16.5 Redox Reactions | EverExams

⚡ 16.5 Oxidation‑Reduction Reactions · EverExams

left‑aligned notes + lesson planner + activities + quick check

🔬 redox definition & KMnO₄ reactions

A chemical reaction which involves simultaneous oxidation and reduction is called an oxidation-reduction or redox reaction. The reaction may involve complete transference of electrons to form ionic bonds or partial transfer to form covalent bonds.

⚡ potassium permanganate – powerful oxidising agent

In acidic medium, KMnO₄ oxidizes oxalic acid into CO₂. The purple solution decolorizes (Fig 16.1).

2KMnO₄(aq) + 3H₂SO₄(aq) + 5H₂C₂O₄(aq) → K₂SO₄(aq) + 2MnSO₄(aq) + 10CO₂(g) + 8H₂O(l)

Oxidation number assignment (from notes):
K⁺¹Mn⁺⁷O₄⁻² , H₂⁺¹S⁺⁶O₄⁻² , H₂⁺¹C₂⁺³O₄⁻² → K₂⁺¹S⁺⁶O₄⁻² , Mn⁺²S⁺⁶O₄⁻² , C⁺⁴O₂⁻² , H₂O⁻²

Mn (+7 → +2) gains 5e⁻ (reduction)
C (+3 → +4) loses 1e⁻ (oxidation)
So KMnO₄ = oxidising agent ; H₂C₂O₄ = reducing agent.

🧪 KI oxidation by KMnO₄

2KMnO₄ + 8H₂SO₄ + 10KI → 6K₂SO₄ + 2MnSO₄ + 5I₂ + 8H₂O

Colourless to yellow‑brown (I₂ formed).

Mn⁺⁷ + 5e⁻ → Mn⁺² (reduction)
2I⁻ – 2e⁻ → I₂⁰ (oxidation)

KMnO₄ = oxidising agent, KI = reducing agent.

🧠 redox shortcuts: “KMnO₄ in acid – always reduced (purple to colourless). Oxidising agent itself gets reduced. For C₂O₄²⁻ : each C +3 to +4 loses one electron.”
⚡ OIL RIG / LEO GER: Oxidation Is Loss, Reduction Is Gain. Loss of Electrons Oxidation, Gain Electrons Reduction.

📅 lesson planner (redox chapter)

day 1 16.4 definitions + three ways oxidation/reduction (notes).
day 2 16.5 redox reactions, KMnO₄ + oxalic acid, oxidation number changes.
day 3 KI + KMnO₄ reaction, identify oxidising/reducing agents. Quick check problems.
day 4 Solve Quick Check! exercises (i) & (ii). Activity: write half reactions.
day 5 Revision + 10 MCQ quiz + answer key discussion.

🧪 activities for mastery

✏️ activity 1 – half equations: For 2KMnO₄ + 3H₂SO₄ + 5H₂C₂O₄ → …, write oxidation half (C₂O₄²⁻ → 2CO₂ + 2e⁻) and reduction half (MnO₄⁻ + 8H⁺ +5e⁻ → Mn²⁺ + 4H₂O). Balance atoms and charges.

✏️ activity 2 – colour watch: Predict colour change when KMnO₄ reacts with KI in acidic medium. (purple → colourless? Actually I₂ gives yellow‑brown, so purple disappears and brown appears).

✏️ activity 3 – design your own redox: Using Zn and CuSO₄, identify oxidised/reduced species, oxidising/reducing agents.

⚡ 16.3 Quick Check! (interactive)

Identify the oxidising agent and the reducing agent in the following reactions. Click each option to reveal correct answer (green = correct, red = wrong).

(i) 2CuSO₄ + 4KI → 2CuI + I₂ + 2K₂SO₄

🔵 oxidising agent: CuSO₄ | reducing agent: KI
🔴 oxidising agent: KI | reducing agent: CuSO₄

(click the correct statement – only one fully correct)

(ii) H₂S + Cl₂ → S + 2HCl

🟢 oxidising agent: Cl₂ | reducing agent: H₂S
🔴 oxidising agent: H₂S | reducing agent: Cl₂

📋 10 MCQs – redox reactions

click option → turns green (correct) / red (wrong). after submit, score + key appear.