The Foundations of Chemistry

STANDARD ELECTRODE POTENTIALS FOR OTHER

HALF-REACTIONS

In some half-cells, the oxidized and reduced species are both in solution as ions in contact
with inert electrodes. For example, the standard iron(III) ion/iron(II) ion half-cell contains
1 Mconcentrations of the two ions. It involves the following half-reaction.

Fe^3 e88nFe^2  E^0 0.771 V

The standard dichromate (Cr 2 O 72 ) ion/chromium(III) ion half-cell consists of a 1 M
concentration of each of the two ions in contact with an inert electrode. The balanced
half-reaction in acidic solution (1.0 MH) is

Cr 2 O 72 14H 6 e88n2Cr^3 7H 2 O E^0 1.33 V

Standard reduction potentials for some other reactions are given in Table 21-3 and in
Appendix J. These potentials can be used like those of Table 21-2.

21-16

21-16 Standard Electrode Potentials for Other Half-Reactions 871

Platinum metal is often used as the

inert electrode material. These two

standard half-cells could be shown in

shorthand notation as

Pt/Fe^3 (1 M), Fe^2 (1 M) and

Pt/Cr 2 O 72 (1 M), Cr^3 (1 M)

TABLE 21-3 Standard Reduction Potential for Selected Half-Cells

Standard Reduction

Reduction Half-Reaction Potential E^0 (volts)

Zn(OH) 42  2 e 888nZn4OH 1.22

Fe(OH) 2  2 e 888nFe2OH 0.877

2H 2 O 2 e 888nH 2 2OH 0.828

PbSO 4  2 e 888nPbSO 42  0.356

NO 3 H 2 O 2 e 888nNO 2 2OH 0.01

Sn^4  2 e 888nSn^2  0.15

AgCle 888nAgCl 0.222

Hg 2 Cl 2  2 e 888n2Hg2Cl 0.27

O 2 2H 2 O 4 e 888n4OH 0.40

NiO 2 2H 2 O 2 e 888nNi(OH) 2 2OH 0.49

H 3 AsO 4 2H 2 e 888nH 3 AsO 3 H 2 O 0.58

Fe^3 e 888nFe^2  0.771

ClOH 2 O 2 e 888nCl2OH 0.89

NO 3 4H 3 e 888nNO2H 2 O 0.96

O 2 4H 4 e 888n2H 2 O 1.229

Cr 2 O 72 14H 6 e 888n2Cr^3 7H 2 O 1.33

MnO 4 8H 5 e 888nMn^2 4H 2 O 1.507

Cl 2  2 e 888n2Cl 1.360

PbO 2 HSO 42 3H 2 e888nPbSO 4 2H 2 O 1.685

Increasing strength as oxidizing agent;

increasing ease of reduction

Increasing strength as reducing agent;

increasing ease of oxidation