Tincture of iodine is dropped into a beaker of starch solution and the starch solution turns purplish-black. After about 30 minutes the starch solution in the tubing is turning purple. In about a day it is completely purplish-black. Osmosis is the movement of a substance across a semi-permeable membrane from an area that is more concentrated in that substance to an area that is less concentrated. Semi-permeable membranes only allow certain substances through.
Tincture of iodine is a poison.
Dialysis tubing is stored in a poisonous substance, sodium azide. Before class Mix 15 mL of corn starch in 500 mL of distilled water. Fill the 2 L beaker with about 2 L of distilled water and add about 5 mL of tincture of iodine. Wearing gloves, rinse the dialysis tubing with distilled water to remove the sodium azide. Fold one end of the tubing over and clamp a closure over the fold.