Who this is for: Cambridge IGCSE Chemistry (0620) students who want corrosion of metals — rusting, conditions and prevention — to become structured explain answers instead of a vague list of “coatings”.
What query it owns: how to understand and revise corrosion of metals in Cambridge IGCSE Chemistry.
Why this is safe: this page owns the corrosion of metals revision-guide angle, while Tutopiya’s [Corrosion Of Metals (New) subtopic page](https://www.tutopiya.com/learning-portal/resource/cambridge-igcse/chemistry/extended/0620/metals/640778fc23df261b5e7495d6/corrosion-of-metals-(new) owns the learning resource.

Corrosion of metals is a high-frequency topic in the Metals unit of Cambridge IGCSE Chemistry (0620). Examiners expect you to describe rusting of iron, state the conditions required (water and oxygen), and explain prevention methods including painting, oiling, galvanising and sacrificial protection. This guide organises each method with the chemistry behind it and the question types that appear every year.

Key takeaways

• Rusting is the corrosion of iron — a slow reaction forming hydrated iron(III) oxide.
• Rusting requires both water and oxygen — removing either prevents rust.
• Galvanising coats iron with zinc; zinc corrodes preferentially because it is more reactive.
• Sacrificial protection uses a more reactive metal (e.g. zinc or magnesium blocks) attached to iron.
• Alloys such as stainless steel resist corrosion because chromium forms a protective oxide layer.

What is corrosion of metals in Cambridge IGCSE Chemistry?

Corrosion is the gradual destruction of a metal by chemical reaction with its environment. At IGCSE level the focus is rusting of iron and methods to prevent it. You must describe conditions for rusting, explain why each prevention method works, and link sacrificial protection to the reactivity series.

Read the full notes on Tutopiya’s [Corrosion Of Metals (New) subtopic page](https://www.tutopiya.com/learning-portal/resource/cambridge-igcse/chemistry/extended/0620/metals/640778fc23df261b5e7495d6/corrosion-of-metals-(new) before attempting questions.

The core ideas you must master

Idea	What it means	How the exam uses it
Rusting	Corrosion of iron to hydrated iron(III) oxide	”Describe rusting of iron.”
Conditions	Water and oxygen both required	”State the conditions needed for rusting.”
Barrier methods	Paint, oil, plastic coating block air/water	”Explain how painting prevents rust.”
Galvanising	Zinc coating — zinc corrodes first	”Explain why galvanised iron does not rust easily.”
Sacrificial protection	More reactive metal corrodes instead of iron	”Explain sacrificial protection using zinc blocks.”

How to explain corrosion prevention — step by step

1. State what rusting needs — water and oxygen.
2. Name the prevention method — barrier, galvanising or sacrificial protection.
3. Explain the mechanism — blocks contact, or more reactive metal corrodes first.
4. Link to reactivity series for sacrificial protection — zinc/magnesium above iron.
5. Give a real-world example — ship hulls, car bodies, buried pipelines.

Once you have worked through a few, revisit the [Corrosion Of Metals (New) subtopic page](https://www.tutopiya.com/learning-portal/resource/cambridge-igcse/chemistry/extended/0620/metals/640778fc23df261b5e7495d6/corrosion-of-metals-(new) to confirm your explain answers match the mark scheme.

Barrier vs sacrificial vs alloy: which method does the question want?

Method	How it works	Typical signal words
Paint / oil / grease	Physical barrier — no water or oxygen reaches iron	”painted”, “oiled”, “coated”
Galvanising	Zinc layer corrodes preferentially	”galvanised”, “zinc coating”
Sacrificial protection	Blocks of Zn or Mg corrode instead of iron	”sacrificial”, “magnesium blocks on ship”
Stainless steel alloy	Chromium forms protective oxide layer	”alloy”, “stainless steel”

Corrosion in past-paper wording: command words that matter

Command word / phrase	What the question wants	Typical corrosion stem
Describe	What rusting is or what happens	”Describe the rusting of iron.”
State	Named conditions or method	”State two conditions needed for rusting.”
Explain	Why a prevention method works	”Explain how galvanising prevents rusting.”
Suggest	Appropriate prevention for a scenario	”Suggest how to protect an iron gate outdoors.”
Compare	Two methods or coated vs uncoated	”Compare painting and galvanising.”

Worked exam-style stems (how to answer the wording)

1. “State the two conditions needed for iron to rust.” Water and oxygen (air). Mark-scheme reward: both named.
2. “Explain how sacrificial protection prevents iron from rusting.” A more reactive metal (e.g. zinc or magnesium) is attached to the iron. It corrodes preferentially (oxidises) instead of the iron because it is higher in the reactivity series. Reward: more reactive + corrodes first + protects iron.
3. “Explain why a galvanised iron bucket does not rust when the zinc coating is intact.” The zinc coating acts as a barrier to water and oxygen. If scratched, zinc still corrodes before iron because it is more reactive. Reward: barrier + sacrificial role of zinc.

When you can recognise the wording instantly, work through the Metals topical past paper questions and Reactivity Series to lock the explanations in.

How corrosion connects to the rest of the Metals unit

Corrosion links directly to Reactivity Series (sacrificial protection), Uses Of Metals (alloys like stainless steel) and Properties Of Metals. The Cambridge IGCSE Chemistry resource hub links every Metals subtopic.

Common mistakes students make

• Stating only water or only oxygen as the condition for rusting — both are required.
• Describing galvanising as “stopping rust” without explaining zinc corrodes first.
• Confusing barrier methods with sacrificial protection.
• Saying aluminium “rusts” — aluminium forms a protective oxide layer, not rust.
• Forgetting that once sacrificial metal is used up, iron can rust again.

When you need more support

If corrosion explain questions keep losing marks — especially sacrificial protection — work through the Metals topical past paper questions and Reactivity Series quiz, then get focused help from a Cambridge IGCSE Chemistry tutor.

Frequently asked questions

What conditions are needed for iron to rust? Both water and oxygen (from air) must be present. Removing either condition prevents rusting.

What is the difference between galvanising and sacrificial protection? Galvanising coats iron with zinc. Sacrificial protection attaches blocks of a more reactive metal. Both rely on zinc (or magnesium) corroding before iron.

Why does stainless steel not rust easily? It is an alloy containing chromium, which forms a thin, protective oxide layer that prevents further corrosion.

How do I revise corrosion of metals effectively? Learn conditions for rusting, practise three explain answers (paint, galvanise, sacrificial), then work Metals topical past paper questions.

Ready to master Cambridge IGCSE Chemistry corrosion of metals?

Start with the [Corrosion Of Metals (New) subtopic page](https://www.tutopiya.com/learning-portal/resource/cambridge-igcse/chemistry/extended/0620/metals/640778fc23df261b5e7495d6/corrosion-of-metals-(new), then book a free trial with a Cambridge IGCSE Chemistry specialist to turn corrosion into guaranteed marks.

Ready to Excel in Your Studies?

Get personalised help from Tutopiya's expert tutors. Whether it's IGCSE, IB, A-Levels, or any other curriculum — we match you with the perfect tutor and your first session is free.

Book Your Free Trial