bio ib idesign experiment on rate of diffusion
DESCRIPTION
Effect of lactose on diffusion of sodium chloride across a membraneTRANSCRIPT
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.