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

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

of lactose.

10 30 50 70 90

rate

of

diffu

sion (µ/s

)

percentage concentration of lactose (%)

Rate of diffusion (change in conductivity over time) against

percentage concentration of lactose

Hee Jean Park

August 15, 2010

Variables

Variable measured Method of measuring/ controlling variable

Dependent

Variables

Rate of diffusion of

sodium chloride across

visking tubing

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.

Independent

Variables

Percentage of lactose

concentration

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

added to 10ml of sodium chloride solution to obtain

different percentage concentration lactose:

0%,10%,30%50%,70%,90%

Controlled

Variables

Length of visking tubes Every visking tube is 15cm

Volume of sodium chloride

solution

10cm3 of sodium chloride concentration is added in each

test tube

Temperature of reactants

Constant temperature is maintained by conducting the

experiment at room temperature since reactants react more

quickly in higher temperature-26°C.

Rate of stirring/magnetic

stirrer

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

more quickly when stirred more quickly.

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

Position of the visking

tube

Each visking tube is dipped into the water in the same

position for every trial

Position/distance of the

conductivity sensor from

the visking tubing

The conductivity sensor is placed in the same position for

every trial.

Source of biological

material used

The same stirrer, conductivity sensor, beaker, and other

biological materials are used for every trial.

Table 1: List of variables

Hee Jean Park

August 15, 2010

Apparatus and materials

100cm3 volumetric flask (±0.12 cm

3)

1M Sodium chloride solution

Lactose

10cm3 pipette (±0.040 cm

3)

Visking tubing strips

250cm3 Beakers

Distilled water

Conductivity sensor probe

Test tubes

Test tube rack

Pipette filler

Electronic balance, correct to 0.001g

Vortex

Magnetic stirrer

Stirring rod

Filter funnel

Probe holder

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 5g 7g 9g

NaCl 10 cm3 10 cm

3 10 cm

3 10 cm

3 10 cm

3 10 cm

3

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

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.

transfer

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,

adsfaa5g, 7g, 9g).

Conductivity visking

sensor probe tubing

150 cm3of distilled water

Magnetic stirrer

Figure 4 : Conducting the experiment

0% 10% 30% 50% 70% 90%

trial1 trial2 trial3

Mean the same process

Figure 5: Conducting triplicate trials

Lactose solution prepared in

visking tubing strips

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

lactose

concentration

(%)

Rate of diffusion (change of conductivity) over time at

different trials (percent gradient) µ/cm/s

Meana)

± S.D.b)

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

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.

conductivity (µ/s) against time(s)

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.

Figure 8 : Graph of average rate of conductivity against percentage lactose concentration.

a) Error bar was labeled by obtaining the S.D.

0

0.5

1

1.5

2

2.5

0 10 20 30 40 50 60 70 80 90

Avera

ge c

hange o

f co

nduct

ivity(µ

/s)

percentage concentration of lactose (%)

change of conductivity(µ/s) against percentage concentration of lactose (%)

a)

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

lactose

concentration

(%)

Rate of diffusion (change of conductivity) over time at

different trials (percent gradient) µ/cm/s

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= 0.02cm

3

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 changes-

either 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.