Question

Describe the preparation of potassium permanganate. How does the acidified permanganate solution react with
Iron

Write the ionic equations for the reactions.

(i) Ions
(ii) $S{o}_2$
(iii) Oxalic acid
Write the ionic equations for the reactions.

Answer 1

Preparation of $KMn{O}_4$ Potassium permangante is prepared by the fusion of $Mn{O}_2$ with an alkali metal hydroxide and an oxidising agent like $KN{O}_3$. It forms dark green, $K_{2}Mn{O}_4$ which disproportionates in a neutral or acidic solution to give permanganate.
(i) $2Mn{O}_2+4KOH+O_2\stackrel{KN{O}_3}{\to }2K_{2}Mn{O}_4+2H_{2}O$
(ii) $3Mn{O}_4^{2-}+4H^{+}\to 2Mn{O}_4^{-}+Mn{O}_2+2H_{2}Oor3K_{2}Mn{O}_4+2H_{2}S{O}_4\to \underset{\begin{array}{c}Potassium\\ permanganate\end{array}}{2KMn{O}_4}+2K_{2}S{O}_4+Mn{O}_2+2H_{2}O$

Reactions of $KMn{O}_4$ in acidic medium
$Mn{O}_4^{-}+8H^{+}+5e^{-}\to M{n}^{2+}+4H_{2}O\dots \dots \left(i\right)$
(i) Iron (II) ions Ferrous is oxidised to ferric.
$[F{e}^{2+}\to F{e}^{3+}+e^{-}]\times 5\dots \dots \left(ii\right)$
Add both Eq. (i) and (ii) x 5 and cancelout the spectator ions and molecules
$5F{e}^{2+}+Mn{O}_4^{-}+8H^{+}\to M{n}^{2+}+4H_{2}O+5F{e}^{3+}$

(ii) $S{O}_2$ : It is oxidised to $S{O}_4^{2-}$ by acidified $KMn{O}_4$
$S{O}_2+2H_{2}O\to S{O}_4^{2-}+4H^{+}+2e^{-}\dots \dots \left(iii\right)$
Add both Eq. (i)x2 and (iii)x5 and cancelout the spectator ions and molecules
$5S{O}_2+2Mn{O}_4^{-}+2H_{2}O\to 2M{n}^{2+}+4H^{+}+5S{O}_4^{2-}$

(iii). Oxalic acid
$C_2{O}_4^{2-}\to 2C{O}_2+2e^{-}\dots \dots \left(iv\right)$
Add both Eq. (i)x2 and (iv)x5 and cancelout the spectator ions and molecules
$5C_2{O}_4^{2-}+2Mn{O}_4^{-}+16H^{+}\to 2M{n}^{2+}+8H_{2}O+10C{O}_2$