With the help of an activity, explain the conditions under which iron articles get rusted.
Generated by claude-sonnet-4-6 · 2026-06-14 10:31 · grounding rag
Model Answer
Activity 3.14:
Take three test tubes (A, B, C) with clean iron nails.
- Test tube A: Add water and cork it. (Nails exposed to both air and water)
- Test tube B: Add boiled distilled water + 1 mL oil, cork it. (Oil prevents air from dissolving; nails exposed to water only)
- Test tube C: Add anhydrous calcium chloride (absorbs moisture), cork it. (Nails exposed to dry air only)
Leave for a few days and observe.
Observation: Iron nails rust only in test tube A.
Conclusion: Iron rusts only when exposed to both air (oxygen) and water simultaneously. Presence of only water (B) or only dry air (C) does not cause rusting.
Source: Chapter 3, Section 3.5 (Activity 3.14)
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Explanation
- Examiners expect the activity to be described with all three test tubes and their specific setups.
- The role of each condition (why oil is added, why anhydrous CaCl₂ is used) must be briefly stated.
- The observation and conclusion are mandatory for full marks — missing either loses a mark.
- Key phrase to include: both air and water are necessary for rusting.