Redox Reactions
Oxidation-reduction, oxidation states, balancing redox
Key Concepts
- Oxidation: loss of electrons / increase in oxidation state
- Reduction: gain of electrons / decrease in oxidation state
- OIL RIG: Oxidation Is Loss, Reduction Is Gain
- Oxidising agent: gets reduced; reducing agent: gets oxidised
- Disproportionation: same element is simultaneously oxidised and reduced
Important Formulae
| Balancing by half-reaction (acidic) | Add H₂O to balance O, H⁺ to balance H, then balance charge |
| Oxidation state of O | Usually −2 (except peroxides −1, OF₂ +2) |
| Oxidation state of H | Usually +1 (except metal hydrides −1) |
Quick Tips
- F₂ is the strongest oxidising agent; Li is the strongest reducing agent.
- In MnO₄⁻: Mn is +7; in Cr₂O₇²⁻: Cr is +6 — both are strong oxidisers in acidic medium.
- Sum of oxidation states in a neutral compound = 0; in an ion = ion charge.
Sample Practice Questions
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In the half-reaction: MnO₄⁻ + 8H⁺ + 5e⁻ → Mn²⁺ + 4H₂O, MnO₄⁻ is:
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Answer: Oxidising agent
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Balancing redox equations in acidic medium: H⁺ and __ are used to balance charge:
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Answer: H₂O
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Equivalent weight of KMnO₄ in acidic medium (M = 158, n-factor = 5):
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Answer: 31.6
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In electrochemical cells, oxidation occurs at:
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Answer: Anode
Practice Questions
Practice 20 randomly selected NEET questions on Redox Reactions. Answers are revealed after each question.
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What are the key concepts in Redox Reactions for NEET?
Oxidation: loss of electrons / increase in oxidation state; Reduction: gain of electrons / decrease in oxidation state; OIL RIG: Oxidation Is Loss, Reduction Is Gain; Oxidising agent: gets reduced; reducing agent: gets oxidised; Disproportionation: same element is simultaneously oxidised and reduced.
Which formulae are important for Redox Reactions in NEET?
Balancing by half-reaction (acidic): Add H₂O to balance O, H⁺ to balance H, then balance charge; Oxidation state of O: Usually −2 (except peroxides −1, OF₂ +2); Oxidation state of H: Usually +1 (except metal hydrides −1).
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