CHEM 214 General Chemistry II Lab - Experiment 005: Chemical Kinetics, Crystal Violet Dye Reaction O

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Christina Allen G#: G01216043 CHEM 214-205 Instructor: Dr. J. Shea Due Date: 09/28/2020 Experiment 005: Chemical Kinetics, Crystal Violet Dye Reaction Order References: Suzanne Slayden, 2018, Chemistry 213, 214, 272 Laboratory Experiments, 7th Edition, pages 186-194.

George Mason University, Department of Chemistry and Biochemistry. Chemical Kinetics; 2020.

Chemical Kinetics, Distance Learning Summer 2020, accessed via Blackboard.

Purpose The purpose of this experiment is to determine the order of a reaction with respect to its reactant organic dye. This will be done by using crystal violet dye and a hydroxide ion for the reaction system and obtaining its spectroscopic data for percent transmittance versus time. The anticipated outcome is that the experimental determination of the reaction order of crystal violet dye will match its true reaction order. The balanced equation for this experiment is: crystV+ (aq) + OH- (aq) → crystV--OH (aq) Materials • • • • •

0.0251-M NaOH Solution 0.05051-M NaOH Solution 0.001-M Crystal Violet Dye Solution Vernier Labquest 2 (Spectrometer) 1-cm Cuvettes

Procedure 1. Turn on spectrometer and set it to 540 nm. Once it is warmed up, grab a cuvette and fill it 2/3 with the first NaOH solution to use as a blank. Zero the spectrometer with the blank. You must remake a new blank and re-zero the instrument after each trial for each NaOH solution.

2. Add one drop of crystal violet dye solution to a test tube with NaOH solution and invert to mix it. Place test tube into the spectrometer and record the percent transmittance reading. Record a percent transmittance reading every 30 seconds for at least 7 minutes.

3. Once the final reading is taken, repeat Step 1 and Step 2 using the first NaOH solution again to measure another trial. Each NaOH solution sample needs two trials in total.

4. Repeat Step 1, Step 2, and Step 3 using the second NaOH solution, collecting data for two trials in total. Log data into database system.

Data Table Table 1: Raw Data for the Chemical Kinetics Experiment. Christina Allen, G01216043, Chem 214-205 Room Temperature (K) Concentration of NaOH (M)

293 0.0251

0.05051

Time (s)

Absorbance Trial 1

Trial 2

Trial 1

Trial 2

0 30 60 90 120 150 180 210 240 270 300 330 360 390 420 450

1.079 0.970 0.861 0.767 0.676 0.590 0.516 0.444 0.383 0.327 0.280 0.239 0.206 0.173 0.150 0.131

1.125 1.019 0.913 0.809 0.716 0.624 0.540 0.467 0.402 0.344 0.297 0.255 0.219 0.189 0.165 0.146

1.026 1.025 1.020 1.021 1.018 1.016 1.014 1.012 1.008 1.006 1.001 0.998 0.993 0.991 0.989 0.986

0.584 0.471 0.372 0.294 0.232 0.182 0.140 0.109 0.085 0.067 0.052 0.042 0.031 0.025 0.020 0.016

Observations The cuvette solution of the NaOH and crystal violet dye at 0 seconds had a very dark purple color that looked almost as dense as the color of the pure crystal violet dye. By the end of the 450 seconds of the trial, the solution was completely colorless, indicating that there is no longer any crystal violet dye, only crystal violet hydroxide complex.

Calculations

Results Trial 1 of the 0.0251-M solution started with 1.079 absorbance and ended with 0.131 absorbance. Trial 2 of the 0.0251-M solution started with 1.125 absorbance and ended with 0.146 absorbance. Trial 1 of the 0.05051-M solution started with 1.026 absorbance and ended with 0.986 absorbance. Trial 2 of the 0.05051-M solution started with 0.584 absorbance and ended with 0.016 absorbance.

Table 1: Processed Data for the Chemical Kinetics Experiment. Christina Allen, G01216043, Chem 214-205

Figure 1: Absorbance for Trial 1 of the 0.0251-M NaOH Solution for the Chemical Kinetics Experiment. Christina Allen, G01216043, Chem-214-205

Figure 2: ln(Absorbance) for Trial 1 of the 0.0251-M NaOH Solution for the Chemical Kinetics Experiment. Christina Allen, G01216043, Chem-214-205

Figure 3: 1/Absorbance for Trial 1 of the 0.0251-M NaOH Solution for the Chemical Kinetics Experiment. Christina Allen, G01216043, Chem-214-205

Figure 4: Absorbance for Trial 2 of the 0.0251-M NaOH Solution for the Chemical Kinetics Experiment. Christina Allen, G01216043, Chem-214-205

Figure 5: ln(Absorbance) for Trial 2 of the 0.0251-M NaOH Solution for the Chemical Kinetics Experiment. Christina Allen, G01216043, Chem-214-205

Figure 6: 1/Absorbance for Trial 2 of the 0.0251-M NaOH Solution for the Chemical Kinetics Experiment. Christina Allen, G01216043, Chem-214-205

Figure 7: Absorbance for Trial 1 of the 0.05051-M NaOH Solution for the Chemical Kinetics Experiment. Christina Allen, G01216043, Chem-214-205

Figure 8: ln(Absorbance) for Trial 1 of the 0.05051-M NaOH Solution for the Chemical Kinetics Experiment. Christina Allen, G01216043, Chem-214-205

Figure 9: 1/Absorbance for Trial 1 of the 0.05051-M NaOH Solution for the Chemical Kinetics Experiment. Christina Allen, G01216043, Chem-214-205

Figure 10: Absorbance for Trial 2 of the 0.05051-M NaOH Solution for the Chemical Kinetics Experiment. Christina Allen, G01216043, Chem-214-205

Figure 11: ln(Absorbance) for Trial 2 of the 0.05051-M NaOH Solution for the Chemical Kinetics Experiment. Christina Allen, G01216043, Chem-214-205

Figure 12: 1/Absorbance for Trial 2 of the 0.05051-M NaOH Solution for the Chemical Kinetics Experiment. Christina Allen, G01216043, Chem-214-205

Discussion Each figure represents a possible order of reaction with respect to crystal violet dye in each trial. The figures for each trial are meant to determine which linear trend matches best with the trend of the data using the R2 correlation constant. For R2 values, 0 means the data is least correlated and 1 means the data is most correlated, so whichever figure for each trial has the greatest R2 value will be the order of the reaction. Absorbance versus time represents zero order, ln(absorbance) versus time represents first order, and 1/absorbance versus time represents second order. The highest R2 values (0.9971 and 0.9978) for trials 1 and 2 of 0.0251M NaOH solution were in the ln(absorbance) versus time figures. The highest R2 value of all trials between the 0.0251-M NaOH solution and the 0.05051-M NaOH solution is 0.9997, shown in Figure 11 representing ln(absorbance) versus time of trial 2 of 0.05051-M NaOH solution.

Because the ln(absorbance) versus time figures have the highest R2 values, the relationship between ln(absorbance) and time is the most linear, indicating that the reaction order with respect to crystal violet dye is first order.

The slopes of the 0.0251-M NaOH solution trials were -0.0047 M/sec, while the slopes of the 0.05051-M NaOH solution trials were -0.0081 M/sec. The slopes of the 0.0251-M NaOH solution trials seem proportional to the slopes of the 0.05051-M NaOH solution trials. Because both the concentration and rate of the 0.05051-M NaOH solution trials are roughly double the amount of the 0.0251-M NaOH concentration and rate, this indicates that the order of the reaction with respect to the hydroxide ion is first order.

The 0.05051-M NaOH solution reached the 90% mark quicker than either trial of the 0.0251-M NaOH solution, which did not even reach the 90% mark by the end of the 450-second interval. Trial 1 of the 0.0251-M NaOH solution only reached 74% and Trial 2 reached even lower at 71.4% by the end of 450 seconds. As shown in Figure 11, the slope of the 0.05051-M NaOH solution trial is twice as large and visually is much steeper than the slopes of the 0.0251M NaOH solution trials in Figure 2 and Figure 5. Because the reaction order of the hydroxide ion is first order and 0.05051-M NaOH solution is twice as large as 0.0251-M NaOH solution, the pseudo rates (the linear slopes) of the 0.05051-M NaOH solution would double as well.

The initial concentration of crystal violet is 1 x 10-3 M. After 240 seconds, the concentration of crystal violet would be 2.10 x 10-20 M, which can be rounded down to just 0 M. The integrated rate law for first order was used to calculate this concentration. K constant was calculated as -0.160 1/s using -0.0081 M/sec as the rate from the slope of Figure 11 and 0.05051-M as the concentration. The absorbance and concentration are directly proportional in Beer-Lambert’s Law. The eo extinction coefficient can be calculated by dividing absorbance by the path length multiplied by the concentration. The extinction coefficient of crystal violet dye at time zero is -507.6 1/(cm*M). These calculations can be found in the “Calculations” section.

Conclusion The purpose of this experiment was to determine the order of a reaction with respect to its reactant organic dye. The purpose was met. This was be done by using crystal violet dye and a hydroxide ion for the reaction system and obtaining its spectroscopic data for percent transmittance versus time. The anticipated outcome was that the experimental determination of the reaction order of crystal violet dye would match its true reaction order, and it did match with both the crystal violet dye and the hydroxide ion being first order. A future improvement that could be made to this experiment would be to carry out the procedure in a more sterile environment to avoid any unwanted particulates interfering with the reaction. Another improvement would be to further shake the crystal violet dye and hydroxide ion solution before it is entered into the spectrometer to avoid any awkward results in the data due to insufficient mixing of the reactants.