Environmental Engineering Reference
In-Depth Information
Table 2.1
Standard oxidation-
reduction (redox) potentials
a
Au
Au
3
3e
1.498
O
2
4H
4e
2H
2
O
1.229
Pt
Pt
2
2e
1.2
Pd
Pd
2
2e
0.987
Ag
Ag
e
0.799
2Hg
Hg
2
2
2e
0.788
Fe
3
e
Fe
2
0.771
O
2
2H
2
O
4e
4OH
0.401
Cu
Cu
2
2e
0.337
Sn
4
2e
Sn
2
0.15
2H
2e
H
2
0.000
Pb
Pb
2
2e
0.126
Sn
Sn
2
2e
0.136
Ni
Ni
2
2e
0.250
Co
Co
2
2e
0.277
Cd
Cd
2
2e
0.403
Fe
Fe
2
2e
0.440
Cr
Cr
3
3e
0.744
Zn
Zn
2
2e
0.763
Al
Al
3
3e
1.662
Mg
Mg
2
2e
2.363
Na
Na
e
2.714
K
K
e
2.925
a
25°C, volts vs. normal hydrogen electrode.
Electrode potential values are given and are
invariant (e.g., Zn
Zn
2
2e, and Zn
2
2e
Zn, are identical and represent zinc in
equilibrium with its ions with a potential of
0.763 V vs. normal hydrogen electrode).
Source
: A. J. de Bethune and N. A. S. Loud,
Standard Aqueous Electrode Potentials and
Temperature Co-efficients at 25
°
C
, Clifford
A. Hampel, Skokie, IL, 1964.
of the reactions in the table have been represented as reduction reactions, follow-
ing the international convention. Accordingly, the redox potentials above hydro-
gen have a positive sign and those below hydrogen have a negative sign. The
sign will change if any reaction is considered for a reverse reaction, i.e., an oxida-
tion reaction. Referring again to the copper-zinc cell in Fig. 2.2, the standard
single-electrode potential for the copper electrode where reduction takes place
is
0.34 V (SHE), whereas for the zinc electrode, which undergoes an oxidation
