A Level Chemistry OCR Practice Exam

What term describes a crystalline substance that includes water molecules?

1. Hydrated

2. Hydrocarbon

3. Hydrolysis

4. Ionic

The correct answer is: Hydrated

The term that describes a crystalline substance including water molecules is "hydrated." In chemistry, hydration refers to the process of water molecules being incorporated into a crystal lattice structure. Hydrated compounds, often referred to as hydrates, have a specific number of water molecules associated with them, which can affect their physical properties, such as color and solubility. The concept of hydrates is particularly important in various fields, such as materials science and biochemistry, where understanding how water interacts with substances can lead to insights about their behavior and stability. For example, a common hydrate is copper(II) sulfate pentahydrate (CuSO4·5H2O), which contains five water molecules for each formula unit of copper(II) sulfate. The other terms do not pertain to the inclusion of water molecules in crystalline substances. "Hydrocarbon" refers to organic compounds consisting solely of hydrogen and carbon, "hydrolysis" involves a chemical reaction with water that breaks bonds in a compound, and "ionic" describes a type of chemical bond rather than a specific substance containing water. Thus, "hydrated" is the appropriate choice because it specifically identifies materials that contain water molecules in their crystalline form.