Question

dry lab: diffusion and osmosis
introduction: dialysis tubing, diffusion, and osmosis
dialysis tubing is an artificial, selectively permeable membrane used in separation techniques. dialysis tubing contains very small pores through which substances can diffuse. in the medical field, it is used to filter toxins from the bloodstream of patients with diminished or lost kidney function. in a more general sense, it is used in labs to separate molecules like glucose from water. dialysis tubing is available with various pore sizes, so the appropriate pore size should be chosen based on the specific application. small solutes and water can pass freely through the semi - permeable membrane, while larger molecules will pass slowly or not at all. remember, diffusion is the spontaneous movement of substances from an area of high concentration to an area of low concentration. osmosis is the diffusion of water down a concentration gradient, which means the movement of water from areas of low solute concentration to areas of high solute concentration. separation techniques often use indicator tests, like lugols test and benedicts reagent, to determine the presence of specific substances.
materials (part 1: diffusion)

• beaker
• pre - prepared solution of 10% glucose and 1% starch
• dialysis tubing
• distilled water
• iodine
• lugols test kit
• benedicts reagent

procedure (part 1: diffusion)

1. fill the dialysis tubing with the pre - prepared glucose and starch solution.
2. fill a beaker with 350 ml water.
3. add a few drops of iodine to the water, just enough so the water has a faint yellow color.
4. test the solution in the dialysis tubing using both lugols test and benedicts reagent.
5. test the water in the beaker using both lugols test and benedicts reagent.
6. place the securely closed dialysis tubing into the beaker.
7. wait 30 minutes. while you wait, answer the analysis questions below.
8. re - test both the solution in the dialysis tubing and the water in the beaker with lugols test and benedicts reagent.

analysis questions

1. based on the principles of diffusion and the properties of dialysis tubing, predict whether starch and glucose will move through the dialysis tubing.
2. research lugols test on your own. explain what lugols test detects in a solution and describe the expected color change that indicates the presence of the detected substance.
3. research benedicts reagent on your own. describe what benedicts reagent detects and the color change that signifies a positive result.

Explanation:

1. Glucose is a small - molecule sugar and can pass through the semi - permeable dialysis tubing due to its small size and the principles of diffusion. Starch is a large polymer molecule and cannot pass through the pores of the dialysis tubing easily.
2. Lugol's test detects starch. In the presence of starch, the solution turns from a faint yellow (of iodine) to a deep blue - black color.
3. Benedict's reagent detects reducing sugars like glucose. A positive result is indicated by a color change from blue to green, yellow, orange, or red depending on the concentration of the reducing sugar.

Answer:

1. Glucose will move through the dialysis tubing, starch will not.
2. Lugol's test detects starch. Color change: from faint yellow to deep blue - black.
3. Benedict's reagent detects reducing sugars. Color change: from blue to green/yellow/orange/red.