Observing condensation in the first row of heating tests indicates what about the solid?

• A. The solid is hydrated.
• B. The solid is anhydrous.
• C. The solid has decomposed.
• D. The solid is volatile.

Answer: (A)

The main idea is dehydration of a hydrated solid. When a hydrated compound is heated, its water of crystallization is driven off as steam. That water vapor then condenses on the cooler parts of the apparatus, so you see condensation forming early in the heating. Seeing this condensation means the solid originally contained water in its crystal structure, i.e., it was hydrated. If the substance were anhydrous, there would be little or no water to condense; if it had decomposed, you’d expect new products or gases rather than plain water vapor condensing; and if it were simply volatile, it would tend to vaporize rather than release water.