# A farmer stores iron machinery outdoors. Some machinery is painted and some is left unpainted. Explain why painting iron machinery slows down rusting, and state what would happen to the rate of rusting if the paint became scratched.

> Cambridge International IGCSE Chemistry (0620) — 9.5 Corrosion of metals · Explain · 4 marks

## Mark scheme (4 marks)

1. Paint acts as a barrier / prevents contact between the iron and water (and oxygen/air)
2. Both water and oxygen are required for rusting, so excluding either prevents rusting
3. If the paint is scratched, the iron beneath is exposed (to water and oxygen)
4. The rate of rusting increases (at the scratched area) / rusting occurs at the exposed iron

## Key terms

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

## Related

- [Revision notes for Cambridge International IGCSE Chemistry (0620)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/a-farmer-stores-iron-machinery-outdoors-4b650f58) · Published by Druglandscape Ltd.