If the concentrations of the oxidised and
the reduced forms of the species in the right hand half-cell are unity,
then the cell potential is equal to standard electrode potential, Eo
R of
the given half-cell Eo = Eo
R – Eo
L
As Eo
L for standard hydrogen electrode is zero Eo = Eo
R – 0 = Eo
R
The measured emf of the cell:
Pt(s) ç H2(g, 1 bar) ç H
+ (aq, 1 M) çç Cu
2+ (aq, 1 M) ú Cu
is 0 34 V and it is also the value for the standard electrode potential
of the half-cell corresponding to the reaction:
Cu
2+ (aq, 1M) + 2 e
–  ®  Cu(s)
Similarly, the measured emf of the cell:
Pt(s) ç H2(g, 1 bar) ç H
+ (aq, 1 M) çç Zn
2+ (aq, 1M) ç Zn
is -0