A Level Chemistry OCR Practice Exam

Which process would remove water of crystallisation from a hydrated salt?

1. Condensation

2. Precipitation

3. Dehydration

4. Crystallization

The correct answer is: Dehydration

Dehydration is the process that effectively removes water of crystallisation from a hydrated salt. Hydrated salts contain water molecules integrated into their crystal structure, and dehydration involves heating the salt to evaporate this water. This process alters the physical and chemical properties of the salt, transforming it into an anhydrous form. In contrast, condensation refers to the process where gas turns into liquid, which does not relate to the removal of water from a salt. Precipitation is a reaction that leads to the formation of a solid from a solution, which can involve the involvement of water, but it does not inherently mean the removal of water from a hydrated salt. Crystallization is the formation of solid crystals from a solution, including the potential introduction of water molecules into the structure rather than their removal. Thus, dehydration is the specific and effective method of eliminating water of crystallisation from a hydrated salt, leading to the formation of an anhydrous substance.