Which of the following is a clue of a chemical change other than color change?

• A. Heating
• B. Melting
• C. Precipitate formation
• D. Evaporation

Answer: (C)

A chemical change often shows up as the formation of a new substance, and precipitate formation is a clear version of that. When ions in solution combine to form an insoluble compound, a solid—called a precipitate—drops out. That solid has different properties from the original dissolved species, indicating new chemical bonds and a new substance have formed. For example, mixing certain soluble salts can produce a solid precipitate, which is evidence of a chemical reaction occurring.

By contrast, heating, melting, and evaporation mainly involve changes in energy or state (solid to liquid, liquid to gas) without creating new substances. They’re typically physical changes, so they don’t serve as definitive clues of a chemical change by themselves.