Procedure 1. Measure and pour 50 mL of water into a 100 mL beaker. Cut a piece of dialysis tubing 15.0 cm long. Submerge the dialysis tubing in the water for at least 10 minutes. 2. Measure and pour 82 mL water into a second 100 mL beaker. This is the beaker you will put the filled dialysis bag into in Step 9. 3. While the dialysis bag is still soaking, make the glucose/sucrose mixture. Use a graduated pipette to add five mL of glucose solution to a third beaker and label it “Dialysis bag solution”. Use a different graduated pipette to add five mL of starch solution to the same beaker. Mix by pipetting the solution up and down the pipette six times.

Diffusion and Osmosis 104 4. Using the same pipette that you used to mix the dialysis bag solution, remove two mL of that solution and place it in a clean beaker. This sample will serve as your positive control for glucose and starch. a. Dip one of the glucose test strips into the two mL of glucose/starch solution in the third beaker. Af- ter one minute has passed, record the final color of the glucose test strip in Table 3. This is your positive control for glucose. b. Use a pipette to transfer approximately 0.5 mL of IKI to into the two mL of glucose/starch solution in the third beaker. After one minute has passed, record the final color of the glucose/starch solution in the beaker in Table 3. This is your positive control for starch. 5. Using a clean pipette, remove two mL of water from the 82 mL of water you placed in a beaker in Step 2 and place it in a clean beaker. This sample will serve as your negative control for glucose and starch. a. Dip one of the glucose test strips into the two mL of water in the beaker. After one minute has passed, record the final color of the glucose test strip in Table 3. This is your negative control for glucose. b. Use a pipette to transfer approximately 0.5 mL of IKI to into the two mL of water in the beaker. Af- ter one minute has passed, record the final color of the water in the beaker in Table 3. This is your negative control for starch. Note : The color results of these controls determine the indicator reagent key. You must use these results to interpret the rest of your results. 6. After at least 10 minutes have passed, remove the dialysis tubing. Use your thumb and pointer finger to rub the tubing between your fingers; this will open the dialysis tubing. Close one end of the tubing by folding over 3.0 cm of one end (this will become the bottom). Fold it again and secure with a rubber band (use two rubber bands if necessary). Add a knot just above or below the rubber band to create a seal. 7. To test that no solution can leak out, add a few drops of water to the tubing and look for water leakage. If any water leaks, tighten the rubber band and/or the knot in the tubing. Make sure you pour the water out of the tubing before continuing to the next step.