Question

An aqueous  CdF₂solution is electrolyzed under 1 bar pressure using platinum electrodes.  

(a) Write the half-reactions predicted to occur at the anode and cathode, based on the standard cell potentials given below.

Standard Reduction Potentials (Volts) at 25 °C
F2(g) +  2 e- --> 2 F-(aq)	2.870
O2(g) + 4 H3O+(aq) + 4 e- --> 6 H2O(l)	1.229
2  H2O(l) + 2  e- --> H2(g) + 2 OH-(aq)	-0.828
Cd2+(aq) +  2 e- --> Cd(s)	-0.403

Half-reaction at anode:

Half-reaction at cathode:

(b) What is the expected decomposition potential? ___V

Answer 1

Half reaction at anode:

Oxidation occurs at anode

2  H2O(l) + 2  e- --> H2(g) + 2 OH-(aq)

Cd2+(aq) +  2 e- --> Cd(s)

since, the reduction potential of these reactions are -ive, hence oxidation is occuring

Half reaction at cathode:

Reduction occurs at cathode

F2(g) +  2 e- --> 2 F-(aq)

O2(g) + 4 H3O+(aq) + 4 e- --> 6 H2O(l)

since, the reduction potential of these reactions are +ive, hence reduction is occuring

B)

Expected decomposition potential:

Decomposition potential is given by NERNEST EQUATION:

E = E₀ - (0.059/n)log [ Cd ⁺² ]

n = no of electron

[Cd+2] concentration of Cd+2

Eo = E_reduction - E_oxidation = 5.33V

E = 5.33 - 0.059log[Cd+2]

for 1 mol of Cd+2

E = 5.33 V