Q1. [3] deep thorough-understanding
Zinc is used to coat iron articles to protect them from rusting (galvanisation). Even if the zinc coating gets scratched or broken, the iron underneath still does not rust immediately. Using your knowledge of the reactivity series, explain why this is so.
Generated by claude-sonnet-4-6 · 2026-06-26 01:06 · grounding rag
Model Answer
Zinc is more reactive than iron in the reactivity series. When the zinc coating is scratched, both zinc and iron are exposed to moisture and air. Since zinc is more reactive, it preferentially reacts with oxygen and moisture instead of iron. Zinc acts as a sacrificial metal, corroding itself while protecting the iron beneath. Thus, iron does not rust until all the zinc in the surrounding area is consumed.
Source: Chapter 3, Section 3.5.1 – Prevention of Corrosion
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Explanation
- The key concept examiners want is reactivity series: zinc is higher (more reactive) than iron.
- The term sacrificial protection (or sacrificial metal) is expected — it often fetches a dedicated mark.
- Avoid just saying "zinc coats iron"; the question specifically asks about what happens after the coating breaks, so you must explain the electrochemical/reactivity reasoning.
- Three marks map to roughly three points: (1) zinc is more reactive than iron, (2) zinc reacts preferentially with oxygen/moisture, (3) iron is thus protected until zinc is fully consumed.