The Foundations of Chemistry

STANDARD ELECTRODE POTENTIALS

We can develop a series of standard electrode potentials by measuring the potentials of
other standard electrodes versus the SHE in the way we described for the standard
Zn–SHE and standard Cu–SHE voltaic cells. Many electrodes involve metals or
nonmetals in contact with their ions. We saw (Section 21-12) that the standard Zn elec-
trode behaves as the anode versus the SHE and that the standard oxidationpotential for
the Zn half-cell is 0.763 volt.

E^0 oxidation

(as anode) Zn88nZn^2  2 e 0.763 V

reduced form88noxidized formne (standard oxidationpotential)

The reductionpotential for the standard zinc electrode (to act as a cathoderelative to the
SHE) is therefore the negative of this, or 0.763 volt.

E^0 oxidation

(as cathode) Zn^2  2 e88nZn 0.763 V

oxidized formne88nreduced form (standard reduction potential)

21-14

21-14 Standard Electrode Potentials 867

H 2 (g) e– e–

(1 atm)

Salt bridge

H 2 → 2H+ + 2e–

Oxidation, anode

Voltmeter

1 M HCl(aq)

Pt black

Cu2+ + 2e– → Cu(s)

Reduction, cathode

1 M CuSO 4 (aq)

H+ Cu^2 +

Cu(s)

K+

K+ Cl–

Cl–

e–

SHE as

anode

H 2 gas

bubble

e–

Copper

atom, Cu

Copper

ion, Cu2+

Figure 21-10 The standard copper–SHE cell,

Pt
H(1 M); H 2 (1 atm)

Cu^2 (1 M)
Cu

In this cell, the standard hydrogen electrode functions as the anode. The net reaction is

H 2 (g)Cu^2 (aq)88n2H(aq)Cu(s)

The activity series (Table 4-12) is

based on standard electrode potentials.