Question

A voltaic cell consists of a Zn/Zn2+ half-cell and a Ni/Ni2+ half-cell at 25 ∘C. The initial concentrations of Ni2+ and Zn2+ are 1.80 M and 0.130 M , respectively. The volume of half-cells is the same.

a) What is the initial cell potential?   

Express your answer using two significant figures.

b) What is the cell potential when the concentration of Ni2+ has fallen to 0.600 M ?   

Express your answer using two significant figures.

Answer 1

a) Nernest equation,

Zn2+ + 2e- ---> Zn(s)    E0 = -0.76 v

Ni2+ + 2e- ----> Ni(s)    E0 = -0.25 v

cell reaction = Zn(s) + Ni^2+(aq) ---> Zn^2+(aq) + Ni(s)

E0cell = E0cathode - E0anode

         = -0.25 - (-0.76)

         = 0.51 v

   Ecell = E0cell - 0.0591/nlog[[Zn^2+]/[Ni^2+]]

         = 0.51-(0.0591/2)log(0.13/1.8)

         = 0.54 V

b)

Ecell = E0cell - 0.0591/nlog[[Zn^2+]/[Ni^2+]]

         = 0.51-(0.0591/2)log(0.13/0.6)

         = 0.53 V