Passivation
Passivation of iron in concentrated HNO₃ is due to formation of:
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About This Question
- Subject
- chemistry
- Chapter
- redox reactions and electrochemistry
- Topic
- passivation
- Difficulty
- Easy
- Year
- 2025
Solution
Correct Answer:
Oxide layer
Passivity is the state where a metal becomes chemically unreactive despite its position in the activity series.
- Reaction with Iron: When Iron (Fe) is dipped in concentrated Nitric acid (HNO3), which is a powerful oxidizing agent, it reacts briefly but then stops.
- Cause: The surface of the iron is oxidized to form an extremely thin, impervious, and protective oxide layer (specifically Fe3O4).
- This layer acts as a physical barrier, preventing the acid from reaching the underlying bulk metal. In contrast, dilute HNO3 dissolves iron normally as it doesn't form this protective passive layer.
This easy difficulty chemistry question is from the chapter redox reactions and electrochemistry, covering the topic of passivation. It appeared in the 2025 exam.
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