A student is assessing the purity of a sample of copper(ii) sulfate solution by adding a small amount to a sample of water. They record the temperature of the water before and after the addition. Explain how the student can use the data to determine the purity of the copper(ii) sulfate solution.

The student measures the temperature rise (ΔT) of the water after adding the CuSO₄ solution. The heat absorbed by the water is calculated using q = m·c·ΔT (m = mass of water, c = specific heat of water). This heat equals the heat released by the dissolution of CuSO₄, which is proportional to the amount of CuSO₄ dissolved. By comparing the calculated heat to the theoretical heat of dissolution for a known mass of pure CuSO₄, the student can calculate the mass of CuSO₄ actually present and thus the purity.

The purity is affected by the presence of impurities that do not dissolve or that dissolve but release a different amount of heat, altering the measured ΔT.

The temperature change is also influenced by the heat capacity of the calorimeter and any heat loss to the surroundings, which must be minimised or corrected for accurate purity determination.