# A ship's hull is made of steel. Blocks of magnesium are bolted to the outside of the hull below the waterline to prevent the steel from corroding. Explain why attaching magnesium blocks protects the steel hull from corrosion.

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

## Mark scheme (4 marks)

1. Magnesium is more reactive than iron/steel
2. Magnesium acts as a sacrificial metal / sacrificial anode
3. Magnesium corrodes/oxidises preferentially instead of the steel
4. The steel is protected even if the magnesium block is not in direct contact with all areas of the hull / protection continues until the magnesium is used up

## Key terms

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

## 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-ship-s-hull-is-made-of-6259aba8) · Published by Druglandscape Ltd.