# Explain why iron rusts more quickly when it is in contact with salt water compared with pure water.

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

## Mark scheme (4 marks)

1. Rusting requires both oxygen (from air) and water
2. Salt water acts as an electrolyte / conducts electricity / allows ions to move
3. This speeds up the electrochemical / oxidation process that causes rusting
4. Pure water is a poor conductor / has very few ions, so rusting is slower

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