Question

investigation 1: they melt a sample of solid copper into liquid copper and record the mass before and after.
investigation 2: they heat copper in a flame until it reacts with oxygen, forming a black substance on the surface. they record the mass before and after.
part a
which statement best explains the difference between the two investigations?
both are physical changes because the mass stayed the same.
investigation 1 is a physical change, but investigation 2 is a chemical change because a new substance formed.
investigation 1 is a chemical change, but investigation 2 is a physical change because only color changed.

Explanation:

In Investigation 1, melting solid copper to liquid copper is a physical change as only the state changes and no new substance is formed. In Investigation 2, heating copper to react with oxygen and form a black - substance is a chemical change as a new substance (copper oxide) is formed.

Answer:

Investigation 1 is a physical change, but Investigation 2 is a chemical change because a new substance formed.