Introduction: In this lab, you willobserve the diffusion of a substance across a semipermeable membrane. Iodineis a known indicator for starch. An indicator is a substance that changescolor in the presence of the substance it indicates. Watch as your teacherdemonstrates how iodine changes in the presence of starch.

Prelab Observations: Describe whathappened when iodine came into contact with starch.

Procedure:

Fill a plasticbaggie with a teaspoon of cornstarch and a half a cup of water tie bag.(This may already have been done for you) Fill a beakerhalfway with water and add ten drops of iodine. Place the baggiein the cup so that the cornstarch mixture is submerged in the iodine watermixture. Wait fifteen minutesand record your observations in the data tmay be While you arewaiting, answer the questions.

Questions:




You are watching: Why is iodine called an indicator?

1. Define diffusion. ______________________________________________

2. Define osmosis. ____________________________________

3. Why is iodine called an indicator? _____________________________________________

4. Molecules tend to move fromareas of _______ concentration to areas of ______ concentration.

What"s in the Bag?

We"re going to think about concentrationsnow, which substances are more or less concentrated depends on which one hasthe most stuff in it.

1. Which is moreconcentrated in starch? < beaker / baggie >

2. Which is moreconcentrated in iodine? < beaker / baggie >

3. With regard to iodine, which is hypertonic? < beaker / baggie >

4. With regard to starch, which is hypertonic? < beaker / baggie >

Make Some Predictions

1. If the bag is permeableto starch, which way would the starch move? < into bag / out of bag >

2. If the bag is permeableto iodine, which way would the iodine move? < into bag / out of bag >

3. If the bag is permeableto iodine, what color would you expect it to change? < orange / purple / no change >

What about the solution in the beaker?< orange / purple / no change >

4. If the bag is permeableto starch, what color would you expect it to change?< orange / purple / no change >

What about the solution in the beaker? < orange / purple / no change >

Observations

Write your observations in the table below:


StartingColor
Colorafter 15 minutes
Solutionin Beaker


See more: What Is The Little Number Below The Big Number S ¹ ³ ⁺ ₄ ₇, Subscript And Superscript

1. Based on your observations,which substance moved, the iodine or the starch?

2. How did you determine this?

3. The plastic baggie was permeableto which substance?

4. Explain how the bag is a model for the cell.

5. Sketch the cup and baggie inthe space below. Use arrows to illustrate how diffusion occurred in this lab.

6. What would happen if you didan experiment in which the iodine solution was placed in the baggie, and thestarch solution was in the beaker? Be detailed in your description.

7. Why is it not a good idea tostore iodine in a plastic bag? Related Documents:


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