Chemistry – The Periodic Table - Transition elements | e-Consult

The titration of a dilute solution of iron(II) ions (Fe²⁺) with a standard solution of potassium permanganate (KMnO₄) is a redox titration. Potassium permanganate acts as the oxidizing agent, and iron(II) ions are oxidized to iron(III) ions. The chemical equation for the reaction is:

5Fe²⁺(aq) + MnO₄^-(aq) + 8H⁺(aq) → 5Fe³⁺(aq) + Mn²⁺(aq) + 4H₂O(l)

To determine the endpoint, a few drops of a suitable indicator are added to the solution. A commonly used indicator is potassium fernicilate (K₃[Fe(CN)₆]). This indicator is initially colourless. As the permanganate is added, it oxidizes the iron(II) ions to iron(III) ions. The iron(III) ions react with the potassium fernicilate to form a deep pink/purple precipitate of iron(III) fernicilate. The endpoint is reached when the solution turns a persistent pink/purple colour, indicating that all the iron(II) ions have been oxidized.

The volume of potassium permanganate solution used to reach the endpoint can then be used to calculate the concentration of the initial iron(II) solution using the stoichiometry of the reaction.