Which laboratory activities involve chemical changes?

The green growing on the penny of copper and the rust forming on the nail of iron are chemical changes.

Boiling away salt water, scraping iron filings from a mixture of sand with a magnet, and breaking a rock with a hammer, are physical changes.

Extracting iron filings from a mixture of sand with a magnet is absolutely no change.  That's merely separating items that got mixed up.

leaving a copper penny in vinegar until it turns green

Explanation:

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