The standard oxidation potential of Ni/Ni²⁺ electrode is 0.236 V. If this is combined with a hydrogen electrode in acid solution, at what pH of the solution will the measured emf be zero at 25°C? Assume [Ni²⁺] = 1 M.

4

The correct answer is option 4. 4.

The standard reduction potential of hydrogen electrode will be 0.236. This will make the cell potential zero.

\(E_{cell} = E^0_{cell} − \frac{0.0591}{2}log\frac{[Ni^{2+}]}{[H^+]^2}\)

or, \(0= 0.236 + 0.0591 log[H^+]\)

or, \(0.236 = − 0.0591log[H^+]\)

or, \(0.236 = 0.0591pH\)

or, \(pH = \frac{0.236}{0.0591}\)

or, \(pH = 3.99\)

∴ \(pH ≈ 4\)