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 76 V corresponding to the standard electrode potential of the
half-cell reaction:
Zn
2+ (aq, 1 M) + 2e
– ®  Zn(s)
The positive  value of the standard electrode potential in the first
case indicates that Cu
2+ ions get reduced more easily than H
+ ions