Henry mixed salt and water together in a cup until he observed a clear solution. He measured the mass of the solution. Then he placed the cup outside for several sunny days during the summer. After a week, he observed that only solid salt remained in the cup and the mass had decreased. Henry concluded that a physical and chemical change occurred in this investigation.

Dissolving salt in water is a physical change: the salt remains salt, just dispersed in the water. As the water evaporates, it changes from liquid to gas, also a physical change; the salt is left behind and can be dissolved again. The mass decreases because water escapes from the cup, not because a chemical reaction occurs. Therefore, Henry is incorrect that both physical and chemical changes occurred.

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