Question

The standard oxidation potential of Ni/Ni^2+ electrode is 0.3 V. If this is combined with a hydrogen electrode in acid solution, at what pH of the solution with the measured e.m.f. be zero at 25°C? (Assume [Ni^2+] = 1M)

(a) 5.08

(b) 4

(c) 4.5

(d) 5.25

I got this question by my college director while I was bunking the class.

I would like to ask this question from Electrochemistry in division Electrochemistry of Chemistry – Class 12

Answer 1

The correct choice is (a) 5.08

Best explanation: Given,

Standard oxidation potential of Ni/Ni^2+ electrode, E°OP = 0.3 V,

Ni → Ni^2+ + 2e

2H^+ + 2e → H2

E°cell = E° (OP) + E° (RP)

E° (cell) = 0.3 + 0.0 = 0.3 V

According to Nernst equation, E (cell) = E°(cell) + \(\frac{0.059}{2}\) log10([H^+]^2 / [Ni]^+2)

0 = 0.3 + \(\frac{0.059}{2}\)log10([H^+]^2)

-log ([H^+]) = 5.08

pH = 5.08.