Without water, especially water of crystallization, the substance is described as what?

• A. Hydration
• B. Solubility
• C. Anhydrous
• D. Immiscible

Answer: (C)

The main idea here is water of crystallization and the distinction between hydrated and anhydrous forms. Some compounds incorporate water molecules into their crystal structure; when that water is removed, the substance is described as anhydrous. Anhydrous is the right term for a solid that has no water of crystallization remaining. For example, copper sulfate pentahydrate contains water in its lattice, but after heating it loses that water and becomes anhydrous copper sulfate, which is white instead of blue. Hydration would mean the substance is in a hydrated form or gaining water; solubility is about how well something dissolves in a solvent; immiscible describes liquids that do not mix. So without water of crystallization, the substance is anhydrous.