Chung 1

Lani Chung

Mr. Nakamura

Biology HL Period 2B

4 February 2012

Diffusion through Membranes Lab Analysis Questions

1. What conclusion can you draw from the data in Table 2?

When the concentration of salt increased from 1% to 5% and then to 10% concentration, the rate

of diffusion consistently increased by about 2 mg/L/s at each step. This might be attributed to the

way diffusion occurs faster when there is a higher concentration inside or outside of a membrane

because a greater amount of molecules are required to flow across the membrane for equilibrium

to be reached. Thus there is a direct correlation between salt concentration and the rate of

diffusion across a membrane: As salt concentration increases, the rate of diffusion increases.

2. How did your conclusion compare to your prediction for Part I? Can you account for any

differences?

My prediction proved to be correct as I predicted that as salt concentration increases, the rate of

diffusion will increase because greater concentrations of salt will need to flow into the

membrane. Just as I had predicted, the results showed that as the salt concentration was gradually

increased from 5-10%, the rate of diffusion had also increased steadily.

3. If the rates in any of the three experiments varied in Part I, calculate how much faster each

rate was compared to that for the 1% salt solution. For instance, if the rate of the 1% solution

was 1 µs/s, then the rate of diffusion for the 10% solution would be (5/1) five times the rate of the

1% salt solution.

Chung 2

In the 1% salt concentration test the rate of diffusion was about 1 mg/L/s, in the 5% it was about

3 mg/L/s, and in the 10% it was about 5 mg/L/s. With these rounded estimates, you can say that

the rate of the 5% salt concentration test was about three times that of the 1% salt concentration

test and the rate of the10% salt concentration test was about five times that of the 1% salt

concentration test.

4. Compare the ionic concentration of pure water with a sugar water solution. How do you

account for this?

The ionic concentration of water is 572 mg/L while the ionic concentration of sugar solution is

506 mg/L. This can be due to the fact that the water that was tested was not purified or distilled.

Since tap water normally has some dissolved molecules, it is quite possible that the conductivity

probe detected the ions found in the water. However, if the water had been distilled like it was

supposed to, there is a great likelihood that the sugar solution would have a higher ionic

concentration than that of the water. This is because sugar ions would be present in the sugar

solution while no ions would be present in the distilled water.

5. What conclusion can you draw from the data in Tables 3 and 4?

Through the data in tables 3 and 4, I can conclude that sugar can be an inhibitor as it prevented

the 5% salt concentration from diffusing through the membrane since the rate of diffusion had

seen a decrease from 3.1946 mg/L/s to 2.5076 mg/L/s. I can also infer that the ionic

concentration of a solution can have an impact on the rate of diffusion of a substance through a

membrane.