Calculate Ecell at 25 ºC when the concentration of [Ni2+] = 3.11 x 10-4 M and [Co2+]= 5.28 x 10-5 M.

Question

A voltaic cell consists of an Ni/Ni²⁺ half-cell and a Co/Co²⁺ half-cell.  The standard reduction potential for Ni²⁺ is -0.247V and for Co²⁺ is -0.277 V.

Answer 1

Ni²⁺ + 2e- ==> Ni(s) Eº = -0.25 V

Co²⁺ + 2e- ==> Co(s) Eº = -0.28 V

Based on these standard reduction potentials, Ni will be the cathode and Co will be the anode.

Eºcell = -0.25 - (-0.28) = 0.03 V

Ni²⁺ + Co ==> Ni + Co²⁺

Nernst equation @ 25ºC:

Ecell = Eºcell - 0.0592 / n ln Q

where n = moles electrons = 2

Q = [Co²⁺] / [Ni²⁺] = 5.28x10^-5 / 3.11x10^-4

Ecell = 0.03 - (0.0592/2 ln 0.1698)

Ecell = 0.03 - (0.0296 x -1.77) = 0.03 + 0.052

Ecell = 0.082 V