Materials and Set Up – this was so easy and inexpensive to do and had the same effect as using dialysis tubing. Great demo/lab as part of our unit on osmosis and diffusion!
For every two students:
- handout from Biology Corner
- large beaker
- inexpensive sandwich bag – non sealing (I used Wegmans 150 ct)
- 1 tbsp corn starch
- 50 mL water
- rubber band
- clothes pin
- graduated cylinder
- 100 mL Iodine dilution
Iodine Preparation
- 20 ml Iodine added to 500 mL of water
- measure out 100 mL of diluted iodine for each group
Prelab Prep:
- Place one bag over each beaker
- Add 1 tbsp of cornstarch to each bag
- Add 50 mL of water to each bag
- Check for leaks
- Use a rubber band on each one to keep closed
- Clip bag to beaker
Observations
- Students will add iodine and make observations – changes will take place within a few minutes and the longer it sits, the darker it will become.
- Iodine is able to pass through the plastic bag, the starch is not
- Have students lift the bag out to see the changes that are taking place
- Discuss
Update – I let the set up sit over the weekend, and when I came in today, the water was almost completely clear – looks like just about all of the iodine moved into the bag:
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