Q1. [5] deep thorough-understanding
Rancidity and corrosion are both consequences of oxidation reactions in daily life. Compare the two phenomena under the following heads: (i) the materials affected, (ii) the chemical process involved, (iii) one method used to prevent each. Use information from the chapter to support your answer.
Generated by claude-sonnet-4-6 · 2026-06-07 16:44 · grounding rag
Model Answer
Comparison of Rancidity and Corrosion:
(i) Materials Affected:
- Corrosion affects metals — iron rusts, silver turns black, copper gets a green coating.
- Rancidity affects fats and oils present in food items like chips, butter, etc.
(ii) Chemical Process:
- Corrosion: Metals react with moisture, oxygen, or other substances in air. E.g., iron exposed to moist air forms reddish-brown rust; silver reacts with sulphur to form silver sulphide.
- Rancidity: Fats and oils are oxidised, changing their smell and taste, making food unfit to eat.
(iii) Prevention:
- Corrosion can be prevented by galvanisation — coating iron/steel with a thin layer of zinc.
- Rancidity can be prevented by adding antioxidants to food, or flushing packaging with nitrogen gas (as chips manufacturers do) to keep oxygen away.
Source: Chapter 1, Section 1.3; Chapter 3, Section 3.5
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Explanation
- The question is a compare-type structured answer — examiners expect parallel treatment of both phenomena under each head. Skipping any head loses marks.
- Use textbook terms: galvanisation, antioxidants, moist air — these signal you've read the chapter.
- Don't write long chemical equations unless asked; brief examples (silver sulphide, rust) are sufficient here.
- 5 marks = ~5 distinct points, one per head per phenomenon + prevention. The structure above maps cleanly to the marking scheme.