Question

make predictions about which substances will move:

1. if the tube is permeable to starch, which way would the starch move?

into the tube / out of tube

1. if the tube is permeable to iodine, which way would the iodine move?

into the tube / out of tube

1. if the tube is permeable to iodine, what color would you expect the

contents to change? orange / purple / no change
what about the solution in the beaker? orange / purple / no change

1. if the tube is permeable to starch, what color would you expect it to

change? orange / purple / no change

1. what about the solution in the beaker?

orange / purple / no change

Explanation:

Step1: Concentration gradient for starch

Substances move from higher to lower concentration. If tube is permeable to starch, and assuming higher starch concentration inside tube (common setup in such experiments), starch moves out.

Step2: Concentration gradient for iodine

Iodine moves from higher to lower concentration. If tube is permeable to iodine, and assuming higher iodine concentration outside (as iodine is often in beaker), iodine moves into tube.

Step3: Iodine - starch reaction

Iodine reacts with starch to form purple - blue complex. If iodine moves into tube (where starch is), tube contents turn purple. Beaker solution (iodine source, no starch) remains orange (original iodine color).

Step4: Starch movement effect on color (if tube permeable to starch)

If starch moves out (step1), and assuming no iodine in tube (if iodine only in beaker and tube not permeable to iodine in this part), tube has no starch - iodine reaction, so no color change.

Step5: Starch in beaker effect

Starch moving out (step1), but if no iodine in beaker (or iodine already reacted in tube), beaker solution shows no color change (starch alone is colorless, and if iodine all used in tube reaction).

Answer:

1. out of tube
2. into the tube
3. tube contents: purple; beaker solution: orange
4. no change
5. no change