Doing the experiment: some suggestions
Put the solution (either iodine or starch) in a plastic bag. Seal it with a twist tie and masking tape. Rinse the outside of the bag to make sure any solution is removed on the outside of the bag. Put the sealed bag into a container filled with water.
• Wait 24 hours. Then record your data.
• Do all your bags at the same time. You will need a container for each solution and different concentrations of the solutions you want to experiment with. At the minimum, you will need one bag with starch and one bag with iodine. You can try different concentrations or even different substances, but you will at least need to have the two just mentioned.