# A student notices that a piece of iron left outside in the rain develops a reddish-brown coating. Explain why iron rusts and describe two ways in which rusting can be prevented.

> Edexcel A-Level Chemistry (9CH0) — Topic 4 Physical chemistry and transition elements · Explain · 5 marks

> Iron is a transition metal widely used in construction and engineering. Rusting is an example of a chemical reaction that causes significant economic damage each year.

## Mark scheme (5 marks)

1. Rusting requires both oxygen (from air) and water to be present
2. The product formed is iron(III) oxide / hydrated iron(III) oxide (rust)
3. First named prevention method (e.g. painting, oiling/greasing, plastic coating, galvanising, sacrificial anode)
4. Correct explanation of how first method prevents rusting — prevents oxygen and/or water reaching the iron surface
5. Second named prevention method that is different from the first, with a correct explanation or statement that it creates a barrier / protects iron

## Key terms

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

## Related

- [Revision notes for Edexcel A-Level Chemistry (9CH0)](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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Source: [GradeNine](https://www.gradenine.co.uk/q/a-student-notices-that-a-piece-777cd85f) · Published by Druglandscape Ltd.