A Level Chemistry OCR Practice Exam 2026 - Free Chemistry Practice Questions and Study Guide

The compound that contains water of crystallisation is CuSO4·5H2O. This notation indicates that for every molecule of copper(II) sulfate (CuSO4), there are five molecules of water (H2O) integrated into its crystalline structure. This incorporation of water molecules into the crystal lattice is called water of crystallisation, and it plays a significant role in the physical properties of the compound, such as its color and solubility.

In contrast, sodium chloride (NaCl) is an inorganic ionic compound that does not include water in its crystalline structure, rather forming a simple ionic lattice. Glucose (C6H12O6) is a simple sugar that does not contain any water of crystallisation; it exists as a solid but does not have water molecules integrated into its structure. Ethanol (C2H5OH), being an alcohol, is a liquid and does not crystallize with water as part of its structure. Therefore, CuSO4·5H2O is the only compound among the options that explicitly includes water of crystallisation in its formula.