The standard oxidation potential for the half-cell

\(NO_2^− (g) + H_2O \rightarrow NO_3^− (aq) + 2H^+(aq) + 2e^−\) is –0.78 V.

Calculate the reduction potential in 9 molar H+ assuming all other species at unit concentration.

–0.0474 V

The cell reaction can be represented as

\(NO_2^− (g) + H_2O \rightarrow NO_3^− (aq) + 2H^+(aq) + 2e^−\)

Given, \(E^0 = 0.78 V\)

\(E_{cell} = E^0_{cell} − \frac{0.0591}{2}log \frac{1}{[H^+]^2}\)

or, \(E_{cell} = 0.78 − \frac{0.0591}{2}log \left(\frac{1}{9}\right)^2\)

or, \(E_{cell} = 0.78 − \frac{0.0591}{2} ×[−log 9]\)

or, \(E_{cell} = 0.78 + 0.056\)

or, \(E_{cell} = 0.836 V\)