A Level Chemistry OCR Practice Exam

What would you call a compound that has lost its water of crystallisation?

1. Hydrated compound

2. Anhydrous compound

3. Suspension

4. Aqueous compound

The correct answer is: Anhydrous compound

A compound that has lost its water of crystallisation is referred to as an anhydrous compound. When a hydrated compound, which contains water molecules integrated into its crystal structure, loses this water, it transitions to an anhydrous form. This process typically occurs when the compound is heated or exposed to conditions that promote the loss of water, resulting in a substance that no longer contains the water molecules that were part of its solid framework. This term is fundamentally linked to the concept of hydration in chemistry, where certain salts and other compounds can exist in forms that are either hydrated or anhydrous. Understanding this distinction is critical when studying properties such as solubility, reactivity, and phase changes in the context of solutions and solid-state chemistry.