DIFFUSION AND OSMOSIS.docx - DIFFUSION AND OSMOSIS Part I Diffusion Introduction In this exercise you will measure the diffusion of small molecules

DIFFUSION AND OSMOSIS.docx - DIFFUSION AND OSMOSIS Part I...

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DIFFUSION AND OSMOSIS Part I: Diffusion Introduction In this exercise you will measure the diffusion of small molecules through dialysis tubing, which we will use as an example of a semi-permeable membrane. The movement of a solute through a semi-permeable membrane is called dialysis. The size of the tiny pores in the dialysis tubing determines which substance can pass through the membrane. A solution of glucose and starch will be placed inside a bag of dialysis tubing. Distilled water will be placed in a beaker, outside the dialysis bag. After 30 minutes have passed, the solution inside the dialysis tubing and the solution in the beaker will be tested for glucose and starch. The presence of glucose will be tested with a glucose test strip. The presence of starch will be tested with Lugol's solution (potassium-iodide). Procedure 1. Obtain a 30 -cm piece of 2.5-cm dialysis tubing that has been soaking in water. Tie off one end of the tubing to form a bag. To open the other end of the bag, rub the end between your fingers until the edges separate. 2. Place 15 mL of the 15% glucose/ 1% starch solution in the bag. Tie off the other end of the bag, leaving sufficient space for the expansion of the bag's contents. Record the color of the solution in Table 1. 3. Test the 15% glucose / 1% starch solution in the bag for the presence of glucose using a glucose test strip. Compare to glucose test strip dipped in water. Record the results in Table 1. 4. Fill a 250 mL beaker or cup 2/3 full with distilled water. Add approximately 4 mL of Lugol's solution (KI) to the distilled water and record the color in Table 1. Test the solution for glucose and record the results in Table 1.

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