Describe the preparation of potassium permanganate from pyrolusite. Write its reactions as an oxidising agent in acid with iron(II), oxalate and iodide ions, and draw the structure of the permanganate ion.

1. 1 · Fusion step. 2MnO₂ + 4KOH + O₂ → 2K₂MnO₄ + 2H₂O (green manganate; KNO₃ or air as oxidant).
2. 2 · Conversion step. 3MnO₄²⁻ + 4H⁺ → 2MnO₄⁻ + MnO₂ + 2H₂O (or electrolytic oxidation in alkali, commercially).
3. 3 · Half-reaction in acid. MnO₄⁻ + 8H⁺ + 5e⁻ → Mn²⁺ + 4H₂O; dilute H₂SO₄, never HCl.
4. 4 · Three reactions.
   • 5Fe²⁺ + MnO₄⁻ + 8H⁺ → Mn²⁺ + 4H₂O + 5Fe³⁺
   • 5C₂O₄²⁻ + 2MnO₄⁻ + 16H⁺ → 2Mn²⁺ + 8H₂O + 10CO₂
   • 10I⁻ + 2MnO₄⁻ + 16H⁺ → 2Mn²⁺ + 8H₂O + 5I₂
5. 5 · Draw the ion. Tetrahedral MnO₄⁻: Mn at the centre, four O at the corners, charge 1⁻.
6. 6 · Link to daily life. Dilute KMnO₄ is used to disinfect water and wash vegetables.
7. 7 · Close in one line. So KMnO₄ is a strong oxidant and its own indicator in titrations.

Scoring tip: Count the charge on both sides of each ionic equation before moving on; the oxalate one is −10 − 2 + 16 = +4 on each side.