Practice Test 10

A school custodian finds an unlabeled white powder near the cafeteria sink. A teacher suggests it might be either baking soda (sodium bicarbonate) or cornstarch. The school wants to know if adding vinegar (aqueous acetic acid) would cause a chemical reaction that could produce gas and pressure in a closed trash bag. Which investigation design best tests whether the powder undergoes a chemical change when mixed with vinegar?

Two students argue about whether tarnishing of copper (a dull dark layer forming on a penny left in air) is a chemical change or just dirt. The science club wants a safe, testable investigation to determine whether a new substance forms on copper over time. Which investigation design best tests for chemical change with appropriate variables and controls?