What does heating condensation observation reliably indicate about water content in the solid?

• A. The solid is hydrated.
• B. The solid is anhydrous.
• C. The solid contains carbonate.
• D. The solid contains no water.

Answer: (A)

When a hydrated solid is heated, the water that is chemically bound as water of crystallization is released as vapour. This vapour may condense on a cooler part of the apparatus, forming droplets of liquid water. Seeing this condensation is a reliable sign that water was present in the solid’s crystal structure, so the solid is hydrated. If the solid were anhydrous, there wouldn’t be water released and condensation wouldn’t occur. A carbonate would release carbon dioxide rather than water, and a substance with no water would also not produce condensation. So the condensation observation specifically points to the solid containing water.