Permeable membranes lab /iodine and vegetable oil

Essay by oglowaHigh School, 10th grade May 2004

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This experiment is based on the problem of whether the Ziploc bag will allow the iodine or starch to diffuse across the plastic "membrane". The hypothesis being tested is if the bag will allow the iodine to travel across the membrane and if it will react with the starch in the Ziploc bag.


1. Pour 25 mL of iodine into beaker

2. Fill about 1/3 of the test tube with Starch solution and place in beaker (DON'T POUR OUT!!!!)

3. Pour 25 mL of starch solution into snack size Ziploc bag

4. Seal Ziploc bag, and place in beaker

5. Wait 24 hours and then record results


The results of this experiment are that the starch in the bag turned a deep purple in color and there is less iodine in the beaker than previously noted. The control starch in the test tube did not change at all.


The starch molecules in the bag were too large to diffuse through the plastic and therefore the iodine diffused into the bag and reacted with the starch changing it to the color purple. The control stayed unaltered because iodine and starch do not diffuse through glass.