International General Certificate of Secondary Education (IGCSE) Chemistry Practice Exam

What method is used to obtain solid copper sulfate from an aqueous solution?

1. Filtration

2. Crystallisation

3. Dissolving

4. Simple distillation

The correct answer is: Crystallisation

To obtain solid copper sulfate from an aqueous solution, crystallisation is the appropriate method. This process involves the evaporation of some of the water in the solution, which allows the copper sulfate to form solid crystals as it becomes supersaturated. During crystallisation, when the solution reaches a point of saturation, copper sulfate molecules begin to aggregate and form solid crystals. This method is effective for separating solutes from solvents, as it exploits the difference in solubility at different temperatures. Once crystals are formed, they can be filtered out of the remaining liquid for purification. In comparison, filtration would separate solids from liquids but is not suitable for recovering dissolved substances like copper sulfate in its crystalline form. Dissolving, on the other hand, refers to the process of a solute entering a solution, not a method for crystal recovery. Lastly, simple distillation is primarily used for separating components of a liquid mixture based on differences in boiling points rather than for recovering solids from solutions. Thus, crystallisation is distinctly the method used to obtain solid copper sulfate from an aqueous solution, as it effectively allows for the transformation of dissolved copper sulfate back into its solid state.