# Copper(II) sulfate solution is a deep blue colour. When excess zinc powder is added to copper(II) sulfate solution, the blue colour disappears and a reddish-brown solid forms. A student notices that the reaction happens much faster when the zinc is ground into a fine powder rather than used as large lumps. Explain why the reaction is faster when fine zinc powder is used, and describe the role of a catalyst as an alternative way to increase the rate of this reaction.

> OCR A-Level Chemistry B: Salters (H433) — 5.3 Transition elements · Explain · 5 marks

> Transition elements such as copper and zinc are common in laboratory reactions. Changing the physical form of a reactant or adding a catalyst are two ways to increase the rate of a chemical reaction.

## Mark scheme (5 marks)

1. Fine powder has a greater surface area (to volume ratio) than large lumps
2. More reacting particles are exposed / available to collide with the copper(II) sulfate solution
3. There are more frequent successful collisions (so the rate of reaction increases)
4. A catalyst increases the rate of reaction by providing a different reaction pathway with a lower activation energy
5. The catalyst is not used up during the reaction

## Key terms

- [catalyst](https://www.gradenine.co.uk/glossary/catalyst)

## Related

- [Revision notes for OCR A-Level Chemistry B: Salters (H433)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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