KMnO4 in acidic medium is a powerful oxidizing agent: MnO4- + 8H+ + 5e- → Mn2+ + 4H2O (E0 = +1.51 V)

The reaction with oxalic acid (primary standard for standardizing KMnO4): 2KMnO4 + 5H2C2O4 + 3H2SO4 → 2MnSO4 + K2SO4 + 10CO2 + 8H2O

Equivalence factors: n-factor of KMnO4 = 5 (Mn goes from +7 to +2). n-factor of H2C2O4 = 2 (each C goes from +3 to +4, two carbons). Normality equation: N1V1 = N2V2. Or using molarity: M1V1/2 = M2V2/5 (from stoichiometry 2:5).

Self-indicating: KMnO4 is deep purple. In acidic medium, as long as reducing agent (oxalic acid) is present, MnO4- is reduced to colorless Mn2+. At equivalence point: the next drop of KMnO4 has no reducing agent to react with → solution turns permanent light pink. No external indicator needed.

Procedure: Take oxalic acid in conical flask + dilute H2SO4 + heat to ~70 degC. Add KMnO4 from burette drop by drop. First drops decolorize slowly (MnO2 formed initially catalyzes reaction — autocatalytic). Then decolorization becomes rapid. Endpoint: persistent pale pink color lasting 30 seconds.

Why heat? The reaction is slow at room temperature. Heating to 60-70 degC provides activation energy. Do NOT boil — H2C2O4 decomposes above 70 degC.