Hee Jean Park August 15, 2010

Internal Assessment-Investigating the relationship between percentage lactose concentration and rate of diffusion of sodium chloride across visking tubing using a conductivity sensor.

Research Question

How will changing percentage lactose concentration affect the rate of diffusion (change in conductivity over time) of sodium chloride across visking tubing using a conductivity sensor?

Introduction

Diffusion is a type of passive transport, which does not require energy for the transportation. It is the movement of particles from a higher concentration to a lower concentration. In this experiment, the relationship of conductivity and amount of lactose is used to investigate the effect of lactose concentration on the rate of diffusion. The concentration of lactose is manipulated using different percentage lactose concentration. The rate of diffusion can be determined by the change in conductivity as reaction proceeds over time. The conductivity inside the visking tubing in which the reaction occurs is measured every second over 60 seconds using a conductivity sensor. The rate of diffusion for different concentration is obtained by calculating the slope of conductivity vs. concentration of lactose graph, since differing rate of diffusion is change in conductivity over time.

Hypothesis

Rate of diffusion(

cannot be affected by anything except for concentration gradient,

temperature, and surface area. Lactose cannot impact diffusion because it is a molecule not an ionic particle; therefore, any concentration of lactose would not affect the rate of diffusion. The rate would stay constant and unchanged throughout.

Hee Jean Park August 15, 2010 Rate of diffusion (change in conductivity over time) against

rate of diffusion (Âľ/s)

percentage concentration of lactose

10

30 50 70 percentage concentration of lactose (%)

90

Figure1 : the predicted trend of rate of diffusion affected by different percentage concentration of lactose.

Hee Jean Park August 15, 2010

Variables

Variable measured

Dependent Variables

Rate of diffusion of sodium chloride across visking tubing

Method of measuring/ controlling variable

The change of conductivity is measured using conductivity sensor. Conductivity of the visking tube only during initial 60 seconds is measured to find the change in conductivity and thus changing rate of diffusion.

Different amount of lactose: 0g,1g,3g,5g,7g,9g was each Independent Variables

Percentage of lactose

added to 10ml of sodium chloride solution to obtain

concentration

different percentage concentration lactose: 0%,10%,30%50%,70%,90%

Length of visking tubes

Every visking tube is 15cm 3

Volume of sodium chloride

10cm of sodium chloride concentration is added in each

solution

test tube Constant temperature is maintained by conducting the

Temperature of reactants

experiment at room temperature since reactants react more quickly in higher temperature-26째C.

Rate of stirring/magnetic

The electronic stirrer is set to rate:2 since reactants react

Controlled

stirrer

more quickly when stirred more quickly.

Variables

Volume of water

150cm3 of water is added in the beaker for every trial

Position of the visking

Each visking tube is dipped into the water in the same

tube

position for every trial

Position/distance of the conductivity sensor from

The conductivity sensor is placed in the same position for every trial.

the visking tubing Source of biological

The same stirrer, conductivity sensor, beaker, and other

material used

biological materials are used for every trial. Table 1: List of variables

Hee Jean Park August 15, 2010

Apparatus and materials 

Test tube rack

1M Sodium chloride solution

Pipette filler

Lactose

Electronic balance, correct to 0.001g

10cm3 pipette (±0.040 cm3)

Vortex

Visking tubing strips

Magnetic stirrer

3

250cm Beakers

Stirring rod

Distilled water

Filter funnel

Conductivity sensor probe

Probe holder

Test tubes

Stopwatch

Procedure

A)Preparation of 1M of sodium chloride solution 1.

Using an electron balance, 58.44 g of sodium chloride is weighed in a small beaker.

2.

Transfer the powder to a volumetric flask by washing down through a filter funnel with distilled water up to 1L.

3.

The volumetric flask is capped and inverted a several times. 1M sodium chloride solution is obtained.

. B)Preparation of different percentage lactose concentration 1. 1g (10%) of lactose powder is weighed in a small beaker 2. Add 10cm3 of sodium chloride solution from the volumetric flask to the powder and stir it with a stirring rod. 3. Transfer the solution into one of the test tubes using a pipette. 4. Use the vortex to make a homogeneous solution. 5. Repeat step 1 to 3 each with different g of lactose powder. (0%, 30%, 50%, 70%, 90%)

Hee Jean Park August 15, 2010

Lactose

0g

1g

3g

10 cm3 10 cm3 10 cm3

NaCl

5g

7g

9g

10 cm3

10 cm3 10 cm3

Solution Figure 2 : Preparation of different percentage lactose concentration

C)Preparation of visking tubing strips 1.

Make a visking tubing strip of 15cm long.

2.

Use a pipette to transfer 10ml the solution prepared in step B) (from a test tube) to a visking tubing strip.

3.

Repeat step #1 to 2 for other visking tubing strips each with different amount of lactose. (0g, 3g, 5g, 7g, 9g) pipette

transfer

Lactose solution

Visking tubing

Figure 3: Transferring lactose solution to visking tubing strips

D) Conducting the experiment 1.

The conductivity sensor probe is connected to the laptop and is fixed with a probe holder.

2.

The magnetic stirrer is set at rate: 2.

3.

Fill a beaker with 150cm3 of distilled water.

4.

Adjust the sensor probe tangential to one side of the beaker, and at the same distance from

dkadthe visking tubing, throughout the experiment.

Hee Jean Park August 15, 2010

5.

Immerse the visking tubing strip with 10% of lactose inside the beaker and immediately start

dlkafjlthe stopwatch. 6.

Data for the first 60 seconds was recorded.

7.

Data of 10% lactose concentration for three triplicate trials was collected to obtain the mean.

8.

Repeat step 1 to 7 for other 5 visking tubing strips with different amount of lactose. (0g, 3g,

visking

sensor probe

tubing

150 cm3of distilled water

Magnetic stirrer Figure 4 : Conducting the experiment

Lactose solution prepared in visking tubing strips

0%

10%

30%

50%

70%

trial1 trial2 trial3

Mean

the same process

Figure 5: Conducting triplicate trials

90%

Hee Jean Park August 15, 2010

Data collection

Table2: Raw data collected for every single trial.

Hee Jean Park August 15, 2010

Quantitative Data

Percentage

Rate of diffusion (change of conductivity) over time at

lactose

different trials (percent gradient) µ/cm/s Meana)± S.D.b)

concentration (%)

T1

T2

T3

Mean

0

1.502

c)

-

1.794

1.648

1.64±0.14

10

-

1.655

1.944

1.800

1.80±0.14

30

1.678

1.856

1.787

1.774

1.77±0.07

50

-

1.372

1.755

1.564

1.56±0.19

70

1.493

1.544

1.893

1.643

1.64±0.17

90

1.481

-

1.788

1.635

1.63±0.15

Table 3:Change in rate of diffusion over time at different percentage lactose concentration.1 a)Average rate of diffusion obtained for the random triplicate samples. b)Standard deviation obtained for the random triplicate samples. c)Results were not included into the mean due to inconsistencies and irregularities.(-)

Qualitative Data: Not much visible change was seen.

Processed Data Percentage lactose concentration (%)

Calculation

Average rate of diffusion±S.D.

0

1.64±0.14

10 30

1.77±0.07

50

1.56±0.19

70

1.64±0.17

90

1.63±0.15 Table 4: Calculation of average rate of diffusion

1

The change in change in rate of diffusion over time at different percentage of lactose concentration was calculated by finding the slope of rate of diffusion vs. time for different percentages of lactose concentration graph using Logger Pro software.

Hee Jean Park August 15, 2010

Hee Jean Park August 15, 2010

Data Presentation

conductivity (Âľ/s) against time(s)

Figure 7 : Graph of conductivity inside test tube against time for every trial of different percentage concentration of lactose solution.2

2

Slopes of lines that have their slope value closest to the average slope value for each concentration are shown in boxes.

Hee Jean Park August 15, 2010

The graph of average change of conductivity was plotted against the concentration of percentage lactose concentration to ascertain the relationship between the two. A line of best fit is drawn with the equation and R-squared value of the line shown. Error bars on both the x-values and the y-values are also included. change of conductivity(Âľ/s) against percentage concentration of lactose (%)

Average change of conductivity(Âľ/s)

2.5

2

a)

1.5

1

0.5

0 0

10

20

30

40

50

60

70

80

percentage concentration of lactose (%)

Figure 8 : Graph of average rate of conductivity against percentage lactose concentration. a) Error bar was labeled by obtaining the S.D.

90

Hee Jean Park August 15, 2010

Uncertainties Standard deviation Standard deviation was calculated and represented in the rate of diffusion(change in conductivity) vs. percentage lactose concentration graph as error bars.

Percentage

Rate of diffusion (change of conductivity) over time at

lactose

concentration

Mean±S.D.

(%)

T1

T2

T3

Mean

0

1.502

c)

-

1.794

1.648

1.64±0.14

10

-

1.655

1.944

1.800

1.80±0.14

30

1.678

1.856

1.787

1.774

1.77±0.07

50

-

1.372

1.755

1.564

1.56±0.19

70

1.493

1.544

1.893

1.643

1.64±0.17

90

1.481

-

1.788

1.635

1.63±0.15

Table5: Standard deviation at different concentrations.

Standard deviation calculation: Lactose=10%

Same calculation was done for 0%, 30%, 50%, 70%, and 90%. Uncertainty due to 10cm3 pipette= 0.02cm3

Hee Jean Park August 15, 2010

Conclusion

The relationship between the rate of diffusion and the concentration of lactose can be seen in Figure 2. The data(average rate of diffusion for different percentage concentrations) creates a linear regression line with very similar slope, which means that the rate of diffusion is constant and is unaffected by the concentration of lactose. Thus, as percentage lactose concentration changeseither increases or decreases, the rate of diffusion is not affected. In conclusion, the hypothesis is valid.

Evaluation

The results, average rates of reaction, are precise by running a several trials to reduce error and evaluate a more precise average. However, the results may not be accurate due to the uncertainties of the pipette, volumetric flask, conductivity sensor probe, and other materials used during the experiment. Although the general trend of the graph proves the hypothesis to be valid, it can be doubted that the values are not accurate because there were data that were not consistent or regular. In order to reduce uncertainty and error, the experiment can be improved by using a 50cm3 pipette or graduated cylinder.

Bio IB IDesign experiment on rate of diffusion

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