The correct option is B At 25oC, Ecell=−0.037 V, non-spontaneous cell reaction
From cell representation,
At anode,
AgL.H.S→Ag+L.H.S
At cathode,
Ag+R.H.S+e−→AgR.H.S
The cell reaction is
AgL.H.S+Ag+R.H.S→Ag+L.H.S+AgR.H.S
Nernst equation for the given concentration cell is
Ecell=E0cell−0.0591 log Ag+L.H.SAg+R.H.S
For concentration cell,
E0cell=0
Ecell=0.0591 log[Ag+]RHS[Ag+]LHS.....eqn(1)
For
AgCl⇌Ag++Cl−
Ksp(AgCl)=2.8×10−10
Ksp(AgCl)=[Ag+][Cl−]
[Ag+]=Ksp(AgCl)[Cl−]
Concentration of KCl is 0.2 M
∴
[Cl−]=0.2 M
[Ag+]=2.8×10−100.2
[Ag+]LHS=14×10−10 M
For
AgBr⇌Ag++Br−
Ksp(AgBr)=3.3×10−13
Ksp(AgBr)=[Ag+][Br−]
[Ag+]=Ksp(AgBr)[Br−]
Concentration of KBr is 0.001 M
∴
[Br−]=0.001 M
[Ag+]=3.3×10−130.001
[Ag+]RHS=3.3×10−10 M
Substituting Ag+ concentrations in equation (1) gives,
Ecell=0.0591 log3.3×10−1014×10−10
Ecell=0.0591 log 0.235
Ecell≈−0.037 V
The emf of cell is negative, hence, the cell reaction is non-spontaneous.