Corn Starch Iodine Lab

Name: ______Date: ______

Period:______

Problem: How does a plastic bag affect the movement of molecules?

Background Information:

• Iodine indicates the presence of starch. Specifically, iodine turns corn starch purple.

• A plastic bag is called semi-permeable which means it has many microscopic openings that allow small amounts of air or water to enter and leave. Larger things cannot pass through these openings.

• Diffusion is the movement of molecules from a crowded area to a less crowded area.

• Osmosis is a special type of diffusion. Osmosis is the movement of water molecules through a membrane (from a crowded area to a less crowded area).

Materials:

• 2 plastic sandwich bag • 1 twist tie

• iodine• corn starch

• masking tape • clear cup

• eye dropper • spoon

Procedure:

1. Use the masking tape to label the cup with your group’s initials and your period #.

2. Fill the cup halfway with water.

3. Put 20 drops of iodine into the water.

4. Using the spoon, put a teaspoon of corn starch into the plastic bag.

5. Pour 10 ml of tap water into the sandwich bag.

6. Tie the bag with the twist tie.

7. Place the bag into the water with the iodine and let it sit for 15 minutes.

8. While you wait answer the questions below:

Data/Observations:

1. Molecules tend to move from areas of ______concentration to areas of ______concentration.

2. Which is more concentrated in starch, the baggie or beaker? ______

3. Which is more concentrated in iodine, the baggie or beaker? ______

4. If the baggie was permeable to starch, which way would the starch move, into the bag or out of the bag? ______

5. If the baggie was permeable to iodine, which way would the iodine move, into or out of the bag? ______

6. If the baggie was permeable to iodine, what color would you expect the liquid in the baggie to turn? ______What about the liquid in the beaker? ______

7. If the baggie was permeable to starch, what color would you expect the liquid in the baggie to turn?______What about the liquid in the beaker? ______

8. Make a prediction about what you think will happen:

______

______

Data Table:

Starting Color / Color after 15 minutes
Solution in Baggie
Solution in Beaker

Conclusions: (Use the back if you need more space, make sure to write the question #)*

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 in the space below. Use arrows to illustrate how diffusion occurred in this lab. Be sure to label the parts of your diagram.

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.

______

______

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7. Why is it not a good idea to store iodine in a plastic bag?

______

______

______

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