Question

How many moles of electrons are required for the reduction of :

(i) 3 moles of Zn²⁺ to Zn, 

(ii) 1 mol of Cr³⁺ to Cr?

How many Faradays of electricity will be required in each case?

Answer 1

(i) Given : 

For reduction of 3 mol Zn²⁺ to Zn; 

Number of moles of electrons required = ? 

Reduction half reaction,

Zn²⁺ + 2e^- → Zn

∵ 1 mole of Zn²⁺ requires 2 moles of electrons

∴ 3 moles of Zn²⁺ will require,

∵ 3 × 2 = 6 moles of electrons 

∴ 1 mole of electrons = 1 F 6 moles of electrons = 6 F

(ii) Given : 

Reduction of 1 mol of Cr³⁺ to Cr : 

Reduction half reaction, 

Cr³⁺ + 3e^- → Cr

Hence 1 mole of Cr³⁺ will require 3 moles of electrons 

∵ 1 mole of electrons = 1 

∴ 3 moles of electrons = 3 F

∴ (i) 6 mol electrons and 6 Faradays.

(ii) 3 mol electrons and 3 Faradays.