Redox titration (KMnO₄)

A/L Chemistry · G.C.E. Advanced Level · Grades 12–13

Aim

To find the concentration of an Fe²⁺ solution by titrating it with KMnO₄.

Apparatus

• Burette, pipette, conical flask
• 0.0200 mol dm⁻³ KMnO₄
• Fe²⁺ solution + dilute H₂SO₄

Method

1. Pipette 25.00 cm³ of Fe²⁺ and add dilute H₂SO₄.
2. Add KMnO₄ from the burette while swirling.
3. Stop at the first permanent pale pink (KMnO₄ is its own indicator).
4. Repeat until 3 titres are concordant.

Conclusion

MnO₄⁻ + 8H⁺ + 5Fe²⁺ → Mn²⁺ + 5Fe³⁺ + 4H₂O. Since n(Fe²⁺) = 5 n(MnO₄⁻), c(Fe²⁺) = 5 × 0.0200 × titre ÷ 25.00.