Redox Reactions

• Oxidation — gain of oxygen / loss of hydrogen / loss of electrons.
• Reduction — loss of oxygen / gain of hydrogen / gain of electrons.
• Redox — oxidation and reduction occur together.
• Oxidising agent — gets reduced; reducing agent — gets oxidised.
• Everyday examples: corrosion, rancidity, respiration.

1. Oxidation (classical) — Cu + ½O₂ → CuO (Cu gains oxygen).
2. Reduction (classical) — CuO + H₂ → Cu + H₂O (CuO loses oxygen).
3. Redox pair — in Zn + CuSO₄ → ZnSO₄ + Cu, Zn oxidised, Cu²⁺ reduced.
4. Oxidising agent — supplies oxygen or accepts electrons (O₂, CuO).
5. Reducing agent — removes oxygen or donates electrons (H₂, C, Zn).
6. Corrosion — oxidation of metals (rust: Fe → Fe₂O₃·xH₂O).
7. Rancidity — oxidation of fats/oils; prevented by antioxidants, nitrogen flushing.
8. Respiration — glucose oxidised to CO₂ and H₂O releasing energy.
9. Mnemonic — OIL RIG (Oxidation Is Loss, Reduction Is Gain of electrons) for advanced view.
10. NCERT examples — blackening of silver sulphide to silver; copper oxide reduction.

Identify oxidised and reduced species: CuO + H₂ → Cu + H₂O

Step 1 — CuO loses oxygen → Cu (reduction of CuO).
Step 2 — H₂ gains oxygen → H₂O (oxidation of H₂).
Step 3 — **Oxidising agent**: CuO (causes oxidation of H₂).
Step 4 — **Reducing agent**: H₂ (causes reduction of CuO).
Conclusion: redox reaction; CuO reduced, H₂ oxidised.

• Saying only oxygen transfer defines all redox (electron transfer is general).
• Misconception: oxidising agent gets oxidised (it gets reduced).
• Confusing reduction with 'reduced amount' of substance.
• Ignoring rancidity as oxidation of food fats.
• Forgetting both processes occur in every redox reaction.

• Define oxidation and reduction in terms of oxygen transfer.
• In Zn + CuSO₄ reaction, which species is oxidised?
• What is an oxidising agent?
• How is rancidity related to redox?

Open the Practice tab for graded questions on Redox Reactions.