Understanding key terms is crucial to understanding what is happening during gummy bear osmosis experiments. Osmosis occurs when liquids flow through a semi-permeable membrane from a hypertonic to a hypotonic environment. This definition also needs some explanation. Semi-permeable membranes allow some things to pass through them -- most frequently liquids -- but not others. Hypertonic and hypotonic are comparative terms: hypertonic solutions have higher concentrations of solutes, while hypotonic ones have a comparatively lower concentration. Diffusion is the active movement of a substance from hypertonic to hypotonic, until an isotonic solution -- equal concentration -- is reached.
Gummy bears are made from gelatin and water, starting as a liquid and cooling into a chewy, gummy solution. This is a result of the presence of gelatin, whose molecules are chain-like and create a solid matrix.
One gummy bear osmosis experiment involves soaking gummy bears overnight in plain water. To complete this experiment, you should first have students measure the height, width, and depth of the gummy bear, and record this information in their lab books. Place the gummy bears in cups of water -- one per student -- and set aside. Then discuss hypotheses -- what do the students think will happen to the bears? The next day, the bears will have expanded, as water moved by diffusion through the bear's semi-permeable membrane to reach an isotonic state where the concentration of water molecules inside and outside the bear were the same. Have the students measure the bears again, and calculate the percentage of growth.
Conduct the same experiment, this time soaking the gummy bears in salt water. Again ask students to predict the outcome: will the addition of salt change the outcome of the experiment in any way? If you soak the original, water-expanded gummy bears in salt water, they will shrink; osmosis will cause water to leave the gummy bear. However, if you soak new gummy bears in salt water, they will shrink immeasurably, as the bears' gelatin construction will cause it to hold its shape and size, for the most part, even when water leaves the bear.