A Level Chemistry OCR Practice Exam

Which of the following statements is true regarding water of crystallisation?

1. It is always present in liquid solutions.

2. It can be removed without altering the chemical identity of the compound.

3. It only exists in organic compounds.

4. It contributes to the stability and structure of crystalline solids.

The correct answer is: It contributes to the stability and structure of crystalline solids.

Water of crystallisation refers to the water molecules that are incorporated into the crystalline structure of certain compounds, often salts. This water is integral to maintaining the stability and structural integrity of these crystalline solids. The presence of water of crystallisation can influence various physical properties, including the melting point and solubility of the compound. In some compounds, the water molecules contribute to the lattice structure, creating a more stable arrangement of ions or molecules. When water of crystallisation is part of a compound, it can affect the way that the compound behaves in terms of its reactivity and how it interacts with other substances, making it a crucial aspect of the solid's properties. The other statements do not accurately reflect the role or nature of water of crystallisation. For instance, it may not always exist in a liquid solution, as it's typically associated with solid crystalline forms. Additionally, while water of crystallisation can be removed through processes such as heating, this can lead to changes in the properties of the compound, and it doesn’t indicate that the chemical identity remains unchanged. Water of crystallisation is predominantly found in inorganic compounds rather than being confined to organic ones. Therefore, the role of water of crystallisation in contributing to the stability and structure of crystalline solids is key