Preparation: Fusion of MnO2 with KOH + air gives K2MnO4 (green manganate). Electrolytic/disproportionation oxidation gives KMnO4. Acidic medium: $MnO4^-$ + 8$H^+$ + 5$e^-$ → $Mn^{2+}$ + 4H2O (colourless). Acts as 5-electron oxidant. Neutral/weakly alkaline: $MnO4^-$ + 2H2O + 3$e^-$ → MnO2(brown) + 4$OH^-$. Acts as 3-electron oxidant. Strongly alkaline: $MnO4^-$ + $e^-$ → $MnO4^{2-}$ (green). Used in titrations as self-indicator $\frac{pink}{purple disappears at endpoint}$. Standardised against oxalic acid: 2KMnO4 + 5H2C2O4 + 3H2SO4 → 2MnSO4 + 10CO2 + 8H2O + K2SO4.