Chemistry · Ch 8 — Transition and Inner Transition Elements

Chemical properties of KMnO₄

8.7.2

a. In acidic medium : The oxidizing reactions of $\mathrm{KMnO_4}$ in acidic medium

i. Oxidation of iodide to iodine :

\mathrm{2MnO_4^- + 10\,I^- + 16H^+ \longrightarrow 2Mn^{2+} + 8H_2O + 5I_2}

ii. Oxidation of $\mathrm{Fe^{2+}}$ to $\mathrm{Fe^{3+}}$

\mathrm{MnO_4^- + 5Fe^{2+} + 8H^+ \longrightarrow 5Fe^{3+} + Mn^{2+} + 4H_2O}

iii. Oxidation of $\mathrm{H_2S}$

\mathrm{H_2S \longrightarrow 2H^+ + S^{2-}}

\mathrm{5S^{2-} + 2MnO_4^- + 16H^+ \longrightarrow 2Mn^{2+} + 5S + 8H_2O}

iv. Oxidation of oxalic acid :

\mathrm{2MnO_4^- + 5H_2C_2O_4 + 6H^+ \longrightarrow 2Mn^{2+} + 10CO_2 + 8H_2O}

b. In neutral or weakly alkaline medium :

i. Oxidation of iodide $\mathrm{I^-}$ to iodate $\mathrm{IO_3^-}$ .

\mathrm{2MnO_4^- + H_2O + I^- \longrightarrow 2MnO_2 + 2OH^- + IO_3^-}

ii. Thiosulphate ( $\mathrm{S_2O_3^{2-}}$ ) is oxidised to sulphate ( $\mathrm{SO_4^{2-}}$ ) …