The e.m.f. (E°) of the following cells are:
Ag | Ag+ (1M) || Cu2+ (1M) | Cu; E° = −0.46 V
Zn | Zn2+ (1M) || Cu2+ (1M) | Cu; E° = +1.10 V
Calculate the e.m.f. of the cell:
Zn | Zn2+ (1M) || Ag+ (1M) | Ag
−0.46 = E°(Cu2+, Cu) − E°(Ag+,Ag) … (i)
1.10 = E°(Cu2+, Cu) − E°(Zn2+,Zn) … (ii)
Subtracting equation (i) from equation (ii), we have:
E°(cell) = 1.10 − (−0.46) = E°(Ag+,Ag) − E°(Zn2+,Zn)
= 1.56 V
In other words, E° of the cell:
Zn | Zn2+ (M) || Ag+ (M) | Ag
is 1.56 V.