Label 8 sections of each ice cube tray as follows: Iodine 1, Iodine 2, Iodine 3, Iodine 4, and Vinegar 1, Vinegar 2, Vinegar 3, Vinegar 4
Ahead of time, place the baking powder, baking soda, cornstarch and powdered sugar into plastic or paper cups and label them Unknown 1, Unknown 2, Unknown 3, and Unknown 4. Make a key for which unknown is which substance, but keep the identities hidden from the students. Keep the unknowns at the front of the classroom and have a student from each group come up and place about half a teaspoon of each unknown into the specified section of the ice cube tray. Students should have two samples of each unknown in the ice cube tray, one to test with vinegar and one to test with iodine.
Caution students to take care not to spill or mix up the samples, and do not taste any samples under any circumstances.
Supply each group with a dropper bottle of iodine and a dropper bottle of vinegar.
Students will add 2-3 drops of vinegar to one sample of each unknown and record the results as "bubbles" or "no bubbles."
Students will add 2-3 drops of iodine to the other sample of each unknown and record the results as "turned black" or "did not turn black."
Caution students to be careful not to spill the iodine, it may stain clothing.
When students have completed the experiment and recorded their results, have them rinse out and dry the ice cube trays.