Corrosion
Cambridge IGCSE Chemistry (0620) · Unit 9: Metals · 10 flashcards
Corrosion is topic 9.5 in the Cambridge IGCSE Chemistry (0620) syllabus , positioned in Unit 9 — Metals , alongside Properties of metals, Reactivity series and Extraction of metals. In one line: The rusting of iron and steel requires the presence of both water (H₂O) and oxygen (O₂). Rust is hydrated iron(III) oxide (Fe₂O₃.xH₂O).
This topic is examined in Paper 1 (multiple-choice) and Papers 3/4 (theory), plus Paper 5 or Paper 6 (practical / alternative to practical). Past papers from 2022 to 2025 show this topic across undefined questions worth 71 marks (around 1.1% of all Chemistry marks in those years).
The deck below contains 10 flashcards — 3 definitions and 7 key concepts — covering the precise wording mark schemes reward. Use the 3 definition cards to lock down command-word answers (define, state), then move on to the concept and application cards to handle explain, describe and compare questions.
The conditions required for the rusting of iron and steel
The rusting of iron and steel requires the presence of both water (H₂O) and oxygen (O₂). Rust is hydrated iron(III) oxide (Fe₂O₃.xH₂O).
What the Cambridge 0620 syllabus says
2026-2028 syllabus, in our wordsWhat the syllabus expects you to be able to do in this topic, in plain English. Match the command word (Describe, Explain, State, etc.) in your answer to score full marks. For the exact wording, see the official syllabus (PDF).
- State State the conditions needed for iron and steel to rust, forming hydrated iron(III) oxide.
- State State some everyday barrier methods, including plastic coating, greasing and painting.
- Describe Describe how a barrier method stops rusting by keeping oxygen or water away from the metal.
- Describe Describe how zinc is used in galvanising, which works as a barrier method and also by sacrificial protection. Supplement
- Explain Explain sacrificial protection using the reactivity series and the idea of losing electrons. Supplement
What are the conditions required for the rusting of iron and steel?
The rusting of iron and steel requires the presence of both water (H₂O) and oxygen (O₂). Rust is hydrated iron(III) oxide (Fe₂O₃.xH₂O).
What is a barrier method of preventing rust?
Barrier methods prevent rust by creating a physical barrier between the iron/steel and the oxygen or water in the environment. Examples include painting, greasing, and coating with plastic.
How does painting prevent rusting?
Painting prevents rusting by creating an impermeable barrier that excludes oxygen and water from contacting the iron or steel surface. This stops the redox reaction that forms rust.
How does greasing prevent rusting?
Greasing prevents rusting by forming a water-repellent layer that excludes water and oxygen from contacting the iron or steel. This prevents the electrochemical process of rusting.
How does coating with plastic prevent rusting?
Coating with plastic provides a non-porous barrier that prevents oxygen and water from reaching the iron or steel surface, thus stopping the formation of rust.
What is galvanising?
Galvanising is a method of rust prevention that involves coating iron or steel with zinc. Zinc acts as both a barrier and provides sacrificial protection.
How does zinc act as a barrier in galvanising?
Zinc acts as a barrier by physically preventing water and oxygen from reaching the iron or steel surface. This is similar to painting.
Explain sacrificial protection in terms of the reactivity series.
A more reactive metal will corrode in preference to a less reactive metal. Zinc is more reactive than iron, so in galvanising, the zinc corrodes instead of the iron, sacrificing itself to protect the iron.
Explain sacrificial protection in terms of electron loss.
Sacrificial protection works because the more reactive metal (
Give an example of sacrificial protection other than galvanising
Attaching blocks of magnesium to the hull of a ship. Magnesium is more reactive than iron so it corrodes instead of the ship's hull.
Key Questions: Corrosion
What are the conditions required for the rusting of iron and steel?
The rusting of iron and steel requires the presence of both water (H₂O) and oxygen (O₂). Rust is hydrated iron(III) oxide (Fe₂O₃.xH₂O).
What is a barrier method of preventing rust?
Barrier methods prevent rust by creating a physical barrier between the iron/steel and the oxygen or water in the environment. Examples include painting, greasing, and coating with plastic.
What is galvanising?
Galvanising is a method of rust prevention that involves coating iron or steel with zinc. Zinc acts as both a barrier and provides sacrificial protection.
More topics in Unit 9 — Metals
Corrosion sits alongside these Chemistry decks in the same syllabus unit. Each uses the same spaced-repetition system, so progress in one informs the next.
Cambridge syllabus keywords to use in your answers
These are the official Cambridge 0620 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.
Key terms covered in this Corrosion deck
Every term below is defined in the flashcards above. Use the list as a quick recall test before your exam — if you can't define one of these in your own words, flip back to that card.
Related Chemistry guides
Long-read articles that go beyond the deck — cover the whole subject's common mistakes, high-yield content and revision pacing.
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