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
100cm3 volumetric flask (±0.12 cm3)
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,
adsfaa5g, 7g, 9g). Conductivity
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
different trials (percent gradient) µ/cm/s
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.