Rusting and how to stop it Cambridge IGCSE Co-ordinated Sciences (Double Award) revision
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In plain words
Leave a bike out in the rain and it rusts. Rust is iron slowly reacting with the oxygen in air and with water: it needs both. Every way of stopping rust either keeps one of them away from the iron, or gives them something else to attack instead.
Three things to know
- Iron rusts only when both oxygen and water are present. Rust is hydrated iron(III) oxide.
- Barrier methods keep air and water out: paint, oil or grease, a plastic coating.
- Galvanising coats iron with zinc. Zinc is more reactive than iron, so it corrodes first and protects the iron even when the coating is scratched (sacrificial protection).
Tips and tricks
- Rusting needs oxygen and water. Experiments with boiled water (no dissolved air) or a drying agent (no water) show that one alone is not enough.
- Sacrificial protection works "because the zinc is more reactive, so it loses electrons in preference to the iron".
It lands in your notebook with its questions as flashcards.
Rusting and how to stop it: 5 questions and answers
These are the quiz’s questions. Do the quiz first, then come back here for the ones that got you.
Which two substances are needed for iron to rust?
Both must be present.
What is galvanising?
The zinc is a barrier and also protects sacrificially.
What does sacrificial protection use?
The more reactive metal corrodes instead of the iron.
In which test tube will an iron nail rust fastest?
Only this one has both water and oxygen.
How does oiling a bicycle chain prevent rust?
Oil is a barrier.
Quiz
5 questions
Tap an answer and you’ll see straight away whether it’s right, and why.
Worksheet
4 questions, 8 marks. Write your answers on paper, then check them.
Rusting and how to stop it
Cambridge IGCSE Co-ordinated Sciences (Double Award) 0654 · 8 marks · papermunch.org
Name ______________________________ Date ______________
Name the two substances that must be present for iron to rust.[2]
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Oxygen (air) and water.
Explain how painting an iron gate stops it rusting.[2]
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The paint is a barrier that keeps oxygen and water away from the iron.
Explain why a galvanised iron bucket does not rust even when the zinc coating is scratched.[3]
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Zinc is more reactive than iron, so the zinc corrodes (is oxidised) instead of the iron. This is sacrificial protection.
State the chemical name of rust.[1]
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Hydrated iron(III) oxide.
Answers: Rusting and how to stop it
- 1. Oxygen (air) and water.
- 2. The paint is a barrier that keeps oxygen and water away from the iron.
- 3. Zinc is more reactive than iron, so the zinc corrodes (is oxidised) instead of the iron. This is sacrificial protection.
- 4. Hydrated iron(III) oxide.