Question

How would you determine the reduction potential of Zn/Zn²⁺ (aq)? (or) How will you calculate the reduction potential of Half cell?

Answer 1

1. Consider the zinc electrode dipped in zinc sulphate solution using SHE

2. Step 1: 

The following galvanic cell is constructed using SHE 

Zn_(s) | Zn²⁺_(aq.1M) | H_2(g.1atm) | Pt_(s)

Step 2: The emf of the above galvanic cell is measured using a voltmeter. In this case the measured emf of the above galvanic cell is 0.76 V

4. Calculation: 

We know that. 

E°_cell = (E°_ox)_zn|zn²⁺ + (E°red)_SHE

E°_cell = 0.76 + 0V 

= 0.76 V 

This oxidation potential corresponds to the below mentioned half cell reaction which takes place at the cathode 

Zn → Zn²⁺ + 2e^- (oxidation) 

(y) The emf of the reverse reaction will give the reduction potential 

Zn²⁺ + 2e^- → Zn 

(E°_red)zn²⁺|zn = – 0.76V