6. Consider an experiment in which starch is dissolved in a liter of water. Some of the solution is placed into a securely tied dialysis bag. The dialysis bag is placed into a beaker containing distilled water and iodine for 30 minutes. What are the correct answers for the questions below? (Note: Iodine reacts with starch to create a black/purple color.)
What would happen to the color of the solution in the bag?
a. The solution in the bag would turn purple as the iodine reacts with the starch.
b. The solution in the bag would grow lighter as the starch leaves the bag and enters distilled water and iodine.
Would there be a color change in the water-iodine solution?
a. The water iodine solution has no color change.
b. The water iodine solution turns purple.
How do substances enter or leave the dialysis bag?
a. The dialysis bag is permeable to iodine so it can move into the bag but is not permeable to starch.
b. There is a leak in the bag allowing starch to flow out.
How would the mass of the bag change after a few hours?
a. The mass of the bag would be lighter as starch leaks out.
b. After several hours, the mass of the bag should increase as water moves by osmosis from the lower concentration outside the bag to the higher concentration (hypertonic solution).
The correct answers to the questions are as follows:
1. What would happen to the color of the solution in the bag?
Answer: b. The solution in the bag would grow lighter as the starch leaves the bag and enters distilled water and iodine.
2. Would there be a color change in the water-iodine solution?
Answer: a. The water iodine solution has no color change.
3. How do substances enter or leave the dialysis bag?
Answer: a. The dialysis bag is permeable to iodine so it can move into the bag but is not permeable to starch.
4. How would the mass of the bag change after a few hours?
Answer: b. After several hours, the mass of the bag should increase as water moves by osmosis from the lower concentration outside the bag to the higher concentration (hypertonic solution).
The correct answers to the questions are as follows:
1. What would happen to the color of the solution in the bag?
The correct answer is b. The solution in the bag would grow lighter as the starch leaves the bag and enters the distilled water and iodine. Since iodine reacts with starch to create a black/purple color, as the starch moves out of the bag and into the water-iodine solution, the color in the bag would become lighter.
2. Would there be a color change in the water-iodine solution?
The correct answer is a. The water-iodine solution has no color change. Since the dialysis bag is selectively permeable and only allows small molecules like water and iodine to pass through, while starch molecules are too large to pass through, the iodine remains in the water-iodine solution and does not undergo any color change.
3. How do substances enter or leave the dialysis bag?
The correct answer is a. The dialysis bag is permeable to iodine so it can move into the bag, but it is not permeable to starch. This is because the dialysis bag has pores or openings that are small enough to allow small molecules like iodine to pass through, but it restricts larger molecules like starch from passing through.
4. How would the mass of the bag change after a few hours?
The correct answer is b. After several hours, the mass of the bag should increase as water moves by osmosis from the lower concentration outside the bag to the higher concentration (hypertonic solution). Since the dialysis bag is permeable to water, but not to starch, the water molecules from the outside will move inside the bag through osmosis to equalize the concentrations of water on both sides of the membrane. This influx of water will increase the mass of the bag.