Corrosion

Key Stage 3

Meaning

Rusting is a form of corrosion.

Corrosion is when a material is worn down by chemical reactions with substances in the environment.

About Corrosion

Rusting is a form of corrosion.

Acid rain causes the corrosion of limestone and marble buildings and statues.

Key Stage 4

Meaning

Corrosion is when a material is worn down by chemical reactions with substances in the environment.

About Corrosion

Corrosion is commonly caused by Water, Oxygen and Acids in the environment.

Metals and stone (such as limestone, marble and chalk) are the most commonly corroded materials.

More reactive metals are more easily corroded.

Examples

The corrosion of Iron forms brown Iron Oxide, known as rust. Rusting happens more quickly in humid air or in salty water.	The corrosion of Copper forms green Copper Carbonate. Initially the Copper is Oxidised to form Copper Oxide, a black solid, but then reacts with Carbonic Acid to form Copper Carbonate.	This statue is made of Limestone which is mostly Calcium Carbonate. It is corroded by Acid Rain to form soluble salts which wash away.

Preventing and Reducing Corrosion

Corrosion can be prevented by making a physical barrier between the object and the chemicals in the environment. This can be done by painting, covering something in grease or by electroplating.

This Iron pipe was painted to prevent corrosion, but where the paint has chipped away, the Iron has rusted.	Electroplating can cover a reactive metal with a less reactive metal such as Copper create a physical barrier between the object and the environment.	Grease is used on bike chains to prevent corrosion. Paint and electroplating cannot be used because they would chip away from constant movement of the chain.

Corrosion of a metal object can also be prevented using a Sacrificial Anode which is a metal more reactive metal placed in electrical contact with the object. This prevents Oxidation of the object because the more reactive metal has a greater tendency to form positive ions causing it to oxidise instead of the object.

A Sacrificial Anode made of Zinc has been attached to the Iron hull of a boat.

References

AQA

Corrosion, page 338-9, GCSE Chemistry; Student Book, Collins, AQA

Corrosion, page 98, GCSE Chemistry; The Revision Guide, CGP, AQA

Corrosion, pages 220-221, GCSE Chemistry; Third Edition, Oxford University Press, AQA

Corrosion, pages 258-9, GCSE Chemistry, Hodder, AQA

Corrosion, pages 287, 288, GCSE Chemistry, CGP, AQA

Corrosion; prevention of, pages 259-60, GCSE Chemistry, Hodder, AQA

Edexcel

Corrosion, page 235, GCSE Combined Science, Pearson Edexcel

Corrosion, page 64, GCSE Chemistry; The Revision Guide, CGP, Edexcel

Corrosion, pages 181-183, GCSE Chemistry, CGP, Edexcel

Corrosion, pages 91, 98-99, GCSE Chemistry, Pearson, Edexcel