GCSE-readyCorrosion, sacrificial protection and electroplating
Corrosion is the slow oxidation of a metal. We can protect metals with barriers or more reactive metals, and coat them by electroplating.
Corrosion is oxidation
Rusting is the corrosion of iron. It needs both oxygen and water: iron + oxygen + water → hydrated iron(III) oxide (rust).
Preventing corrosion
Galvanising: coating iron with zinc. The zinc is a barrier, and if scratched it still protects the iron.
Sacrificial protection: attaching a more reactive metal such as magnesium or zinc. It is oxidised (corrodes) instead of the iron, because it loses electrons more easily. Ships' hulls and pipelines use blocks of magnesium or zinc.
Electroplating
The object to be plated is the cathode (−). The anode is made of the plating metal. The electrolyte contains ions of the plating metal.
Example: silver plating a spoon uses a silver anode and a solution of a silver salt. Silver ions gain electrons at the spoon: Ag+ + e− → Ag.
Uses: to improve appearance (silver, gold) and to resist corrosion (chromium on steel, tin on food cans).
A student wants to copper-plate an iron key. Describe the set-up.
- The key must be where metal ions gain electrons: the cathode.
- The anode should be copper, which dissolves to replace the ions.
- The electrolyte must contain copper ions, for example copper sulfate solution.
Answer: Key as the cathode, copper as the anode, copper sulfate solution as the electrolyte.
Corrosion is oxidation; rusting needs oxygen and water. Barriers, galvanising and sacrificial protection with a more reactive metal stop rusting. Electroplating makes the object the cathode, uses an anode of the plating metal and an electrolyte containing its ions.
- Corrosion
- The gradual destruction of a metal by reaction with substances around it, such as oxygen and water. Rusting is the corrosion of iron.
- Oxidation
- Gain of oxygen, or loss of electrons.
- Cathode
- The negative electrode in electrolysis. Cations gain electrons there (reduction).
- Anode
- The positive electrode in electrolysis. Anions lose electrons there (oxidation).
- Electrolyte
- An ionic compound that is molten or dissolved, so its ions can move and carry a current.
- Hydrated
- Containing water of crystallisation, for example blue hydrated copper(II) sulfate, CuSO_{4}·5H_{2}O.
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Rusting needs which two substances?
- Oxygen and carbon dioxide
- Water and nitrogen
- Salt and nitrogen
- Oxygen and water
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Answer: Oxygen and water
Iron reacts with oxygen and water to form rust.
Zinc blocks are attached to steel pipes. Why does this stop the steel rusting?
- Zinc turns the steel into stainless steel
- Zinc is more reactive, so it is oxidised instead of the iron
- Zinc is less reactive than iron
- Zinc keeps water out completely
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Answer: Zinc is more reactive, so it is oxidised instead of the iron
This is sacrificial protection.
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Checked by the GCSE-ready editorial team, 17 October 2026. Last updated 2 October 2026. Spotted a mistake? Tell us and we will fix it.
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