4. Identify each of the following observations

Question

as evidence of either a physical change or a
chemical change.
(a) A piece of copper is heated until it
melts.
(b) A piece of aluminum corrodes in a
solution of acid.
(c) A piece of paper burns in a candle
flame.
(d) A piece of plastic is stretched until it
breaks.
(e) Table salt boils at 1465°C.

Answer 1

Here are the observations identified as either a physical change or a chemical change:

(a) A piece of copper is heated until it melts.

• Physical change (melting is a change of state)

(b) A piece of aluminum corrodes in a solution of acid.

• Chemical change (corrosion involves a chemical reaction)

(c) A piece of paper burns in a candle flame.

• Chemical change (burning is a combustion reaction, resulting in new substances)

(d) A piece of plastic is stretched until it breaks.

• Physical change (stretching does not change the chemical composition of the plastic)

(e) Table salt boils at 1465°C.

• Physical change (boiling is a change of state)