Question

How much charge is required for the following reductions?

(i) $1mol$ of $A{l}^{3+}$ to $Al$
(ii) $1mol$ of $C{u}^{2+}$ to $Cu$
(iii) $1mol$ of ${Mn{O}_4}^{-}$ to $M{n}^{2+}$

Answer 1

$A{l}^{3+}+3e^{-}\to Al$
The reduction will require 3 Faraday of electricity or $3\times 96500=2.895\times {10}^{5}C$.

$C{u}^{2+}+2e^{-}\to Cu$
The reduction will require 2 Faraday of electricity or $2\times 96500=1.93\times {10}^{5}C$.

${Mn{O}_4}^{-}+5e^{-}\to M{n}^{2+}$

The reduction will require 5 Faraday of electricity or $5\times 96500=4.825\times {10}^{5}C$.

Note: 1 mole of electron has a charge of 1 faraday.