Calculate the percentage yield of copper (II) sulphate crystals. Actual yield = 4.2 g.

The actual yield of copper (II) sulphate crystals obtained by the student is given.

To calculate the percentage yield, we use the formula:

The theoretical yield of copper (II) sulphate is required to complete this calculation. The theoretical yield is the maximum amount of product that can be formed from the given amounts of reactants, based on stoichiometry. This value is typically calculated from previous parts of the question (e.g., parts a or b) which would provide information about the initial reactants. Since this information is not provided in the current question part (c), the theoretical yield cannot be determined.

Once the theoretical yield is known, substitute both the actual yield and the theoretical yield into the formula to find the percentage yield.

For example, if the theoretical yield were, say, 5.0 g, the calculation would be:

Since the theoretical yield is not provided, a numerical answer for the percentage yield cannot be given.