Diffusion Demonstration Questions

Starch-iodine test Definition noun A test for the presence of starch in which the sample turns blue-black in color when a few drops of potassium iodide solution is placed on the sample. Supplement The reaction is due to the formation of polyiodide chains from the reaction of starch and iodine. The amylose in starch forms helices where iodine molecules assemble, forming a dark blue or black color. When starch is broken down or hydrolyzed into smaller carbohydrate units, the blue-black color is not produced. Therefore, this test can also indicate completion of hydrolysis when a color change does not occur. Also called as: Iodine test.

Some Questions students asked after observing this test:

1. what would happen if we just mixed iodine and cornstarch?

2. what caused it to turn purple?

3. how did the iodine get into the bag?

4. what caused the water in the cup to turn clear?

5. did the water go through the bag? How?

6. why was the iodine yellow in the cup, but purple in the bag?

7. what would happen if we emptied the contents of the bag into the water in the cup?

8. did any water from inside the bag get out?

9. did any cornstarch get out of the bag?