5.0 Potassium permanganate

  d and f Block Elements

• Pyrolusite ($Mn{O_2}$) when fused with $KOH$ in presence of oxygen or $KN{O_3}$ or $KCl{O_4}$ produces potassium manganates. \[2Mn{O_2} + 4KOH + {O_2}\xrightarrow{\Delta }2{K_2}Mn{O_4} + 2{H_2}O\]

• The green mass is extracted with water oxidized in potassium permanganate as follows:

• The potassium manganate solution is electrolyzed by iron electrodes. $${K_2}Mn{O_4} \to 2K + Mn{O_4}^{ - 2}{\text{ }}{{\text{H}}_2}O \to {H^ + } + O{H^ - }$$
  

• During this process manganate ions are oxidized to permanganate ions at anode.

• Hydrogen gas is evolved at cathode.

• ${K^ + }$ and $Mn{O_4}^ - $ ions react with each other and form $KMn{O_4}$. $${K^ + } + Mn{O_4}^ - \to KMn{O_4}$$

${K_2}Mn{O_4}$ is oxidized in $KMn{O_4}$ by using ${H_2}S{O_4}$, $C{O_2}$, $C{l_2}$ or ${O_3}$. $$2{K_2}Mn{O_4} + 2{H_2}S{O_4} \to 2{K_2}S{O_4} + 2KMn{O_4} + 2{H_2}O + Mn{O_2}$$$$3{K_2}Mn{O_4} + 4C{O_2} + 2{H_2}O \to 2KMn{O_4} + 4KHC{O_3} + Mn{O_2}$$$$2{K_2}Mn{O_4} + C{l_2} \to 2KMn{O_4} + 2KCl$$$$2{K_2}Mn{O_4} + {O_3} + {H_2}O \to 2KMn{O_4} + 2KOH + {O_2}$$