Question

$5$ moles of ferric oxalate are oxidised by how many number of moles of $KMn{O}_4$ in acid medium?

• A. $6$
• B. $4$
• C. $2$
• D. None of these

Answer 1

The correct option is A $6$

1 mole of ferric oxalate on dissociation gives 3 moles of oxalate ions.
$F{e}_2(C_2{O}_4{)}_3\rightleftharpoons 2F{e}^{3+}+3C_2{O}_4^{2-}$
The total number of electrons involved per mole oxidation of ferric oxalate is 6 moles.
The oxidation of oxalate ions to carbon dioxide involves 2 moles of electrons.
$3C_2{O}_4^{2-}\to 6C{O}_2+6e^{-}$......(1)
In acidic medium, one mole of $KMn{O}_4$ requires 5 moles of electrons.
${MnO}_4^{-}+8H^{+}+5e^{-}\to M{n}^{2+}+4H_{2}O$......(2)
To balance the number of electrons, multiply equation (1) with 5 and equation (2) with 6
$15C_2{O}_4^{2-}\to 30C{O}_2+30e^{-}$......(3)
$6{MnO}_4^{-}+48H^{+}+30e^{-}\to 6M{n}^{2+}+24H_{2}O$......(4)
Add equations (3) and (4)
$15C_2{O}_4^{2-}+6{MnO}_4^{-}+48H^{+}\to 30C{O}_2+6M{n}^{2+}+24H_{2}O$
Thus five mole of Ferric oxalate are oxidized by six moles of $KMn{O}_4$ in acid medium.