Was the membrane-tubing-permeable to starch

Answer 1

I'm assuming this is in reference to an experiment where you put a starch in dialysis tubing, and then put iodine in surrounding solution.

Dialysis tubing has a limit of roughly mwco (molecular weight cut off of 10,000). Iodine has a molecular weight of roughly 126, so it can pass through. On the other hand, starch is a polymer of 1000's of glucose molecules. Glucose (C6H12O6) has a molecular weight of roughly 180. 1000 * 180 = 180,000, so glucose cannot pass through the dialysis tubing.

In this experiment you should see the sealed tubing turn purple-pinkish after the iodine diffuses through. The outside solution should remain the same color.