and figures. There should be a narrative that accompanies the presentation of the data) Table I (data organization for the sample prep. Two trials including masses and limiting reactant) Table II (data organization for the percent composition determination, mass, moles, limiting reactant, percent mass)

and figures. There should be a narrative that Table III (for group A–F:of average moles accompanies theeach presentation the data) of CuI, average moles of Cu(NO3)2, average moles Table I (data organization for the sample of KI, theoretical moles of product base on Cu(NO3)2 prep. trials including masses and KI,Two limiting reagent, and percent error)and limiting reactant) (moles of Cu(NO3)2, moles of Calculations Table (data organization for theof KI, moles II of product (CuI), average number moles observed, theoretical moles of productmass, based percent composition determination, Cu(NO 2, theoretical moles of product based on KI, moles,3)limiting reactant, percent mass)

calculation of the entire process for a trial. Mass of initial sample and barium phosphate, moles of barium phosphate, identification, mass, moles, and percentage of limiting reactant)

determination of the limiting reagent and percent error.)

Calculations (step by step sample calculation of the entire process for a trial. Mass of Questions initial sample and barium phosphate, moles of barium Totalphosphate, identification, mass, moles, and percentage of limiting reactant)

Questions Total Grade

Grade Questions Total Grade

Calculations (step by step sample

100 /

%

100 /

%

100 /

%

Experiment 7: Limiting and Excess Reagents Section Points Points Worth Earned

Experiment 7: Limiting and Excess Reagents Section Points Points Worth Earned

Title page (name, title, date, TA,

Title page (name, title, date, TA,

course, section, partner’s name) (you lose points for not having these from now on) Purpose (at least three points)

course, section, partner’s name) (you lose points for not having these from now on) Purpose (at least three points)

Copyright(cited/changes) © 2020 Pearson Education, Inc. Procedure Data (observation, balanced equation)

Procedure (cited/changes) Data (observation, balanced equation)

55

Experiment 8: Redox Reactions in Voltaic Cells: Construction of a Potential Series Instructor Notes and Lab Preparation Chemicals and Equipment Foam cups Pieces of white card stock 1 box of large (15 cm circles) coarse filter paper Sheets of sand paper Multi- or voltmeters and alligator clips 1.0 M NH4NO3 1.0 M Cu(NO3)2 1.0 M Mg(NO3)2 1.0 M Pb(NO3)2 1.0 M Fe(NO3)3 1.0 M AL(NO3)3 0.010 M HNO3 Pieces of the following metals: Cu, Mg, Fe, Pb, Al Aqueous metals waste jar in hood

Preparation Prepare solutions in 0.010 M HNO3. Due to the large quantity of substance required, prepare in advance, as it will take several hours to completely dissolve. Heat may be applied to speed up the process. Also, add small quantities at a time for easier dissolving.

1.0 M NH4NO3: 80.04 g/L 1.0 M Cu(NO3)2: 187.56 g/L 1.0 M Mg(NO3)2: 148.31 g/L 1.0 M Pb(NO3)2: 331.00 g/L 1.0 M Fe(NO3)3: 241.86 g/L 1.0 M AL(NO3)3: 213.00 g/L In class instructions: Do NOT discard the foam cups or metals. Metals MUST be cleaned, dried, and returned to the correct container. *** Mg and Fe are often confused, so make sure you are using the right chemicals. ***

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Instruction Notes This is a very simple lab for the students to perform and takes only about an hour to complete.

We use foam cups to minimize the volume of solution we need to use. 100 mL beakers can be used instead but will require almost 100 mL of solution in each to enable the filter papers to make good contact with the solution. The foam cups only require about 20 to 30 mL, which cuts the chemical cost way down. We ask the students to clean and dry the foam cups at the end of the lab so that we can reuse them from class to class to minimize waste.

Depending on the number of multi- or voltmeters you have available, you can make this an individual, pairs, or group lab experiment. You should assign the 10 metal combinations so that all 10 are completed and reported to the class as a whole. If you have sufficient numbers of students/groups, you can also introduce more statistics into the experiment based on more than one experimental potential value being determined for each of the metal combinations.

Potential Problems The only problem we have ever experienced with this lab is experimental potentials not matching up well with those predicted by calculation. This is generally caused by a poor connection to the voltmeter or poor contact via one or more of the salt bridges. Make sure that both the metals and alligator clips are clean and making good contact with each other and the solution. Also make sure that the salt bridge is soaked through with solution. If the filter paper is wound too tight, it often appears wet but may be dry on the inside.

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Experiment 8 Prelaboratory Assignment KEY Name: ___________________________ Date: _________________ Instructor: ____________________________ Sec. #: ___________

Show all work for full credit.

Following is a diagram of a voltaic cell.

1) Identify the parts of the cell shown above by selecting the appropriate letter from the figure. __ __ __ __ __

E_ This is the positive electrode.

E_ Reduction occurs at this electrode.

E_ This electrode is the cathode B_ Anions depart from the salt bridge here.

A_ Oxidation occurs at this electrode.

2) Write the shorthand notation for the following voltaic cell reaction: Fe(s) + Cu2+(aq) → Fe2+(aq) + Cu(s)

Fe(s)|Fe2+ (1 M)||Cu2+ (1 M)|Cu(s) Write the reaction represented by the following voltaic cell notation: Zn(s)|Zn2+ (1 M)||Cu2+ (1 M)|Cu(s)

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58

Zn(s) + Cu2+(aq) → Zn2+(aq) + Cu(s) 3) The list below shows the reduction potentials for 10 different metal ions.

Calculate ΔE for the redox reaction: Co(s) + Pb2+(aq) → Co2+(aq) + Pb(s) Will this reaction occur spontaneously?

0.15 V; yes Calculate ΔE for the redox reaction: Mn(s) + Fe2+(aq) → Mn2+(aq) + Fe(s) Will this reaction occur spontaneously?

0.74 V; yes Half-Reaction

E˚(V)

Cu2+(aq) + 2e− → Cu(s) +0.34 Pb2+(aq) + 2e− → Pb(s)

–0.13

Sn2+(aq) + 2e− → Sn(s)

–0.14

Ni2+(aq) + 2e− → Ni(s)

–0.25

Co2+(aq) + 2e− → Co(s) –0.28 Cd2+(aq) + 2e− → Cd(s) –0.40 Fe2+(aq) + 2e− → Fe(s)

–0.44

Zn2+(aq) + 2e− → Zn(s) –0.76 Mn2+(aq) + 2e− → Mn(s) –1.18 Mg2+(aq) + 2e− → Mg(s) –2.37

Lab Report Key The title page should include: Student’s full name Date of experiment Complete title of lab report Name of partner(s) Instructor’s name Lab and section number (e.g., CHM1045L-02) The purpose should include: This experiment deals with several subjects, including voltaic cells, redox reactions, oxidation numbers, electricity, and metal ions. The purpose should include references to most of these topics and should not be a copy of what is given in the manual; criteria for success should be mentioned. Full credit can be given if at least three of the aforementioned topics are discussed.

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59

Procedure: This should be an MLA form reference to the lab manual with any changes in the procedure noted. This section should also state which three metals were used for the experiment.

Data: A completed table such as the following should be included.

Cell Representation

o

2+

2+

Fe |Fe || Cu |Cu

o

Anode Half-Reaction Feo to Fe2+ + 2e–

E0anode

Cathode HalfReaction Cu2+ + 2e– to Cuo

E0cathode

Overall Reaction

Ecell Theo.

Ecell Exp .

%err or

Feo + Cu2+ to Fe2+ + Cuo

Second cell Third cell Fourth cell ...nth cell

Calculations: The calculation section should include sample calculations for determining Ecell theoretical and Ecell experimental.

Conclusions: The conclusion section should be several well-developed paragraphs and cover the following information: a) a potential series by ranking the metals according to which is the strongest reducing agent, which is the next strongest, and which is the weakest and b) a potential series by ranking metal ions according to which is the strongest oxidizing agent, which is the next strongest, etc. Students should support both of these potential series rankings using their own results. A discussion on the relationship between the weakest reducing metal and the strongest oxidizing metal should also be included. Another discussion should be included on the comparison of the Ecell theoretical and Ecell experimental along with the percent error values.

Finally, a discussion of any errors that might have lead to the discrepancies in the Ecell values is required.

Question: 1) What is a reactivity series, and how is it related to this experiment?

The activity series of metals, or reactivity series, arranges all metals in order of their decreasing chemical activity. The greater the ease with which an element loses its electrons and acquires a positive charge, the greater is its reactivity. This series can therefore be used to predict which metal in a pair will act as the oxidizing agent (more reactive, higher on list) and which will act as the reducing agent (less reactive, lower on the list).

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60

Experiment 8: Redox Reactions in Voltaic Cells: Construction of a Potential Series Points Points Section Worth

Experiment 8: Redox Reactions in Voltaic Cells: Construction of a Potential Series Points Points Section

Earned

Title page (name, title, date, TA, course,

Title page (name, title, date, TA, course,

section, partner’s name) Purpose (at least three points)

section, partner’s name) Purpose (at least three points)

Procedure (cited/changes + 3 metals) Data Table I (10 cell representations, ½ anode

Procedure (cited/changes + 3 metals) Data Table I (10 cell representations, ½ anode

reaction, ½ cathode reaction, overall reactions, Ecell theoretical, Ecell experimental, %error) Calculations (Ecell theoretical and %error)

reaction, ½ cathode reaction, overall reactions, Ecell theoretical, Ecell experimental, %error) Calculations (Ecell theoretical and %error)

Conclusions (discussion with support of

Conclusions (discussion with support of

the potential series by ranking the metals according to which is the strongest oxidizing agent and according to which is the strongest reducing agent; discussion on the relationship of the weakest reducing metal to the strongest oxidizing metal should also be included, a comparison of the Ecell theoretical and Ecell experimental along with the %error values, and any errors that might have led to the discrepancies in the Ecell values)

the potential series by ranking the metals according to which is the strongest oxidizing agent and according to which is the strongest reducing agent; discussion on the relationship of the weakest reducing metal to the strongest oxidizing metal should also be included, a comparison of the Ecell theoretical and Ecell experimental along with the %error values, and any errors that might have led to the discrepancies in the Ecell values)

Questions Total Grade

Questions Total Grade

100 /

%

Experiment 8: Redox Reactions in Voltaic Cells: Construction of a Potential Series Points Points Section Worth

Earned Title page (name, title, date, TA, course,

section, partner’s name) Purpose (at least three points)

section, partner’s name) Purpose (at least three points)

Procedure (cited/changes + 3 metals) Data Table I (10 cell representations, ½ anode

Procedure (cited/changes + 3 metals) Data Table I (10 cell representations, ½ anode

reaction, ½ cathode reaction, overall reactions, Ecell theoretical, Ecell experimental, %error) Calculations (Ecell theoretical and %error)

reaction, ½ cathode reaction, overall reactions, Ecell theoretical, Ecell experimental, %error) Calculations (Ecell theoretical and %error)

Conclusions (discussion with support of

Conclusions (discussion with support of

the potential series by ranking the metals according to which is the strongest oxidizing agent and according to which is the strongest reducing agent; discussion on the relationship of the weakest reducing metal to the strongest oxidizing metal should also be included, a comparison of the Ecell theoretical and Ecell experimental along with the %error values, and any errors that might have led to the discrepancies in the Ecell values)

the potential series by ranking the metals according to which is the strongest oxidizing agent and according to which is the strongest reducing agent; discussion on the relationship of the weakest reducing metal to the strongest oxidizing metal should also be included, a comparison of the Ecell theoretical and Ecell experimental along with the %error values, and any errors that might have led to the discrepancies in the Ecell values)

Questions Total Grade

Questions Total Grade

.

Earned

100 /

%

Experiment 8: Redox Reactions in Voltaic Cells: Construction of a Potential Series Points Points Section

Title page (name, title, date, TA, course,

100 /

Worth

%

Worth

Earned

100 /

% 61

Experiment 9: Reactions in Aqueous Solutions: Strong Acids and Bases Instructor Notes and Lab Preparation Chemicals and Equipment 0.5 M HCl 1 L, dyed red 0.5 M NaOH 1 L, dyed blue 1 mL graduated pipette (plastic) 3-way rubber bulb 25 mL volumetric flasks 50 mL beaker as needed Hotplates pH meter Power supply Calibration instructions Buffer solutions

Setup The 0.5 M solutions are purchased in standardized form, and a few drops of food color are added to make it easier for the students to differentiate the solutions. A hotplate and a pH meter should be provided for every two students.

Instruction Notes Points to Stress This is a relatively straightforward lab that allows students to observe the reaction of a strong acid and base and how the concentrations of each relate to their pH. We also use the lab to point out the predictability of the production of salt from the acid–base reaction. This reinforces the limiting and excess reagents lab just completed. The lab also introduces the use of pipettes, serial dilution, pH meters, and calibration.

Potential Problems The only problem we have had with the experiment is the pH of the DI water not being 7 or even very close to 7. This complicates the calculation of pH and makes for much greater errors between the students’ calculated and experimental values.

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Experiment 9 Prelaboratory Assignment KEY Name: ___________________________ Date: _________________ Instructor: ____________________________ Sec. #: ___________

Show all work for full credit.

1) Constant boiling HCl has a concentration of 11.6 M. Your laboratory assistant is going to dilute this acid for you to create a stock solution of HCl for you to use in this experiment.

What volume of the 11.6 M HCl must the assistant add to a 1 L volumetric flask so that the concentration of the stock solution will be 0.62 M after dilution to the mark with water?

53.4 mL What is the pH of this stock solution? (Remember the significant figure rules for logarithms!)

0.21 You will now use this 0.62 M HCl solution to carry out a series of dilutions, measuring the pH of each diluted sample. Calculate the [Cl–] and [H+] concentrations and the pH of each sample. (Remember the significant figure rules for logarithms!)

Sample A will be produced by pipetting 1.00 mL of the stock solution into a 25 mL volumetric flask and diluting to volume with distilled water.

[Cl–] = 2.5e – 2 M [H+] = 2.5e – 2 M pH = 1.61 Sample B will be produced by pipetting 1.00 mL of sample A into a 25 mL volumetric, and diluting to volume with distilled water.

[Cl–] = 9.9E – 4 M [H+] = 9.9E – 4 M pH = 3.00 Sample C will be produced by pipetting 1.00 mL of sample B into a 25 mL volumetric, and diluting to volume with distilled water.

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63

[Cl–] = 4.0e – 5 M [H+] = 4.0e – 5 M pH = 4.40 Sample D will be produced by pipetting 1.00 mL of sample C into a 25 mL volumetric, and diluting to volume with distilled water.

[Cl–] = 1.6e – 6 M [H+] = 1.6e – 6 M pH = 5.80 Sample E will be produced by pipetting 1.00 mL of sample D into a 25 mL volumetric, and diluting to volume with distilled water.

[Cl–] = 6.3e – 8 M [H+] = 1.4e – 7 M pH = 6.86 Sample F will be produced by pipetting 1.00 mL of sample E into a 25 mL volumetric, and diluting to volume with distilled water.

[Cl–] = 2.5e – 9 M [H+] = 1.0e – 7 M pH = 6.99 2) Your laboratory assistant is going to prepare a stock solution of sodium hydroxide (NaOH) for you. What mass of NaOH must the assistant add to water in a 1 L volumetric flask so that the stock solution has a concentration of 0.35 M after dilution to the mark with water?

14 g What is the pH of this stock solution? (Remember the significant figure rules for logarithms!)

13.54 You will now use this 0.35 M NaOH solution to carry out a series of dilutions in the same manner as in problem 1, measuring the pH of each diluted sample. Calculate the [Na+] and [OH–] concentrations and the pH of each sample A–F.

(A) [Na+] = 1.4e – 2 M [OH–] = 1.4e – 2 M pH = 12.15 (B) [Na+] = 5.6e – 4 M [OH–] = 5.6e – 4 M pH = 10.75

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64

(C) [Na+] = 2.2e – 5 M [OH–] = 2.2e – 5 M pH = 9.35 (D)[Na+] = 9.0e – 7 M [OH–] = 9.1e-7 M pH = 7.96 (E)[Na+] = 3.6e – 8 M [OH–] = 1.2e – 7 M pH = 7.08

Lab Report Key The title page should include: Student’s full name Date of experiment Complete title of lab report Name of partner(s) Instructor’s name Lab and section number (e.g., CHM1045L-02) The purpose should include: This experiment deals with several subjects, including what is a strong acid or base, pH, neutralization reactions, pipetting, and salt production. The purpose should include references to most of these topics and should not be a copy of what is given in the manual. Full credit can be given if at least three of the aforementioned topics are discussed.

Procedure: This should be an MLA form reference to the lab manual with any changes in the procedure noted.

Data: The data section should include three tables. The first table should be for the acid and include the following information: a) concentration of acid after each dilution, b) experimental pH of each dilution, c) theoretical pH of each dilution, and d) percent error in the pH value.

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65

The second table should be for the base and include the following information: a) concentration of acid after each dilution, b) experimental pH of each dilution, c) theoretical pH of each dilution, and d) percent error in the pH value.

The third table is for the combined acid and base solutions and should include a) concentration of acid and base for each combination, b) experimentally determined pH, c) the theoretical pH (HINT: Think DI water), and d) the percent error in the pH value.

Also make sure to include the pH of the DI water used for the dilution.

Finally, state the balanced chemical equation for this experiment, the theoretical and experimental yield of the salt obtained from heating the acid/base mixture, and percent yield of the reaction.

Calculations: In the calculation section be sure to include examples calculation for the following: a) concentration of dilution, b) pH, c) pH from pOH, d) experimental error, e) theoretical yield of salt, and f) percent yield of salt.

Also include Excel graphs of the pH versus concentration for both the acid and base. Remember all graphing guidelines apply here.

Conclusions: The conclusion section should be several paragraphs in length and include the following information: a) a discussion on the experimental and theoretical pH as well as the percent error for both the acid and the base, be sure to discuss in detail any discrepancies in the values (within this discussion, explain the trends seen in the graphs you made); and b) a discussion on the pH of the combined solutions and the error in the values, be sure to include a statement about what is expected from these mixtures and why that was not achieved. Finally, discuss the percent yield of salt and any error that may have caused a yield less than or greater than 100%.

Questions: 1) Explain how this experiment can be related to limiting and excess reagent problems.

The determination of the salt yield is based on the amount of reagents that are added.

2) The acid and base used in this experiment are monoprotic. What does this mean, and how would the experimental results differ if a diprotic acid had been used instead?

If the acid were diprotic, it would take twice as much base to neutralize the acid because the molar ratio between H and OH would be 2:1. If the same volumes were used, half as much product would be produced because the base would run out.

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66

Experiment 9: Reactions in Aqueous Solutions: Strong Acids and Bases Section Points Points Worth Earned Title page (name, title, date, TA,

Experiment 9: Reactions in Aqueous Solutions: Strong Acids and Bases Section Points Points Worth Earned Title page (name, title, date, TA,

course, section, partner’s name)

course, section, partner’s name)

Purpose Procedure (cited & changes) Data Tables: [acid/base/combo],

Purpose Procedure (cited & changes) Data Tables: [acid/base/combo],

experimental and theoretical pH, %error in pH, pH of DI water and balanced equation, salt experimental and theoretical yield.

experimental and theoretical pH, %error in pH, pH of DI water and balanced equation, salt experimental and theoretical yield.

Calculations concentration of dilution,

Calculations concentration of dilution,

pH, pH from pOH, graphs (acid and base), experimental error, theoretical yield of salt, and percent yield of salt

pH, pH from pOH, graphs (acid and base), experimental error, theoretical yield of salt, and percent yield of salt

Conclusions (discussion of the

Conclusions (discussion of the

experimental and theoretical pH, percent error for both the acid and base, trends seen in the graphs, pH of the combined solutions and error in the values [including what the value should be], and percent yield of salt and any errors)

experimental and theoretical pH, percent error for both the acid and base, trends seen in the graphs, pH of the combined solutions and error in the values [including what the value should be], and percent yield of salt and any errors)

Questions Total Grade

Questions Total Grade

100 /

%

Experiment 9: Reactions in Aqueous Solutions: Strong Acids and Bases Section Points Points Worth Earned Title page (name, title, date, TA, course, section, partner’s name)

%

course, section, partner’s name)

Purpose Procedure (cited & changes) Data Tables: [acid/base/combo],

experimental and theoretical pH, %error in pH, pH of DI water and balanced equation, salt experimental and theoretical yield.

experimental and theoretical pH, %error in pH, pH of DI water and balanced equation, salt experimental and theoretical yield.

Calculations concentration of dilution,

Calculations concentration of dilution,

pH, pH from pOH, graphs (acid and base), experimental error, theoretical yield of salt, and percent yield of salt

pH, pH from pOH, graphs (acid and base), experimental error, theoretical yield of salt, and percent yield of salt

Conclusions (discussion of the

Conclusions (discussion of the

experimental and theoretical pH, percent error for both the acid and base, trends seen in the graphs, pH of the combined solutions and error in the values [including what the value should be], and percent yield of salt and any errors)

experimental and theoretical pH, percent error for both the acid and base, trends seen in the graphs, pH of the combined solutions and error in the values [including what the value should be], and percent yield of salt and any errors)

.

/

Experiment 9: Reactions in Aqueous Solutions: Strong Acids and Bases Section Points Points Worth Earned Title page (name, title, date, TA,

Purpose Procedure (cited & changes) Data Tables: [acid/base/combo],

Questions Total Grade

100

100 /

%

Questions Total Grade

100 /

67

%

Experiment 10: The Copper Cycle Instructor Notes and Lab Preparation Chemicals and Equipment Concentrated HNO3 Copper pellets/strips 3.0 M NaOH Water Bunsen Burner Striker 6.0 M H2SO4 Zinc pellets 6.0 M HCl Blue litmus paper Acetone

Setup •

•

.

The first step of the copper cycle involves the oxidation of copper in nitric acid. The students will be working with concentrated nitric acid and, as such, should be sure to wear gloves and be careful. o While it is not important that they use exactly 4 mL of concentrated HNO3, it is important they do not use a large excess, as they need to neutralize all of the acid in a subsequent step. o The reaction of Cu(s) and HNO3(aq) produces nitrogen dioxide, which is dangerous.

Therefore, the students will perform the first step in the hoods on the bench tops. They must have the beaker pushed to the back of the hood for the hood to actually pull the evolved gas away from them. Please urge them to be very careful. o They should swirl the reaction to make sure that all of the copper reacts. They must also make sure that the copper is immersed in the acid by coiling the copper wire and placing it in the bottom of the beaker. Once all of the copper has reacted, they should wash any material on the watch glass into the solution and make sure that no more gas is produced when the solution is swirled.

After adding the nitric acid, the solution should be green in color and transparent. The addition of sodium hydroxide will lead to the formation of a light blue precipitate (unless NaOH is added too quickly, which can lead to heat generation and the formation of CuO, which is black). Heating the blue precipitate should produce a black precipitate. The solution should be digested thoroughly to avoid the formation of small particulates. The addition of sulfuric acid will lead to a transparent blue solution. The addition of zinc will produce bubbles (hydrogen gas) and cause solid copper (which is not shiny, but a dull red-brown) to form. The blue solution should vanish completely.

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•

•

•

The zinc addition and removal can cause some problems for the students. Emphasize that they should add the zinc stepwise to minimize excess zinc in the solution. They will likely have a lot of questions as to what to do at this step.

Because of the evolution of H2(g) in the final step of this experiment, and the fact that students work at different paces, the students should use hot plates rather than Bunsen burners for the conversion of Cu(OH)2(s) to CuO(s).

The decanting step after the formation of CuO(s) will generate many student questions (as in “Is this settled enough?”). It is okay to lose some floaters. It generally takes 10 to 15 min for the precipitate to settle. They should try to avoid disturbing the precipitate during the pouring off of the supernatant.

In this lab, you will examine a series of reactions that begin and end with elemental copper. The types of reactions that you will carry out include those that you have discussed—precipitation, acid–base, dehydration, and oxidation–reduction reactions.

The first reaction you will carry out is the dissolution of solid copper in concentrated nitric acid.

The products of this reaction are copper(II) nitrate and nitrogen dioxide. Because we begin with an element and produce an ionic compound, this is a redox reaction. The compound produced is a soluble compound, so that Cu2+ is present in solution. The use of concentrated nitric acid requires caution (i.e., gloves must be worn). In addition, the NO2 gas produced is toxic; therefore, this reaction will be carried out in the hoods in the lab (the small hoods on the bench tops). The reaction typically proceeds quickly; you should swirl the reaction occasionally to check its progress. Be sure that the copper is all at the bottom of the beaker before adding the acid, or it will not react. You will cover the solution with a watch glass while the reaction occurs.

When done, rinse the watch glass, swirl to make sure that all of the copper has reacted, and take the beaker back to your work station.

Cu

(1)

Cu(NO3)2

(5)

(2)

CuSO4

Cu(OH)2

(4)

CuO

(3) 

After adding deionized water to the products of Reaction 1, you will add sodium hydroxide. This leads to the formation of Cu(OH)2. Would you expect this to be soluble or insoluble? It is insoluble, as are the vast majority of hydroxides and oxides. For the third reaction, you will dehydrate the hydroxide to form copper(II) oxide, or cupric oxide. This reaction should look familiar to you, as you carried out a similar reaction in the empirical formula lab. As you did in the limiting reagent lab, you will digest the cupric oxide precipitate to form larger particulates that will settle faster. **Change to the procedure: use a hot plate instead of Bunsen burner.** After decanting the supernatant from this step and washing the precipitate, you will add sulfuric acid to form copper(II) sulfate. Soluble or insoluble? Soluble—most sulfates are soluble

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(exceptions are Ca2+, Ba2+, Pb2+, Sr2+, and Ag+). Finally, to get back to elemental copper from Cu2+, what kind of a reaction will be needed? Another redox reaction is needed. Zinc will be oxidized while copper is reduced. Zinc will also be oxidized by a reaction with the excess sulfuric acid: Zn(s) + 2H+(aq) → Zn2+(aq) + H2(g). The formation of bubbles in the solution indicates that hydrogen gas has been evolved. It is because of the evolution of H2(g) that we will use the hotplates instead (just in case someone is heating next to someone evolving hydrogen gas).

The final reaction of the copper cycle provides some challenges. You should be sure to read your lab manual very carefully and make clear notes in your lab notebook so that you can make the appropriate decisions in the lab. You will add the solid zinc in increments to try to avoid adding a substantial excess. You must first make sure that the solution is no longer blue—if any blue remains, there is still Cu2+ in solution. This could be because you have not added enough zinc.

To see, add some zinc. If bubbling resumes, then you have run out of zinc. If bubbling does not resume, then you have run out of acid, which is needed to keep the copper from forming on the zinc particles. You will add some acid and wait for the solution to turn colorless. Once the solution is colorless, all of the Cu2+ has been reduced to Cu. Now, you need to remove any excess Zn in the beaker so that it does not contribute to your final mass. To do so, you should add HCl to the solution and wait for the bubbling to stop. This can take quite a bit of time (20 to 30 min), so you should manage your time during the experiment. You should also be patient when adding the zinc, as adding too much in the beginning will only lead to a longer waiting time at the end.

When you have your final sample, you will rinse the solid copper with acetone to remove excess water, and leave the evaporating dish containing the copper in your drawer for next week. When you write your report, leave space to include your final results. Leave space in your table for the final mass, space in the report for the percent recovery calculation, and space to write your percent recovery in a sentence.

Lab Report Key Purpose: The goal of this experiment was to take a sample of copper wire and run it through a series of chemical reactions that ultimately led back to the recovery of the initial sample of copper. The data collected during this experiment was mainly qualitative data concerning what occurred during each of the chemical reactions. The small amount of quantitative data collected such as the mass (g) of the original copper sample and the mass (g) of the final sample and evaporating dish led into the final calculation of the sample recovered. The general concepts displayed in this experiment involved the ability to accurately and scientifically record observations pertaining to each chemical reaction, as well as performing accurate decanting and measuring.

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70

Procedure: Deviations: • A very slight amount of the sample may have been lost during the decanting process.

• The removal of excess zinc step was not performed due to the absence of any excess zinc.

• The evaporating dish was first placed into oven; however, the sample did not dry entirely, and the evaporating dish was then left in the drawer to dry.

Data and Results: The mass (g) of the initial copper sample was taken to determine the percent recovery in the end.

The mass (g) of the zinc added to the solution in Step 5 was also recorded. The mass (g) of the evaporating dish was recorded in order to determine the final mass (g) of copper recovered using mass by difference.

Table 1: Summary Raw Data Equipment/Materials Copper wire Zinc Evaporating dish Evaporating dish + copper Final copper sample

Mass (g) 0.2953 3.0010 44.2915

Observations of Chemical Reactions in Each Step: Step 1: The addition of 4.0 mL of HNO3 to the copper wire dissolved the copper wire. The copper wire began to bubble when the 4.0 mL of HNO3 was added, and a brown gas started to form inside of the beaker. The solution turned a blue-green color, and when the bubbling of copper wire ceased and the copper wire was completely dissolved, the gas also ceased to form.

Each of these events occurred as expected.

Cu(s) + 4HNO3(aq) → Cu(NO3)2(aq) + 2H2O(l) + 2NO2(g) Step 2: The addition of 30 mL of 3.0 M NaOH to the dissolved copper solution first turned the solution a very bright, vivid blue. The blue color change was expected, but the change to a dark color happened more rapidly than expected. Then as a precipitate began to form, the solution turned into a dark black color. The resulting precipitate consisted of numerous black flakes and was bulky.

Cu(NO3)2(aq) + 2NaOH(aq) → Cu(OH)2(s) + 2NaNO3(aq)

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71

Step 3: As the beaker containing the precipitate was heated on the hot plate, the precipitate began to fall to the bottom of the beaker. The supernatant began as a muddy brown color, but became clearer as the precipitate dropped to the bottom of the beaker. These events occurred as expected.

Cu(OH)2(s) → CuO(s) + H2O(l) Step 4: The addition of 15 mL of 6.0 M H2SO4 to the precipitate resulted in the disappearance of the dark precipitate, and the solution turned to a uniform, light blue color. These events occurred as expected.

CuO(s) + H2SO4(aq) → CuSO4(aq) + H2O(l) Step 5: The addition of 3.0 g of zinc to the solution resulted in the bubbling of the zinc within the beaker. The reaction within the beaker caused the beaker to warm up, and the zinc began to turn to a red-orange color. The solution also became lighter and eventually clear and colorless as the reaction came to an end. The resulting precipitate also clumped together into one large mass.

These events occurred as expected.

CuSO4(aq) + Zn(s) → Cu(s) + ZnSO4(aq)

Step 6: After it was added to the evaporating dish and washed with acetone, the resulting copper product has a similar orange-red color as the initial copper wire, but it was not shiny as the wire was. The final sample looked as it was expected to look.

Calculations: The final mass of the copper sample is determined by subtracting the mass (g) of the evaporating dish from the mass (g) of the evaporating dish with the sample inside of it: mass of evaporating dish and copper sample (g) – mass of evaporating dish (g) = final mass of copper sample (g) g – 44.2915 g = final mass of copper sample (g) g = final mass of copper sample (g)

The percent recovery is determined by dividing the mass (g) of the final copper sample by the mass (g) of the initial copper sample, and multiplying that value by 100%:

Final mass of copper sample( g )  100% = percent recovery of copper Initial mass of copper wire(g ) g  100% = percent recovery of copper 0.2953 g % = percent recovery of copper sample

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Discussion: It is possible that after the final calculations have been performed, the percent recovery is greater than 100% for the copper cycle experiment. However, it is not possible to create more copper than what was started with. There are two explanations that can account for a percent recovery that is greater than 100%. One explanation is that the final copper product was massed before it was fully dry, and the mass (g) of water or acetone that had not fully evaporated from the dish could account for the extra mass (g) that would lead to a percent recovery greater than 100%.

Another explanation could be that all of the excess zinc was not removed from the beaker, and the mass (g) of the excess zinc plus the mass (g) of the final copper produced could account for a percent recovery that is greater than 100%. Both of these possible explanations can account for a percent recovery that is greater than 100%.

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73

Experiment 10: Copper Cycle Section Points Points Worth Earned

Experiment 10: Copper Cycle Section Points Points Worth Earned

Title page (name, title, date, TA,

Title page (name, title, date, TA,

course, section, partner’s name)

course, section, partner’s name)

Purpose (at least three

Purpose (at least three

discussion points)

discussion points)

Raw Data Table Sample Calc. (% Recovery) (calculation is

Raw Data Table Sample Calc. (% Recovery) (calculation is

complete, correct, and reported with the correct number of significant figures)

complete, correct, and reported with the correct number of significant figures)

Summary of Observations and Chemical Reactions

Summary of Observations and Chemical Reactions

(observations describe events in complete sentences; colors, consistency, and other details describe each reaction step; both expected and unexpected events are reported; and chemical equations for each reaction are properly balanced and include states of matter)

(observations describe events in complete sentences; colors, consistency, and other details describe each reaction step; both expected and unexpected events are reported; and chemical equations for each reaction are properly balanced and include states of matter)

Total Grade

100 /

%

Total Grade

100 /

%

Experiment 10: Copper Cycle Section Points Points Worth Earned

Experiment 10: Copper Cycle Section Points Points Worth Earned

Title page (name, title, date, TA,

Title page (name, title, date, TA,

course, section, partner’s name)

course, section, partner’s name)

Purpose (at least three

Purpose (at least three

discussion points)

discussion points)

Raw Data Table Sample Calc. (% Recovery) (calculation is

Raw Data Table Sample Calc. (% Recovery) (calculation is

complete, correct, and reported with the correct number of significant figures)

complete, correct, and reported with the correct number of significant figures)

Summary of Observations and Chemical Reactions

Summary of Observations and Chemical Reactions

(observations describe events in complete sentences; colors, consistency, and other details describe each reaction step; both expected and unexpected events are reported; and chemical equations for each reaction are properly balanced and include states of matter)

(observations describe events in complete sentences; colors, consistency, and other details describe each reaction step; both expected and unexpected events are reported; and chemical equations for each reaction are properly balanced and include states of matter)

Total Grade .

100 /

%

Total Grade

100 /

%

74

Experiment 11: Atomic Spectra Instructor Notes and Lab Preparation Chemicals and Equipment

6 M HCl 1 bottle of mossy zinc 1 striker 2 Petri dishes with opening, labeled as unknown 1 and unknown 2 2 coffee cans with opening for flames Spectroscopes Helium lamp, labeled as helium Sodium flame (NaCl), labeled as unknown 1 Lithium (LiCl) flame, labeled as unknown 2 Hydrogen lamp, labeled as unknown 3 Krypton lamp, labeled as unknown 4 Mercury lamp, labeled as unknown 5 2 Bunsen burners with vacuum tubing Procedure There will be a set up that displays one unknown flame. Place the unknown salt in the Petri dish. Cover and place the Bunsen burner over the opening in the Petri dish. Then cover with the coffee can. When ready to start the experiment, place a few pieces of zinc and a few milliliters of HCl in the Petri dish, cover, and light the Bunsen burner. Place one lamp on each of the remaining four lab benches.

Place the zinc, HCl, striker, and spectroscopes on the front counter.

Example coffee can flame setup and lamp setup .

75

Spectroscopes are inexpensive (< $10) and are available from both Fisher Scientific and SargentWelch as well as many other sources. Lamps and bulbs can also be bought from Fischer Scientific, and bulbs are available for many other elements as well.

Instruction Notes We generally set up five unknown light sources for this lab. Every other semester, I change a few of the sources to keep the experiment fresh. As mentioned above, there are a variety of light bulbs available for the lamps, and most of the alkali metals and alkaline earth metals can be vaporized using mossy zinc and HCl to produce colored flames.

Having the students calculate their own wavelengths in the prelab and then determine the identity of those elements in the lab really exemplifies the use of spectrometry for identification of materials both near and far.

Points to Stress We ask the students to work in pairs to ensure that the measurements taken are reproducible.

This introduction to the necessity of reproducibility in science should be pointed out. Another important point is the introduction of the need to calibrate instrumentation. To this point, we have assumed that the instruments and equipment being used are in good condition and operating correctly. This experiment is the first time the fallacy of that assumption is explained and corrected. The creation of a calibration graph is an important tool that the students will need in future experiments and should not be overlooked as a teaching point in an effort to complete the rest of the lab.

Potential Problems The majority of the problems associated with this lab come from inappropriate use of the spectrometers. Make sure the students are aligning the slit in the spectrometer, not the grating, with the light source. Also, too much ambient light will make the lines of the source difficult to see. Keep the light in the lab dim if at all possible. Unfortunately, you cannot turn off all the lights because then the calibration lines in the spectrometer are invisible as well. Goggles make reading the spectrometers more difficult. I generally allow students to work around the lamp sources without the goggles, but because of the acid, have them use the goggles around the flames.

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Experiment 11 Prelaboratory Assignment KEY Name: ___________________________ Date: _________________ Instructor: ____________________________ Sec. #: ___________

Show all work for full credit.

1) You have just carried out the calibration of your spectroscope’s diffraction grating and you get the values shown in the table for the visible emission lines of helium. Plotting these values gives the graph shown below.

Color

Wavelength, Spectrometer nm Reading

Violet

388.9

5.3

Blue

447.1

5.7

Green

501.6

6.1

Yellow

587.6

6.8

Orange

667.8

7.7

Red

706.5

8.3

What would be the wavelength of spectral lines that give the following readings on this spectrometer?

Spectrometer Reading: 6.5; wavelength: 554 nm Spectrometer Reading: 7.5; wavelength: 652 nm Spectrometer Reading: 8.1; wavelength: 695 nm What would be the frequency of these spectral lines?

Spectrometer Reading: 6.5; frequency: 5.4e+14 hz Spectrometer Reading: 7.5; frequency: 4.6e+14 hz Spectrometer Reading: 8.1; frequency: 4.3e+14 hz

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What would be the energy of a photon from each line?

Spectrometer Reading: 6.5; energy of one photon: 3.6e-19 J Spectrometer Reading: 7.5; energy of one photon: 3.0e-19 J Spectrometer Reading: 8.1; energy of one photon: 2.9e-19 J What would be the energy of a mole of photons from each line?

Spectrometer Reading: 6.5; energy of one mole of photons: 2.2e+05 J Spectrometer Reading: 7.5; energy of one mole of photons: 1.8e+05 J Spectrometer Reading: 8.1; energy of one mole of photons: 1.7e+05 J

2) The following atomic line spectra display six of the more prominent lines observed in the visible region for the indicated element. The number by each line represents its the relative intensity. A photograph of the actual spectrum of the element may show many more lines, or sometimes fewer lines, depending on the overall intensity of the spectrum. If two lines are within 1 nm of each other, they are shown as a single line. You can find a complete listing of the lines for each element at the NIST Atomic Spectra Database.

Some spectral lines of Krypton:

Identify the line in the spectrum of Kr with each of the following characteristics: Light with a photon energy of 256.8 kJ/mol. C Light with a frequency of 7.014 × 1014 s–1. A Light with a photon energy of 3.566 × 10–19 J/photon. E

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Lab Report Key The title page should include: Student’s full name Date of experiment Complete title of lab report Name of partner(s) Instructor’s name Lab and section number (e.g., CHM1045L-02) The purpose should include: This experiment deals with several subjects, including spectra, wavelengths, frequencies, spectrometers, and colors. The purpose should include references to most of these topics and should not be a copy of what is given in the manual. Full credit can be given if at least three of the aforementioned topics are discussed, along with criteria for success.

Procedure: This should be an MLA form reference to the lab manual with any changes in the procedure noted.

Data: The data section for this report should have the two data tables. The first table should have helium calibration data. This should include a) known He wavelengths and b) experimental wavelengths observed. The second data table is for unknown data. This should include the following: a) unknown light source, b) observed values from the unknown light source, c) corresponding colors, d) corrected wavelength, and e) identity of the unknowns.

Calculations: The calculation section should include the calibration graph for the helium data. This graph should have the experimental value for helium on the x-axis and the known helium wavelength on the y-axis. All graphing guidelines apply. An example calculation of how the wavelengths were corrected should be included.

Conclusions: The conclusion section should be several well-developed paragraphs that include the identity of each unknown and supporting arguments with wavelength values as to why the identities were assigned. A discussion of possible errors should be included as usual.

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Questions: 1) What is the difference between an emission and absorption spectrum?

An emission spectrum is produced as the electrons of an element release energy in the form of photons. The colors emitted depend on the spacing of the quantum levels inside the structure of the atom. An absorption spectrum is formed when white light energy is shown on an atom and the atom absorbs certain frequencies of the light—again based on the structure of the atom. Both types of spectrums depend on the structure of the atom because it determines the energy released and the energy absorbed.

2) Each element has a unique set of wavelengths associated with it. How are these different wavelengths generated?

The structure of each element’s atoms is unique in the spacing of its quantum energy levels (shells). These differences in energy generate a unique set of wavelengths when electrons are traveling from level to level.

3) How does NASA use spectroscopy to explore far-away planets?

Using telescopic spectroscopy, NASA can determine the emission spectrums of the light being emitted from planets, stars, etc. far across the galaxy. Because each element has a unique set of wavelengths, scientists can then determine what elements are present on that planet, star, etc.

4) We say that the Sun is a yellow star. What does this really mean?

Star classification is based on the stellar spectral lines. They indicate the color and the temperature of a star. Our sun is classified as G2, which is a “yellow” star with about 5500 °C surface temperature.

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Experiment 11: Atomic Spectra Section Points Worth

Points Earned

Experiment 11: Atomic Spectra Section Points Worth

Title page (name, title, date, TA,

Title page (name, title, date, TA,

course, section, partner’s name) Purpose (at least three points)

course, section, partner’s name) Purpose (at least three points)

Procedure (cited/changes) Data Table I (known He wavelengths and

Procedure (cited/changes) Data Table I (known He wavelengths and

experimental wavelengths you observed.)

Table II (unknown light source, observed values from the unknown light source, corresponding colors, corrected wavelength, and identity of unknowns) (3 points for correct identity of all unknowns) Graphs (calibration graph)

experimental wavelengths you observed.)

Table II (unknown light source, observed values from the unknown light source, corresponding colors, corrected wavelength, and identity of unknowns) (3 points for correct identity of all unknowns) Graphs (calibration graph)

Conclusions (discussion of the

Conclusions (discussion of the

identity of each unknown light source, including the identity, a detailed explanation of how the identity of each light source was determined, and discussion of possible errors)

identity of each unknown light source, including the identity, a detailed explanation of how the identity of each light source was determined, and discussion of possible errors)

Questions Total Grade

Questions Total Grade

100 /

Experiment 11: Atomic Spectra Section Points Worth

%

Points Earned

100 /

%

Experiment 11: Atomic Spectra Section Points Worth

Points Earned

Title page (name, title, date, TA,

Title page (name, title, date, TA,

course, section, partner’s name) Purpose (at least three points)

course, section, partner’s name) Purpose (at least three points)

Procedure (cited/changes) Data Table I (known He wavelengths and

Procedure (cited/changes) Data Table I (known He wavelengths and

experimental wavelengths you observed.)

Table II (unknown light source, observed values from the unknown light source, corresponding colors, corrected wavelength, and identity of unknowns) (3 points for correct identity of all unknowns) Graphs (calibration graph)

experimental wavelengths you observed.)

Table II (unknown light source, observed values from the unknown light source, corresponding colors, corrected wavelength, and identity of unknowns) (3 points for correct identity of all unknowns) Graphs (calibration graph)

Conclusions (discussion of the

Conclusions (discussion of the

identity of each unknown light source, including the identity, a detailed explanation of how the identity of each light source was determined, and discussion of possible errors)

identity of each unknown light source, including the identity, a detailed explanation of how the identity of each light source was determined, and discussion of possible errors)

Questions Total Grade

Questions Total Grade

.

100 /

%

Points Earned

100 /

%

81

Experiment 12: Colligative Properties of Solutions Instructor Notes and Lab Preparation Chemicals and Equipment

.

Equipment

Quantity

Large test tubes

4

250 mL Erlenmeyer flask

1

400 mL beaker (for salt H2O bath)

1

600 mL beaker (for ice)

1

15 mL graduated cylinder

1

Digital thermometer

1

Stopwatch

1

Ring stand

1

Rubber stopper

1

Chemicals

Quantity

Cyclohexane (d = 0.779 g/mL, MW 84.162 g/mol)

30 mL

Naphthalene (MW 128.174 g/mol)

0.2 g

Maleic Anhydride (MW 98.06 g/mol)

0.2 g

Anthracene (MW 178.23 g/mol)

0.2 g

Salt, NaCl

As needed

Ice

As needed

Unknown solid or liquid

0.1–0.15 g

Water

As needed

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Possible Unknowns for Colligative Properties Compound

Physical State

Molar Mass (g/mol)

Anthracene

Solid

178.23

Bromobenzene

Liquid

157.02

Camphor

Solid

152.24

Carvone

Liquid

150.22

Maleic Anhydride

Solid

98.06

Biphenyl

Solid

154.21

Naphthalene

Solid

128.17

Benzophenone

Solid

182.22

2-Octanol

Liquid

130.23

Instructor Notes: •

•

•

• •

• • •

.

For the naphthalene/cyclohexane trials, they should take the mass of the test tube, cyclohexane, and stopper as a combined unit before each run to account for any evaporative loss.

The cooling curves should plateau at the freezing point of the solvent or the solution. There can also be a continual drift of the freezing temperature to lower values, rather than a plateau.

In this case, as stated in the lab manual, the students should draw best fit lines through the cooling portion and the freezing portion, and take the intersection of the two as the freezing point.

The students should use the graph paper in the lab to make the cooling curve plots. They should use a separate piece of graph paper for each plot. They do not have to duplicate these graphs for the pair when turning in the lab reports. They have three trials for each part of the lab—they only need to turn in one plot from each part, so they can divide the plots accordingly. They can also turn in one of the Tf plots before leaving the lab as part of their lab notebook sheets. They do need to each make their own plot of Tf vs. m, from which they can determine the value of Kf (this can be done outside of lab).

In order to be efficient, one student of the pair can plot the data while the other student masses the test tube and gets the sample ready for the next trial.

It is important to remind the students that they must each have a full set of data in their lab notebooks before they leave the lab. They must copy all of the time/temperature data before leaving the lab.

Remind the students to minimize evaporative loss from their samples by keeping the stopper in the test tube whenever possible.

Remind the students to check the setting on the digital readout for the thermocouple so that they are reading the temperature to one decimal place.

Time is of the essence in this lab. If data can be taken (i.e., the sample is warmed up, massed, and so on), then it should be taken. It is fine if they leave the plotting until the end of the lab

83

•

period, although they should work on the plots when time permits. If time appears to be running short, reduce the number of trials for the unknown to one or two. The selection of the unknown is also an issue. Of the unknown available, the liquids and naphthalene are the only ones that dissolve in a reasonable amount of time. Of the possible unknowns (I will make sure all of you have the list of unknowns before your lab starts), I would pull out all of the solids except naphthalene.

I think the real key is to stay on top of your students and to encourage them to do the plots at the end of the lab. Although we would like them to complete all of the Tf plots before leaving lab, if they can complete two Tf plots total (one for cyclohexane, and one for naphthalene in cyclohexane), then that would be sufficient. I would not recommend announcing this to your students at the start of lab. Rather, if they are running out of time, simply tell them that two graphs is a sufficient amount.

A summary of the prelab lecture I will give to the students appears below.

You will be exploring a colligative property, freezing point depression, in lab this week.

Specifically, you will examine the nonpolar solvent cyclohexane and solutions of this solvent in order to determine the value of Kf for cyclohexane. With the value of Kf determined, you will then use this value to determine the identity of an unknown substance dissolved in cyclohexane.

Your first task will be to determine the value of Kf for cyclohexane. In order to do so, you will find the freezing point (Tf) of pure cyclohexane and the freezing points of three solutions of cyclohexane and naphthalene with varying molalities. You will be working in pairs for this experiment, as it will take two people to perform this experiment.

It is likely that your TA will have removed the test tubes from the oven prior to the start of lab.

You will be working with a 15 mL sample of cyclohexane same sample for Parts 1 and 2. Be sure to record the mass of the test tube both before and after adding the cyclohexane, include the stopper in both cases. Please keep the stopper in the test tube as much as possible to avoid evaporative loss. Get a saltwater/ice bath ready, temperature probe, etc. You will also have a scraper inserted into the stopper during the experiment; the scraper or temperature probe can be used for stirring the sample. Please stir and scrape vigorously and continually, but carefully to avoid breaking the test. One partner in the pair will do the stirring, while the other will record the time and the temperature every 15 seconds. Be sure that your table has at least 20 rows so that you can record 300 seconds worth of data.

While one of the partners is dealing with the sample after a trial, the other should begin to plot the data. You should plot each trial on a separate piece of graph paper. Graph paper will be available in the lab. When you have plotted the data, you should determine the freezing point by drawing lines through the cooling portion of the curve and the freezing portion (the plateau, or near plateau) and observing the intersection point of these two lines. The freezing point is likely to be the temperature at which the temperature plateaus.

After acquiring three trials for pure cyclohexane, you will examine solutions of naphthalene in cyclohexane. You will use the same sample of cyclohexane for this part. The mass of cyclohexane may change slightly over the course of the three trials, so be sure to carefully mass

.

84

the test tube before and after each addition of naphthalene. For this part of the experiment, you will perform one freezing point determination after each addition of naphthalene (be sure to sum the masses of naphthalene added to the solution—the mass should increase from Trial 1 to 2 to 3). Your overall results should look somewhat similar to the following plot (draw example).

Similarly to your pure cyclohexane data, you should determine the freezing point. As the freezing point depression increases, you may (will) not always achieve a nice plateau. (Why is this? As the cyclohexane freezes, what happens to the concentration/molality of the solute? It increases, as pure cyclohexane freezes, all solute is left in solution. Therefore, the freezing point is continually changing as more cyclohexane freezes according to Tf = −iKfm. The intersection point between the cooling and region and the “plateau” becomes more critical in this case. Be sure to draw your line through your data points and look for the point of intersection.

From these data, you can determine the value of Kf, as you are asked to do in the prelab exercise.

By convention, Tf is the freezing point of the solution minus the freezing point of the pure solvent, so that your Tf values are negative. You can find Kf from a plot of Tf vs. molality, according to the equation: Tf = −iKfm As this equation suggests, Kf is the slope for a nondissociating solute, such as naphthalene. You do not have to determine Kf in the lab—you can perform this calculation later, and move on to the unknown determination first. If time permits, of course, you should try to calculate Kf before leaving. The acquisition of the data in this experiment takes some time—be sure that you collect all of the data rather than focusing overly much on the graphs and analyzing the graphs at the outset.

To find the identity of the unknown, you will again perform freezing point measurements. You will perform three trials on the same sample (one addition of the unknown only). By knowing Tf for your unknown, Kf for cyclohexane, and the mass of cyclohexane, you can manipulate the above expression for Tf to find the moles of unknown present. If you know the moles and the mass, you can calculate the molar mass and determine the identity of your unknown. Keep in mind that all of the possible unknowns are nondissociating, so that you can assume that i is equal to 1 in all cases. As the value of Kf determined from your data may or may not be close to known value, you should calculate the molar mass of your unknown using your data and the known value of 20.0 °C∙kg/mol and compare the values obtained.

Things to keep in mind: even if you are not the data recorder in the lab, you must have all of the values in your lab notebook before leaving. You can transcribe the values while the other partner cleans up. Throughout the lab, try to divide up the work evenly and efficiently so that you can perform as much of the data analysis as possible in the lab. Make sure that there is salt and ice in the beaker so that you can achieve temperatures below 0 ˚C. Record T to one decimal place (check setting on probe).

You should turn in the plot for one trial of each step at the end of the lab. You can divide the plots up between the partners—that is, both partners do not need to make all of the same graphs.

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Experiment 12 PreLaboratory Preparation KEY Name: _______________________ Date: _________________ Instructor: _________________________ Sec. #: ___________

1. Below is a sample set of data. Using Excel, plot ΔTf vs. molality, draw a best fit line (through the origin), and determine Kf. Complete and attach the printed graph to this prelab sheet (2 Points).

Tf cyclohexane:

6.9 ºC

Tf of a 0.075m cyclohexane:naphthalene solution:

5.4 oC

Tf of a 0.100m cyclohexane:naphthalene solution:

4.8 oC

Tf of a 0.125m cyclohexane:naphthalene solution:

4.2 oC

3 2.5

T (K)

2 1.5 y = 21.429x − 0.0321 R² = 0.9976

1 0.5 0

0 -0.5

0.02

0.04

0.06

0.08

0.1

0.12

0.14

Concentration of naphthalene (m)

Kf = 21.4 oC m–1 2. 1.00 kg of ethylene glycol is added to 4450 g of water the ΔTf measured is equal to 6.73 oC. The Kf of water is given at 1.86 oC/m and the empirical formula of ethylene glycol is C3H3O.

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Calculate the molar mass of ethylene glycol (3 Points). molality =

moles of solute = m * mass of solvent =

MW of solute =

ΔTf 6.73 C = = 3.62 m Kf 1.86 C m−1

3.618 mol  4.450 kg solvent = 16.10 mol solute kg solvent

mass of solute 1000 g = = 62.11 g mol −1 mol of solute 16.10 mol

Lab Report Key The title page should include: They should know this by now. Only take away points if incorrect!

Student’s full name Date of experiment Complete title of lab report Name of partner(s) Instructor’s name Lab and section number (e.g., CHM1045L-02) The purpose should include: There are several topics covered in this lab which include exploring the colligative properties of cyclohexane and determine the molecular mass of a cyclohexane-soluble unknown substance.

Explore. Determine (1) the freezing point (Tf) of cyclohexane, (2) its molal freezing point constant (Kf), and (3) the freezing point depression (ΔTf) introduced by a known mass of an unknown contaminant.

Procedure: This should be an MLA form reference to the lab manual with any changes in the procedure noted.

Data: Data Tables Include data tables similar to the suggested format. Each table should include a title and labels for each column and row. Units should be included where appropriate. Significant figures should be correct.

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Graphs Include one Tf determination graph from each part of the lab. Follow instructions on the report cover sheet.

Include a graph of ΔTf vs. m for Part 2 data. Include a line of best fit and an equation. Text below the graph should state the determined Kf value for this data.

Sample Calculations In a step-by-step fashion, show each calculation step for the lab. Provide a brief description of each step in your own words. When equations are displayed in written work, they should be centred on the page. The sample calculations may either be typewritten or handwritten. In either case, the work must be well organized and neat. If the instructor cannot read or follow the sample calculations, no credit will be awarded to this section of the report.

Provide only the following sample calculations: molality of naphthalene (Trial 1, Part 2), ΔTf (Trial 1, Part 2), and molar mass of unknown (Part 3).

The data section for this experiment will include the following chart (values will vary): Table 1: Suggested Data Organization, Part 1 Mass of test tube Mass of test tube and cyclohexane Mass of cyclohexane

Time (s)

Trial 1 Temp (oC)

0 15 30 45 60 75 90 105 120 135

Trial 2 Temp (oC)

Trial 3 Temp (oC)

Continue data to 300 seconds

Tf from graph Average Tf for cyclohexane

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The reported Tf of cyclohexane is 6.5 oC; calculate percent error as:

6.5 oC − experimental Tf × 100 6.5 oC

Table 2: Suggested Data Organization, Part 2

Time (s) 0 15 30 45 60

Trial 1 Temp (oC)

Trial 2 Temp (oC)

Trial 3 Temp (oC)

Continue on to 300 seconds

Mass of tube and solution before solute addition (g) Mass of tube and solution after solute addition (g) Mass of cyclohexane (kg) Mass of solute (g) Moles of solute (mol) Molality of solute solution(molsolute/kgcyclohexane) Tfs from plots (oC) ΔTfs (oC) Kfs (oC kg/mol) Kf (oC kg/mol) from ΔTf vs. molality plot The reported Kf for cyclohexane is 20.0 oC kg/mol – experimental Kf × 20.0 oC kg/mol. Calculate the 100 percent error as: 20.0 oC kg/mol

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Table 3: Suggested Data Organization, Part 3 Mass test tube (g) Mass of test tube and solution before addition of solute (g) Mass of test tube and solution after addition of solute (g) Mass of cyclohexane (kg) Mass of unknown (g) Trial 1

Trial 2

Trial 3

* Trial 1 Temp(ºC)

Trial 2 Temp(ºC)

Trial 3 Temp(ºC)

Tf from plots (ºC) ΔTf (ºC) Using the Kf from Part 2, MW of unknown Average MW of unknown using Kf from Part 2 Using reported Kf of 20.0 ºC kg/mol, MW of unknown Average MW of unknown using Kf of 20.0 ºC kg/mol Freezing runs Time (s) 0 15 30 45

Continue to 300 seconds

Questions: (Answers will vary) 1. Briefly discuss the agreement between the experimentally determined value of Tf for cyclohexane and the literature value. Do the same for Kf. Answers will vary, discussions should be about how close the actual values are when compared to the experimental values. What possible errors could have occurred?

2. Identify the unknown from the materials listed in Table 1. If the percent error for Parts 1 and 2 were greater than 5%, calculate the molar mass again using the literature values.

Compare this second molar mass to your own.

Answer will vary depending on the sample (unknown) used.

MWsolute =

.

−K f ( C  kg  mol−1 )  masssolute (g) Tf  masssolvent (kg)

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Experiment 12: Colligative Properties of Solutions

Experiment 12: Colligative Properties of Solutions

Section

Section

Points Worth

Points Earned

Title page (name, title, date, TA,

Title page (name, title, date, TA,

course, section, partner’s name) Purpose (at least three points)

course, section, partner’s name) Purpose (at least three points)

Procedure (cited/changes/salt) Data Table I (mass of solutions and

Procedure (cited/changes/salt) Data Table I (mass of solutions and

temperatures, Tf of cyclohexane, and percent error)

temperatures, Tf of cyclohexane, and percent error)

Table II (mass of solute, cyclohexane,

Table II (mass of solute, cyclohexane,

solution, change of Tf and Kf values.

Percent error) Table III (mass of various solutes, solvents, solutions, test tubes, unknown, molecular weight of unknown, and freezing runs) Calculations (identify unknown)

solution, change of Tf and Kf values.

Percent error) Table III (mass of various solutes, solvents, solutions, test tubes, unknown, molecular weight of unknown, and freezing runs) Calculations (identify unknown)

Conclusions (include percent error)

Conclusions (include percent error)

Questions Total Grade

Questions Total Grade

%

Points Worth

Points Earned

%

Experiment 12: Colligative Properties of Solutions

Experiment 12: Colligative Properties of Solutions

Section

Section

Points Worth

Points Earned

Title page (name, title, date, TA,

Title page (name, title, date, TA,

course, section, partner’s name) Purpose (at least three points)

course, section, partner’s name) Purpose (at least three points)

Procedure (cited/changes/salt) Data Table I (mass of solutions and

Procedure (cited/changes/salt) Data Table I (mass of solutions and

temperatures, Tf of cyclohexane, and percent error)

temperatures, Tf of cyclohexane, and percent error)

Table II (mass of solute, cyclohexane,

Table II (mass of solute, cyclohexane,

solution, change of Tf and Kf values.

Percent error) Table III (mass of various solutes, solvents, solutions, test tubes, unknown, molecular weight of unknown, and freezing runs) Calculations (identify unknown)

solution, change of Tf and Kf values.

Percent error) Table III (mass of various solutes, solvents, solutions, test tubes, unknown, molecular weight of unknown, and freezing runs) Calculations (identify unknown)

Conclusions (include percent error)

Conclusions (include percent error)

Questions Total Grade

Questions Total Grade

.

%

Points Worth

Points Earned

%

91

Experiment 13: Building Molecular Models Instructor Notes and Lab Preparation Chemicals and Equipment

12 to 14 protractors 6 different molecular models Instruction Notes This lab was developed after many years of trying to get students to build models for themselves and meeting with heavy resistance. To make the lab more investigative, I started building the models myself and asked the students to identify them. I use the large scale models normally used for demonstrations in lecture. They are glued together to make them more durable for use from class to class. You can also use Styrofoam balls and dowels purchased from the local craft shop if you don’t want to purchase the demonstration model kits. We spray-painted the models ourselves to expand the normal number of central atoms available. I don’t recommend using the smaller model kits because then fewer students can work on a model at one time. I set out six models at a time and switch out the models from section to section.

Potential Problems When using the protractors, it is important to center them over the central atom. If the protractor is set to the outside of the central atom, the angles are not accurate. The students should also first be sure to determine the number of valence electrons based on the atoms in the structure. This allows for better identification of the ions.

Below is a list of the molecules we build and the color code we use for each element: Unknown A, BeF2

Unknown H, SO42–

Unknown B, CO2

Unknown I, NH4+

Unknown C, BH3

Unknown J, PF5

Unknown D, SO3

Unknown K, I3–

Unknown E, NO3–

Unknown L, XeO2F2

Unknown F, CO32–

Unknown M, XeOF4

Unknown G, H3O+

Unknown N, ICl4–

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Bonds Double, red Single, yellow Elements O, red N, blue C, black S, yellow P, brown Xe, silver Cl, green I, purple F, orange Be, gold B, light blue H, white Lone-pair electrons—clear sticks (Important for ionic structures)

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Experiment 13 Prelaboratory Assignment KEY Name: ___________________________ Date: _________________ Instructor: ____________________________ Sec. #: ___________

Show all work for full credit.

1) Below are three resonance structures for the thiocyanate ion.

Identify the formal charge on the atoms indicated by the letters below.

A ____0____ C ____–1____ E ____+1____ H ____–1____ Which of the three structures is the most stable? structure 2 2) For each of the molecules or ions below, draw its Lewis structure and then answer the question based on that structure. (The central atom in each case is the atom with the lowest electronegativity).

How many valence electrons are in the following? (Remember to add an electron for each negative charge or to subtract one for each positive charge).

.

BeF2

PF5

AsCl3

16

40

26

94

How many lone pairs of electrons are on the central atom of the following?

PCl3

ClF3

SF4

1

2

1

What is the electron pair geometry of the following?

ClO3−

IF5

BrF5

tetrahedral

octahedral

octahedral

What is (are) the bond angle(s) at the central atom of the following?

H3O+ 109°

ClF5 90° and 180°

BCl3 120°

3) Following is a Lewis structure of the essential amino acid tryptophan. Tryptophan is one of the 20 amino acids found in proteins but is also a precursor of the neurotransmitter serotonin.

Estimate the values of the bond angles in the tryptophan structure indicated by the following letters: A ___120°___ G ___109°___ D ___109° ___ E ___109° ___

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Lab Report Key The title page should include: They should know this by now. Only take away points if incorrect!

Student’s full name Date of experiment Complete title of lab report Name of partner(s) Instructor’s name Lab and section number (e.g., CHM1045L-02) The purpose should include: This experiment deals with several subjects, including molecular structure, Lewis structures, formal charges, electron pairs, and molecular geometry. The purpose should include references to most of these topics and should not be a copy of what is given in the manual. Full credit can be given if at least three of the aforementioned topics are discussed.

Procedure: This should be an MLA form reference to the lab manual with any changes in the procedure noted.

Data: The data section for this experiment should include the six worksheets that were completed during the course of the laboratory experiment.

Calculations: The calculation section should include sample calculations for determining the formal charges and molecular weight (MW) for each molecule.

Conclusions: The conclusion section should be several well-developed paragraphs and cover the following information: a) identification of each of the molecular model unknowns, b) discussion of how the polarity of each molecule was determined and what contributed to that polarity, and c) discussion of which molecules were capable of resonance and why.

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Questions: 1) What physical forces create the three-dimensional structure of a molecule?

Electron repulsion creates distance between atoms until the molecule assumes its lowest energy state, creating the 3D structure of the molecule.

2) What is the purpose in calculating formal charges?

Formal charges indicate the distribution of electrons around atoms within a molecule.

These charges can be used to find the most logical (lowest energy) resonance form of a molecule.

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Experiment 13: Building Molecular Models Section Points Points Worth Earned

Experiment 13: Building Molecular Models Section Points Points Worth Earned

Title page (name, title,

Title page (name, title,

date, TA, course, section, partner’s name) Purpose (at least three points) Procedure (cited/changes)

date, TA, course, section, partner’s name) Purpose (at least three points) Procedure (cited/changes)

Data (six unknowns from

Data (six unknowns from

lab, correctly filled out; 6 points each) Calculations (molecular weight and formal charge) Conclusions (discussion with support of the identification of each of the molecular model unknowns, how to determine the polarity of each molecule and what contributed to the polarity, and which molecules were capable of resonance and why)

lab, correctly filled out; 6 points each) Calculations (molecular weight and formal charge) Conclusions (discussion with support of the identification of each of the molecular model unknowns, how to determine the polarity of each molecule and what contributed to the polarity, and which molecules were capable of resonance and why)

Questions Total Grade

Questions Total Grade

%

%

Experiment 13: Building Molecular Models Section Points Points Worth Earned

Experiment 13: Building Molecular Models Section Points Points Worth Earned

Title page (name, title,

Title page (name, title,

date, TA, course, section, partner’s name) Purpose (at least three points) Procedure (cited/changes)

date, TA, course, section, partner’s name) Purpose (at least three points) Procedure (cited/changes)

Data (six unknowns from

Data (six unknowns from

lab, correctly filled out; 6 points each) Calculations (molecular weight and formal charge) Conclusions (discussion with support of the identification of each of the molecular model unknowns, how to determine the polarity of each molecule and what contributed to the polarity, and which molecules were capable of resonance and why)

lab, correctly filled out; 6 points each) Calculations (molecular weight and formal charge) Conclusions (discussion with support of the identification of each of the molecular model unknowns, how to determine the polarity of each molecule and what contributed to the polarity, and which molecules were capable of resonance and why)

Questions Total Grade

Questions Total Grade

.

%

%

98

Experiment 14: Calorimetry and Hess’s Law Instructor Notes and Lab Preparation Chemicals and Equipment Styrofoam cups Thermometers Cardboard lids with hole in center Bottle of 1.0 M HCL Container of Mg metal 2.5 cm strips cut from Mg ribbon Bottle of MgO Bunsen burners Vacuum tubing Pieces of wire gauze Small weighing boats Aqueous metals waste container (in hood) ** adjust pH before disposing **

Preparation 1.0 M HCL (83.3 mL of concentrated HCL per 2 L of 1.0 M HCL solution prepared) Prepare a large quantity Procedure Place one Styrofoam cup and one piece of cardboard per pair of students.

Place the aqueous waste container in the hood.

The rest of the supplies should be set up on the front counter.

Instruction Notes After years of running the typical coffee cup calorimetry solving for the heat capacity of a metal, I decided that the experiment didn’t cover enough of the material covered in the thermodynamics chapter in the textbook. The process of solving for heats of reaction and use of Hess’s law to determine an otherwise undeterminable heat of reaction provides a more complete coverage of the thermodynamics covered in the book and also gives the students a realistic reason to use Hess’s law.

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99

Points to Stress The first part of the experiment asks the students to determine the calorimeter constant. We currently use a single 12 oz Styrofoam coffee cup for the calorimetry runs. (We tested the experiment with both single and doubled cups with no appreciable difference in results.) The first part of the experiment is repeated because the students often have difficulty with the technique. This leads to differences in the results of the two experimental runs. It is important to discuss with the students whether they should use the results of both experimental runs or to favor one run over the other and how to justify this decision in their conclusion.

Potential Problems The only difficulty with the experiment occurs when the students do not stir continuously when adding the MgO powder. If they use stir bars, this problem can be avoided. We currently do not have enough stir plates to use this fix, so we stress the need for one student to “swirl” the cup continuously while adding the powder.

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Experiment 14 Prelaboratory Assignment KEY Name: ___________________________ Date: _________________ Instructor: ____________________________ Sec. #: ___________

Show all work for full credit.

1) Use the graph of temperature (°C) versus time (s) provided to answer the following questions: What is the initial temperature?

23.8 °C What is the final temperature?

37.3 °C The Cp for the calorimeter (including the HCl solution and the Mg) was calculated to be 0.247 kJ/°C. For the temperature curve shown above, 0.174 g Mg was reacted with HCl. What is the ΔH of the reaction?

–4.652e+2 kJ/mol

2) To calibrate your calorimeter cup, you first put 45 mL of cold water in the cup, and measure its temperature to be 21.7 °C. You then pour 59 mL of hot water, temperature = 50.1 °C, into the cup and measure the temperature every 30 sec over a 10 min period.

You extrapolate this “cooling curve” back to the time of addition and find that the “final temperature” after mixing is 36.2 °C. What is the heat change of the hot water, qhw? –3431 J (Assume the density of the water is 1.00 g/mL and remember that the specific heat of water is 4.184 J/g-K or J/g-°C.) What is the heat change of the cold water, qcw? +2730 J

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What is the heat change of the calorimeter cup, qcup? +701 J What is the heat capacity of the calorimeter cup, Ccup? +48 J/K 3) You would like to measure the heat of neutralization of an acid with a base. You mix 225 mL each of 0.65 M HNO3 and 0.65 M LiOH, both at a temperature of 18.1 °C in a calorimeter cup equilibrated to that same temperature. After following the temperature change for 10 min and extrapolating it back to the time of addition, you find that the “final temperature” after mixing was 22.3 °C. Previously, you measured the heat capacity of the calorimeter cup (Ccup) to be 47 J/°C. Assuming that the density of the two solutions is 1.00 g/mL and that their specific heats are the same as water, 4.184 J/g-°C, what is the heat absorbed by the two solutions, qsoln? +7908 J What is the heat absorbed by the calorimeter cup, qcup? +197 J What is the heat change for the neutralization reaction, qrxn? –8105 J What is the ΔH for the neutralization? –55.4 kJ/mol Write the net ionic equation for this neutralization reaction, including the states of matter (i.e., H+aq) for the reactants and products.

H+(aq) + OH–(aq) → H2O(l) 4) Given the following data: 2C2H6(g) + 7O2(g) → 4CO2(g) + 6H2O(l) ΔH = –3120 kJ 2H2O(l) → 2H2(g) + O2(g)

ΔH = +572 kJ

C2H2(g) → 2H2(g) → C2H6(g)

ΔH = –312 kJ

Find the ΔH of the following reaction: 4CO2(g) + 2H2O(l) → 2C2H2(g) + 5O2(g)

ΔH = + 2600 kJ

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Lab Report Key The title page should include: They should know this by now. Only take away points if incorrect!

Student’s full name Date of experiment Complete title of lab report Name of partner(s) Instructor’s name Lab and section number (e.g., CHM1045L-02) The purpose should include: This experiment deals with several subjects, including calorimetry, enthalpy of reaction, Hess’s law, thermodynamics, specific heats, and heat capacity. The purpose should include references to most of these topics plus criteria for determining success of the experiment, and should not be a copy of what is given in the manual. Full credit can be given if at least three of the aforementioned topics are discussed.

Procedure: This should be an MLA form reference to the lab manual with any changes in the procedure noted.

Data: A completed table such as the following should be included.

Part A Exact volume of cold water (to the nearest 0.1 mL) Temperature of cold water (in cup) Exact volume of hot water (to the nearest 0.1 mL) Temperature of hot water (in cylinder)

Trial 1 ___________ ___________ ___________ ___________

Trial 2 ___________ ___________ ___________ ___________

Part A Calculations: Mass of cold water (assume density = 1.00 g/mL) ___________ Tf from graph by extrapolation ___________ Thw for hot water ___________ Tcw for cold water ___________ qhw for hot water (use qhw = m cThw) ___________ qcw for cold water (use qcw = m c Tcw) ___________ qcal for the cup (use |qhw| = |qcw|1 qcal, solve for qcal) ___________ Ccup for the cup (use qcal = Ccup T) ___________ Which T should be used?

Part B Description of sample ___________ Exact volume of 100 mL HCl (to the nearest 0.1 mL) ___________ Initial temperature of HCl (in cup) ___________ Exact mass of Mg (to the nearest 0.001g) ___________

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Part B Calculations: Mass of HCl solution (use the density of water for HCl = 1.00 g/mL) ___________ ___________ Tcw for HCl ___________ qHCl for HCl solution (use qcw = m c THCl) ___________ qcal for the cup (use qcal = CcupTHCl) ___________ qrxn (use qRxn = qHCl + qcal) ___________ Hrxn for Mg (use Hrxn = qrxn/nMg) ___________ The net reaction that took place in the cup ___________ Part C Description of sample Exact volume of 100 mL HCl (to the nearest 0.1 mL) ___________ Temperature of HCl (in cup) ___________ Exact mass of MgO (to the nearest 0.001g) ___________ Part C Calculations: Highest temperature reached ___________ Tcw for HCl ___________ qHCl for HCl solution (use qcw = m c THCl) ___________ qcal for the cup (use qcal = Ccup THCl) ___________ qrxn (use qrxn = qHCl + qcal) ___________ Hrxn for MgO (use Hrxn = qrxn/nMg)___________

There should be four sets of time versus temperature data given in neat tables. A balanced chemical reaction should also be presented.

Calculations: One graph should be present for each water run, one graph for the Mg, and one graph for the MgO runs and extrapolations for each section. Example calculations should be given for determination of heat capacity of the calorimeter, determination of q (heat of reaction) for Mg in HCl, determination of q (heat of reaction) for MgO in HCl, determination of ∆H for Mg in HCl, determination of ∆H for MgO in HCl, calculation of ∆Hrxn using Hess’s law, and %error for ∆Hf. Conclusions: The conclusion section for this experiment should be several well-developed paragraphs. These paragraphs should cover the following information: Part A discussion on how the various data were obtained, including 1) the calculation of the maximum temperature of the reaction in Experiment A, 2) the heat of reaction for hot and cold water, 3) the heat capacity of the calorimeter cup, and 4) the heat capacity of the cup.

For Parts B and C: 1) the maximum temperature achieved; 2) the heat of reaction of the solution, cup, and reaction; and 3) Hrxn. Be sure some type of discussion of these values is provided.

Also required is a report of the overall reaction being studied and the Hrxn values found using both experimental and literature values. A discussion of the differences in these values as well as the %error in the experiment should be present. Finally, a discussion of any errors in the experiment should be included as usual.

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Questions: 1) What is the difference between the heat (q) of a reaction and the reaction enthalpy (Hrxn)?

The heat of a reaction is simply the energy created by a temperature difference. The enthalpy is sum of all of these internal energy differences for a reaction.

2) Why is Tfinal taken from extrapolating back to the beginning of the experimental run rather than from the last temperature reading taken?

Tfinal is the theoretical temperature that would be reached in a reaction were all substances to reach thermal equilibrium instantaneously. The extrapolation based on the temperature decay line allows for the estimation of what this temperature would be.

The last temperature reading is at the end of the temperature decay and does not directly indicate the temperature of instantaneous equilibrium.

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105

Experiment 14: Calorimetry and Hess’s Law Section Points Points Worth Earned

Experiment 14: Calorimetry and Hess’s Law Section Points Points Worth Earned

Title page (name, title, date, TA, course, section,

Title page (name, title, date, TA, course, section,

partner’s name) Purpose (at least three points)

partner’s name) Purpose (at least three points)

Procedure (cited/changes) Data (net reaction for parts B and C and

Procedure (cited/changes) Data (net reaction for parts B and C and

description of sample for parts B and C) Table I (Part A: volume hot and cold, Tf and Ti, T hot and cold, qhw, qcw, qcal, Ccup) (Parts B and C: volume HCl, mass solid, T, qHCl, qcal, qrxn, Hrxn) Table II (time and temperature data)

description of sample for parts B and C) Table I (Part A: volume hot and cold, Tf and Ti, T hot and cold, qhw, qcw, qcal, Ccup) (Parts B and C: volume HCl, mass solid, T, qHCl, qcal, qrxn, Hrxn) Table II (time and temperature data)

Graphs (temperature vs. time; ×4) Calculations (heat capacity of the calorimeter,

Graphs (temperature vs. time; ×4) Calculations (heat capacity of the calorimeter,

heat of reaction for parts B and C, H for parts B and C; Hrxn from Hess’s law, %error of Hrxn) Conclusions (discussion on how the various data were arrived upon and values, including max temp for part A, qhw and qcw, qcup, Ccal, max temp for parts B and C, qsolution, qreaction, Hrxn; report of the overall reaction being studied and the Hrxn values found using both experimental and literature values, %error discussion and errors)

heat of reaction for parts B and C, H for parts B and C; Hrxn from Hess’s law, %error of Hrxn) Conclusions (discussion on how the various data were arrived upon and values, including max temp for part A, qhw and qcw, qcup, Ccal, max temp for parts B and C, qsolution, qreaction, Hrxn; report of the overall reaction being studied and the Hrxn values found using both experimental and literature values, %error discussion and errors)

Total Grade

Total Grade

%

%

Experiment 14: Calorimetry and Hess’s Law Section Points Points Worth Earned

Experiment 14: Calorimetry and Hess’s Law Section Points Points Worth Earned

Title page (name, title, date, TA, course, section,

Title page (name, title, date, TA, course, section,

partner’s name) Purpose (at least three points)

partner’s name) Purpose (at least three points)

Procedure (cited/changes) Data (net reaction for parts B and C and

Procedure (cited/changes) Data (net reaction for parts B and C and

description of sample for parts B and C) Table I (Part A: volume hot and cold, Tf and Ti, T hot and cold, qhw, qcw, qcal, Ccup) (Parts B and C: volume HCl, mass solid, T, qHCl, qcal, qrxn, Hrxn) Table II (time and temperature data)

description of sample for parts B and C) Table I (Part A: volume hot and cold, Tf and Ti, T hot and cold, qhw, qcw, qcal, Ccup) (Parts B and C: volume HCl, mass solid, T, qHCl, qcal, qrxn, Hrxn) Table II (time and temperature data)

Graphs (temperature vs. time; ×4) Calculations (heat capacity of the calorimeter,

Graphs (temperature vs. time; ×4) Calculations (heat capacity of the calorimeter,

heat of reaction for parts B and C, H for parts B and C; Hrxn from Hess’s law, %error of Hrxn) Conclusions (discussion on how the various data were arrived upon and values, including max temp for part A, qhw and qcw, qcup, Ccal, max temp for parts B and C, qsolution, qreaction, Hrxn; report of the overall reaction being studied and the Hrxn values found using both experimental and literature values, %error discussion and errors)

heat of reaction for parts B and C, H for parts B and C; Hrxn from Hess’s law, %error of Hrxn) Conclusions (discussion on how the various data were arrived upon and values, including max temp for part A, qhw and qcw, qcup, Ccal, max temp for parts B and C, qsolution, qreaction, Hrxn; report of the overall reaction being studied and the Hrxn values found using both experimental and literature values, %error discussion and errors)

Total Grade

Total Grade

%

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%

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Experiment 15: Gas Laws and Airbags Instructor Notes and Lab Preparation Chemicals and Equipment 1 bottle of 6 M acetic acid 1 bottle of solid sodium bicarbonate 1 box each of three different types of zipper-type plastic bags: sandwich, freezer, and storage Small weighing boats

Preparation For the 6 M acetic acid, fill the large container labeled 6 M acetic acid partially with DI water. In the hood, add 6.90 L of concentrated acetic acid. Dilute to the 20 L mark with DI water and mix thoroughly.

Instruction Notes The concept of this lab is very simple, yet it combines gas law, stoichiometry, and limiting and excess reagents. The lab is short, normally taking no more than an hour to complete. A successful airbag should have a full pillow-like appearance, and there should be no particulate residue from the bicarbonate left unreacted. Although we require that the bags be tested in the hood, the reaction is not really fast enough to explode.

The heavier zipper-style bags with a double zipper work better than the lighter single-zipper bags. They are slightly more expensive but are far less likely to leak. To save on expense, the bags can be used more than once as long as they are well rinsed and dried between classes.

Points to Stress The comparison of the airbags the students are building in the laboratory to the ones found in cars is a very valid one. The requirement for an exact calculation of the materials needed to completely fill but not overfill the bag is an important point to make.

Potential Problems The only problem in the experiment occurs when the bag leaks. The reason we started determining the volume of the bags by filling them with water instead of simply converting the measurements given on the box is to test the bag for leaks, that is, if the water leaks, so will the gas.

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Experiment 15 Prelaboratory Assignment KEY Name: ___________________________ Date: _________________ Instructor: ____________________________ Sec. #: ___________

Show all work for full credit.

1) Airbags in cars are devices that inflate very rapidly (in about 30 ms) when there is a collision, creating a cushion that deflates slowly and cushions the impact of the collision on the driver and/or the passenger(s). The bag is inflated by a gas, which is generated by the rapid heating of sodium azide (NaN3) to about 300 °C, causing it to decompose into sodium metal and nitrogen gas.

Complete and balance the equation for this reaction, indicating the states of the reactant (NaN3(s)) and products (Na(s) and N2(g)).

2NaN3(s) → 2Na(s) + 3N2(g) Enough nitrogen must be generated in the bag to create a total pressure of 3.10 atm, which then drops as the bag slowly deflates. Assuming the volume of the bag is 58.0 L and the temperature in the car is 25 °C, calculate the molar quantity of N 2 that must be generated.

7.35 mol What molar quantity of sodium azide is required to generate this much nitrogen?

4.90 mol What mass of sodium azide is required?

319 g The sodium metal produced in the reaction is highly reactive and potentially explosive, so it is removed in a reaction with excess KNO3(s) that produces K2O(s) and Na2O(s), and additional nitrogen. Write a balanced equation for this process, showing the states of the reactants and products.

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10 Na(s) + 2 KNO3(s) → K2O(s) + 5 Na2O(s) 2) In this laboratory experiment you are to generate sufficient carbon dioxide to inflate a plastic zipper type bag. You first must carry out some calculations to determine the quantity of reagents needed.

Carbon dioxide will be generated by reacting solid sodium bicarbonate (NaHCO3) with a solution of acetic acid (CH3COOH) as follows: Step 1: NaHCO3(s) + CH3COOH(aq) → H2CO3(aq) + CH3COO−(aq) + Na+(aq) Step 2: H2CO3(aq) → H2O(l) + CO2(g) You measure the plastic bag dimensions to be 7.15 in. by 7.97 in. Assuming the average thickness of the bag when inflated will be 1.50 in., what do you calculate the volume of the bag to be?

1401 mL Of course, this volume is only approximate as the width of the inflated bag is not uniform. To get a better value for the volume, you fill the bag with water, then measure the volume of the water to be 1274.7 mL. Now, you measure room temperature to be 21 °C, and the barometer on the wall gives a reading of 756 torr for the atmospheric pressure. Using the ideal gas law, calculate the number of moles of CO2 that will be required to fill the bag at this temperature and pressure.

0.0526 mol Now, inspect the reactions above that are generating CO2 and calculate the molar quantity of NaHCO3 and CH3COOH needed.

Quantity of NaHCO3: 0.0526 mol Quantity of CH3COOH: 0.0526 mol What mass of NaHCO3 will be needed? 4.42 g You have a solution of 6.03 M acetic acid. What volume of this solution will be needed?

8.72 mL

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Lab Report Key The title page should include: They should know this by now. Only take away points if incorrect!

Student’s full name Date of experiment Complete title of lab report Name of partner(s) Instructor’s name Lab and section number (e.g., CHM1045L-02) The purpose should include: This experiment deals with several subjects, including ideal gas law, air bags, stoichiometry, and acid–base reactions. The purpose should include references to most of these topics and should not be a copy of what is given in the manual. It should also include a statement of the criteria for determining the success of the experiment.

Procedure: This should be an MLA form reference to the lab manual with any changes in the procedure noted.

Data: The data section for this experiment should include a table like the one below. A balanced chemical equation for the reaction being studied should also be included.

Title Bag Dimensions

Bag Moles Moles Moles Grams Volume 6.0 Success Volume CO2 NaHCO3 CH3COOH NaHCO3 M or (L) Needed Needed Needed Needed CH3COOH Failure Needed

Room temperature: ______________ Room pressure:_________________

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Calculations: The calculation section should include sample calculations for each column in the data table, including conversions of units.

Conclusions: The conclusion section should be in paragraph format and discuss the success or failure of each airbag design. This should include the volume of each air bag and the amount of materials used.

Along with the components of the airbag, a discussion of the reasons for the success or failure of each bag should be included. Also required is a discussion of any problems or errors that may have occurred in the experiment, and any second trials that may have taken place should be present.

Questions: 1) Is the gas used in this experiment really an “ideal” gas? Explain.

An ideal gas is one that completely obeys the ideal gas law. Most gases deviate in some fashion from the law in its absolute form due to intermolecular forces, and thus the gas we are working with is most likely not an ideal gas.

2) The gas production in this experiment is fairly slow, but the production in a car airbag is quite rapid. What is the reason for the difference in the two reactions?

The sodium azide in an airbag is ignited, and thus a combustion reaction takes place.

The input of energy creates a much faster reaction than the simple mixing that takes place during our experiment.

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Experiment 15: Gas Laws and Airbags

Experiment 15: Gas Laws and Airbags

Section

Section

Points Points Worth Earned

Title page (name, title, date, TA, course,

Title page (name, title, date, TA, course,

section, partner’s name) Purpose (at least three points)

section, partner’s name) Purpose (at least three points)

Procedure (cited/changes) Data (balanced chemical equation, room

Procedure (cited/changes) Data (balanced chemical equation, room

temperature and pressure) Table I (title, bag dimensions, bag volume, moles CO2, NaHCO3 and CH3COOH, grams of NaHCO3, volume of CH3COOH, success or failure) Calculations (bag dimensions, bag volume, moles CO2, NaHCO3 and CH3COOH, grams of NaHCO3, volume of CH3COOH, unit conversions for T and P) Conclusions (discussion of the success or failure of each airbag design, including the volume of each air bag and the amount of materials used; reasons for the success or failure of each bag; and any problems or errors that may have occurred in the experiment and any second trials)

temperature and pressure) Table I (title, bag dimensions, bag volume, moles CO2, NaHCO3 and CH3COOH, grams of NaHCO3, volume of CH3COOH, success or failure) Calculations (bag dimensions, bag volume, moles CO2, NaHCO3 and CH3COOH, grams of NaHCO3, volume of CH3COOH, unit conversions for T and P) Conclusions (discussion of the success or failure of each airbag design, including the volume of each air bag and the amount of materials used; reasons for the success or failure of each bag; and any problems or errors that may have occurred in the experiment and any second trials)

Questions Total Grade

Questions Total Grade

%

Points Points Worth Earned

%

Experiment 15: Gas Laws and Airbags

Experiment 15: Gas Laws and Airbags

Section

Section

Points Points Worth Earned

Title page (name, title, date, TA, course,

Title page (name, title, date, TA, course,

section, partner’s name) Purpose (at least three points)

section, partner’s name) Purpose (at least three points)

Procedure (cited/changes) Data (balanced chemical equation, room

Procedure (cited/changes) Data (balanced chemical equation, room

temperature and pressure) Table I (title, bag dimensions, bag volume, moles CO2, NaHCO3 and CH3COOH, grams of NaHCO3, volume of CH3COOH, success or failure) Calculations (bag dimensions, bag volume, moles CO2, NaHCO3 and CH3COOH, grams of NaHCO3, volume of CH3COOH, unit conversions for T and P) Conclusions (discussion of the success or failure of each airbag design, including the volume of each air bag and the amount of materials used; reasons for the success or failure of each bag; and any problems or errors that may have occurred in the experiment and any second trials)

temperature and pressure) Table I (title, bag dimensions, bag volume, moles CO2, NaHCO3 and CH3COOH, grams of NaHCO3, volume of CH3COOH, success or failure) Calculations (bag dimensions, bag volume, moles CO2, NaHCO3 and CH3COOH, grams of NaHCO3, volume of CH3COOH, unit conversions for T and P) Conclusions (discussion of the success or failure of each airbag design, including the volume of each air bag and the amount of materials used; reasons for the success or failure of each bag; and any problems or errors that may have occurred in the experiment and any second trials)

Questions Total Grade

Questions Total Grade

.

Points Points Worth Earned

%

%

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Experiment 16: Intermolecular Forces and the Triple Point of CO2 Instructor Notes and Lab Preparation: Chemicals and Equipment: Liquids: 1 L bottles of each, labeled only as unknowns Unknown A, methanol Unknown B, acetone Unknown C, water Unknown D, 2-propanol Unknown E, hexane 1 box of small (4.25 in.) 1 m filter paper 1 bag of small rubber bands Buret or ring stands and clamps Thermometers (glass, preferably non-Hg; not digital temperature probes) Clear plastic cups Thick-stemmed pipettes Thin-stemmed pipettes Pliers Bottle of blue food coloring Metric rulers Hot glue gun with glue sticks Bucket of dry ice, ~1 to 1.5 lbs for a class of 28 students String

Preparation Place equipment and chemicals on front lab bench.

Place five waste containers in the hood, labeled A, B, C, D, and E. Jars C and D can be disposed of in the sink drain with running water. Waste from jars A, B, and E goes into an organic waste jar.

Instruction Notes This is currently the first wet lab (emphasis on wet) of our second semester of general chemistry at Florida State University. It is a good lab to start with because it requires a minimal amount of lab skills (no new techniques), and the exploding cups of water refresh the students’ memories regarding the need for goggles in the lab.

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The first part of the experiment is about as exciting as watching paint dry, but it does quite effectively reinforce the concepts of intermolecular forces and their effect on physical properties.

The second part of the experiment, which deals with the triple point of CO2, is a student favorite (mostly because of the exploding cups of water).

The setup for this experiment is easy because there are no solutions to make, and the equipment is pretty standard. I have found that the buret stands and clamps are best for supporting the thermometers. Doing so also allows simultaneous determination of the temperature change for two solvents at one time. Students can work as groups or benches to determine the T values for the solvent unknowns. This saves on chemical cost. It is advisable to have the two parts of the experiment running at opposite ends of the bench or table due to the possible splash of water.

Also, make sure the students keep their lab notebooks and other personal items clear of the impact area. I generally have students work in teams of four, with two students working on the first part of the lab while the other two complete the second part. At some point, the pairs switch to complete all of the experiment. This also halves the need for thermometers and pliers.

The amount of dry ice needed for the experiment is not as great as it might seem. One or two ~2 cm pellets are sufficient to fill the pipet bulb a third full. We use about 30 lbs during a week for 20 sections of ~28 students. We collect a large amount (~10 lbs) at a time and store it all day in a sealed cooler for easy access.

I suggest purchasing glue guns and pliers from a store like Walmart or KMart. The mini glue guns and glue sticks are generally less than $5, and you only need one or two for a class of 28 students. We actually purchased the pliers at a local flea market for $1 per pair.

Points to Stress The correlation between the strength of the intermolecular forces and the magnitude of the observed change in temperature is a difficult concept for the students to grasp. I have done the best I can to explain it in the background, but a discussion in lab is probably wise.

Students often rush through the observations of the CO2 phase change, but it should be mentioned that very few people get the opportunity to observe liquid CO2.

Potential Problems There are no known difficulties with either part of this experiment.

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Experiment 16 Prelaboratory Assignment KEY Name: ___________________________ Date: _________________ Instructor: ____________________________ Sec. #: ___________

Show all work for full credit.

Copy the information gathered in Parts I and II of this prelab into your lab notebook for later use.

1) For liquids such as, methanol, isopropanol, n-hexane, acetone, and water, (a) write the molecular formula, (b) draw a Lewis structure for each compound, and (c) calculate the molecular weight of each compound. methanol: CH3OH

MW = 32 g/mol

isopropanol : (CH3)2CHOH

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MW = 60 g/mol

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n-hexane: C6H14

MW = 86 g/mol

acetone: C3H4O

MW = 58 g/mol

water: H2O

MW = 18 g/mol

2) The relative strength of the intermolecular forces depends on the size (i.e., MW) and structure of the molecules and include, in rough order of strength, ion–ion, ion–dipole, hydrogen bonding, dipole–dipole (polar), dipole–induced dipole, and induced dipole–induced dipole (dispersion) forces. The latter increases with molecular weight and can sometimes become the most predominant force. There are no ions in these liquids, and all the molecules are alike, leaving primarily hydrogen bonding, dipole–dipole, and dispersion forces to consider.

What are the strongest intermolecular forces in acetone? Dipole–dipole What are the strongest intermolecular forces in methanol? H bonding What are the strongest intermolecular forces in 2-propanol? H bonding What are the strongest intermolecular forces in water? H bonding What are the strongest intermolecular forces in hexane? dispersion

3) The figure at the right shows your experimental set-up for estimating the triple point of CO2. Carefully mark off your capillary tube in ten 1 cm segments, and note the position of the drop of dye solution when the capillary is inserted in the open plastic tube. When the top of the plastic tube is sealed, the pressure inside will increase as the CO2 sublimes, and the drop of dye will be forced up the capillary, compressing the air inside it. Note the position of the drop of dye when liquid CO2 starts to form. The pressure inside the capillary should then correspond to the pressure at the triple point of CO2.

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You can calculate the pressure from a modification of Boyle’s law, P1V1 = P2V2. The volume of the capillary = hA, where h is the height and A is the cross-sectional area, which is constant.

Boyle’s law therefore reduces to P1h1 = P2h2, where P1 is the pressure in the open tube, h1 is the distance of the drop from the top of the capillary in the open tube, h2 is the distance of the drop from the top of the capillary in the closed tube, and P2 is the pressure in the closed tube, the pressure at the triple point.

What are the heights of the air columns in the two capillaries to the right? (Measure from the top of the dye droplet).

Height of column in the open tube (h1): 10 cm Height of column in the closed tube (h2): 2 cm Calculate the pressure in the closed tube, assuming the pressure in the open tube is 1.0 atm.

Pressure in the closed tube: 4.5 atm

Lab Report Key The title page should include: They should know this by now. Only take away points if incorrect!

Student’s full name Date of experiment Complete title of lab report Name of partner(s) Instructor’s name Lab and section number (e.g., CHM1045L-02) The purpose should include: There are several topics covered in this lab: triple points, pressure, phase changes, heats of vaporization, hydrogen bonding, and intermolecular forces. The purpose should include references to most of these topics plus criteria for determining success of the experiment, and it should not be a copy of what is given in the manual.

Procedure: This should be an MLA form reference to the lab manual with any changes in the procedure noted.

Data: The data section should include the following for part I: In table format, a) the five T values for the unknown liquids studied (T = Tfinal – Tinitial), where the initial temperature is room temperature and the final temperature is that recorded for each liquid.

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For part II, a report of all the observations made during lab of the CO2 alone and inside the microgauge and a report of the triple point of CO2 found during lab.

Calculations: Boyle’s law should be used to calculate the pressure at the triple point. The percent error of the microgauge should be reported.

Conclusions: A statement of the conclusions of both sections of the lab should be given here, including identification of each liquid and an explanation to support each conclusion. Based on the T value, the rankings of the unknown liquids in terms of their intermolecular forces from strongest to weakest should be discussed. The triple point of CO2 determined experimentally should be given here as well. A comparison of the observed pressure at the triple point with the theoretical value should be included. A discussion of possible errors is always expected.

Questions: 1) How is the change in temperature we observe as the various solvents evaporate related to their Hvap? Explain this relationship.

The Hvap is a physical quantity that measures the amount of energy required to vaporize the liquid. Evaporation is an endothermic process that results in a drop in temperature of the surroundings. The compound requiring the least amount of energy (smallest Hvap) and thus the weakest intermolecular forces will exhibit the largest temperature drop. This occurs because as the molecules evaporate, they carry heat away from the thermometer, which registers each loss as a drop in temperature.

Molecules with stronger intermolecular forces require a larger amount of energy to accumulate before they can evaporate, so their removal of heat from the thermometer is a much slower process. The length of time between evaporation events allows the thermometer to recover heat from the surrounding air, and thus we do not observe as great a drop in temperature for these molecules.

2) In our use of the microgauge to determine the triple point pressure of CO2, we measure only the height change (distance the dye moves) in the gauge, not the actual volume. Why does this approximation not ruin our results?

From the rules of multiplication and division, we know that any equivalent value found on two sides of an equality can be ignored in the calculation, as they cancel out. Since the diameter of the gauge is a constant, it is an equivalent value that appears on both sides of the P1V1 = P2V2 equation, and thus it cancels out and can be left out of the overall calculation.

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Experiment 16: Intermolecular Forces and the Triple Point of CO2 Section Points Points Worth Earned

Experiment 16: Intermolecular Forces and the Triple Point of CO2 Section Points Points Worth Earned

Title page (name, title, date, TA,

Title page (name, title, date, TA,

course, section, partner’s name)

course, section, partner’s name)

Purpose Procedure (cited and

Purpose Procedure (cited and

changes)

changes)

Data

Data

Part I (delta Ts, ID, and ranking of unknowns). Part II (CO2 observations)

Part I (delta Ts, ID, and ranking of unknowns). Part II (CO2 observations)

Calculations

Calculations

Delta Ts, Boyle’s law, and % error Conclusions (part I, part II, errors)

Delta Ts, Boyle’s law, and % error Conclusions (part I, part II, errors)

Questions Total Grade

100 %

Questions Total Grade

100 %

Experiment 16: Intermolecular Forces and the Triple Point of CO2 Section Points Points Worth Earned

Experiment 16: Intermolecular Forces and the Triple Point of CO2 Section Points Points Worth Earned

Title page (name, title, date, TA,

Title page (name, title, date, TA,

course, section, partner’s name)

course, section, partner’s name)

Purpose Procedure (cited and

Purpose Procedure (cited and

changes)

changes)

Data

Data

Part I (delta Ts, ID, and ranking of unknowns). Part II (CO2 observations)

Part I (delta Ts, ID, and ranking of unknowns). Part II (CO2 observations)

Calculations

Calculations

Delta Ts, Boyle’s law, and % error Conclusions (part I, part II, errors)

Delta Ts, Boyle’s law, and % error Conclusions (part I, part II, errors)

Questions Total Grade

Questions Total Grade

.

100 %

100 %

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Experiment 17: The Purification of Water Instructor Notes and Lab Preparation Chemicals and Equipment pH probes and meters (students work individually but share a pH meter) pH 4 buffer pH 7 buffer Dropping bottles of 3 M HCl 1 L bottles of 10 ppm phosphate stock solution Dropping bottles of ammonium molybdate reagent Dropping bottle of stannous chloride Dropping bottles of sodium hypochlorite reagent 1 jar of lime powder (CaO) 1 jar of aluminum sulfate powder (Al2(SO4)3) 1 jar of sand 1 jar of activated charcoal (fish tank rocks) 1 box of 0.1 m filter paper Buchner funnels 250 mL filtering flasks Vacuum tubing Ring stands Clamps Spectrometers Cuvettes 10 mL glass pipettes Pipette pumps or bulbs 25 mL volumetric flasks

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Preparation Ammonium Molybdate Reagent Prep a 1 L volume: In a 1 L volumetric flask, dilute 280 mL of concentrated sulfuric acid by adding it to 400 mL of DI water. Meanwhile, dissolve 25 g of ammonium molybdate (NH4)6Mo7O24.4H2O in about 150 mL of DI water. When the acid mixture has cooled down, combine it with the molybdate and dilute the entire solution to 1 L with DI water.

To prep a 100 mL volume: 2.5 g of ammonium molybdate and 28 mL of concentrated sulfuric acid.

Prepared as stated.

0.1 M Stannous Chloride In a 1 L beaker, dissolve 12.0 g of tin(II) chloride dihydrate in 500 mL of glycerol.

Warm the solution on a hotplate to speed up the process.

10 ppm Stock Phosphate Solution Dissolve 0.07 g of K2HPO4 in 7 L of DI water.

Sodium Hypochlorite Reagent Dissolve 250 mL of nonscented commercial-grade (5.25%) bleach in a 1 L volumetric flask and dilute with DI water to the mark.

Phenolphthalein Indicator Dissolve 0.5 g of phenolphthalein in 50 mL of ethanol and 50 mL of DI water.

Setup On every bench, place a Spectronic 20® (or similar spectrometer), a 25 mL volumetric flask, 2 pH 4 buffers, 2 pH 7 buffers, and 1 box of Kimwipes®.

Place an aqueous metals waste container in the hood.

Instruction Notes This lab serves to introduce the spectrophotometer for a purpose, rather than just as an exercise.

This is a full-length lab intended to run for approximately 2.5 to 3 hr. Students should work in groups for the creation of the standard solutions and when using the spectrophotometer. This will reduce the amount of standard solution and the number of spectrophotometers needed for a class.

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They may also share a pH meter, since its use is limited. pH paper can be used instead if you prefer. Because this lab has several parts and is longer than other labs, I generally set time goals for the completion of each section to minimize student “dawdling.” If they can complete the serial dilutions and initial absorbance measurements by the end of an hour, they will be able to complete the purification process and retest the phosphate concentration within the 3 hr limit.

Points to Stress The first part of this lab requires the students to go into the field and collect their own water samples. Even though it is stated in the manual, you should re-emphasize that they should not use detergents to clean the sample bottle. We ask that students bring the collection bottles they will be using into the lab a week early so that they can use a mild acid wash to clean the bottle(s).

This will help them remember that they need to collect samples the week before the lab is run.

This need for advance preparation, which is so typical of actual research, is an important point to stress.

There are many different techniques used in this lab that should be carefully presented to the students: (1) the calibration and use of a pH meter, (2) the proper use of a spectrophotometer, and (3) the setup and use of a filter funnel system.

True serial dilution is a process that can be invaluable in an actual research lab due to the ever rising cost of chemicals, but it was very seldom taught in laboratories I had seen previously. As a public university, we are also trying to lower the cost per student for our labs. When we changed the process from a simple creation of solutions to a serial dilution process, we reduced the amount of stock solution needed by 65%. This point should be made to the students as well.

The steps of the purification process are based on the typical process used by water treatment plants.

There are three principal stages in water purification: 1. Primary treatment: Collecting and screening, including pumping from rivers and initial storage 2. Secondary treatment: Removing fine solids and the majority of contaminants using filters, coagulation, flocculation, and membranes 3. Tertiary treatment: Adjusting pH, treating with carbon to remove taste and smells, disinfecting, and temporarily storing to allow the disinfecting agent to work The EPA has a nice website (http://www.epa.gov/safewater/kids/watertreatmentplant/) that shows the typical process used to treat waste water and that will help students see the similarities between the real process and the procedure they are completing in the lab.

Potential Problems We have had some problems with our distilled water blank in combination with the coloring agent, probably due to some contamination in the water.

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Students often bring in water from duck ponds. Unfortunately, some municipalities treat these duck ponds with antibacterial agents and other chemicals to reduce odor and clear the water.

These chemicals can produce unknown reactions when processed in the lab. (We had one water sample that foamed like elephant toothpaste for 20 min when we added the CaO and Al powder.)

Just try to be aware of any water sources in your area that may be quality controlled and warn your students away from them.

The only other consistent source of error for the students is in the filtration process. They tend to get in a hurry and swamp the filter paper. It is important to show the students the proper way to use the filtration system.

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Experiment 17 Prelaboratory Assignment KEY Name: ___________________________ Date: _________________ Instructor: ____________________________ Sec. #: ___________

Show all work for full credit.

1) Calculate the [PO43–] concentrations corresponding to the following ppm values: Concentration = 0.37 ppm; [PO43–] = 3.9e-6 M Concentration = 333 ppm; [PO43–] = 3.51e-3 M Concentration = 15 ppm; [PO43–] = 1.6e-4 M Calculate the ppm values corresponding to the following [PO43–] concentrations: [PO43–] = 7.90 × 10–5 M; Concentration = 7.50 ppm [PO43–] = 2.42 × 10–6 M; Concentration = 0.230 ppm [PO43–] = 6.75 × 10–3 M; Concentration = 641 ppm 2) Use the following table of standard concentrations and absorbances for the phosphate ion to create a calibration graph. What are the slope and intercept of the calibration curve?

Phosphate Analysis

0.0937 ppm/abs; 0.074 ppm

Concentration Absorbance (ppm) (AU)

What is the concentration of phosphate in a solution that has an absorbance of 0.708 AU? 6.8 ppm

0

0.040

2

0.288

One of your samples shows a reading of 1.541 AU, which is beyond the range of the calibration curve. The lab is over and it is too late to redo the calibration over a broader range or to dilute the sample and determine it a second time. Assume that Beer’s law still holds up to the value of the sample and calculate the concentration using the equation for the calibration line.

(Path length = 1.0 cm) 15.7 ppm

4

0.466

6

0.635

8

0.833

10

0.991

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3) Phosphate standards used to generate the calibration curve are usually made by first preparing a stock solution of known concentration and then diluting it to the required concentration.

First, prepare a stock solution that is 1.00 × 10–2 M in phosphate ion. How many grams of Na3PO4 would you add to a 250 mL volumetric flask to prepare this solution?

Mass Na3PO4: 0.410 g What is this concentration in ppm of phosphate? (i.e., as PO43−, not Na3PO4.)

PO43− concentration: 950. ppm What volume of this ppm solution would you dilute with water into a 1.000 L volumetric flask to make a solution of 10.0 ppm? 10.5 mL

This much of the work will be done for you by the laboratory assistant. You will be given a stock solution of 10.0 ppm phosphate to use in calibrating your phosphate assay. To preserve the ammonium molybdate reagent, you will create the calibrating standards by doing a serial dilution, using an aliquot of each diluted solution to create the next dilution.

After adding 1 mL of ammonium molybdate reagent and 2 drops of stannous chloride to 25 mL of the 10.0 ppm solution to develop the color, use a 20 mL aliquot to dilute with 5 mL of water to make 25 mL of a solution of 8.0 ppm.

Using the dilution equation: V1 × Conc1 = V2 × Conc2 and rearranging: 20 mL = 25 mL

8 ppm 10 ppm

To create 25 mL of a 6.0 ppm solution, what volume of the 8.0 ppm solution and what volume of water should be mixed? 18.75 mL solution and 6.25 mL water To create 25 mL of a 4.0 ppm solution, what volume of the 6.0 ppm solution and what volume of water should be mixed? 16.67 mL solution and 8.33 mL water To create 25 mL of a 2.0 ppm solution, what volume of the 4.0 ppm solution and what volume of water should be mixed? 12.50 mL solution and 12.50 mL water 4) What is the molar concentration of each of your calibration solutions?

Concentration = 10 ppm; [PO43–] = 1.05e-4 M Concentration = 8 ppm; [PO43–] = 8.42e-5 M Concentration = 6 ppm; [PO43–] = 6.32e-5 M Concentration = 4 ppm; [PO43–] = 4.21e-5 M Concentration = 2 ppm; [PO43–] = 2.11e-5 M

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Lab Report Key The title page should include: They should know this by now. Only take away points if incorrect!

Student’s full name Date of experiment Complete title of lab report Name of partner(s) Instructor’s name Lab and section number (e.g., CHM1045L-02) The purpose should include: There are several topics covered in this lab: spectroscopy, water contamination and purification, pH, colorimetry and the Beer-Lambert law. For full credit, a statement of the purpose of this lab should encompass at least three of these topics as well as the criteria used to determine success and should not be a copy of the purpose in the manual.

Procedure: This should be an MLA form reference to the lab manual with any changes in the procedure noted. In this report, the location the water sample was taken from should be included in the procedure as well.

Data: The data section should include a data table with the phosphate concentrations and absorbance values of the five standard solutions and the student’s water sample before and after purification.

The concentration of phosphate in the student’s water sample before and after purification should be reported both in ppm and molarity. The pH of the water sample before and after purification must also be reported. Finally, all observations of the water sample made before and after purification should be included.

Calculations: A completely labeled concentration vs. absorbance calibration graph for the PO43– standards should be included. Using the Beer-Lambert law and the calibration graph, an example calculation for the concentrations of PO43– before and after purification should be shown.

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Conclusions: The conclusion should be several paragraphs that address the following: the location where the water sample was obtained; the phosphate concentration and pH of the water sample before and after purification; an explanation of the phosphate concentration level and pH value of the water sample before and after, in other words, what might be causing these values; a discussion on how “pure” the water sample was before purification; and a discussion of any possible errors in the experiment.

Questions: 1) Why should we care about the amount of PO43– found in a natural water source?

High concentrations of PO43– are indicative of human effects on an ecosystem (i.e., pollution). Generally, phosphorous is a limiting reagent in an ecosystem. In this way, it regulates the amount of growth various species of plants and animals can achieve.

Adding excess phosphorous to the ecosystem can lead to explosive growth (especially in plants), and this overgrowth can endanger the balance of the ecosystem.

2) If you really wanted to be sure your water was drinkable, what further purification step(s) would you take?

Distillation predominantly, but allow for other examples.

3) Blue light has a wavelength between 450 and 495 nm. Why don’t we measure the absorbance of a blue solution within this wavelength range?

The solution appears blue because it transmits light in the blue wavelength region, but it absorbs light at other wavelengths. Therefore, very little absorption would be seen within the region of blue light.

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Experiment 17: The Purification of Water Section Points Points Worth Earned Title page (name, title, date, TA,

Experiment 17: The Purification of Water Section Points Points Worth Earned Title page (name, title, date, TA,

course, section, partner’s name)

course, section, partner’s name)

Purpose Procedure (cited and

Purpose Procedure (cited and

changes, where you got your data)

changes, where you got your data)

Data

Data

Absorbance values of standards.

Water before and after ppm. mol/L, pH. Observations of water before and after.

Absorbance values of standards.

Water before and after ppm. mol/L, pH. Observations of water before and after.

Calculations

Calculations

Graph. Beer’s law, %purity, ppm, mol/L conversion Conclusions (errors, location, purity, [PO43– ] and pH before and after) Questions (answer and source sited)

Graph. Beer’s law, %purity, ppm, mol/L conversion Conclusions (errors, location, purity, [PO43– ] and pH before and after) Questions (answer and source sited)

Total Grade

%

Total Grade

%

Experiment 17: The Purification of Water Section Points Points Worth Earned Title page (name, title, date, TA,

Experiment 17: The Purification of Water Section Points Points Worth Earned Title page (name, title, date, TA,

course, section, partner’s name)

course, section, partner’s name)

Purpose Procedure (cited and

Purpose Procedure (cited and

changes, where you got your data)

changes, where you got your data)

Data

Data

Absorbance values of standards.

Water before and after ppm. mol/L, pH. Observations of water before and after.

Absorbance values of standards.

Water before and after ppm. mol/L, pH. Observations of water before and after.

Calculations

Calculations

Graph. Beer’s law, %purity, ppm, mol/L conversion Conclusions (errors, location, purity, [PO43– ] and pH before and after) Questions (answer and source sited)

Graph. Beer’s law, %purity, ppm, mol/L conversion Conclusions (errors, location, purity, [PO43– ] and pH before and after) Questions (answer and source sited)

Total Grade

%

.

Total Grade

%

128

Experiment 18: Kinetics: The Iodine Clock Instructor Notes and Lab Preparation Chemicals and Equipment 1 bottle of 0.2 M KI 1 bottle of 0.05 M (NH4)2S2O8 1 bottle of 0.00175 M Na2S2O3 Dropping bottles of 3% starch solution Hotplates Cooler of ice 1 box of salt Waste container in hood Preparation For an average section of up to 28 students, prepare the following.

For 0.2 M KI, put 66.40 g of KI in a 2 L volumetric flask and dilute to the mark with DI water.

For 0.05 M (NH4)2S2O8, add 22.82 g to a 2L volumetric flask and dilute to the mark with DI water.

For 0.00175 M Na2S2O3, add 0.553 g of anhydrous Na2S2O3 to a 2 L volumetric flask and dilute to the mark with DI water.

For 3% starch, in a 2 L beaker, bring 1000 mL of DI water to a boil. Weigh 30 g of starch in a large weighing boat and dissolve the starch in the weighing boat with DI water. Once the water is boiling, slowly add the liquid starch, while stirring. Place a large watch glass on top of the beaker. Continue heating and stirring to dissolve. Be careful not to overboil. If you will not be preparing the starch fresh for each lab session, keep it refrigerated and check it during the week by combining a few drops of each reagent and observing the dark color.

Setup Place a hotplate on each bench.

Place the chemicals on the front counter.

Place the waste container in the hood.

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129

Instruction Notes The experiment itself can be completed in about 1 to 1.5 hr. There are no special techniques needed to complete the experiment, so instructional time at the front end of lab is minimal. The time that remains available at the end of the lab should be used to help students understand how to process their data. I have always advised my teaching assistants to spend the first few minutes of lab on technique and wait until the end of lab to deal with concepts. Students generally find it easier to understand how to analyze their data once they have collected them.

Points to Stress The final run of the experiment changes the concentration of the limiting reagent, S2O32–.

Students often assume that this will change the rate of the reaction. It should be pointed out that for this experiment, only variations in temperature change the rate.

Potential Problems The reaction procedure is very simple, and thus we haven’t seen very many problems occur.

Difficulties can arise, however, if the reagents are not fresh enough. Do not make substantial amounts of reagent in advance of the class. Small amounts as described above should be produced instead.

Results can also be damaged by contamination of the reagents. Make sure students do not pour excess reagent back into the lab supply. I say this repeatedly, but I am always catching students who accidentally take too much reagent trying to return it to the reagent bottle. On occasion, we have had an entire class’s results become “skewed” and have deduced that this type of contamination was the culprit.

Finally, the students need to be careful to use different graduated cylinders to measure each reagent. If they cross-contaminate their cylinders, the reaction may start early and completely destroy the timing of the reaction.

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Experiment 18 Prelaboratory Assignment KEY Name: ___________________________ Date: _________________ Instructor: ____________________________ Sec. #: ___________

Show all work for full credit.

1) For KI, Na2S2O3, and (NH4)2S2O8, calculate the initial concentration (M) based on the table of solution concentrations and volumes given in the procedure section.

Copy the completed table into your lab notebook for later use. The shaded columns will be completed in lab.

Run [KI] [Na2S2O3] [(NH4)2S2O8] Time Rate of Temp.

K Number (M) (M) (M) (sec) Reaction (K) (determine (M/sec) units) 1 2 3 4 5 6 7 8

0.075 0.050 0.025 0.075 0.075 0.075 0.075 0.075

0.00044 0.00044 0.00044 0.00044 0.00044 0.00044 0.00044 0.00022

0.019 0.019 0.019 0.012 0.0062 0.019 0.019 0.019

2) A first order chemical reaction has a rate constant of 9.1 × 101 s–1 at 12 °C and a rate constant of 4.1 × 102 s–1 at 36 °C. Calculate the activation energy, Ea, for the reaction.

4.6e-1 kJ/mol 3) In the iodine clock reaction, you are measuring the rate of the reaction of iodide ion (I−) with peroxydisulfate ion (S2O82−): .

131

S2O82− + 2I− → 2SO42− + I2 (Reaction 1) The rate of the reaction is measured by measuring the amount of I2 formed in a particular time, or Δ[I2]/Δt. The I2 is measured by titrating it with a fixed amount of thiosulfate ion (S2O32−), which rapidly converts the I2 formed in Reaction 1 back to iodide ion: I2 + 2S2O32− → 2I− + S4O62− (Reaction 2) (While Reaction 2 is said to be “fast” with respect to Reaction 1, it actually can proceed no faster than the rate at which I2 is produced, so its actual rate is controlled by the rate of Reaction 1.)

When the S2O32− is completely used up, then I2 begins to accumulate. It combines with starch to form a dark blue complex, so the end point of the titration occurs when the solution turns blue.

The time it takes for the blue color to appear is called the period of the clock, or Δt, the time it takes for Reaction 2 to go to completion. The rate of S2O32− disappearance is therefore given by its initial concentration divided by the clock period, or [S2O32−]/Δt. Because the rate of disappearance of I2 in Reaction 2 is controlled by its rate of appearance in Reaction 1, the rate of both reactions can be determined from the value of ½ × [S2O32−]/Δt. (Two S2O32− ions are consumed for every I2 consumed.)

(Actually, the I2 in solution combines with iodide ion to form triiodide ion, I3−, which is the species that forms the blue color with starch. That step is not shown to keep the equations simple, but adding it would not change the conclusions.)

The following graphs illustrate what is happening to the concentration of each of the species involved in these two reactions. Show you understand the reaction by identifying the species associated with each of the lines in the graphs.

Initial conditions: [S2O82−] = [I−] = 0.055 M; [S2O32−] = 0.0015 M

.

[SO42−] =

____F_______

[I−] =

____E_______

[I2] =

____D_______

[S2O32−] =

____B_______

[S4O62−] =

____A_______

[S2O82−] =

____C_______

132

Lab Report Key The title page should include: They should know this by now. Only take away points if incorrect!

Student’s full name Date of experiment Complete title of lab report Name of partner(s) Instructor’s name Lab and section number (e.g., CHM1045L-02) The purpose should include: There are several topics covered in this lab: kinetics and rate laws, color indicators, rate law, order, and procedure design. A statement of the purpose of this lab should encompass at least three of these topics and criteria for success for full credit and should not be a copy of the purpose in the manual.

Procedure: This should be an MLA form reference to the lab manual with any changes in the procedure noted.

Data: Completed tables such as the ones below should be present.

Run Number

[KI] (M)

[Na2S2O3] (M)

[(NH4)2S2O8] (M)

Time (sec)

Rate of Reaction (M/sec)

Temp. (K)

K (determine units)

1 2 3 4 5 6 7 8

Run Number 1 2 3 4 5 6 7 8

.

log[KI] (M)

log[(NH4)2S2O8] log Rate of (M) Reaction (M/sec)

133

Calculations: The calculation section should include three graphs. All graphing guidelines apply. Also included should be sample calculations for the following: [KI], [Na2S2O3], [(NH4)2S2O8], rate, k, Ea, and A. Conclusions: The conclusion section should be several paragraphs containing all of the values obtained, including the rate equation. This section should also include a comparison of the rate constants at the same temperature. A well-developed discussion of the rate constants for all runs, including both similarities and differences, should be present. Also, an explanation of the value for Ea must be present. Finally, a discussion of the accuracy and errors in this experiment is required.

Question: 1) The kinetic molecular theory (KMT) was introduced earlier in the chapters of the textbook that accompanies this lab manual. Use KMT to explain how temperature affects the rates of chemical reactions. Be detailed in your explanation.

Increased temperature provides increased energy to the molecules in the reaction. The molecules increase their kinetic energy and thus move more rapidly, increasing the number of collisions between molecules. More collisions increase the number of reactions that take place, thus increasing the overall rate of the reaction.

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Experiment 18: Kinetics: The Iodine Clock Section Points Points Worth Earned

Experiment 18: Kinetics: The Iodine Clock Section Points Points Worth Earned

Title page (name, title, date, TA,

Title page (name, title, date, TA,

course, section, partner’s name) Purpose (at least three points)

course, section, partner’s name) Purpose (at least three points)

Procedure (cited/changes) Data (values for n, m, Ea, and A) Table I (For all 8 runs: [KI], [Na2S2O3],

Procedure (cited/changes) Data (values for n, m, Ea, and A) Table I (For all 8 runs: [KI], [Na2S2O3],

[(NH4)2S2O8], time, rate, temp., and K) Table 2 (For all 8 runs: log [KI], log [(NH4)2S2O8], and log rate) Calculations ([KI], [Na2S2O3], [(NH4)2S2O8], rate, K, Ea, and A) Graph (log-log graph for n, log-log graph for m and ln(k) vs. 1/T) Conclusions (discussion covering all of the values obtained and the rate equation; comparison of the rate constants at the same temperature; discussion of the rate constants for all runs, including both similarities and differences; explanation of the value for E; accuracy and error)

[(NH4)2S2O8], time, rate, temp., and K) Table 2 (For all 8 runs: log [KI], log [(NH4)2S2O8], and log rate) Calculations ([KI], [Na2S2O3], [(NH4)2S2O8], rate, K, Ea, and A) Graph (log-log graph for n, log-log graph for m and ln(k) vs. 1/T) Conclusions (discussion covering all of the values obtained and the rate equation; comparison of the rate constants at the same temperature; discussion of the rate constants for all runs, including both similarities and differences; explanation of the value for E; accuracy and error)

Questions Total Grade

Questions Total Grade

%

%

Experiment 18: Kinetics: The Iodine Clock Section Points Points Worth Earned

Experiment 18: Kinetics: The Iodine Clock Section Points Points Worth Earned

Title page (name, title, date, TA,

Title page (name, title, date, TA,

course, section, partner’s name) Purpose (at least three points)

course, section, partner’s name) Purpose (at least three points)

Procedure (cited/changes) Data (values for n, m, Ea, and A) Table I (For all 8 runs: [KI], [Na2S2O3],

Procedure (cited/changes) Data (values for n, m, Ea, and A) Table I (For all 8 runs: [KI], [Na2S2O3],

[(NH4)2S2O8], time, rate, temp., and K) Table 2 (For all 8 runs: log [KI], log [(NH4)2S2O8], and log rate) Calculations ([KI], [Na2S2O3], [(NH4)2S2O8], rate, K, Ea, and A) Graph (log-log graph for n, log-log graph for m and ln(k) vs. 1/T) Conclusions (discussion covering all of the values obtained and the rate equation; comparison of the rate constants at the same temperature; discussion of the rate constants for all runs, including both similarities and differences; explanation of the value for E; accuracy and error)

[(NH4)2S2O8], time, rate, temp., and K) Table 2 (For all 8 runs: log [KI], log [(NH4)2S2O8], and log rate) Calculations ([KI], [Na2S2O3], [(NH4)2S2O8], rate, K, Ea, and A) Graph (log-log graph for n, log-log graph for m and ln(k) vs. 1/T) Conclusions (discussion covering all of the values obtained and the rate equation; comparison of the rate constants at the same temperature; discussion of the rate constants for all runs, including both similarities and differences; explanation of the value for E; accuracy and error)

Questions Total Grade

Questions Total Grade

.

%

%

135

Experiment 19: Photometric Determination of an Equilibrium Constant Instructor Notes and Lab Preparation Chemicals and Equipment 0.200 M Fe(NO3)3 acidified (0.5 M nitric acid) 0.002 M Fe(NO3)3 acidified (0.5 M nitric acid) 0.002 M KSCN 0.5 M nitric acid 10 mL volumetric pipettes Mohr pipettes Bulbs for transfer pipettes Cuvettes Spectrophotometers Kimwipes Preparation To prepare 7 L of 0.200 M Fe(NO3)3 in amber bottle, dissolve 565.60 g of Fe(NO3)3.H2O in 0.5 M HNO3 and dilute to the mark with 0.5 M nitric acid. Fill 1 L amber bottles with the reagent.

To prepare 7 L of 0.002 M Fe(NO3)3 in amber bottle, place 70 mL of 0.200 M Fe(NO3)3 and dilute to the mark with 0.5 M nitric acid. Fill 1 L amber bottles with the reagent. *** LIGHT SENSITIVE*** Make sure to cover the bottle in foil or use an amber bottle.

To prepare 7 L of 0.002 M KSCN, dissolve 1.36 g of KSCN in DI water and dilute to the mark.

Setup • • •

Place one spectrophotometer on each lab bench.

Place a waste container in the hood.

Place remaining chemicals and supplies on the front counter.

Instruction Notes This experiment is extremely simple to execute and takes approximately 1.5 hr to complete. The time left at the end of the lab can be put to good use going over the calculations required to complete the lab report. The experiment again uses a spectrophotometer and requires the production of a graph to determine the extinction coefficient. This process has been done several times in previous experiments, so students should require minimal instruction to complete this portion of the report. The calculation of the equilibrium constant, however, is best completed

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136

using a spreadsheet program such as Excel. The calculations are not difficult, but with their repetitive nature, they can be tedious.

Points to Stress Students will be using Mohr pipettes to make accurate concentrations of solution. This is the only technique being introduced in the experiment. Whether using bulbs or pumps, the proper technique should be demonstrated. The correct determination of the equilibrium constant depends on the accuracy of the solution concentrations.

Potential Problems For obvious reasons, contamination of the solutions is one of the most serious sources of error.

Luckily, the solution changes color if contamination occurs and can therefore be corrected.

Another problem we have had is students not rinsing the cuvette completely between measurements. This can lead to skewed results.

The solutions themselves are light/heat sensitive. If the iron(III) nitrate solution loses its color, the results are no longer reliable. The solution should be kept in an amber bottle and made fresh as often as possible or practical.

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137

Experiment 19 Prelaboratory Assignment KEY Name: ___________________________ Date: _________________ Instructor: ____________________________ Sec. #: ___________

Show all work for full credit.

1) You would like to determine the equilibrium constant for the binding of a ligand to a metal ion: M3+ + L− <=> ML2+, where K = [([ML2+])/([M3+][L–])]. The ML2+ complex has a unique absorbance in the visible region, so its concentration at equilibrium can be determined by measuring the absorbance of the solution at an appropriate wavelength. An ICE table can be used to determine the concentrations of M3+ and L− from their initial concentrations and the concentration change in going to equilibrium. The following experiment is carried out first in order to determine the extinction coefficient of the complex at the wavelength chosen.

Calculate the complex concentration in each solution, and then its extinction coefficient.

0.200 M Solution Metal Ion (mL)

0.1 M HNO3 (mL)

0.0011 M Ligand Ion (mL)

Solution Concentration (M)

Absorbance

Extinction Coefficient (M–1cm–1)

A

5.0

4.0

1.0

0.00011

0.113

1027

B

5.0

3.0

2.0

0.00022

0.227

1032

C

5.0

2.0

3.0

0.00033

0.337

1021

D

5.0

1.0

4.0

0.00044

0.431

980

E

5.0

0.0

5.0

0.00055

0.562

1022

Plot the absorbance versus the solution concentration and determine the slope and intercept of the resulting line.

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138

2) Now, you will determine the equilibrium constant, K, at several starting concentrations of M3+ and L−. The following table summarizes your measurements.

0.0023 M Solution Metal Ion (mL)

.

[M3+]init

0.0011 M Ligand Ion (mL)

[L–]init Absorbance

F

3.0

0.00069

7.0

0.00077

0.286

G

4.0

0.00092

6.0

0.00066

0.312

H

5.0

0.00115

5.0

0.00055

0.308

I

6.0

0.00138

4.0

0.00044

0.276

J

7.0

0.00161

3.0

0.00033

0.221

139

Using an ICE table, calculate the equilibrium concentrations of ML2+, M3+, L−, and K for each of the five solutions.

Solution

[ML2+] = x

[M3+]eq

[L–]eq

F

0.000285481

0.00040

0.000485

1456.556

G

0.000311434 0.0006086

0.000349

1468.157

H

0.000307441 0.0008426

0.000243

1504.334

I

0.000275499 0.0011045

0.000165

1516.302

J

0.000220599 0.0013894

0.000109

1451.29

K

What value of K do you get for solution H? 1504 What average value of K do you get? 1483

Lab Report Key The title page should include: They should know this by now. Only take away points if incorrect!

Student’s full name Date of experiment Complete title of lab report Name of partner(s) Instructor’s name Lab and section number (e.g., CHM1045L-02) The purpose should include: There are several topics covered in this lab, including chemical equilibrium, stoichiometry, spectroscopy, and calibration graphs. A statement of the purpose of this lab should encompass at least three of these topics and the criteria for a successful experiment for full credit and should not be a copy of the purpose in the manual.

Procedure: This should be an MLA form reference to the lab manual with any changes in the procedure noted.

Data: The data section for this experiment will include two sections—one for the calibration data (determination of the extinction coefficient) and one for the equilibrium data (determination of

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140

the equilibrium constant). For the calibration data, a table with the solution numbers A through E, the volume of Fe3+, the volume of KSCN, the total volume, [Fe3+], [KSCN], and the absorbance values should be present.

A completed table such as the one below should be present for both parts: Soln

Initial Initial Volume of Volume of Fe3+ KSCN (mL) (mL)

Total Volume (mL)

Initial [Fe3+] (M)

Initial [SCN–] (M)

Abs

[Fe(SCN)x(3-x)] (M)

Eq [Fe3+] (M)

Eq [SCN–] (M)

K

F G H I J

Calculations: The calculation section should include a calibration graph of the concentration versus absorbance from part 1. All graphing guidelines apply. Example calculations of the molar absorptivity or extinction coefficient should be presented. Sample calculations for the concentrations used in the calibration graph and each calculation done for the equilibrium data are also required.

Conclusions: The conclusion section should include several paragraphs discussing the value for x that is determined and how the conclusion was reached. The average values of K should be included in the discussion. Information about the calibration curve and the value of the molar absorptivity or extinction coefficient should be presented. A comparison of the values calculated when each of the three values for x is used should also be included. Do not forget to discuss with the students any errors that can and have been made.

Questions: 1) How constant were your K values at room temperature? Explain any variation.

This should be a detailed explanation of the K values with numbers. Explanations should be reasonable and contain good scientific reasoning.

2) See if you can find literature and/or Internet references for the equilibrium constant for this equilibrium. Please cite the reference(s). How does your result compare with the one(s) you cited? Perhaps you will even find a similar experiment, with sample results, posted out on the Web. Should give at least two citations for full credit. There are many versions of this same lab on the web.

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Experiment 19: Photometric Determination of an Equilibrium Constant

Experiment 19: Photometric Determination of an Equilibrium Constant

Section

Section

Points Worth

Points Earned

Title page (name, title, date, TA, course,

Title page (name, title, date, TA, course,

section, partner’s name) Purpose (at least three points)

section, partner’s name) Purpose (at least three points)

Procedure (cited/changes) Data Table I: Calibration Data

Procedure (cited/changes) Data Table I: Calibration Data

(solution number, volume of Fe+3, volume of KSCN, [Fe+3], [KSCN], absorbance) Table 2: Equilibrium Data (table completed for x = 1, 2, and 3 [3 tables total], average K, stdev, and correct x value) Calculations ([Fe+3], [KSCN], [Fe(SCN)x(3x) ], Eq [Fe+3], Eq [KSCN], K, average, stdev) Graph (calibration graph)

(solution number, volume of Fe+3, volume of KSCN, [Fe+3], [KSCN], absorbance) Table 2: Equilibrium Data (table completed for x = 1, 2, and 3 [3 tables total], average K, stdev, and correct x value) Calculations ([Fe+3], [KSCN], [Fe(SCN)x(3x) ], Eq [Fe+3], Eq [KSCN], K, average, stdev) Graph (calibration graph)

Conclusions (discussion covering the value

Conclusions (discussion covering the value

for x that you determined and how you reached your conclusion; average values of K and information about the calibration curve and the value of the molar absorptivity; compare and contrast the values calculated when each of the three values for x are used and possible errors)

for x that you determined and how you reached your conclusion; average values of K and information about the calibration curve and the value of the molar absorptivity; compare and contrast the values calculated when each of the three values for x are used and possible errors)

Questions Total Grade

Questions Total Grade

%

Points Worth

Points Earned

%

Experiment 19: Photometric Determination of an Equilibrium Constant

Experiment 19: Photometric Determination of an Equilibrium Constant

Section

Section

Points Worth

Points Earned

Title page (name, title, date, TA, course,

Title page (name, title, date, TA, course,

section, partner’s name) Purpose (at least three points)

section, partner’s name) Purpose (at least three points)

Procedure (cited/changes) Data Table I: Calibration Data

Procedure (cited/changes) Data Table I: Calibration Data

(solution number, volume of Fe+3, volume of KSCN, [Fe+3], [KSCN], absorbance) Table 2: Equilibrium Data (table completed for x = 1, 2, and 3 [3 tables total], average K, stdev, and correct x value) Calculations ([Fe+3], [KSCN], [Fe(SCN)x(3x) ], Eq [Fe+3], Eq [KSCN], K, average, stdev) Graph (calibration graph)

(solution number, volume of Fe+3, volume of KSCN, [Fe+3], [KSCN], absorbance) Table 2: Equilibrium Data (table completed for x = 1, 2, and 3 [3 tables total], average K, stdev, and correct x value) Calculations ([Fe+3], [KSCN], [Fe(SCN)x(3x) ], Eq [Fe+3], Eq [KSCN], K, average, stdev) Graph (calibration graph)

Conclusions (discussion covering the value

Conclusions (discussion covering the value

for x that you determined and how you reached your conclusion; average values of K and information about the calibration curve and the value of the molar absorptivity; compare and contrast the values calculated when each of the three values for x are used and possible errors)

for x that you determined and how you reached your conclusion; average values of K and information about the calibration curve and the value of the molar absorptivity; compare and contrast the values calculated when each of the three values for x are used and possible errors)

Questions Total Grade

Questions Total Grade

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%

Points Worth

Points Earned

%

142

Experiment 20: Analysis of Vitamin C in Fruit Juices By Titration Instructor Notes and Lab Preparation Chemicals and Equipment Vitamin C tables (with the bottle…need info).

250-mL beakers 250-mL volumetric flasks Burets (titration lab) Buret clamps Buret stands 1% starch solution 6M acetic acid Iodine solution Iodine crystals Potassium iodide 1 bottle of white cranberry juice (Ocean Spray) Mortar/Pestle 25-mL volumetric pipets with bulbs 10-mL graduated cylinder glass stir rods Squirt water bottle with dI water 125-mL Erlenmeyer flasks Brushes to clean burets Marker and label

Preparation 1. The iodine solution must be prepared at a minimum of 24 hours in advanced in order to allow the iodine to dissolve. a. Dissolve 6 grams of potassium iodide into 200 mL of deionized water. b. Slowly add the 3 grams of iodine crystals to the solution. c. Dilute the iodine solution with water to create 1L of the iodine solution.

2. The starch should be prepared fresh. It allows for the titration to be more accurate with regards to the color change. To prepare the starch, place 100 mL of deionized water into a 250-mL beaker. Bring the water to a boil, add 1g of soluble starch to it and let cool. Once cooled, place into a dropper bottle.

3. Make sure the students label all their beakers and flasks 4. Make sure the correct solution is in the buret

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143

Experiment 20 PreLaboratory Preparation KEY Name: ___________________________ Date: _____________ Instructor: ____________________________ Sec. #: ________

1. What is RDA? RDA (Recommended Daily Allowance) depends on your age and gender. To eat a nutritionally balanced diet, one thing you must know is which foods deliver adequate amounts of the vitamins you need. It is good to build a diet around a variety of foods to help attain the adequate amounts of vitamins.

2. What is the RDA of vitamin C for adults between the ages of 18 and 35?

The current RDA for vitamin C for adult nonsmoking men and women is 60 mg/d, which is based on a mean requirement of 46 mg/d to prevent the deficiency disease scurvy.

Lab Report Key The title page should include: They should know this by now. Only take away points if incorrect!

Student’s full name Date of experiment Complete title of lab report Name of partner(s) Instructor’s name Lab and section number (e.g., CHM1045L-02) The purpose should include: There are several topics covered in this lab, including calibration curves, extrapolation of data and understanding the requirements of vitamin C in your diet.

Procedure: This should be an MLA form reference to the lab manual with any changes in the procedure noted.

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144

Data: The data section for this experiment will include the following chart (values will vary):

Titration of Standard Vitamin C Solution Volume of standard vitamin C solution delivered Volume

Sample 1

Sample 2

Sample 3

Sample 2

Sample 3

Final volume Initial volume Volume vitamin C

Volume of vitamin C = mg of vitamin C Volume of iodine used for titration Volume

Sample 1

Final volume Initial volume Volume of I2 used Calculation;

(Volume I 2ml) /(ml of vitamin C) = ml I2/mg vitamin C

ml l2/mg vitamin C =

Calculations: Average = (s1 + s2 + s3) / 3 Average volume of I2/mg of vitamin C = ______________ Analysis of Vitamin C for Fruit Juice

Titration of Vitamin C in Fruit Juice Volume of fruit juice delivered Volume

Sample 1

Sample 2

Sample 3

Final volume Initial volume Volume of fruit juice

.

145

Volume of iodine used for titration Volume

Sample 1

Sample 2

Sample 3

Final volume Initial volume Volume of I2 used Volume I2ml  (1mg of vitamin C/volume of I2 ) = mg vitamin C Mg vitamin C Calculation: Average = (s1 + s2 + s3) / 3 Average mg of vitamin C = ________________ Percent of RDA = _______________ Questions: (Answers will vary) 1. Define titration and describe its purpose Using titration, a laboratory procedure used for finding the concentrations of substances in solutions, the amount of vitamin C can be determined.

2. How does one know that all the vitamin C has reacted?

When you notice a color change for longer than 30 seconds.

3. How many milligrams of vitamin C are there in 25 mL of standard vitamin C solution?

250 mL of water and a 250 mg tablet, therefore, in 25 mL of solution, you would have 25 mg of vitamin. C. 4. If the vitamin C solution from #3 required 30.00 mL of iodine to reach the end point, what is the volume of I2 / mg. of vitamin C.?

30 L of iodine divided by 25 mg of vitamin C = 1.2 mL/mg 5. When a 25 mL sample of fruit juice was titrated with the iodine solution, it was found that 12.5 mL of iodine was required to titrate to the end point. Calculate the mg of vitamin C in the sample of fruit juice.

12.5 mL of iodine  (1 mg vitamin C/1.2 mL of iodine) = 10.4 mg vitamin C. 6. What percent of RDA is the above sample of fruit juice?

Answers will vary with regards to what juice is used.

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146

Experiment 20: Analysis of Vitamin C in Fruit Juices by Titration Section Points Points Worth Earned Title page (name, title, date, TA, course,

Experiment 20: Analysis of Vitamin C in Fruit Juices by Titration Section Points Points Worth Earned Title page (name, title, date, TA, course,

section, partner’s name)

section, partner’s name)

Purpose Procedure (cited and changes) Data ( Charts for standard vitamin C solution and iodine used for titration for both the standard and the fruit juice) Calculations (mg I2 per mg of vit.

C, average vol of I2 per mg of vit.

C, mg of vit. C per vol. of juice)

Purpose Procedure (cited and changes) Data ( Charts for standard vitamin C solution and iodine used for titration for both the standard and the fruit juice) Calculations (mg I2 per mg of vit.

C, average vol of I2 per mg of vit.

C, mg of vit. C per vol. of juice)

Conclusions (amount of vit. C in fruit juice vs standard, discussion of difference in errors, what this tells the public?)

Questions Total Grade

Conclusions (amount of vit. C in fruit juice vs standard, discussion of difference in errors, what this tells the public?)

Questions Total Grade

%

Experiment 20: Analysis of Vitamin C in Fruit Juices by Titration Section Points Points Worth Earned Title page (name, title, date, TA, course,

Experiment 20: Analysis of Vitamin C in Fruit Juices by Titration Section Points Points Worth Earned Title page (name, title, date, TA, course,

section, partner’s name)

section, partner’s name)

Purpose Procedure (cited and changes) Data ( Charts for standard vitamin C solution and iodine used for titration for both the standard and the fruit juice) Calculations (mg I2 per mg of vit.

C, average vol of I2 per mg of vit.

C, mg of vit. C per vol. of juice)

Purpose Procedure (cited and changes) Data ( Charts for standard vitamin C solution and iodine used for titration for both the standard and the fruit juice) Calculations (mg I2 per mg of vit.

C, average vol of I2 per mg of vit.

C, mg of vit. C per vol. of juice)

Conclusions (amount of vit. C in fruit juice vs standard, discussion of difference in errors, what this tells the public?)

Questions Total Grade

Conclusions (amount of vit. C in fruit juice vs standard, discussion of difference in errors, what this tells the public?)

Questions Total Grade

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%

%

%

147

Experiment 21: Murder Solved by the Analysis of a Kiss Instructor Notes and Lab Preparation Chemicals and Equipment Jar with Lid Lipsticks TLC Plate Mobile phase/Solvent Plastic Transfer Pipette Ruler Pencil Toothpicks Filter Paper Chemicals n- Butyl Alcohol Acetone Water Ammonium Hydroxide

Preparation 1. Mobile Phase/Solvent: 5 parts n-butyl alcohol, 5 parts acetone, 1 part water, and 2 parts ammonium hydroxide. Use in hood if possible. Shelf life is about one month.

2. Label lipstick samples—W (wife), D (daughter), A (attorney), C (crime scene) 3. Filter paper pieces should be cut so they fit completely into the jar and wrap around the inside of the jar for the purpose of saturating the jar environment with mobile phase vapors.

4. If using chromatography paper instead of TLC plates, cut each sheet of paper into 2  4 inch

strips. (Cut 8  8 sheet in half and then into four 2-inch strips. Get 8 strips from one sheet of paper.)

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148

Experiment 21 PreLaboratory Preparation KEY Name: _______________________ Date: _________________ Instructor: _________________________ Sec. #: ___________

1. In this experiment, what is the purpose of the n-butyl alcohol, acetone, water, and ammonium hydroxide solution?

In this lab, the acetone dissolves the lipsticks, the n-butyl alcohol moves the organic components, the water moves the polar components, and the ammonium hydroxide moves the ionic components.

2. Do you think water could have been used in place of the mobile phase/solvent? Why or why not?

Water could not have been used. Lipsticks are designed to be insoluble in water so that they will stay on the lips.

Laboratory Report Key The title page should include: They should know this by now. Only take away points if incorrect!

Student’s full name Date of experiment Complete title of lab report Name of partner(s) Instructor’s name Lab and section number (e.g., CHM1045L-02) The purpose should include: There are several topics covered in this lab, including pigmentation, calculation of Rf values, color components, mobile phase, stationary phase, chromatography, and TLC sheets.

Procedure: This should be an MLA form reference to the lab manual with any changes in the procedure noted.

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149

Data: The data section for this experiment will include the following chart:

Lipstick Samples

C (crime scene)

Color of Components

Column 3

Column 4

Distance Lipstick Components Moved (cm)

Distance Mobile Phase Moved in cm

Rf Values for Each Colored Component

1.

2.

3.

4.

W (Mrs. Conley)

1.

2.

3.

4.

D (Ms. Conley)

1.

2.

3.

4.

A (Ms. Justice)

1.

2.

3.

4.

Calculations: The calculation section should include a table of the calculated Rf values.

Conclusions: The conclusion section should include several paragraphs discussing the value for x that is determined and how the conclusion was reached. The average values of Rf should be included in the discussion, coefficient should be presented. A comparison of the values calculated when each of the given Rf values. Do not forget to discuss with the students any errors that can and have been made.

Rf =

.

Distance traveled by one lipstick component from the origin (column 3) Distance the solvent moved from the origin (column 4)

150

Questions: 1. According to your results, who drank coffee with Mr. Conley before he was killed?

The answer depends on which lipstick you used as the crime sample.

2. Do you think the discovery of this person’s lipstick in Mr. Conley’s apartment is enough evidence to link that person with the crime? Why or why not?

Answers may vary. The determination that someone was present in a location before a crime was committed does not necessarily tie that person to the crime.

3. What are some other mixtures that you think can be separated by chromatography?

Answers will vary, but could include inks, cosmetics, dyes, food colorings, and lubricants.

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151

Experiment 21: Murder Solved by the Analysis of a Kiss

Experiment 21: Murder Solved by the Analysis of a Kiss

Section

Section

Points Worth

Points Earned

Title page (name, title, date, TA, course,

Title page (name, title, date, TA, course,

section, partner’s name)

section, partner’s name)

Purpose Procedure (cited and changes, and

Purpose Procedure (cited and changes, and

mobile phase prep and lipsticks used) Data Chart completed with all distances measured for the lipstick, mobile phase and Rf values added.

Calculations (Rf value calculations)

mobile phase prep and lipsticks used) Data Chart completed with all distances measured for the lipstick, mobile phase and Rf values added.

Calculations (Rf value calculations)

Conclusions (mobile phase used,

Conclusions (mobile phase used,

summary of results, discussion of differences between tables, errors)

summary of results, discussion of differences between tables, errors)

Questions Lab Pages Total Grade

Questions Lab Pages Total Grade

%

Points Worth

Points Earned

%

Experiment 21: Murder Solved by the Analysis of a Kiss

Experiment 21: Murder Solved by the Analysis of a Kiss

Section

Section

Points Worth

Points Earned

Title page (name, title, date, TA, course,

Points Earned

Title page (name, title, date, TA, course,

section, partner’s name)

section, partner’s name)

Purpose Procedure (cited and changes, and

Purpose Procedure (cited and changes, and

mobile phase prep and lipsticks used) Data Chart completed with all distances measured for the lipstick, mobile phase and Rf values added.

Calculations (Rf value calculations)

mobile phase prep and lipsticks used) Data Chart completed with all distances measured for the lipstick, mobile phase and Rf values added.

Calculations (Rf value calculations)

Conclusions (mobile phase used,

Conclusions (mobile phase used,

summary of results, discussion of differences between tables, errors)

summary of results, discussion of differences between tables, errors)

Questions Lab Pages Total Grade

Questions Lab Pages Total Grade

.

Points Worth

%

%

152

Experiment 22: Entropy, Free Energy, and Chemical Equilibrium Instructor Notes and Lab Preparation Chemicals and Equipment 50 mL burets Ring stands Buret clamps 1 L bottle of 0.05 M HCl 1 bottle of calcium hydroxide 1 rack of thermometers 2 dropping bottles of bromothymol blue Hotplates or Bunsen burners 1 pack of 0.1 nm filters (Whatman #5 or 6, or equivalent) Corks Transfer pipettes Bulbs for transfer pipettes Buchner funnels Filter flasks 1 box of rock salt 1 cooler of ice Ice trays Waste container Preparation To make 250 mL of bromothymol blue: to a 250 mL volumetric flask, add 0.1 g of bromothymol blue powder in 16 mL of 0.01 M NaOH. Dilute to the mark with DI water.

Setup Place 1 hotplate on each bench.

The rest of the chemicals are placed on the front counter.

Place a waste container in the hood.

Instruction Notes The maximum in solubility for Ca(OH)2 is around 4 °C. The lab requires students to determine the trend in solubility and calculate the thermodynamic properties related to the solubility.

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153

Points to Stress Students will be using the filtration flasks again. Because the determination of concentration is very dependent on good technique in this lab, it is extremely important that they filter their solutions carefully and that they don’t attempt to titrate cloudy solutions, as this will throw off the results significantly.

Within the calculations they complete for their lab report, the dilution of the saturated solution before titration should be discussed. Because we are approximate in the volume of water added in the dilution, the students get confused as to how to determine the concentration. It should be stressed that we are titrating to determine the number of moles of hydroxide ion that were in the original 10 mL sample.

Potential Problems As mentioned above, technique is very important. The most significant problem with this lab has come from students titrating cloudy solutions. Remind them that they need only a small amount of filtrate to titrate so that they can filter very slowly and carefully without a significant loss of time.

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154

Experiment 22 Prelaboratory Assignment KEY Name: ___________________________ Date: _________________ Instructor: ____________________________ Sec. #: ___________

Show all work for full credit.

1) You add an excess of Ca(OH)2 to water maintained at a particular temperature, stir until the solution is saturated, filter, then determine the [OH−] in the solution by titration with acid.

Titration of 10.0 mL of the calcium hydroxide solution to the endpoint requires 4.86 mL of 0.070 M HCl solution.

What is the molar quantity of OH− in the 10.0 mL of solution? 0.340 mmol What are the concentrations of Ca2+ and OH−? 0.0170 M and 0.0340 M, respectively What is the solubility of Ca(OH)2 under these conditions? 0.126 g/dL What is the Ksp for Ca(OH)2 under these conditions? 1.97e-5 2) You measure the solubility of a salt at four different temperatures and calculate the following Ksp values: Temperature (°C): Ksp:

ΔGosoln (kJ/mol)

15

31

51

70

2.89 × 10–2 4.11 × 10–2 6.08 × 10–2 8.45 × 10–2

8.5

8.1

7.5

7.0

ΔGosoln for the solubility process is given by the relationship ΔGosoln = –RT ln Ksp, where R = 8.314 J/(K × mol), and T is the absolute temperature in degrees K. Calculate ΔGosoln (in kJ/mol) at each of these temperatures. (in table) As the temperature increases, how does the solubility of the salt change? increases

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155

According to Le Chatelier’s principle, dissolving this salt should therefore be which type of process? endothermic In other words, what is the sign of ΔHosoln? positive 3) It is possible to determine both ΔHosoln and ΔSosoln for the solution process from this data.

One or both of two graphical methods can be used: Method 1: From the equation: Method 2: Alternatively, rearranging the equation relating ΔGosoln = ΔHosoln – TΔSosoln Ksp and ΔGosoln: o o o o a plot of ΔG soln versus T will Gsoln H soln Ssoln o lnK = = − + give –ΔS soln as the slope sp RT RT R o and ΔH soln as the intercept. o H soln 1 and plotting ln Ksp versus will give − as the R T o S soln slope and as the intercept.

R

Using one or both of these graphical methods, determine ΔHosoln (in kJ/mol) and ΔSosoln (in J/(K × mol)) for this salt. (Be sure to play close attention to your units and signs in both your plots and your calculations.)

Hosoln = 16 kJ/mol Sosoln = 26 J/(K × mol)

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156

Lab Report Key The title page should include: They should know this by now. Only take away points if incorrect!

Student’s full name Date of experiment Complete title of lab report Name of partner(s) Instructor’s name Lab and section number (e.g., CHM1046L-02) The purpose should include: There are several topics covered in this lab: equilibria, titration, thermodynamics, entropy, enthalpy, solubility, and free energy. A statement of the purpose of this lab should encompass at least three of these topics for full credit and should not be a copy of the purpose in the manual. A statement of the criteria required for success should be included.

Procedure: This should be a reference to the lab manual, with any changes noted.

Data: The hydroxide ion concentration, [OH–], and corresponding molar solubilities of Ca(OH)2 should be reported for each temperature. The Ksp of Ca(OH)2 should be reported for each temperature. The Gibbs free energy should also be reported for each temperature. In addition, the enthalpy and entropy values for two temperatures should be reported.

Calculations: A graph of molar solubility versus temperature should be included.

A calculation of the data used to determine a temperature of maximum solubility should be included. In addition, an example of the following calculations should be shown: • [OH–] by titration • molar solubility of Ca(OH)2 • Ksp of Ca(OH)2 • Gibbs free energy • Enthalpy of dissociation • Entropy of dissociation

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157

Conclusions: A summary of the results of the experiment should include the Ksp and thermodynamic values found. A discussion of possible errors should be included.

Questions: 1. Why do you have to filter the Ca(OH)2 solution before titrating it?

As you are making a saturated solution, there will be nondissolved particles of salt left over. Removal of these particles is essential to get an accurate concentration of the dissolved salt.

2. Why don’t you have to accurately record the amount of Ca(OH)2(s) used in the saturated solution?

Since you remove all of the nondissolved salt and titrate the saturated solution to determine its concentration, accurate measurement of the amount of solid salt placed in the solution is a waste of time.

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158

Experiment 22: Entropy, Free Energy, and Chemical Equilibrium Section Points Points Worth Earned

Experiment 22: Entropy, Free Energy, and Chemical Equilibrium Section Points Points Worth Earned

Title page (name, title, date, TA, course,

Title page (name, title, date, TA, course,

section, partner’s name)

section, partner’s name)

Purpose Procedure (cited and changes) Data

Purpose Procedure (cited and changes) Data

Delta Vs, molar solubility, Ksp, delta Gs, 2 delta Hs, and delta Ss Concentration of [OH]

Delta Vs, molar solubility, Ksp, delta Gs, 2 delta Hs, and delta Ss Concentration of [OH]

Calculations

Calculations

Graphs Delta Vs, molar solubility, Ksp , delta Gs, 2 delta Hs, and delta Ss Conclusions (all values, max solubility, explanation, errors)

Graphs Delta Vs, molar solubility, Ksp , delta Gs, 2 delta Hs, and delta Ss Conclusions (all values, max solubility, explanation, errors)

Questions Total Grade

Questions Total Grade

%

%

Experiment 22: Entropy, Free Energy, and Chemical Equilibrium Section Points Points Worth Earned

Experiment 22: Entropy, Free Energy, and Chemical Equilibrium Section Points Points Worth Earned

Title page (name, title, date, TA, course,

Title page (name, title, date, TA, course,

section, partner’s name)

section, partner’s name)

Purpose Procedure (cited and changes) Data

Purpose Procedure (cited and changes) Data

Delta Vs, molar solubility, Ksp, delta Gs, 2 delta Hs, and delta Ss Concentration of [OH]

Delta Vs, molar solubility, Ksp, delta Gs, 2 delta Hs, and delta Ss Concentration of [OH]

Calculations

Calculations

Graphs Delta Vs, molar solubility, Ksp , delta Gs, 2 delta Hs, and delta Ss Conclusions (all values, max solubility, explanation, errors)

Graphs Delta Vs, molar solubility, Ksp , delta Gs, 2 delta Hs, and delta Ss Conclusions (all values, max solubility, explanation, errors)

Questions Total Grade

Questions Total Grade

.

%

%

159

Experiment 23: Electrochemistry: The Nernst Equation Instructor Notes and Lab Preparation Chemicals and Equipment Bottle of 0.1 M CuNO3 solution Bottle of 0.1 M Mg(NO3)2 solution Bottle of 0.1 M Fe(NO3)3 solution Bottle of 0.1 M Pb(NO3)2 solution Bottle of 0.1 M Al(NO3)3 solution Bottle of 0.1 M KNO3 1 bottle of each of metal strips: copper, lead, aluminum, iron, magnesium 1 container of agar powder (inexpensive type, Fisher Scientific #AC40039-5000 or equivalent) 1 container of cotton 1 sheet of sandpaper, cut into about 12 × 15 cm pieces 1 cooler with ice U-tubes Thick-stemmed disposable pipets Hotplates, 2 per lab bench Multimeters with alligator clips

Preparation The salt solutions should be prepared as nitrates in a 0.1 M nitric acid solution.

Setup Place all chemicals and supplies on the front counter.

Place a metals waste container in the hood.

Place 2 hotplates on each lab bench.

Instruction Notes Experiment 23 is all about electrochemistry. Each student builds his or her own unit cell and measures the potential. There are actually only five metals: Fe3+, Cu+, Mg2+, Al3+, and Pb2+. You should assign each combination to at least two students (if possible) so that the data are reproduced when pooled together. I normally create a table on the front board so that as the students complete the measurements, they can report their findings to the class. They pool only the room temperature data. We recently dropped the concentration to 0.1 M to save on chemical costs. This appears to work just as well as the 1.0 M solutions. We use small pieces (0.3 cm × 1 cm strips) of each metal

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160

cut from either thin sheet or ~14 gauge wire. You have to really watch the students so that they don’t throw them away and that they are returned to the correct container at the end of the lab.

Points to Stress The students should have calculated the theoretical potentials for all of the cells before coming into class. The experiment allows them to confirm their calculations and should also help them decide which metal should act as the cathode and which should act as the anode. In other words, if they have prepped their lab properly, the potentials should be positive and similar to the ones they have calculated.

The inclusion of the Nernst equation and temperature dependence of cell potential allows this experiment to bridge the gap between Chapters 17 and 18, making another use of the thermodynamic properties of enthalpy, entropy, and free energy. The importance and relevance of the relationship of these properties to yet another chemical process should be discussed.

Potential Problems When setting up the U-tubes, make sure the students soak the cotton in the respective solutions before placing them in the tubes. If the cotton is not soaked through, the students will get bad readings.

We use multimeters (set to VDC) for this experiment. Occasionally, we have had problems with students not setting the meters to VDC. This error is the first thing to check when students report anomalous readings.

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161

Experiment 23 Prelaboratory Assignment KEY Name: ___________________________ Date: _________________ Instructor: ____________________________ Sec. #: ___________

Show all work for full credit.

1) Using literature values for the half-cell reactions of the following metals, calculate the total cell potentials for each of the 10 possible cells. Assume complete reduction of the metals.

Copy the resulting potentials into your lab notebook.

Metals: Fe3+, Cu+, Mg2+, Al3+, Pb2+ Numerical corrections are for SF. If the reagent used for copper is copper(II) nitrate, five of these reactions need to be changed to reflect that.

3Cu+ + Fe ↔ Fe3+ + 3Cu Ecell = 0.521 V + 0.04 V = 0.561 V 2Fe3+ + 3Mg ↔ 2Fe + 3Mg2+ Ecell = –0.04 V + 2.37 V = 2.33 V Fe3+ + Al ↔ Fe + Al3+ Ecell = –0.04 V + 1.66 V = 1.62 V 2Fe3+ + 3Pb ↔ 2Fe + 3Pb2+ Ecell = –0.04 V + 0.126 V = 0.086 V 2Cu+ + Mg ↔ 2Cu + Mg2+ Ecell = 0.521 V + 2.37 V = 2.89 V 3Cu+ + Al ↔ 3Cu + Al3+ Ecell = 0.521 V + 1.66 V = 2.18 V 2Cu+ + Pb ↔ 2Cu + Pb2+ Ecell = 0.521 V + 0.126 V = 0.647 V

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162

3Mg + 2Al3+ ↔ 3Mg2+ + 2Al Ecell = –1.66 + 2.37 V = 0.71 V Mg + Pb2+ ↔ Mg2+ + Pb Ecell = –0.126 + 2.37 V = 2.24V 2Al + 3Pb2+ ↔ 2Al3+ + 3Pb Ecell = –0.126 + 1.66 V = 1.53 V 2) The standard potential of a galvanic cell (Eocell) can be determined from thermochemical data such as the free energy of formation (ΔGof) of each of the species in the reaction.

For example, given the reaction: Fe3+(aq) Fe(s) Al3+(aq) Al(s)

Species

Fe3+(aq) + Al(s)  Al3+(aq) + Fe(s)

ΔGof (kJ/mol)

–10.5

0

–481.2

0

First, use the data to the right to calculate the ΔGorxn. –470.7 kJ/mol Then calculate Eocell from ΔGorxn. 1.626 V

3) Following is the shorthand notation for a galvanic cell: Al(s)|Al3+(1M)||Cu+(1M)|Cu(s) Write the overall balanced equation occurring in this cell and indicate the physical states of reactants and products, that is, Al(s), Cu+(aq), and so on.

3Cu+(aq) + Al(s) → Al3+(aq) + 3Cu(s) Identify the anode and cathode of this cell.

cathode: Cu(s), anode: Al(s) You make the following voltage measurements at four different temperatures.

Temperature (°C):

10

35

55

74

Eocell (V):

2.190

2.176

2.165

2.154

ΔGorxn (kJ/mol) –633.9 –629.9 –626.7 –623.5 Calculate the ΔGorxn at each of these temperatures. (in table)

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163

Now, graph this data using the relationship ΔG = ΔH – TΔS, and determine ΔHorxn (in kJ/mol) and ΔSorxn (in J/[K ⋅ mol]) for this process. (This assumes that ΔHorxn and ΔSorxn do not vary with temperature. Remember to use absolute temperature and pay attention to units and signs in your plot and your calculations.)

ΔHorxn = –679.8 kJ/mol, ΔSorxn = –162.2 J/(K ⋅ mol)

Lab Report Key The title page should include: They should know this by now. Only take away points if incorrect!

Student’s full name Date of experiment Complete title of lab report Name of partner(s) Instructor’s name Lab and section number (e.g., CHM1046L-02) The purpose should include: The purpose should include a majority of the topics and techniques covered in the experiment and a description of the criteria for success.

Procedure: The procedure section should cite the lab manual and include any changes made to the procedure during lab work. The assigned metals should be noted.

Data: The data section should include a table with the following: a) experimental values for cell potentials for each of the 10 cells, b) theoretical cell potentials based on literature values for each of the 10 cells, and c) the percent error for the potentials of the 10 cells.

A second table should be constructed to contain the data collected on the student’s assigned cell regarding its temperature dependence and should include the following: a) the temperatures at which each measurement was made, b) the cell potential recorded at each temperature, c) G° at each temperature, d) K at each temperature, and e) H and S for the cell.

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Calculations: The calculation section should include a graph of G versus Kelvin temperature. All graphing guidelines apply. Example calculations of the following should also be included: percent error between the theoretical and experimental potentials for each cell, G, and K. Make sure that the units are correct in all of the calculations and answers.

Conclusions: The conclusion should be several paragraphs with discussions of the following: (1) The values for G, K, H, and S; (2) a description and discussion of the potential series developed from the class data and the discrepancies between the experimental cell potentials and the literaturebased cell potentials; (3) a discussion of the relationship between temperature and cell potential (values from the student’s data and calculations should be included to support the conclusions and discussions); and (4) all possible errors.

Question: 1) What is a watt? How is it related to the potential of a battery?

A watt is a unit of energy defined as a joule per second. Battery power is defined as the amount of energy that can be delivered by a unit of time. The greater the potential of the battery, the more energy can be delivered in a unit of time; thus, the watt is a unit of energy that can be used to describe the potential (power) of a battery.

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Experiment 23: Electrochemistry: The Nernst Equation Section Points Points Worth Earned

Experiment 23: Electrochemistry: The Nernst Equation Section Points Points Worth Earned

Title page (name, title, date, TA,

Title page (name, title, date, TA,

course, section, partner’s name)

course, section, partner’s name)

Purpose Procedure (cited and changes) Data

Purpose Procedure (cited and changes) Data Experimental values, literature values, and %error of each cell Cell potential at each temperature Delta G and K for each temperature Delta H and S for the cell

Experimental values, literature values, and %error of each cell Cell potential at each temperature Delta G and K for each temperature Delta H and S for the cell

Calculations

Calculations Graph %error, delta G and K

Graph %error, delta G and K

Conclusions (discussion of all values,

Conclusions (discussion of all values,

comparison of cell potentials in prelab and experiment, discussion of differences between the two, discussion of the relationship between temperature and cell potential, errors)

comparison of cell potentials in prelab and experiment, discussion of differences between the two, discussion of the relationship between temperature and cell potential, errors)

Questions Total Grade

Questions Total Grade

%

%

Experiment 23: Electrochemistry: The Nernst Equation Section Points Points Worth Earned

Experiment 23: Electrochemistry: The Nernst Equation Section Points Points Worth Earned

Title page (name, title, date, TA,

Title page (name, title, date, TA,

course, section, partner’s name)

course, section, partner’s name)

Purpose Procedure (cited and changes) Data

Purpose Procedure (cited and changes) Data

Experimental values, literature values, and %error of each cell Cell potential at each temperature Delta G and K for each temperature Delta H and S for the cell

Experimental values, literature values, and %error of each cell Cell potential at each temperature Delta G and K for each temperature Delta H and S for the cell

Calculations

Calculations

Graph %error, delta G and K

Graph %error, delta G and K

Conclusions (discussion of all values,

Conclusions (discussion of all values,

comparison of cell potentials in prelab and experiment, discussion of differences between the two, discussion of the relationship between temperature and cell potential, errors)

comparison of cell potentials in prelab and experiment, discussion of differences between the two, discussion of the relationship between temperature and cell potential, errors)

Questions Total Grade

Questions Total Grade

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%

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166

Experiment 24: Qualitative Analysis: Anions Instructor Notes and Lab Preparation Chemicals and Equipment Dropping bottles of each chemical below 1 M Na2SO3 1 M NaNO2 0.1 M NaNO2 3 M H2SO4 Conc. H2SO4 0.1 M Na2Cr2O7 0.2 M BaCl2 0.3 M AgNO3 1 M Na2SO4 0.2 M Fe(NO3)3 0.1 M K2Cr2O7 0.2 M NaNO3 1 M Ba(NO3)2 1 M NaI 1 M NaBr Sat. FeSO4 Sat. Na2CO3 0.1 M K2Cr2O4 0.2 M Na3PO4 (NH4)2MoO4 1 M Na3PO3 1 M NH4Cl 6 M HNO3 0.5 M NaC2H3O2 0.1 M KMnO4 Starch packing material Ethanol pH paper Hexane Ice Dilute H2O2 (on ice) Plastic pipettes Aqueous metals waste container

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Preparation To make MOO, you will need to make two solutions, A and B. Solution A: Dissolve 20.0 g of MoO3 in 60 mL of water and 50 mL of concentrated ammonium hydroxide.

Solution B: Combine 230 mL of water with 100 mL of concentrated nitric acid.

Slowly add solution A to solution B and mix thoroughly.

Unknowns: 1. Combine saturated Na2CO3, 0.2 M Na3PO4, and 1 M NH4Cl. 2. Combine 1 M Na2SO4, 0.1 M Na2Cr2O7, and 1 M NaI. 3. Combine 1 M NaBr, 1 M Na2SO3, and 0.5 M NaC2H3O2.

Instruction Notes The anions lab is a good warm up for the cations lab that follows. There is virtually no technique required, so the students can concentrate on the chemistry. We generally put all the chemicals needed in dropping bottles so that we don’t run through thousands of pipettes. This can also be used as a teaching point regarding qualitative analysis versus quantitative analysis.

Points to Stress A confirmation should be verified based on the descriptions in the background and procedure sections. It may be necessary to do negative tests to make sure that the result is not a false positive. You should also explain that a cloudy solution normally means that a precipitate has formed but lacks the density to fall out of solution. A centrifuge can be used to confirm the presence of a precipitate. Students should also be told to put only enough sample anion in a clean test tube to fill the lower bowl portion; any more and the lab will take much longer to finish.

Potential Problems Students don’t recognize aqueous ammonia. We generally explain the process during the introduction to the lab.

NH3 + H2O → NH4OH or NH4+ + OH–

When in aqueous solution (in water), ammonia (NH3) is actually ammonium (NH4+). NH3 is also referred to as aqueous ammonia.

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Experiment 24 Prelaboratory Assignment KEY Name: ___________________________ Date: _________________ Instructor: ____________________________ Sec. #: ___________

Show all work for full credit.

1) Tell how you could distinguish chemically between the following pairs of substances in one or two steps. In each case, tell what you would observe. Include equations for reactions occurring. (a) HCl and H2SO4 Adding Ba(NO3)2 will yield soluble BaCl2 with HCl and

insoluble BaSO4 with H2SO4.

2HCl + Ba(NO3)2 → 2HNO3 + BaCl2 H2SO4 + Ba(NO3)2 → 2HNO3 + BaSO4 With the addition of HCl, the solution of Na2CO3 will bubble since CO2 gas forms. There will be no notable reaction from the NaBr solution.

(b) NaBr and Na2CO3

Na2CO3 + HCl → NaCl + H2CO3 → H2O + CO2 (c) NaSO4 and Na2CO3 With the addition of HNO3, the SO4 solution will not

show reaction, but the carbonate solution will bubble.

Na2CO3 + HCl → KCl + H2CO3 → H2O + CO2 (d) KNO3 and K3PO4 Adding nitric acid and ammonium molybdate will form a

yellow precipitate with PO4, but there will be no reaction with KNO3.

H3PO4 + 21H+ + 3NH4+ + 12MoO42– → (NH4)3PMo12O40 + 12H2O

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2) You are given three unlabeled containers and are told that they contain nitric acid, sulfuric acid, and phosphoric acid. How could you determine which acid is in which container?

Add barium nitrate to a sample from each container. The only container that does not form a precipitate is nitric acid. To the remaining two containers, add copper(II) nitrate. The phosphoric acid will form a blue/green precipitate, and the sulfuric acid will not form a precipitate.

Lab Report Key The purpose should include a majority of the topics and techniques covered in the experiment and a description of the criteria you will use to determine its success or failure.

The procedure section should cite the lab manual and include any changes made to the procedure during lab work. The procedure section should also include a step-by-step explanation of how the students determined the identity of their unknown.

The data section should include a table for Parts 1 and 2. There should be a record of the initial observations, with notes on the color of each solution. The remaining sections should describe the results upon mixing. Be sure to look for specifics such as colors and formulas of precipitates.

All observations written in this table must match those made during lab and recorded in the student’s lab notebook.

Part 2 should include observations made during each step the students took in lab while testing their unknown, along with the code and identity of the anion(s) in the unknown.

For the calculation section for this experiment, there should be a balanced net ionic equation for each reaction from Part 1.

The conclusion section should include several detailed paragraphs that include both the identities of the ions in the unknown and how students reached these conclusions. This should include a discussion of the known reactions students did in Part 1 and how they compare to the unknown reactions. Students should be sure to include a description of both supporting and eliminating experiments that they conducted. Finally, they should include all possible errors found in this experiment.

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Questions: 1) If you were given an unknown solution that you were told contained either Cl– or I–, both anions, or neither, explain how you would confirm or deny the presence or absence of the ions.

The addition of lead nitrate to the solution would provide a test that would verify one or both of the anions. A white precipitate would confirm chloride, a bright yellow precipitate would confirm iodide, a light “creamy” yellow precipitate would confirm both, and no precipitate would confirm that neither were present.

2) Why are the reagents used to test for anions usually a nitrate of the cation that is reacting rather than other salts of that cation?

All nitrates are soluble.

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Experiment 24: Qualitative Analysis: Anions Section Points Points Worth Earned

Experiment 24: Qualitative Analysis: Anions Section Points Points Worth Earned

Title page (name, title, date, TA,

Title page (name, title, date, TA,

course, section, partner’s name)

course, section, partner’s name)

Purpose Procedure (cited and changes) Data

Purpose Procedure (cited and changes) Data

Table Parts 1 and 2: observations

Table Parts 1 and 2: observations

Calculations

Calculations

Net ionic equations

Net ionic equations

Conclusions (discussion of identities of

Conclusions (discussion of identities of

the ions in the unknown and how students reached these conclusions; comparison of known and unknown reactions; discussion of possible errors)

the ions in the unknown and how students reached these conclusions; comparison of known and unknown reactions; discussion of possible errors)

Questions Total Grade

Questions Total Grade

%

%

Experiment 24: Qualitative Analysis: Anions Section Points Points Worth Earned

Experiment 24: Qualitative Analysis: Anions Section Points Points Worth Earned

Title page (name, title, date, TA, course,

Title page (name, title, date, TA, course,

section, partner’s name)

section, partner’s name)

Purpose Procedure (cited and changes) Data

Purpose Procedure (cited and changes) Data

Table Parts 1 and 2: observations

Table Parts 1 and 2: observations

Calculations

Calculations

Net ionic equations

Net ionic equations

Conclusions (discussion of identities of

Conclusions (discussion of identities of the

the ions in the unknown and how students reached these conclusions; comparison of known and unknown reactions; discussion of possible errors)

ions in the unknown and how students reached these conclusions; comparison of known and unknown reactions; discussion of possible errors)

Questions Total Grade

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%

Questions Total Grade

%

172

Experiment 25: Qualitative Analysis: Cations Instructor Notes and Lab Preparation Chemicals and Equipment Bunsen burners 1 M HCl 6 M HCl Concentrated HCl 0.1 M K2CrO4 1.0 M KOH Concentrated aq. ammonia Aluminon reagent (Fisher scientific AC10306-0250 or equivalent) 6 M NH3 6 M HNO3 pH (wide range, litmus) paper 5% thioacetamide 8 M NaOH 0.2 M SnCl4 6 M acetic acid 0.2 M K4Fe(CN)6 1.0 M NaNO2 Solid NaBiO3 Solid NH4SCN 3.0 M ammonium carbonate Aqueous metals waste container Test tubes (13 × 100 mm, approximately 10 per student) Three unknowns: 0.1 M solutions containing three cations each, from no more than two groups. Mark the unknowns A, B, and C.

Preparation Place each chemical solution in a dropping bottle(s). NOTE: If students will be sharing chemicals, we have found it helpful to mark the paper covering the counter with the names of each chemical so that students return the bottles to where they found them.

Set up a hot water bath in the hood.

Set out small weighing boats.

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Instruction Notes This cation experiment is the abbreviation of what was previously four weeks of experiments where students were required to perform all of the tests on known solutions containing all of the Groups I through IV cations and then were given two weeks to determine the contents of an unknown mixture. Spending so much time on processes that are historical in nature and are now run much more quickly on spectrometers and other equipment prevented us from covering other topics such as electrochemistry. By consolidating the experiment into one day, the students still benefit from the experience of using qualitative analysis to determine the contents of an unknown without spending weeks of valuable time doing so.

Potential Problems The experiment itself is fairly straightforward, but students often get confused when a group of cations is not present. Each unknown contains only two of the possible five groups. It is important that once students have ascertained that a group is not present, they continue on and not spend valuable time trying to confirm cations that are not present.

Time management can be aided by setting goals for the students, such as everyone should have the first two groups’ separations completed by the end of the first hour, and so on.

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Experiment 25 Prelaboratory Assignment KEY Name: ___________________________ Date: _________________ Instructor: ____________________________ Sec. #: ___________

Use the following flowchart to answer the questions below:

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1) Which box in the above scheme contains all of the ions, and only those ions, in each of the following groups?

Group I = N Group II = F Group III = M Group IV = J Group V = R

2) Consult your lab manual, or another source, for the confirmatory reactions within each group that lead to specific identification of each cation. Then identify the box in the above scheme that contains the confirmatory product for each of the following ions.

Ag+ = H Pb2+ = L Cd2+ = G Ba2+ = E

Lab Report Key The title page should include: They should know this by now. Only take away points if incorrect!

Student’s full name Date of experiment Complete title of lab report Name of partner(s) Instructor’s name Lab and section number (e.g., CHM1046L-02) The purpose should include: There are several topics covered in this lab: qualitative analysis, ions, cation groups I through V, physical properties, chemical properties, reactivity, solubility, and acid–base equilibria. For full credit, a statement of the purpose of this lab should encompass at least three of these topics and the criteria for experimental success and should not be a copy of the purpose in the manual.

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Procedure: This should be a reference to the lab manual, with any changes noted. Details regarding which procedures were skipped should be noted here.

Data: A flow chart with the steps the student followed to identify the unknowns should be included.

They should include all observations made, including no reaction.

Calculations: They should include the net ionic reaction for each precipitation reaction.

Conclusions: Test results should be used to support the cations reported in the unknown. Any problems or possible errors in the experiment should be discussed.

Questions: 1) The confirmation test used in this experiment for copper produces a reddish-brown precipitate. There is another test that produces a blue precipitate. What is the difference in the tests?

When copper ions are in solution, they form hexaaquacopper(II) ion—[Cu(H2O)6]2+.

Since our test is in acidic conditions, we use thiocyanide to precipitate the copper metal, which results in a reddish-brown, “copper”-colored precipitate. If the reaction were run in basic solution, the addition of hydroxide ions would form a copper(II) hydroxide complex ion—Cu(H2O)4(OH)2—which is insoluble and blue in color.

2) Based on your knowledge of acid–base equilibria and solubility, describe why the solubility of different cation groups can be affected by the acidification of their solutions.

Acid affects solubility by means of the common ion effect. For example, if the compound being separated is CaCO3, the acid will react with the carbonate ion, forming carbonic acid and finally carbon dioxide and water. As the carbonate is removed from the solution, this allows more CaCO3 to dissolve. The degree to which the solubility is affected is dependent on the strength of the acid that is formed. The stronger the acid that is formed, the weaker the effect on solubility.

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177

Experiment 25: Qualitative Analysis: Cations Section Points Points Worth Earned

Experiment 25: Qualitative Analysis: Cations Section Points Points Worth Earned

Title page (name, title, date, TA,

Title page (name, title, date, TA,

course, section, partner’s name)

course, section, partner’s name)

Purpose Procedure (cited and changes) Data

Purpose Procedure (cited and changes) Data

Table containing all observations

Table containing all observations

Calculations

Calculations

Net ionic equations; flowchart

Net ionic equations; flowchart

Conclusions (discussion of identities of

Conclusions (discussion of identities of

the ions in the unknown and how they reached these conclusions; comparison of known and unknown reactions; discussion of possible errors)

the ions in the unknown and how they reached these conclusions; comparison of known and unknown reactions; discussion of possible errors)

Questions Total Grade

Questions Total Grade

%

%

Experiment 25: Qualitative Analysis: Cations Section Points Points Worth Earned

Experiment 25: Qualitative Analysis: Cations Section Points Points Worth Earned

Title page (name, title, date, TA,

Title page (name, title, date, TA,

course, section, partner’s name)

course, section, partner’s name)

Purpose Procedure (cited and changes) Data

Purpose Procedure (cited and changes) Data

Table containing all observations

Table containing all observations

Calculations

Calculations

Net ionic equations; flowchart

Net ionic equations; flowchart

Conclusions (discussion of identities of

Conclusions (discussion of identities of

the ions in the unknown and how they reached these conclusions; comparison of known and unknown reactions; discussion of possible errors)

the ions in the unknown and how they reached these conclusions; comparison of known and unknown reactions; discussion of possible errors)

Questions Total Grade

Questions Total Grade

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%

%

178

Experiment 26: Qualitative Analysis: Cations, Anions, and Complex Ions Instructor Notes and Lab Preparation Chemicals and Supplies Well plates Wax pencils Bunsen burners Hoses Wire pieces 2 flame tests in the hood Metals waste jar Kimwipes Multiple sets of the reagents: 6 M NaOH 6 M NH3 6 M HCL 6 M nitric acid Concentrated sulfuric acid 0.1 M nitrates: Na, Mg, Ni, Cr, Zn, Ag, Pb 0.1 M NaNO3, NaCI, NaCl, NaSO4 0.5 M NaI (acidified) 0.5 M FeSO4*7H2O Unknown containing two metals Setup Set up two flame tests in the hood.

Place waste jar in the hood.

Place one set of reagents on each lab bench.

Place all other supplies and chemicals on front lab bench.

Preparation Prepare three or four unknowns, each containing two different metals. Label as unknowns 1 through 7.

Place each chemical solution in a dropping bottle(s). NOTE: If students will be sharing chemicals, we have found it helpful to mark the paper covering the counter with the names of each chemical so that students return the bottles to where they found them.

Set up a hot water bath in the hood.

Set out small weighing boats.

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Instruction Notes This is a shortened one-day, all-inclusive qualscheme lab. We have cut way down on both waste and chemical costs by microscaling the tests used to confirm the unknown content.

Points to Stress Good note taking and careful observations are very important in this lab. Make sure that students know to not only write about the color of the precipitates but also their texture and so on. Make sure that the students understand that having a plan of attack when starting on the unknown is essential to complete the lab in a timely fashion and to be confident about their results. This is supposed to be a qualscheme activity, so they should proceed through a standard set of reactions to separate the various ions and to avoid false positives.

Potential Problems We have white well plates, which can sometimes make seeing the detail of white precipitates difficult. We tell students that they can also run the tests in a test tube if they have trouble making good observations. Students also often forget about the anions in the mixture and since they should be finding both, they must be reminded of this aspect of the lab.

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Experiment 26 Prelaboratory Assignment KEY Name: ___________________________ Date: _________________ Instructor: ____________________________ Sec. #: ___________

Show all work for full credit.

1) The qualitative analysis scheme depends on the relative solubilities of the salts of the cations with various anions. Ksp, the solubility product constant, describes the equilibrium reaction between the solid salt and the ions in solution: MxAy(s)  xMy+(aq) + yAx–(aq), Ksp = [My+]x[Ax–]y (MxAy does not appear in the expression because the pure solid is considered to be in its standard state with an activity of 1.)

The actual solubility may differ slightly from the calculated value, though, if the undissociated salt itself is slightly soluble, and if there are intermediate ion-pair structures formed in solution.

Nevertheless, the calculated value is still very useful in comparing solubility relationships of various ions and predicting whether a precipitate will form when two ionic solutions are mixed.

For the salt BaSO4, Ksp = 1.1 × 10–10.

What is [Ba2+] for a saturated solution of BaSO4? 1.0e-5 M What is the calculated solubility for BaSO4? 2.4e-4 g/dL Addition of a soluble sulfate, such as Na2SO4, will suppress the solubility of the Ba2+ ion because of the common ion effect.

What will [Ba2+] be in the presence of 0.15 M Na2SO4? 7.3e-10 M 2) For the salt SrF2, Ksp = 4.3 × 10–9.

What is [Sr2+] for a saturated solution of SrF2? 1.0e-3 M What is the calculated solubility for SrF2? 1.3e-2 g/dL What will [Sr2+] be in the presence of 0.10 M NaF? 4.3e-7 M

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3) To estimate whether a salt will precipitate under a particular set of conditions, a reaction quotient, Qsp, can be calculated from given concentrations of the cation and anion using the equation: Qsp = [My+]x[Ax–]y If Qsp is less than or equal to Ksp, no precipitate will form, but if Qsp is greater than Ksp, a precipitate will form, and the ion concentrations will decrease until they reach values that satisfy the Ksp expression.

In the case of metal hydroxides, the anion is the hydroxide ion, and its concentration depends on the pH of the solution. Whether a precipitate occurs will therefore depend both on the Ksp of the hydroxide and on the pH. For the reaction: Mg(OH)2  Mg2+ + 2OH−, Ksp = 5.6 × 10–12.

You prepare a solution of 0.20 M Mg2+ and adjust the pH to 6.0.

What is the value of the reaction quotient, Qsp, under these conditions? 2.0e-7 Will a precipitate form? No What will be the equilibrium concentration of the Mg2+ ion? 2.0e-1 M 4) Insoluble salts can sometimes be dissolved in the solution by the formation of a soluble complex ion. For example, AgCl(s) can be dissolved in ammonia solutions by the formation of the soluble Ag(NH3)2+ complex ion. The ammonia competes with the Cl− ion for reaction with Ag+ as follows:

AgCl(s)  Ag+(aq) + Cl−(aq)

K sp = [Ag + ][Cl − ] = 1.8×10−10

Ag+(aq) + 2NH3(aq)  Ag(NH3)2+(aq)

K formation =

[ Ag( NH 3 )2+ ] = 1.6×107 + 2 [ Ag ][ NH 3 ]

Sum: AgCl(s) + 2NH3(aq)  Ag(NH3)2+(aq) + Cl−(aq) K net = K formation  K sp =

[ Ag( NH 3 )2+ ][Cl − ] = 2.9×10−3 2 [ NH 3 ]

Assuming all the Cl− comes from the dissociation of AgCl, then [Ag(NH3)2+] = [Cl−], and

[ Ag( NH 3 )2+ ]2 = [ NH 3 ]2  2.9×10−3 or

[ Ag( NH 3 )2+ ] = [ NH 3 ]2  2.9×10−3

What is the maximum [Ag(NH3)2+] that can be obtained by dissolving AgCl in 1.5 M ammonia?

8.0e-2 M

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5) For another silver salt, AgBrO3, Ksp = 5.4 × 10–5.

What is Knet for the reaction AgBrO3 + 2NH3  Ag(NH3)2+ + BrO3−? 8.6e-2 What is the maximum [Ag(NH3)2+] that can be obtained by dissolving AgBrO3 in 4.1 M ammonia? 1.2e-2M

Lab Report Key The title page should include: They should know this by now. Only take away points if incorrect!

Student’s full name Date of experiment Complete title of lab report Name of partner(s) Instructor’s name Lab and section number (e.g., CHM1046L-02) The purpose should include: There are several topics covered in this lab: qualitative analysis, ions, groups, physical properties, chemical properties, reactivity, solubility, and acid–base equilibria. For full credit, a statement of the purpose of this lab should encompass at least three of these topics and should not be a copy of the purpose in the manual. The criteria for a successful experiment should be described.

Procedure: This should be a reference to the lab manual, with any changes noted. Details regarding which procedures were used in the determination of the unknown should be given.

Data: The data section should include a table for Parts I and III listing the seven cations down the side and with five columns labeled: Initial Observation, OH–, xs OH–, NH3, and Anion PPT. All observations written in this table must match those made during lab and recorded in the students’ lab notebooks.

For Part II, a table with the observations recorded in lab after each step is required. For Parts IV and V, observations should be presented in a systematic fashion.

For Part VI (the identity of the unknown), observations made during each step should be listed, along with the code and identity of the cation(s) and anion(s) in the unknown.

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Calculations: The calculation section for this experiment will include balanced net ionic equations. For each reaction shown in the data table that results in either a precipitant or complex ion, an equation should be included.

Conclusions: The conclusion section should include several detailed paragraphs, a paragraph explaining how a stability series works and how the observations made specifically illustrate the stability series for silver ions (this is from Part II). The identity of the ions in the unknown and how the conclusions were reached should be discussed. This section should also include a discussion of the known reactions done in Parts I through V and how they compare to the unknown reactions. Also required is a description of both supporting and eliminating experiments conducted. Finally, all possible errors found in this experiment should be discussed.

Questions: 1) Which cation forms a two ligand complex with NH3? silver 2) Which anion does not form a precipitate with lead? Nitrate 3) Write the balanced equation for the dissociation of the compound in Question 2 in water.

Pb(NO3)2(aq) Pb2+(aq) + 2NO3–(aq)

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184

Experiment 26: Qualitative Analysis: Cations, Anions, and Complex Ions Section Points Points Worth Earned

Experiment 26: Qualitative Analysis: Cations, Anions, and Complex Ions Section Points Points Worth Earned

Title page (name, title, date, TA, course,

Title page (name, title, date, TA, course,

section, partner’s name) Purpose (at least three points)

section, partner’s name) Purpose (at least three points)

Procedure (cited/changes, step-by-step of

Procedure (cited/changes, step-by-step of

how unknown was determined) Data (observation of Parts II, IV, and V after each step in a systematic fashion) Table I (observations for Parts I and III)

how unknown was determined) Data (observation of Parts II, IV, and V after each step in a systematic fashion) Table I (observations for Parts I and III)

Unknown (code of unknown and

Unknown (code of unknown and

observation for each step) Calculations (balanced net ionic equations for each reaction; there should be nine equations with states)

observation for each step) Calculations (balanced net ionic equations for each reaction; there should be nine equations with states)

Conclusions (a paragraph explaining how a

Conclusions (a paragraph explaining how a

stability series works, including how the observations you made specifically illustrate the stability series for silver ions [this is from Part II]; the identity of the ions in unknown and conclusions reached with both supporting and eliminating experiments; discussion of the known reactions for Parts I through V and how they compare to the unknown reactions; possible errors)

stability series works, including how the observations you made specifically illustrate the stability series for silver ions [this is from Part II]; the identity of the ions in unknown and conclusions reached with both supporting and eliminating experiments; discussion of the known reactions for Parts I through V and how they compare to the unknown reactions; possible errors)

Questions Total Grade

Questions Total Grade

100 /

%

100 /

%

Experiment 26: Qualitative Analysis: Cations, Anions, and Complex Ions Section Points Points Worth Earned

Experiment 26: Qualitative Analysis: Cations, Anions, and Complex Ions Section Points Points Worth Earned

Title page (name, title, date, TA, course,

Title page (name, title, date, TA, course,

section, partner’s name) Purpose (at least three points)

section, partner’s name) Purpose (at least three points)

Procedure (cited/changes, step-by-step of

Procedure (cited/changes, step-by-step of

how unknown was determined) Data (observation of Parts II, IV, and V after each step in a systematic fashion) Table I (observations for Parts I and III)

how unknown was determined) Data (observation of Parts II, IV, and V after each step in a systematic fashion) Table I (observations for Parts I and III)

Unknown (code of unknown and

Unknown (code of unknown and

observation for each step) Calculations (balanced net ionic equations for each reaction; there should be nine equations with states)

observation for each step) Calculations (balanced net ionic equations for each reaction; there should be nine equations with states)

Conclusions (a paragraph explaining how a

Conclusions (a paragraph explaining how a

stability series works, including how the observations you made specifically illustrate the stability series for silver ions [this is from Part II]; the identity of the ions in unknown and conclusions reached with both supporting and eliminating experiments; discussion of the known reactions for Parts I through V and how they compare to the unknown reactions; possible errors)

stability series works, including how the observations you made specifically illustrate the stability series for silver ions [this is from Part II]; the identity of the ions in unknown and conclusions reached with both supporting and eliminating experiments; discussion of the known reactions for Parts I through V and how they compare to the unknown reactions; possible errors)

Questions Total Grade

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100 /

%

Questions Total Grade

100 /

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Experiment 27: Whodunit? A Forensic Investigation Instructor Notes and Lab Preparation Chemicals and Equipment Gloves in appropriate sizes for all students Tweezers Scissors Precut 5 cm × 12 cm silica gel UV active TLC plates (2 TLC plates per group) 1 L of 1:1:1 solution of pentanol, ethanol, and 2 M NH4OH Dropper bottles of methanol Well plates (glass or plastic, 4+ wells) 1 bottle of open-ended capillary tubes Parafilm 250 mL beakers or tall thin beakers (180 mL) if available Bunsen burners Iodine crystals 1,000 mL beaker Hotplate Watch glass Waste jar in the hood for the chromatography solvent Paperclips Sample pens String Evidence packages with evidence # on them (see instruction note below) Letter in a bag with evidence # on it Cloth sample in a bag with evidence # on it

Preparation Cut TLC plates in half and then in thirds (approximately 5 cm × 12 cm so that they fit snuggly in the beaker without bending). Each group gets only two TLC plates.

Prepare letters by using gloves to write the letter and then fingerprint the letter (see note below).

Some letters should have fingerprints that match those given as references, and some should not.

Place in a bag and label with evidence #.

Place a small cloth sample in a bag and label with evidence #.

Setup Place hotplate in hood. Place watch glass with iodine crystals on hotplate. Cover with 1,000 mL beaker.

Place a waste container in the hood.

Place one evidence bag on each lab bench.

Place remaining chemicals and supplies on the front counter.

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Instruction Notes Each bench in the lab will work as a forensics team that will be presented with evidence in sealed zippered bags. They are required to wear gloves and because the threatening note is used to determine both the type of ink used and to fingerprint, conservation of materials is a key teaching point.

Each group should also be given a set of reference fingerprints to compare. The FBI provides a downloadable fingerprint card that can be used (http://www.fbi.gov/hq/cjisd/pdf/fpcardb.pdf).

Whoever makes up the evidence should also be one of the suspects who is fingerprinted so that some of the threatening notes will confirm that the suspect wrote the note. We generally just write something like, “You are going to pay!” or “Watch your back, I am coming for you!” on the notes. The notes must be written in one of the inks that will be tested using the TLC method.

Potential Problems The only problem we have had thus far is not seeing the development of fingerprints on the notes. This can occur if the person preparing the notes does not have enough oil on his or her hands. When you are placing fingerprints on the notes to be developed later, be sure to wipe your face with your fingers several times first. Your hands do not actually contain oils that will transfer. The skin on your face is predominantly where these oils reside.

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Experiment 27 Prelaboratory Assignment KEY Name: ___________________________ Date: _________________ Instructor: ____________________________ Sec. #: ___________

Show all work for full credit.

1) Classify the following prints as to “arch,” “tented arch,” “loop,” or “whorl.”

ARCH

TENTED ARCH

WHORL

TENTED ARCH

Fingerprint images are from NIST and Bergen County Technical Schools web pages.

2) The figure to the right shows a TLC plate in which an ink sample to be identified has been separated into three different pigment components.

Determine the Rf value for each of the three pigments.

(Measure the distance from the origin to the center of the spot).

Top Rf = 0.65 Middle Rf = 0.38 Bottom Rf = 0.23

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3) Below are TLC plates for ink from six different reference sources.

Identify the ink source that corresponds to the unknown sample in problem 2. Show

calculations to support your answer. C

Lab Report Key The title page should include: They should know this by now. Only take away points if incorrect!

Student’s full name Date of experiment Complete title of lab report Name of partner(s) Instructor’s name Lab and section number (e.g., CHM1046L-02) The purpose should include: There are several topics covered in this lab: TLC, fiber analysis, forensic methods, fingerprint analysis, and so on. A statement of the purpose of this lab should encompass at least three of these topics for full credit and should not be a copy of the purpose in the manual. A statement of the criteria required for success should be included.

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Procedure: This should be a reference to the lab manual, with any changes noted. The procedure section must include details about where the investigation took students with respect to the evidence.

Data: The data section should include a completed copy of the: Crime scene unit property report Property receipt Request for comparison Latent print report It should also include any and all observations recorded during the lab.

Calculations: There are no calculations needed for this report.

Conclusions: The conclusion section should be several well-developed paragraphs containing a complete description of the results of each forensic test and the analysis of those results. A discussion of possible errors in the testing is required.

Questions: 1) What are the criteria for determining the guilt or innocence of a suspect? Does the evidence you have collected meet that criteria?

Suspects must be determined guilty beyond a reasonable doubt. None of the data that can be collected in this lab would be conclusive as to the identity of the killer, so the answer is no.

2) As a scientist analyzing data, should you have an agenda?

This is a subjective question, but we would hope that the answer is no. A scientist should care only about the accuracy of his or her results and not bend the data to prove a suspect guilty or innocent.

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3) Iodine fuming is used in this lab to develop latent fingerprints. What are latent fingerprints? What are some other methods by which latent prints can be developed?

What are some of the advantages to using iodine crystals for the development? What are some of the disadvantages?

Latent means that the prints are invisible to the naked eye.

Latent prints are also developed using fingerprint powders, ninhydrin, and super glue.

Iodine crystals are inexpensive and require very little in the way of equipment.

Iodine prints fade over time if they are not set using starch or some other fixative. The fumes are also caustic, so proper ventilation is required.

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Experiment 27: Whodunit? A Forensic Investigation Section Points Points Worth Earned

Experiment 27: Whodunit? A Forensic Investigation Section Points Points Worth Earned

Title page (name, title, date, TA,

Title page (name, title, date, TA,

course, section, partner’s name)

course, section, partner’s name)

Purpose Procedure (cited/changes, details

Purpose Procedure (cited/changes, details about

about location of investigation) Data (completed copies of crime scene unit property report, property receipt, request for comparison, and latent print report)

location of investigation) Data (completed copies of crime scene unit property report, property receipt, request for comparison, and latent print report)

Observations

Observations

Conclusions (several well-developed

Conclusions (several well-developed

paragraphs containing a complete description of the results of each forensic test and your analysis of those results; discussion of possible errors in the testing is required)

paragraphs containing a complete description of the results of each forensic test and your analysis of those results; discussion of possible errors in the testing is required)

Questions Total Grade

Questions Total Grade

%

%

Experiment 27: Whodunit? A Forensic Investigation Section Points Points Worth Earned

Experiment 27: Whodunit? A Forensic Investigation Section Points Points Worth Earned

Title page (name, title, date, TA,

Title page (name, title, date, TA,

course, section, partner’s name)

course, section, partner’s name)

Purpose Procedure (cited/changes, details about

Purpose Procedure (cited/changes, details

location of investigation) Data (completed copies of crime scene unit property report, property receipt, request for comparison, and latent print report)

about location of investigation) Data (completed copies of crime scene unit property report, property receipt, request for comparison, and latent print report)

Observations

Observations

Conclusions (several well-developed

Conclusions (several well-developed

paragraphs containing a complete description of the results of each forensic test and your analysis of those results; discussion of possible errors in the testing is required)

paragraphs containing a complete description of the results of each forensic test and your analysis of those results; discussion of possible errors in the testing is required)

Questions Total Grade

Questions Total Grade

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192

Experiment 28: Chemical Structure and Smell Instructor Notes and Lab Preparation Chemicals and Equipment For each of the following smells: Organic model kits Disposable food storage boxes (Gladware type, plastic with lid) Cotton balls Sour wine—vinegar Butter, cheese—butter or cheese Pear—potpourri oil Rose—potpourri oil Pineapple—food flavoring oil (can be found on the baking aisle of most groceries) Cinnamon—potpourri oil Spearmint—potpourri oil or food flavoring oil (can be found on the baking aisle of most groceries) Rotten fish, ammonia-like—Thai fish sauce Sour, putrid (coal tar)—pyridine (in hood) Rotting flesh—putrescine (in hood) Skunk—t-butyl mercaptan (in hood) Garlic—use minced garlic

Preparation Prepare a molecular model (using your school’s recommended organic model kit if possible) of each of the smell molecules.

Poke several holes in the top of each plastic box and place several cotton balls in each box. Coat the cotton balls with whichever smell you like and mark the box with an unknown code A through F. Keep an accurate record of which unknown is each smell.

Place six molecular models marked as unknowns I through VI on the front bench.

Place one unknown smell on each lab bench. Place the really stinky smells in the hood.

Switch out both sets of unknowns between classes.

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Instruction Notes This is a simple lab that forces the student to address the structure of several organic molecules.

The students should be instructed to start the lab by walking from bench to bench, smelling and identifying the unknowns. Make sure you stress the correct way to smell a chemical substance.

Although we use predominantly food and potpourri oils to mimic the chemical smells, inhaling too much of these can still result in a headache. After the students believe they have identified each of the unknown smells, they then need to identify the corresponding structure. If they cannot find a correct structure, they should reassess their original conclusion regarding the smell.

Potential Problems None.

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Experiment 28 Prelaboratory Assignment KEY Name: ___________________________ Date: _________________ Instructor: ____________________________ Sec. #: ___________

Show all work for full credit.

1) For each molecule listed in the table in the background section: (a) draw a correct Lewis structure and (b) circle and identify all of the functional groups in the molecule. Copy your answers into your lab notebook for use during lab.

Acetic Acid

H

H

O

C

C

O

H

H

carboxylic acid group

Diacetyl (2,3-butanedione) O H3C

C O

.

C

CH3

ketone

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Isoamyl Acetate (3-methylbutyl acetate) CH3 HC

O H2 C

H2 C

O

C

CH3

H3C

ester

2-Phenylethanol

alcohol, phenyl

Isoamyl Propionate (1-butanol, 3-methyl,propanoate) CH3 HC

O H2 C

H2 C

O

C

H3C

H2 C

CH3

ester

Cinnamaldehyde ((E)-3-phenyl-2-propenal) O C

C C

H

H H

phenyl, aldehyde

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l-Carvone (2-methyl-5-(prop-1-en-2-yl) cyclohex-2-enone) CH3 O

C CH3

H2C

ketone

Trimethylamine (N,N-dimethyl-methanamine) N

H3C

CH3

H3C

amine

Pyridine (Azabenzene) N

phenyl, amine

Putrescine (1,4-diaminobutane) H2 C H2N

.

H2 C C H2

NH2 C H2

amine

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t-Butyl Mercaptan (1,1-Dimethylethanethiol) H3C

SH C

H3C

CH3

thiol

Allicin (2-propene-1-sulfinothioic acid S-2-propenyl ester) O H2 C

H2C C H

H C

S S

C H2

CH2

alkene, diallyl disulfide

2) Odor receptors detect molecules according to their size, shape, and the presence of certain functional groups. For the unknowns in your laboratory, see if you can first identify the presence of the following functional groups in their structures. (yes answers in bold) Which of the following have an alkene functional group? acetic acid cinnamylaldehyde allicin benzene ethanol Do the following have an aromatic functional group? isoamyl acetate cinnamylaldehyde diacetyl Do the following have a ketone functional group? l-carvone pyridine putrescene

isoamyl propionate

isoamyl propionate

Do the following have an aldehyde functional group? t-butyl mercaptan acetic acid trimethylamine Do the following have a carboxyl functional group? acetic acid cinnamylaldehyde pyridine

pyridine

isoamyl propionate

Do the following have an ester functional group? diacetyl allicin l-carvone t-butyl mercaptan Do the following have an amine functional group? benzeneethanol trimethylamine isoamyl acetate Do the following have an alcohol functional group? acetic acid benzeneethanol cinnamylaldehyde

.

putrescene

allicin 198

Lab Report Key The title page should include: They should know this by now. Only take away points if incorrect!

Student’s full name Date of experiment Complete title of lab report Name of partner(s) Instructor’s name Lab and section number (e.g., CHM1046L-02) The purpose should include: There are several topics covered in this lab: chemical structure, functional groups, smells, hybridization, and so on. A statement of the purpose of this lab should encompass at least three of these topics for full credit. The criteria for experimental success should be included for full credit. The purpose should not be a copy of the purpose in the manual.

Procedure: This should be a reference to the lab manual, with any changes noted. For this experiment, the procedure section should also include the steps that the students took to determine the identity of the molecules; this should be complete enough so that someone else could read the procedure and redo the experiment and theoretically obtain the same results.

Data: The data section should have the following for each molecule: a) the unknown number associated with the molecule, b) the name of the molecule, c) the molecular formula of the molecule, d) the observations of the molecule made during lab, e) the Lewis dot structure of the molecule (drawn in ink), f) the molecular shape of the molecule, g) the hybridization of each atom in the molecule excluding hydrogen, and h) any functional groups in the molecule. Be sure that all observations match those in students’ lab notebook and that if they used any outside sources to get information, they cite them.

Calculations: There are no calculations or graphs for this experiment.

Conclusions: The conclusion for this experiment should be several paragraphs long and include a discussion of the identity of each of the unknown molecules. This should be supported by observations and background knowledge. Students must support each identity sufficiently to receive full credit. Be

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sure they include in their discussion the information in the data section such as molecular shape, hybridization, functional groups, and anything else that allows them to make the correct identity of the molecule. BE SURE THEY CLEARLY STATE THE IDENTITY OF EACH UNKNOWN. A discussion of how smell is related to molecular structure should be included. As always, any possible errors in the experiment or identification of the unknowns should be presented.

Questions: 1) Give an example of two molecules with the same molecular formula but different smells.

Explain why this difference occurs.

Example: Esters contain COO groups, and so do carboxylic acids, but esters are normally sweet or spicy, whereas the acids are sour. The different placement of similar structures within a molecule will change the overall structure of the molecule and thus change the receptor(s) that react to the molecule.

2) Long-time use of cigarettes often leads to a loss or change of the sense of taste. Based on this experiment, describe how receptors for taste might function.

A lot of the sense of taste is actually contributed to by the sense of smell. Smoking damages the nerve cells and receptors in the nasal epithelium, lessening the ability to discern delicate odors and thus diminishing the flavors experienced by the smoker.

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200

Experiment 28: Chemical Structure and Smell Section Points Points Worth Earned

Experiment 28: Chemical Structure and Smell Section Points Points Worth Earned

Title page (name, title, date, TA, course,

Title page (name, title, date, TA, course,

section, partner’s name)

section, partner’s name)

Purpose Procedure (cited/changes, steps taken to

Purpose Procedure (cited/changes, steps taken to

determine identity of molecules)

determine identity of molecules)

Data (for each molecule: the unknown number

Data (for each molecule: the unknown number

associated with the molecule, the name of the molecule, the molecular formula of the molecule, the observations made during lab of the molecule, the Lewis dot structure of the molecule [drawn in ink], the molecular shape of the molecule, the hybridization of each atom in the molecule excluding hydrogen, any functional groups in the molecule)

associated with the molecule, the name of the molecule, the molecular formula of the molecule, the observations made during lab of the molecule, the Lewis dot structure of the molecule [drawn in ink], the molecular shape of the molecule, the hybridization of each atom in the molecule excluding hydrogen, any functional groups in the molecule)

Conclusions (discussion of the identity of each

Conclusions (discussion of the identity of each

of the unknown molecules, sufficiently supported by observations and background knowledge; MUST include information from the data section such as molecular shape, hybridization, functional groups, and any things else that allows one to make the correct identity of the molecule; CLEARLY STATE THE IDENTITY OF EACH UNKNOWN; discussion of how smell is related to molecular structure; any possible errors in the experiment or identification of the unknowns)

of the unknown molecules, sufficiently supported by observations and background knowledge; MUST include information from the data section such as molecular shape, hybridization, functional groups, and any things else that allows one to make the correct identity of the molecule; CLEARLY STATE THE IDENTITY OF EACH UNKNOWN; discussion of how smell is related to molecular structure; any possible errors in the experiment or identification of the unknowns)

Questions Total Grade

Questions Total Grade

%

%

Experiment 28: Chemical Structure and Smell Section Points Points Worth Earned

Experiment 28: Chemical Structure and Smell Section Points Points Worth Earned

Title page (name, title, date, TA, course,

Title page (name, title, date, TA, course,

section, partner’s name)

section, partner’s name)

Purpose Procedure (cited/changes, steps taken to

Purpose Procedure (cited/changes, steps taken to

determine identity of molecules)

determine identity of molecules)

Data (for each molecule: the unknown number

Data (for each molecule: the unknown number

associated with the molecule, the name of the molecule, the molecular formula of the molecule, the observations made during lab of the molecule, the Lewis dot structure of the molecule [drawn in ink], the molecular shape of the molecule, the hybridization of each atom in the molecule excluding hydrogen, any functional groups in the molecule)

associated with the molecule, the name of the molecule, the molecular formula of the molecule, the observations made during lab of the molecule, the Lewis dot structure of the molecule [drawn in ink], the molecular shape of the molecule, the hybridization of each atom in the molecule excluding hydrogen, any functional groups in the molecule)

Conclusions (discussion of the identity of each

Conclusions (discussion of the identity of each

of the unknown molecules, sufficiently supported by observations and background knowledge; MUST include information from the data section such as molecular shape, hybridization, functional groups, and any things else that allows one to make the correct identity of the molecule; CLEARLY STATE THE IDENTITY OF EACH UNKNOWN; discussion of how smell is related to molecular structure; any possible errors in the experiment or identification of the unknowns)

of the unknown molecules, sufficiently supported by observations and background knowledge; MUST include information from the data section such as molecular shape, hybridization, functional groups, and any things else that allows one to make the correct identity of the molecule; CLEARLY STATE THE IDENTITY OF EACH UNKNOWN; discussion of how smell is related to molecular structure; any possible errors in the experiment or identification of the unknowns)

Questions Total Grade

Questions Total Grade

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201

Experiment 29: Proteins, Carbohydrates, and Fats: Analysis of a Peanut Instructor Notes and Lab Preparation Chemicals and Equipment Green unprocessed peanuts in the shell (available at most grocery stores and pet supply stores) Fehling’s reagent (A + B; recipe below) 2% KHSO4 Ethanol 10% NaOH 65% HNO3 Dilute HCl

Preparation For Fehling’s A, dissolve 7 g of hydrated copper(II) sulfate (CuSO4.5H2O) in 100 mL of DI water containing 2 drops of 0.01 M sulfuric acid.

For Fehling’s B, dissolve 35 g of potassium tartrate and 12 g of NaOH in 100 mL of distilled water.

Place each solution in a separate dropping bottle.

For dilute HCl, place 33.3 mL of concentrated HCl in a 100 mL volumetric flask and dilute to 100 mL with distilled water.

Instruction Notes This is an experiment that could be used in reference to either organic or biochemistry chapters.

General chemistry labs are quite often ill prepared to complete experiments related to these topics due to lack of equipment and/or chemicals. This experiment uses simple glassware available in any general chemistry laboratory and requires very little in the way of expensive chemicals, but it does teach several important aspects of biochemical analysis. In addition, the students get a kick out of working with the peanuts.

Potential Problems Students with allergies. Please make sure that there are no peanut allergies.

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Experiment 29 Prelaboratory Assignment KEY Name: ___________________________ Date: _________________ Instructor: ____________________________ Sec. #: ___________

Show all work for full credit.

1) What is a nonreducing sugar? How does Fehling’s test work to show the presence of nonreducing sugars?

Nonreducing sugars are not oxidized by Benedict’s, Tollen’s, or Fehling’s reagents. They are polysaccharides and as rings do not structurally contain the OH group needed for a reaction to occur. In a solution of nonreducing sugars, once the solution is boiled and the reagent added, the solution will remain blue-green in the presence of nonreducing sugars.

If reducing sugars are present, the solution will turn rust or dark red.

2) There is a general belief that the tryptophan found in turkey is what causes the “sleepiness” that often follows the Thanksgiving meal. Act as a myth buster and investigate the accuracy of this belief. Is there a lot of tryptophan in turkey? How does tryptophan cause sleepiness?

Or does it?

Although there is a fair amount of tryptophan in turkey (0.333 g of tryptophan per 100 g edible portion), other dishes—including chicken (0.292 g of tryptophan per 100 g edible portion)—contain about the same amount. Tryptophan can cause sleepiness because the amino acid can be converted into serotonin and melatonin. These are the neurotransmitters that regulate sleep.

For tryptophan to cause sleepiness, it would need to be taken on an empty stomach and alone. Because there are many other amino acids in the protein found in turkey, it is not the tryptophan that makes you sleepy.

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3) Hydrolysis is a process the human body uses to break down food in the process of digestion.

Look up and explain the process of three enzymes that use hydrolysis as part of their enzymatic function.

Here are a few of the more common answers (there are many more…): Amylase: Digests complex sugars into simple sugars. Amylase hydrolyzes starch, glycogen, and dextrin to form in all three instances glucose, maltose, and the limitdextrins.

Lactase (or beta-galactosidase): The enzyme involved in the hydrolysis of lactose to galactose and glucose.

Papain: Hydrolyzes proteins to form oligopeptides and amino acids.

Chymotrypsin: Hydrolyzes the peptide bond of amino acids with large hydrophobic side chains such as phenylalanine, tryptophan, and tyrosine.

Trypsin: A proteolytic enzyme that hydrolyzes peptide bonds on the carboxyl side of the amino acids arginine and lysine.

Lab Report Key The purpose should include a majority of the topics and techniques covered in the experiment and the criteria for determining the success of the experiment.

The procedure section should cite the lab manual and include any changes made to the written procedure during lab work.

The data section should include a table containing all of the observations made during the experiment for each of the confirmation reactions. Mass data should be included for the amount of peanut oil extracted from the peanut, and the percent error between the experimental value and theoretical values given in the background section should be listed. All observations written in this table must match those made during lab and recorded in students’ lab notebooks.

The calculation section for this experiment should include sample calculations for the mass of the peanut oil and the percent error in its mass.

The conclusion section should include several detailed paragraphs that include a discussion of the presence or absence of each biochemical constituent of the peanut and the test results that support these conclusions as well as a discussion on the lipid content of the peanut. Finally, all possible errors found in this experiment should be discussed.

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Questions: 1) You used a xanthoproteic test to confirm the presence of proteins in this lab. What is another test that you could use to confirm the presence of proteins? How does it work?

The Biuret test (peptide linkages react with copper to form colored complexes), ninhydrin test (amino group and carboxyl group interaction), and the Millon’s test (the phenol groups are acidified and reacted with mercury) are the three possible answers here.

2) What does acrolein smell like? When have you smelled something similar to acrolein?

What (chemically) caused the smell?

Acrolein is said to smell like burning fat. The smell would be most likely to occur when meat has been burned. The structure of acrolein (2-propenal) polymerizes at room temperature, causing its unpleasant odor.

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205

Experiment 29: Proteins, Carbohydrates, and Fats: Analysis of a Peanut Section Points Points Worth Earned

Experiment 29: Proteins, Carbohydrates, and Fats: Analysis of a Peanut Section Points Points Worth Earned

Title page (name, title, date, TA,

Title page (name, title, date, TA,

course, section, partner’s name)

course, section, partner’s name)

Purpose Procedure (cited/changes) Data (observations made during the

Purpose Procedure (cited/changes) Data (observations made during the

confirmation reactions and mass data of the peanut oil)

confirmation reactions and mass data of the peanut oil)

Calculations: (mass of the peanut oil

Calculations: (mass of the peanut oil

and the percent error in the mass)

and the percent error in the mass)

Conclusions (several detailed

Conclusions (several detailed

paragraphs: discussion of the presence or absence of each biochemical constituent of the peanut and the test results that support these conclusions; discussion of the peanut’s lipid content; all possible errors found in this experiment)

paragraphs: discussion of the presence or absence of each biochemical constituent of the peanut and the test results that support these conclusions; discussion of the peanut’s lipid content; all possible errors found in this experiment)

Questions Total Grade

Questions Total Grade

%

%

Experiment 29: Proteins, Carbohydrates, and Fats: Analysis of a Peanut Section Points Points Worth Earned

Experiment 29: Proteins, Carbohydrates, and Fats: Analysis of a Peanut Section Points Points Worth Earned

Title page (name, title, date, TA,

Title page (name, title, date, TA,

course, section, partner’s name)

course, section, partner’s name)

Purpose Procedure (cited/changes) Data (observations made during the

Purpose Procedure (cited/changes) Data (observations made during the

confirmation reactions and mass data of the peanut oil)

confirmation reactions and mass data of the peanut oil)

Calculations: (mass of the peanut oil

Calculations: (mass of the peanut oil

and the percent error in the mass)

and the percent error in the mass)

Conclusions (several detailed

Conclusions (several detailed

paragraphs: discussion of the presence or absence of each biochemical constituent of the peanut and the test results that support these conclusions; discussion of the peanut’s lipid content; all possible errors found in this experiment)

paragraphs: discussion of the presence or absence of each biochemical constituent of the peanut and the test results that support these conclusions; discussion of the peanut’s lipid content; all possible errors found in this experiment)

Questions Total Grade

Questions Total Grade

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%

%

206