Crystals of copper sulfate are prepared by reacting copper oxide, a base, with dilute sulfuric acid - Edexcel - GCSE Chemistry Combined Science - Question 5 - 2023 - Paper 1

The student knows to stop adding copper oxide when the mixture remains pale blue, indicating that no more copper oxide can dissolve in the dilute sulfuric acid. This observation shows that all the sulfuric acid has reacted with the copper oxide, forming copper sulfate.

The best way to obtain crystals of copper sulfate from an aqueous solution is to heat the solution with a Bunsen burner until dry.

As crystals of copper sulfate are formed from the solution, the particles of the dissolved substance begin to arrange themselves into a structured lattice. Initially, the particles in solution are freely moving and randomly arranged. Once the water evaporates, the particles lose energy, slow down, and form a solid crystal lattice, where they are tightly packed and vibrate in fixed positions.

In copper oxide (CuO), copper is in the +2 oxidation state. During the reaction to form copper sulfate, it gains electrons and is reduced, moving to a lower oxidation state in CuSO₄.

To calculate the mass of copper sulfate dissolved in 0.300 dm³ of a solution with a concentration of 39.875 g dm⁻³, use the formula:

$\text{mass} = \text{concentration} \times \text{volume}$

Substituting the values:

$\text{mass} = 39.875 \, \text{g dm}^{-3} \times 0.300 \, \text{dm}^3 = 11.9625 \, \text{g}$

Therefore, the mass of copper sulfate is approximately 11.96 g.