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.

Question

Which statements correctly defend or dispute his conclusion?

He is correct. Dissolving salt in water is a physical change, but evaporating the water is a chemical change. Formation of a solid is evidence that a chemical change occurred.
He is correct. Evaporation is a physical change, but dissolving salt in water is a chemical change. The change in mass is evidence that a chemical change occurred.
He is incorrect. Dissolving salt in water and evaporation of the water are both physical changes. The reappearance of salt is evidence that the change was reversible by a physical change, so it could not be a chemical change.
He is incorrect. Dissolving salt in water and

Answer 1

evaporating the water are both physical changes. The reappearance of solid salt is evidence that the change was reversible by a physical change. Therefore, no chemical change occurred in this investigation.

To summarize:

• He is correct. Dissolving salt in water is a physical change, but evaporating the water is a chemical change. (This statement is incorrect.)
• He is correct. Evaporation is a physical change, but dissolving salt in water is a chemical change. (This statement is incorrect.)
• He is incorrect. Dissolving salt in water and evaporation of the water are both physical changes. The reappearance of salt is evidence that the change was reversible by a physical change, so it could not be a chemical change. (This statement is correct.)
• He is incorrect. Dissolving salt in water and evaporating the water are both physical changes. The reappearance of solid salt is evidence that the change was reversible by a physical change. (This statement is also correct.)

In conclusion, Henry's conclusion about the occurrence of a chemical change is incorrect, as both dissolving salt in water and evaporating water are physical changes. The presence of solid salt after evaporation further supports the idea that these changes were physical and reversible.