Question

tudents investigated how four common white substances reacted with three other substances. Their observations are shown in the table.



Substance Description Observations When Combined With:
Iodine Water Vinegar
baking soda white powder turned yellow/orange fizzed fizzed
cornstarch white silky powder turned purple and then black turned cloudy became thick and hard
salt white crystals no reaction dissolved no reaction
sugar white crystals turned yellow dissolved dissolved


Which TWO pieces of data indicate that a chemical change occurred during the investigation?



A.
Salt dissolved in water.

B.
Sugar dissolved in water.

C.
Baking soda fizzed in vinegar.

D.
Cornstarch became hard in vinegar.

E.
Cornstarch turned black when iodine was added.

Answer 1

C and E.

Fizzing (baking soda + vinegar) indicates gas was produced — a chemical reaction. Cornstarch turning black with iodine is a color change from a chemical interaction (starch–iodine reaction). Dissolving (salt or sugar in water) is a physical change.