8 Crystals of copper sulfate are prepared by reacting copper oxide, a base, with dilute sulfuric acid - Edexcel - GCSE Chemistry - Question 8 - 2023 - Paper 1

The student knows to stop adding copper oxide when:

1. Observation of Color Change: Initially, the mixture is pale blue due to the presence of dissolved copper sulfate. When copper oxide is added, it causes the solution to become darker blue. If more copper oxide is added and the mixture remains pale blue, it indicates that no more copper sulfate can be formed.

2. Excess Copper Oxide: There will be visible excess of copper oxide that does not dissolve in the solution. The student can observe that the black powder of copper oxide remains after the reaction is complete.

3. Neutralization: The student can also infer that all the sulfuric acid has reacted with copper oxide when no further bubbling or fizzing occurs, indicating that the acid has been neutralized.

The best way to obtain crystals of copper sulfate from an aqueous solution is:

A) Pour the solution through filter paper in a funnel.

This method allows for the removal of any unreacted solids, resulting in a clear solution which can then be evaporated to obtain crystals.