Introduction: In this lab you will observe the diffusion of a substance across a semi-permeable membrane. Iodine is a known indicator for starch. An indicator is a substance that chances color in the presence of the substance it indicates. Iodine turns purplish black in the presents of starch.
1. Fill a plastic baggie with a teaspoon of corn starch and a 60 ml water, spin the baggy shut and tie it tight.
2. Fill a beaker up to 150ml with water and add ten drops of iodine solution.
3. Place the baggie in the beaker of water so that the baggy of cornstarch is submerged.
4. Wait twenty minutes and record your observations in the data table
5. While you are waiting record your starting data and predict what you think you will see.
Color after 20 minutes
Solution in Beaker
Solution in Bag
1. Define diffusion
2. Define osmosis
3. What is the main difference between osmosis and diffusion?
1. Based on your observations, which substance moved, the iodine or the starch?
2. The plastic baggie was permeable to which substance?
3. Is the plastic baggie selectively permeable?