Question

Classify the following as physical or chemical changes. a. Moth balls gradually vaporize in a closet. b. Hydrofluoric acid attacks glass and is used to etch calibration marks on glass laboratory utensils. c. A French chef making a sauce with brandy is able to boil off the alcohol from the brandy, leaving just the brandy flavoring. d. Chemistry majors sometimes get holes in the cotton jeans they wear to lab because of acid spills.

Short answer

a. Physical change b. Chemical change c. Physical change d. Chemical change

Step-by-step solution

Classification of Moth balls in a closet

Since moth balls gradually vaporize in a closet, their state changes from solid to gas. However, the moth balls' chemical identity remains the same. Therefore, this is a physical change.

Classification of Hydrofluoric acid etching on glass

In this case, hydrofluoric acid reacts with the glass surface and forms a new substance in the process of etching. This is a chemical change since the original substance's chemical identity changes during the reaction.

Classification of boiling off alcohol from brandy

When alcohol is boiled off from the brandy, it changes its state from liquid to vapor. However, no new substance is formed, and both alcohol and brandy maintain their chemical identities. Hence, this is a physical change.

Classification of holes in cotton jeans due to acid spills

When an acid spill occurs on cotton jeans, the acid reacts with the cotton fibers, destroying their structure and creating holes. This is a chemical change as the acid reacts with the cotton, forming new substances.