KMnO$$_4$$ is titrated with ferrous ammonium sulphate hexahydrate in presence of dilute H$$_2$$SO$$_4$$. Number of water molecules produced for 2 molecules of KMnO$$_4$$ is _____.

KMnO$$_4$$ is titrated with ferrous ammonium sulphate in the presence of dilute H$$_2$$SO$$_4$$. We need to find the number of water molecules produced for 2 molecules of KMnO$$_4$$.

The half-reactions in acidic medium are:

Reduction: $$\text{MnO}_4^- + 8\text{H}^+ + 5e^- \to \text{Mn}^{2+} + 4\text{H}_2\text{O}$$

Oxidation: $$\text{Fe}^{2+} \to \text{Fe}^{3+} + e^-$$

Multiplying oxidation half-reaction by 5 and adding:

$$\text{MnO}_4^- + 8\text{H}^+ + 5\text{Fe}^{2+} \to \text{Mn}^{2+} + 5\text{Fe}^{3+} + 4\text{H}_2\text{O}$$

$$2\text{MnO}_4^- + 16\text{H}^+ + 10\text{Fe}^{2+} \to 2\text{Mn}^{2+} + 10\text{Fe}^{3+} + 8\text{H}_2\text{O}$$

The number of water molecules produced for 2 molecules of KMnO$$_4$$ is $$\mathbf{8}$$.