Diffusion Through Dialysis Tubing

Partners: ______Date: ______Block: ______

Diffusion through Dialysis Tubing

Problem: How does dialysis tubing affect the movement of molecules?

Background Information:  Iodine changes color in the presence of starch. Specifically, iodine turns corn starch purple.  Dialysis tubing 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 (down the concentration gradient)  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) down the concentration gradient

Materials: Beaker, iodine solution, cornstarch solution, string, dropper

Procedure: 1. Label the beaker with your group’s initials and the block. 2. Fill the beaker with 60mL of water. 3. Put 10 drops of iodine into the water. 4. Tie the bottom of the dialysis tubing with string. 5. Using the dropper, put three droppers full of cornstarch solution into the tubing. 6. Tie the other end of the tubing with string 7. Place the bag into the water with the iodine and let it sit overnight.

Observations: 1. Molecules tend to move from areas of ______to ______concentration.

2. Which is more concentrated with cornstarch: the tubing or beaker? ______

3. Which is more concentrated with iodine: the tubing or beaker? ______

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

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

6. If the tubing 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 tubing 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 will happen. ______Data Table: Material Beginning Color Ending Color Solution in Beaker Solution in Tubing

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

2. How did you determine this? ______

3. What substance was the tubing permeable to? ______

4. In the sketch below, identify the parts of the experiment: dialysis tubing, iodine solution, and cornstarch solution.

**Draw 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 tubing, and the starch solution was in the beaker? ______

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