Corrosion and its prevention — AQA GCSE Chemistry
Test yourself on Corrosion and its prevention with AQA GCSE practice questions.
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Corrosion and its prevention explained
Corrosion is the breakdown of a material caused by chemical reactions with substances around it, such as oxygen, water or acids.
Read the full explanation
The material is destroyed because it is chemically changed into new substances. Rusting is the corrosion of iron and steel. It needs both oxygen and water, and it forms hydrated iron(III) oxide, which is the familiar orange-brown rust. The rust flakes away, exposing fresh iron, so the metal gradually weakens and is destroyed. Corrosion is not only about iron: copper reacts slowly with oxygen and water to form a green layer, and acid rain can corrode limestone and some metals. Understanding corrosion helps explain why prevention methods such as painting, oiling, galvanising or sacrificial protection are used.
Your focus
- Define corrosion as the destruction of materials by chemical reactions with substances in the environment.
- Describe rusting as an example of corrosion that requires oxygen and water.
- Give another example of corrosion and state the substance formed.
Corrosion and its prevention exam tips
Marking Points
- Corrosion is the destruction of a material by chemical reactions with substances in the environment.
- The material is chemically changed into new substances, so corrosion is a chemical process, not just physical wear.
- Rusting is the corrosion of iron and steel and is one example of corrosion.
- Rusting requires both oxygen and water, and produces hydrated iron(III) oxide.
- Other examples include the green layer on copper and the action of acid rain on limestone or metals.
- Corrosion weakens a material because the new substance does not have the same useful properties as the original material.
Examiner Tips
- 💡Define corrosion in terms of chemical reactions with substances in the environment.
- 💡When explaining rusting, name both reactants, oxygen and water, and name the product, hydrated iron(III) oxide.
- 💡Use a second example, such as copper or acid rain on limestone, to show that rusting is only one type of corrosion.
Common Mistakes
- Saying rusting needs only water or only oxygen. Correction: rusting requires both oxygen and water.
- Writing that rust is iron oxide without the water of crystallisation. Correction: rust is hydrated iron(III) oxide.
- Treating corrosion as physical wear such as scratching. Correction: corrosion is a chemical reaction that forms new substances.