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.

Semi-permeable: which means some things can pass through while other cannot.

Diffusion: is the movement of molecules from a high concentration to a low concentration.

Osmosis: is a special type of diffusion. Osmosis is the movement of water molecules through a membrane (from a high concentration of water to a low concentration of water).

Materials:

1 plastic sandwich bag

iodine

corn starch

masking tape

200-400 ml beaker

eye dropper

Procedure:

1.Use the masking tape to label the cup with your groups initials and the period.

2.Fill the beaker halfway with water.

3.Put 10 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 clean water into the sandwich bag using a graduated cylinder.

6.Tie the bag with a knot.

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

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 Beaker

Solution in Baggie

Conclusions: (Use lined paper if you need more space)*

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? _______ How do you know?

_________________________________________________________________

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.

___________________________________________________________________

___________________________________________________________________

7.

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

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________