9.5.2 — Barrier Methods of Rust Prevention
Cambridge IGCSE Chemistry (0620) · Topic 9: Metals
Visual Reference — Barrier Methods
Section A — Methods of Barrier Protection
5 questions · 12 marks
State three barrier methods used to prevent iron from rusting.
State two methods used to protect iron car bodies from rusting.
Name the process in which iron is coated with a layer of zinc to prevent rusting. State one other barrier method that also uses a metal coating.
Identify THREE barrier methods suitable for protecting an iron garden gate. For each method, name the barrier substance used.
State two barrier methods used to prevent rusting of iron food cans. Explain why these are preferred over painting for food storage.
Section B — How Barrier Methods Work
5 questions · 12 marks
Describe how painting prevents the rusting of an iron bridge.
Explain how applying a layer of grease prevents iron machinery from rusting. Include a description of what happens at the surface of the iron.
A student coats an iron nail with plastic by dip-coating. Explain how this plastic coating prevents the nail from rusting.
A steel bridge is regularly repainted. Explain: (a) why the bridge must be repainted, and (b) why a chipped area of paint leads to rapid rusting even though most of the surface is still painted.
Electroplating iron with chromium is used to protect some metal surfaces. Explain how this method prevents rusting.
Section C — Choosing the Right Method
5 questions · 13 marks
Why is oiling used to protect a bicycle chain instead of painting?
A manufacturer needs to protect iron pipes used for underground water supply. Suggest the most appropriate barrier method and explain why it is chosen over alternatives such as painting or oiling.
Tin cans used for food storage are made from iron coated with tin, not iron coated with paint. Suggest two reasons why tin plating is preferred over painting for this use.
A coastal lighthouse is made of iron. The engineering team is deciding between painting and galvanising as barrier methods. Evaluate both methods for this specific environment, and recommend which is more suitable.
A student states: 'Any barrier method will prevent rusting as long as it covers the iron surface completely.' Evaluate this statement. Suggest one limitation that applies to ALL barrier methods.
🎯 Top 3 Examiner Traps — Barrier Methods
- Trap 1: Writing "keeps oxygen away" — always state BOTH oxygen AND water are excluded.
- Trap 2: Saying galvanising is "just a barrier" — zinc also provides sacrificial/cathodic protection if scratched.
- Trap 3: Recommending paint for all situations — always consider the environment (moving parts, food contact, underground, coastal) before choosing.
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