When a hydrated solid is heated to remove water of crystallization, what is the likely outcome?

• A. The solid becomes anhydrous.
• B. The solid forms a new compound with the water.
• C. The solid melts but does not lose water.
• D. The solid sublimes.

Answer: (A)

Hydration means water is built into the crystal structure of the compound. When you heat it, energy breaks the bonds holding that water in place, so the water leaves the solid as steam and you’re left with the substance in its non-water-containing, anhydrous form. That’s why the likely outcome is anhydrous solid. The idea of forming a new water-containing compound isn’t how dehydration works here, and subliming isn’t the typical path for removing water from hydrated salts. Some hydrates may melt during heating, but the defining result of heating is loss of water to give the anhydrous salt.