Oxidation-Reduction Titration

Oxidation-reduction titration or Redox titration is a volumetric analysis involving an oxidizing agent and a reducing agent. In this titration, an oxidizing agent (also known as the oxidant) is titrated against a reducing agent (otherwise known as the reductant).

The unknown concentration of the analyte is then determined using calculations. At the end of it, the oxidizing agent becomes reduced and the reducing agent becomes oxidized. Examples of redox titration are potassium tetraoxomanganate(VII), iron(II) and thiosulphate-iodine titrations.

Redox Titrations of Acidified KMnO₄ Solution and a Fe²⁺ Salt:

Example 2.2.1:

When 0.011 mol dm^–3 potassium tetraoxomanganate(VII), KMnO_4(aq) solution acidified with teraoxosulphate(VI) acid was titrated against a solution containing 14.0 g of an iron(II) salt in 500 cm³ of solution, 21.30 cm³ of acidified KMnO_4(aq) oxidized 25.00 cm³ of the iron(II) salt solution.

The equation for the reaction is: 

MnO₄^–_(aq) + 5Fe²⁺_(aq) + 8H⁺_(aq) → Mn²⁺_(aq) + 5Fe²⁺_(aq) + 4H₂O_(l)

(a) From the information provided, calculate the:

(i). moles of MnO₄^– used in the titration.
(ii). moles of Fe²⁺ titrated
(iii). concentration of Fe²⁺ in mol dm^–3
(iv). concentration of Fe²⁺ in g dm^–3
(v). percentage of iron in the salt

(b) Give reason(s) why

(i). It is necessary to acidify KMnO_4(aq) in the titration
(ii). Hydrochloric acid cannot be used to acidify KMnO₄ solution in the titration

Results and Calculations:

Molar concentration of oxidant, C_ox = 0.0110 mol dm^-3