Class Copy

Iodine Diffusion Activity

Modified from the Biology Corner. http://www.biologycorner.com. Accessed 3/26/2007.

Introduction:

In this activity you will observe the diffusion of a substance across a semi-permeable membrane. Record you work on a separate sheet of paper using complete sentences.

Procedure:

  1. Fill a plastic baggie with a teaspoon of corn starch and a half a cup of water tie bag.
  2. Fill a beaker halfway with water and add ten drops of iodine solution.
  3. Place the baggie in the cup so that the cornstarch mixture is submerged in the iodine water mixture.
  4. Wait fifteen minutes and record your observations in the data table.
    Data Table
    Starting Color
    Color after 15 minutes
    Solution in Beaker
       
    Solution in Bag
       
  5. While you are waiting, answer the questions.

Questions:

  1. Define diffusion.
  2. Define osmosis.
  3. What is the main difference between osmosis and diffusion.
  4. Why is iodine called an 'indicator'?
  5. Molecules tend to move from areas of _______ concentration to areas of ______ concentration.
  6. Is the baggie or beaker more concentrated in starch?
  7. Is the baggie or beaker more concentrated in iodine?
  8. Iodine solution: is the baggie or the beaker hypertonic?
  9. Starch solution: is the baggie or the beaker hypertonic?
  10. Which one is hypotonic in relation to starch, baggie or beaker?
  11. If the baggie was permeable to starch, which way would the starch move, into the bag or out of the bag?
  12. If the baggie was permeable to iodine, which way would the iodine move, into or out of the bag?
  13. If the baggie was permeable to iodine, what color would you expect the solution in the baggie to turn? What about the solution in the beaker?
  14. If the baggie was permeable to starch, what color would you expect the solution in the baggie to turn? What about the solution in the beaker?
  15. Make a prediction about what you think will happen:

Post Activity Analysis

  1. Based on your observations, which substance moved, the iodine or the starch?
  2. How did you determine this?
  3. The plastic baggie was permeable to which substance?
  4. Is the plastic baggie selectively permeable?
  5. Sketch the cup and baggie. Use arrows to illustrate how diffusion occurred in this lab.
  6. What would happen if you did an experiment in which the iodine solution was placed in the baggie, and the starch solution was in the beaker. Be detailed in your description.
  7. Why is it not a good idea to store iodine in a plastic bag?