P1: Standard Reduction Potentials by Element

The following table provides E^o and E^o´ values for selected reduction reactions. Values are from the following sources: Bard, A. J.; Parsons, B.; Jordon, J., eds. Standard Potentials in Aqueous Solutions, Dekker: New York, 1985; Milazzo, G.; Caroli, S.; Sharma, V. K. Tables of Standard Electrode Potentials, Wiley: London, 1978; Swift, E. H.; Butler, E. A. Quantitative Measurements and Chemical Equilibria, Freeman: New York, 1972.

Solids, gases, and liquids are identified; all other species are aqueous. Reduction reactions in acidic solution are written using H⁺ in place of H₃O⁺. You may rewrite a reaction by replacing H⁺ with H₃O⁺ and adding to the opposite side of the reaction one molecule of H₂O per H⁺; thus

\(\ce{H3AsO4 + 2H^{+} + 2e^{–} <=> HAsO2 + 2H2O} \nonumber\)

becomes

\(\ce{H3AsO4 + 2H3O^{+} + 2e^{–} <=> HAsO2 + 4H2O} \nonumber\)

Conditions for formal potentials (E^o´) are listed next to the potential.

Aluminum	E° (V)
Al^3^+ + 3e^− \(\rightleftharpoons\) Al(s)	–1.676
Al(OH)4^− + 3e^− \(\rightleftharpoons\) Al(s) + 4OH^−	–2.310
AlF6^3^− + 3e^− \(\rightleftharpoons\) Al(s) + 6F^−	–2.07

Antimony	E° (V)
Sb + 3H^+ + 3e^− \(\rightleftharpoons\) SbH3(g)	–0.510
Sb2O5(s) + 6H^+ + 4e^− \(\rightleftharpoons\) 2SbO^+ + 3H2O(l)	0.605
SbO^++ 2H^+ + 3e^− \(\rightleftharpoons\) Sb(s) + H2O(l)	0.212

Arsenic	E° (V)
As + 3H^+ + 3e^− \(\rightleftharpoons\) AsH3(g)	–0.225
H3AsO4 + 2H^+ + 2e^− \(\rightleftharpoons\) HAsO2 + 2H2O(l)	0.560
HAsO2 + 3H^+ + 3e^− \(\rightleftharpoons\) As(s) + 2H2O(l)	0.240

Barium	E° (V)
Ba^2^+ + 2e^− \(\rightleftharpoons\) Ba(s)	–2.91
BaO(s) + 2H^+ + 2e^−\(\rightleftharpoons\) Ba(s) + H2O(l)	2.365

Beryllium	E° (V)
Be^2^+ + 2e^− \(\rightleftharpoons\) Be(s)	–1.99

Bismuth	E° (V)
Bi^3^+ + 3e^− \(\rightleftharpoons\) Bi(s)	0.317
BiCl4^− + 3e^− \(\rightleftharpoons\) Bi(s) + 4Cl^−	0.199

Boron	E° (V)
B(OH)3 + 3H^+ + 3e^− \(\rightleftharpoons\) B(s) + 3H2O(l)	–0.890
B(OH)4^− + 3e^− \(\rightleftharpoons\) B(s) + 4OH^−	–1.811

Bromine	E° (V)
Br2 + 2e^− \(\rightleftharpoons\) 2Br^−	1.087
HOBr + H^+ + 2e^− \(\rightleftharpoons\) Br^− + H2O(l)	1.341
HOBr + H^+ + e^− \(\rightleftharpoons\) ½Br^− + H2O(l)	1.604
BrO^− + H2O(l) +2e^− \(\rightleftharpoons\) Br^− + 2OH^−	0.76 in 1 M NaOH
BrO3^− + 6H^+ + 5e^− \(\rightleftharpoons\) ½Br2(l) + 3H2O	1.5
BrO3^− + 6H^+ + 6e^− \(\rightleftharpoons\)Br^− + 3H2O	1.478

Cadmium	E° (V)
Cd^2^+ + 2e^− \(\rightleftharpoons\) Cd(s)	–0.4030
Cd(CN)4^2− + 2e^− \(\rightleftharpoons\) Cd(s) + 4CN^−	–0.943
Cd(NH3)4^2+ + 2e^− \(\rightleftharpoons\) Cd(s) + 4NH3	–0.622

Calcium	E° (V)
Ca^2^+ + 2e^− \(\rightleftharpoons\) Ca(s)	–2.84

Carbon	E° (V)
CO2(g) + 2H^+ + 2e^− \(\rightleftharpoons\) CO(g) + H2O(l)	–0.106
CO2(g) + 2H^+ + 2e^− \(\rightleftharpoons\) HCO2H	–0.20
2CO2(g) + 2H^+ +2e^− \(\rightleftharpoons\) H2C2O4	–0.481
HCHO + 2H^+ + 2e^− \(\rightleftharpoons\) CH3OH	0.2323

Cerium	E° (V)
Ce^3^+ + 3e^− \(\rightleftharpoons\) Ce(s)	–2.336
Ce^4^+ + e^− \(\rightleftharpoons\) Ce^3^+	1.61

Cesium	E° (V)
\(Cs^+(aq) + e^- \rightleftharpoons Cs (s) \)	-2.92

Chlorine	E° (V)
Cl2(g) + 2e^−\(\rightleftharpoons\) 2Cl^−	1.396
ClO^− + H2O(l) + e^−\(\rightleftharpoons\)½Cl2(g) + 2OH^−	0.421 in 1 M NaOH
ClO^− + H2O(l) + 2e^− \(\rightleftharpoons\) Cl^− + 2OH^−	0.890 in 1 M NaOH
HClO2 + 2H^+ + 2e^− \(\rightleftharpoons\) HOCl + H2O	1.64
ClO3^− + 2H^+ + e^− \(\rightleftharpoons\) ClO2(g) + H2O	1.175
ClO3^− + 3H^+ + 2e^−\(\rightleftharpoons\)HClO2 + H2O	1.181
ClO4^− + 2H^+ + 2e^−\(\rightleftharpoons\) ClO3^− + H2O	1.201
ClO4^-(aq) + H2O(l) + 2e- \(\rightleftharpoons\) ClO3^-(aq) + 2OH^-(aq)	0.17
ClO3^-(aq) + H2O(l) + 2e^- \(\rightleftharpoons\) ClO2^-(aq) + 2OH^-(aq)	0.35
ClO2^-(aq) + H2O(l) + 2e^- \(\rightleftharpoons\) ClO^-(aq) + 2OH^-(aq)	0.59

Chromium	E° (V)
Cr^3^+ + e^− \(\rightleftharpoons\) Cr^2^+	–0.424
Cr^2^+ + 2e^− \(\rightleftharpoons\) Cr(s)	–0.90
Cr2O7^2− + 14H^+ + 6e^−\(\rightleftharpoons\) 2Cr^3^+ + 7H2O(l)	1.36
CrO4^2^− + 4H2O(l) + 3e^−\(\rightleftharpoons\)2Cr(OH)4^− + 4OH^−	–0.13 in 1 M NaOH

Cobalt	E° (V)
Co^2^+ + 2e^− \(\rightleftharpoons\) Co(s)	–0.277
Co^3^+ + e^− \(\rightleftharpoons\) Co^2^+	1.92
Co(NH3)6^3+ +e^− \(\rightleftharpoons\) Co(NH3)6^2+	0.1
Co(OH)3(s) + e^− \(\rightleftharpoons\) Co(OH)2(s) + OH^−	0.17
Co(OH)2(s) + 2e^− \(\rightleftharpoons\) Co(s) + 2OH^−	–0.746

Copper	E° (V)
Cu^+ + e^− \(\rightleftharpoons\) Cu(s)	0.520
Cu^2^+ + e^− \(\rightleftharpoons\) Cu^+	0.159
Cu^2^+ + 2e^− \(\rightleftharpoons\) Cu(s)	0.3419
Cu^2^+ + I^− +e^− \(\rightleftharpoons\) CuI(s)	0.86
Cu^2^+ + Cl^− + e^− \(\rightleftharpoons\) CuCl(s)	0.559

Fluorine	E° (V)
F2(g) + 2H^+ + 2e^− \(\rightleftharpoons\) 2HF	3.053
F2(g) + 2e^− \(\rightleftharpoons\) 2F^−	2.87

Gallium	E° (V)
\(Ga^{3+} + 3e^− \rightleftharpoons Ga(s)\)	-0.56

Gold	E° (V)
Au^+ + e^− \(\rightleftharpoons\) Au(s)	1.83
Au^3^+ + 2e^− \(\rightleftharpoons\) Au^+	1.36
Au^3^+ + 3e^− \(\rightleftharpoons\) Au(s)	1.52
AuCl4^− + 3e^− \(\rightleftharpoons\) Au(s) + 4Cl^−	1.002

Hydrogen	E° (V)
\(2H^+ + 2e^− \rightleftharpoons H_2(g) \)	0.00000
H2O + e^− \(\rightleftharpoons\) ½H2(g) + OH^−	–0.828

Iodine	E° (V)
\(I_2(s) + 2e^− \rightleftharpoons 2I^−\)	0.5355
I3^− + 2e^− \(\rightleftharpoons\) 3I^−	0.536
HIO + H^+ + 2e^− \(\rightleftharpoons\) I^− + H2O(l)	0.985
IO3^− + 6H^+ + 5e^− \(\rightleftharpoons\) ½I2(s) + 3H2O(l)	1.195
IO3^−+ 3H2O(l) + 6e^− \(\rightleftharpoons\) I^− + 6OH^−	0.257

Iron	E° (V)
Fe^2^+ + 2e^− \(\rightleftharpoons\) Fe(s)	–0.44
Fe^3^+ + 3e^− \(\rightleftharpoons\) Fe(s)	–0.037
Fe^3^+ + e^− \(\rightleftharpoons\) Fe^2^+	0.771
Fe(CN)6^3− + e^−\(\rightleftharpoons\) Fe(CN)6^4−	0.356
Fe(phen)6^3+ +e^−\(\rightleftharpoons\)Fe(phen)6^2+	1.147

Lanthanum	E° (V)
La^3^+ + 3e^− \(\rightleftharpoons\) La(s)	–2.38

Lead	E° (V)
Pb^2^+ + 2e^− \(\rightleftharpoons\) Pb(s)	–0.126
PbO2(s) + 4H^+ +2e^- \(\rightleftharpoons\) Pb^2^+(aq) + 2H2O(l)	1.46
PbO2(s) + SO4^2^− + 4H^+ + 2e^− \(\rightleftharpoons\) PbSO4(s) + 2H2O(l)	1.690
PbSO4(s) + 2e^− \(\rightleftharpoons\) Pb(s) + SO4^2−	–0.356

Lithium	E° (V)
Li^+ + e^− \(\rightleftharpoons\) Li(s)	–3.040

Magnesium	E° (V)
Mg^2^+ + 2e^− \(\rightleftharpoons\) Mg(s)	–2.356
Mg(OH)2(s) + 2e^− \(\rightleftharpoons\) Mg(s) + 2OH^−	–2.687

Manganese	E° (V)
Mn^2^+ + 2e^− \(\rightleftharpoons\) Mn(s)	–1.17
Mn^3^+ + e^− \(\rightleftharpoons\) Mn^2^+	1.5
MnO2(s) + 4H^+ + 2e^− \(\rightleftharpoons\) Mn^2^+ + 2H2O(l)	1.23
MnO2(s) + 4H^+ + e^- \(\rightleftharpoons\) Mn^3^+ (aq) + 2H2O(I)	0.95
MnO4^− + 4H^+ +3e^− \(\rightleftharpoons\) MnO2(s) + 2H2O(l)	1.70
MnO4^−+ 8H^+ + 5e^− \(\rightleftharpoons\) Mn^2^+ + 4H2O(l)	1.51
MnO4^− + 2H2O(l) + 3e^− \(\rightleftharpoons\) MnO2(s) + 4OH^−	0.60

Mercury	E° (V)
Hg^2^+ + 2e^− \(\rightleftharpoons\) Hg(l)	0.8535
2Hg^2^+ + 2e^− \(\rightleftharpoons\) Hg2^2^+	0.911
Hg2^2^+ + 2e^− \(\rightleftharpoons\) 2Hg(l)	0.7960
Hg2Cl2(s) + 2e^− \(\rightleftharpoons\) 2Hg(l) + 2Cl^−	0.2682
HgO(s) + 2H^+ + 2e^− \(\rightleftharpoons\) Hg(l) + H2O(l)	0.926
Hg2Br2(s) + 2e^− \(\rightleftharpoons\) 2Hg(l) + 2Br^−	1.392
Hg2I2(s) + 2e^− \(\rightleftharpoons\) 2Hg(l) + 2I^−	–0.0405

Molybdenum	E° (V)
Mo^3^+ + 3e^− \(\rightleftharpoons\) Mo(s)	–0.2
MoO2(s) + 4H^+ + 4e^− \(\rightleftharpoons\) Mo(s) + 2H2O(l)	–0.152
MoO4^2^− + 4H2O(l) + 6e^− \(\rightleftharpoons\)Mo(s) + 8OH^−	–0.913

Nickel	E° (V)
Ni^2^+ + 2e^− \(\rightleftharpoons\) Ni(s)	–0.257
Ni(OH)2 + 2e^− \(\rightleftharpoons\) Ni(s) + 2OH^−	–0.72
Ni(NH3)6^2+ + 2e^− \(\rightleftharpoons\) Ni(s) + 6NH3	–0.49

Nitrogen	E° (V)
\(N_2(g) + 5H^+ + 4e^− \rightleftharpoons N_2H_5^+\)	–0.23
N2O(g) + 2H^+ + 2e^− \(\rightleftharpoons\) N2(g) + H2O(l)	1.77
2NO(g) + 2H^+ + 2e^− \(\rightleftharpoons\) N2O(g) + H2O(l)	1.59
HNO2 + H^+ +e^− \(\rightleftharpoons\) NO(g) + H2O(l)	0.996
2HNO2 + 4H^+ + 4e^− \(\rightleftharpoons\) N2O(g) + 3H2O(l)	1.297
NO3^− + 3H^+ + 2e^− \(\rightleftharpoons\) HNO2 + H2O(l)	0.94
\(\ce{ NO2(g) + H+ (aq) + e- \rightleftharpoons HNO2(aq) } \)	1.07
NO3^-(aq) + 4H^+(aq) + 3e^- \(\rightleftharpoons\) NO(g) + 2H2O(l)	0.96

Oxygen	E° (V)
\( O_2(g) + 2H^+ + 2e^− \rightleftharpoons H_2O_2\)	0.695
O2(g) + 4H^+ + 4e^− \(\rightleftharpoons\) 2H2O(l)	1.229
H2O2 + 2H^+ + 2e^− \(\rightleftharpoons\) 2H2O(l)	1.763
O2(g) + 2H2O(l) + 4e^− \(\rightleftharpoons\) 4OH^−	0.401
O3(g) + 2H^+ + 2e^− \(\rightleftharpoons\) O2(g) + H2O(l)	2.07
O2 (g) + e^- \(\rightleftharpoons\) O2^-(aq)	-0.33
O2 (aq) + e^- \(\rightleftharpoons\) O2^-(aq)	-0.16

Phosphorous	E° (V)
\(P(s,white) + 3H^+ + 3e^− \rightleftharpoons PH_3(g)\)	0.06
H3PO3+ 2H^+ + 2e^− \(\rightleftharpoons\) H3PO2 + H2O(l)	-0.50
H3PO4 + 2H^+ + 2e^− \(\rightleftharpoons\) H3PO3 + H2O(l)	-0.28

Platinum	E° (V)
Pt^2^+ + 2e^− \(\rightleftharpoons\) Pt(s)	1.2
PtCl4^2^− + 2e^− \(\rightleftharpoons\) Pt(s) + 4Cl^−	0.73
PtCl6^2^− + 2e^− \(\rightleftharpoons\) PtCl4^2^- + 2Cl^−	0.68

Potassium	E° (V)
K^++ e^− \(\rightleftharpoons\) K(s)	-2.93

Rubidium	E° (V)
Rb^+ + e^- \(\rightleftharpoons\) Rb (s)	-2.98

Ruthenium	E° (V)
Ru^3^+ + e^− \(\rightleftharpoons\) Ru^2^+	0.249
RuO2(s) + 4H^+ + 4e^− \(\rightleftharpoons\) Ru(s) + 2H2O(l)	0.68
Ru(NH3)6^3+ + e^− \(\rightleftharpoons\) Ru(s) + Ru(NH3)6^2+	0.10
Ru(CN)6^3− +e^− \(\rightleftharpoons\) Ru(s) + Ru(CN)6^4−	0.86

Selenium	E° (V)
\(Se(s) + 2e^−\rightleftharpoons Se^{2−}\)	–0.67 in 1 M NaOH
Se(s) + 2H^+ + 2e^− \(\rightleftharpoons\) H2Se(g)	–0.115
H2SeO3 + 4H^+ + 4e^− \(\rightleftharpoons\) Se(s) + 3H2O(l)	0.74
SeO4^3− + 4H^+ + e^− \(\rightleftharpoons\) H2SeO3 + H2O(l)	1.151

Silicon	E° (V)
\(SiF_6^{2−} + 4e^− \rightleftharpoons Si(s) + 6F^−\)	–1.37
SiO2(s) + 4H^+ + 4e^− \(\rightleftharpoons\) Si(s) + 2H2O(l)	–0.909
SiO2(s) + 8H^+ + 8e^− \(\rightleftharpoons\) SiH4(g) + 2H2O(l)	–0.516

Silver	E° (V)
Ag^+ + e^− \(\rightleftharpoons\) Ag(s)	0.7996
AgBr(s) + e^− \(\rightleftharpoons\) Ag(s) + Br^−	0.071
Ag2C2O4(s) + 2e^− \(\rightleftharpoons\) 2Ag(s) + C2O4^2−	0.47
AgCl(s) + e^− \(\rightleftharpoons\) Ag(s) + Cl^−	0.2223
AgI(s) + e^− \(\rightleftharpoons\) Ag(s) + I^−	–0.152
Ag2S(s) + 2e^− \(\rightleftharpoons\) 2Ag(s) + S^2−	–0.71
Ag(NH3)2^+ + e^− \(\rightleftharpoons\) Ag(s) + 2NH3	–0.373

Sodium	E° (V)
\(Na^+ + e^− \rightleftharpoons Na(s)\)	–2.713

Strontium	E° (V)
\(Sr^{2+} + 2e^− \rightleftharpoons Sr(s)\)	–2.89

Sulfur	E° (V)
\(S(s) + 2e^− \rightleftharpoons S^{2−}\)	–0.407
S(s) + 2H^+ + 2e^− \(\rightleftharpoons\) H2S	0.144
S2O6^2^− + 4H^+ + 2e^− \(\rightleftharpoons\) 2H2SO3	0.569
S2O8^2^− + 2e^− \(\rightleftharpoons\)2SO4^2^−	1.96
S4O6^2^− + 2e^− \(\rightleftharpoons\)2S2O3^2^−	0.080
2SO3^2^− + 2H2O(l) + 2e^−\(\rightleftharpoons\) S2O4^2^− + 4OH^−	–1.13
2SO3^2− + 3H2O(l) + 4e^−\(\rightleftharpoons\)S2O3^2− + 6OH^−
2SO4^2− + 4H^+ + 2e^−\(\rightleftharpoons\) S2O6^2− + 2H2O(l)	–0.25
SO4^2^− + H2O(l) + 2e^−\(\rightleftharpoons\) SO3^2^−+ 2OH^−	–0.936
SO4^2^− + 4H^+ + 2e^−\(\rightleftharpoons\) H2SO3^2^−+ H2O(l)	0.172

Thallium	E° (V)
\(Tl^{3+} + 2e^− \rightleftharpoons Tl^+\)	0.77 in 1 M HCl
Tl^3^+ + 3e^− \(\rightleftharpoons\) Tl(s)	0.742

Tin	E° (V)
Sn^2^+ + 2e^−\(\rightleftharpoons\) Sn(s)	-0.14
Sn^4^+ + 2e^− \(\rightleftharpoons\) Sn^2^+	0.154

Titanium	E° (V)
\(Ti^{2+} + 2e^− \rightleftharpoons Ti(s)\)	–0.163
Ti^3^+ + e^− \(\rightleftharpoons\) Ti^2^+	–0.37

Tungsten	E° (V)
\(WO_2(s) + 4H^+ + 4e^− \rightleftharpoons W(s) + 2H_2O(l)\)	–0.119
WO3(s) + 6H^+ + 6e^− \(\rightleftharpoons\) W(s) + 3H2O(l)	–0.090

Uranium	E° (V)
U^3^+ + 3e^− \(\rightleftharpoons\) U(s)	–1.66
U^4^+ + e^− \(\rightleftharpoons\) U^3^+	–0.52
UO2^+ + 4H^+ + e^−\(\rightleftharpoons\)U^4^+ + 2H2O(l)	0.27
UO2^2^+ + e^−\(\rightleftharpoons\)UO2^+	0.16
UO2^2^+ + 4H^+ + 2e^−\(\rightleftharpoons\) U^4^+ + 2H2O(l)	0.327

Vanadium	E° (V)
\(V^{2+} + 2e^− \rightleftharpoons V(s)\)	–1.13
V^3^+ + e^− \(\rightleftharpoons\) V^2^+	–0.255
VO^2^+ + 2H^+ +e^− \(\rightleftharpoons\)V^3^+ + H2O(l)	0.337
VO2^2^+ + 2H^+ +e^− \(\rightleftharpoons\) VO^2^+ + H2O(l)	1.000

Zinc	E° (V)
Zn^2^+(aq) + 2e− \(\rightleftharpoons\) Zn(s)	–0.7618
Zn(OH)4^2− + 2e^− \(\rightleftharpoons\) Zn(s) + 4OH^−	–1.285
Zn(NH3)4^2+ + 2e^− \(\rightleftharpoons\) Zn(s) + 4NH3	–1.04
Zn(CN)4^2− + 2e^− \(\rightleftharpoons\) Zn(s) + 4CN	–1.34
ZnO2 + 4H^++ 4e^− \(\rightleftharpoons\) Zn(s) + 2H2O	-1.473

Contributors and Attributions

• David Harvey (DePauw University)

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