A student investigated the temperature change when zinc reacts with copper sulfate solution - AQA - GCSE Chemistry - Question 2 - 2015 - Paper 2

One improvement the student could make to the apparatus is to use a plastic or polystyrene cup or add a lid. This improves the investigation by reducing heat loss to the environment, thereby making the temperature readings more accurate.

The results show a positive correlation between the concentration of copper sulfate and the increase in temperature. As the concentration of copper sulfate increases from 0.1 moles per dm³ to 0.5 moles per dm³, the temperature change also increases from 5 °C to 25 °C. However, beyond a concentration of 0.5 moles per dm³, the temperature change levels off, with no further increase observed.

This trend suggests that the reaction between zinc and copper sulfate is exothermic and that as more copper sulfate reacts, more heat energy is released. Once the concentration of copper sulfate exceeds a certain level, such as at 0.8 moles per dm³, there is sufficient copper sulfate in the solution, and any additional zinc does not significantly increase the temperature change, indicating that the reaction has reached completion.