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.
Answer & explanation
Correct answer: option 4
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, \(E_{cell} = 0.836 V\)