How Can Diffusion Be Observed Lab Handout PDF

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Diffusion Observations...

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Diffusion & Osmosis Lab Introduction: In this lab you will observe the diffusion of a substance across a semi permeable membrane. Iodine is a known indicator for starch. An indicator is a substance that changes color in the presence of the substance it indicates. Watch as your teacher demonstrates how iodine changes in the presence of starch. Prelab Observations: Describe what happened when iodine came into contact with starch. The white substance of starch turned purple once the orange iodine was put into the starch.

Procedure: 1. Fill a plastic baggie with a teaspoon of corn starch and a half a cup of water tie bag. (This may already have been done for you) 2. Fill a beaker halfway with water and add ten drops of iodine. 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 5. While you are waiting, answer the questions. Questions: 1. Define diffusion. Random movement of particles from an area of high concentration to an area of low concentration. 2. Define osmosis. Diffusion of water through a selectively permeable membrane 3. What is the main difference between osmosis and diffusion? Osmosis is the transport of water molecules and diffusion is the transport of particles in the cell through the membrane. 4. Why is iodine called an indicator? It is called an indicator because after few minutes of diffusion, it changed the starch from white to a purple like color. 5. Molecules tend to move from areas of higher concentration to areas of _low_ concentration. What's in the Bag?

We're going to think about concentrations now, which substances are more or less concentrated depends on which one has the most stuff in it. 1. Is the baggie or beaker more concentrated in starch? baggie 2. Is the baggie or beaker more concentrated in iodine? beaker 3. Iodine solution: is the baggie or the beaker hypertonic? A hypertonic solution contains a higher concentration of solutes.(Iodine) beaker 4. Starch solution: is the baggie or the beaker hypertonic? baggie 5. Which one is hypotonic in relation to starch, baggie or beaker? A hypotonic solution contains a lower concentration of solutes. beaker

Make Some Predictions 1. If the baggie was permeable to starch, which way would the starch move, into the bag or out of the bag? _Out of the bag __ 2. If the baggie was permeable to iodine, which way would the iodine move, into or out of the bag? _ Move into the bag ___ 3. If the baggie was permeable to iodine, what color would you expect the solution in the baggie to turn? _ Brown __ What about the solution in the beaker? _Clear__ 4. If the baggie was permeable to starch, what color would you expect the solution in the baggie to turn? _Clear_ What about the solution in the beaker? __Light Brown__ 5. Make a prediction about what you think will happen: I think the iodine will enter the bag and change the color of the starch.

What's in the Bag? Data Table

Solution in Beaker Solution in Bag

Starting Color orange white

Color after 15 minutes Reddish/Orange Dark Purple

Post Lab Analysis 1. Based on your observations, which substance moved, the iodine or the starch? The iodine moved from the breaker to the baggie. 2. How did you determine this? I determine this because iodine is a know indicator for starch. An indicator is a substance that chances color in the presence of the substance it indicates.

3. The plastic baggie was permeable to which substance? The plastic baggie was permeable to the iodine.

4. Is the plastic baggie selectively permeable? The plastic is a selectively permeable.

5. Sketch the cup and baggie in the space below. 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. If we did an experiment in which the iodine solution was placed in the baggie and the starch solution was in the breaker the iodine would move out the baggie. Once the iodine makes it way out the baggie the starch would change color.

7. Why is it not a good idea to store iodine in a plastic bag? Iodine has the ability to permeate the bag so it’s not a good idea to store it in a plastic bag....