Case study·Standard multi-step (3/5)·No calculator
Difficulty guide
The label describes the problem, not your ability.
1/5 - Foundational
Warm-up setup; checks one basic idea.
2/5 - Routine exam skill
Normal syllabus skill; usually one main rule or interpretation.
3/5 - Standard multi-step
Exam-style problem with multiple steps or a common trap.
4/5 - Hard exam skill
High-end exam problem; combines methods carefully.
5/5 - Challenge
Stretch problem beyond normal exam pressure.
Question
A painted iron gate develops a scratch. After rainwater remains on the scratched region, rusting begins near the exposed iron. Zinc coating on another gate continues to protect iron even when a small scratch appears.
Total: 4 marks
(a) Write the anodic reaction for rusting of iron. (1 mark)
(b) Write the cathodic oxygen-reduction reaction in neutral medium. (1 mark)
(c) Explain why zinc coating protects scratched iron better than ordinary paint. (1 mark)
(d) Name the protection principle involved in zinc coating. (1 mark)
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