A voltaic cell is constructed from an Ni2 + (aq) - Ni (s) Ni2 + (aq) - Ni (s) half-cell and an Ag + (aq) - Ag (s) Ag + (aq) - Ag (s) half-cell. The initial concentration of Ni2 + (aq) Ni2 + (aq) in the Ni2+-NiNi2+-Ni half-cell is [Ni2+]=[Ni2+] = 1.40*10-2 MM. The initial cell voltage is + 1.12 VV. Calculate the standard emf of this voltaic cell.

+1.03 V

Explanation:

The standard emf of the voltaic cell is the value of the standard potential of it, which is calculated by the standard reduction potential (E°).

The standard reduction potential is the potential needed for the reduction reaction happen, and it's determined by the reaction with the hydrogen cell (which has E° = 0.0V). The half-reactions of reduction of Ni⁺² and Ag⁺, are:

Ni⁺² (aq) + 2e⁻ → Ni (s) E° = - 0.23 V

Ag⁺ (aq) + e⁻ → Ag (s) E° = + 0.80 V

The value is calculated by a spontaneous reaction, in which the cell with the greater E° is reduced (gain electrons), and the other is oxidized (loses electrons). So, Ag⁺ reduces.

emf = E°reduces - E°oxides

emf = 0.80 - (-0.23)

emf = + 1.03 V