Question

B. Permeability of starch and iodine

1. Data table:

Color of starch solution in bag at start of experiment	Weight of bag (containing starch solution) at start of experiment	Weight of bag after 30 minutes	Color of solution in bag after 30 minutes	Color of solution in beaker after 30 minutes	Weight of bag after 45 total minutes	Color of solution in bag after 45 total minutes	Color of solution in beaker after 45 total minutes
Cloudy	24.5 grams	26.1 grams	Dark blue	Light brown	27.3 grams	Dark blue	Light brown

2. Based on your results, you can tell that the pores in the dialysis tubing are

( larger or smaller ) than the size of molecule of I₂KI. Explain your answer using your results.

3. Based on your results, you can tell that the pores in the dialysis tubing are

( larger or smaller ) than the size of molecule of starch. Explain your answer using your results.

4.   Describe the results of the weight of the tubing before and after the incubation period. What does this result illustrate about the ability of starch to pass through the pores of the dialysis tubing?

Answer 1

During the process of dialysis, the solvent moves from lower to higher concentration of the solute across a semi permeable membrane. Here the dialysis bag serves as the membrane across which the solvent or small solutes, which are lower than the size of the pore of the dialysis membrane, can move.

The result shows-

The colour of the starch solution in the dialysis bag changes from cloudy to dark blue. This means that the solution in the beaker has iodine which moves across the dialysis bag to react with starch solution in it and turn the colour to deep blue. That is why we can tell that the pores in the dialysis tubing are larger than the size of molecule of I2KI which is why iodine could go in and turn the bag solution to blue as iodine reacts with starch and changes the colour to blue.

Since the solution in the beaker had brown color and not blue color, thus we can say that the starch could not pass across the membrane of the dialysis bag. Iodine and starch reacts to give purple to deep blue colour. That is why we can tell that the pores in the dialysis tubing are smaller than the size of molecule of starch as the beaker solution did not turn purple to deep blue colour.

The bag weight increases with time. This means that the solution in the beaker moves across the dialysis bag to the starch solution.