Ncert Exercises & Solutions

3.12 How much charge is required for the following reductions:

(i) 1 mol of Al³⁺ to Al?

(ii) 1 mol of Cu²⁺ to Cu?

(iii) 1 mol of MnO₄^– to Mn²⁺?

Hint: 1 mole electron charge = 96487 C

(i)

{Al}^{3 +} + 3 e^{-} \to Al

∴

Required charge=3 F

= 3 x 96487 C

= 289461 C

(ii)

{Cu}^{2 +} + 2 e^{-} \to Cu

∴

Required charge=2 F

= 2 x 96487 C

= 192974 C

(iii)

{MnO}_{4}^{-} \to {Mn}^{2 +}

i.e.,

{Mn}^{7 +} + 5 e^{-} \to {Mn}^{2 +}

∴

Required charge=5 F

= 5 x 96487 C

= 482435 C