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P1: Standard Reduction Potentials by Element

The following table provides Eo and Eo´ 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

H3AsO4 + 2H+ + 2e \(\rightleftharpoons\) HAsO2 + 2H2O

becomes

H3AsO4 + 2H3O+ + 2e \(\rightleftharpoons\) HAsO2 + 4H2O

Conditions for formal potentials (Eo´) are listed next to the potential.

Aluminum E° (V)
Al3+ + 3e \(\rightleftharpoons\) Al(s) –1.676

Al(OH)4 + 3e \(\rightleftharpoons\) Al(s) + 4OH

–2.310

AlF63− + 3e \(\rightleftharpoons\) Al(s) + 6F

–2.07
Antimony  
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  
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  
Ba2+ + 2e \(\rightleftharpoons\) Ba(s) –2.91

BaO(s) + 2H+ + 2e\(\rightleftharpoons\) Ba(s) + H2O(l)

2.365
Beryllium  
Be2+ + 2e \(\rightleftharpoons\) Be(s) –1.99
Bismuth  
Bi3+ + 3e \(\rightleftharpoons\) Bi(s) 0.317

BiCl4 + 3e \(\rightleftharpoons\) Bi(s) + 4Cl

0.199
Boron  
B(OH)3 + 3H+ + 3e \(\rightleftharpoons\) B(s) + 3H2O(l) –0.890

B(OH)4 + 3e \(\rightleftharpoons\) B(s) + 4OH

–1.811
Bromine  
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  
Cd2+ + 2e \(\rightleftharpoons\) Cd(s) –0.4030

Cd(CN)42− + 2e \(\rightleftharpoons\) Cd(s) + 4CN

–0.943

Cd(NH3)42+ + 2e \(\rightleftharpoons\) Cd(s) + 4NH3

–0.622
Calcium  
Ca2+ + 2e \(\rightleftharpoons\) Ca(s) –2.84
Carbon  
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  
Ce3+ + 3e \(\rightleftharpoons\) Ce(s) –2.336
Ce4+ + e \(\rightleftharpoons\) Ce3+ 1.44
Cesium  
\[Cs^+(aq) + e^- \rightleftharpoons Cs (s) \] -2.92
Chlorine  
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  
Cr3+ + e \(\rightleftharpoons\) Cr2+ –0.424
Cr2+ + 2e \(\rightleftharpoons\) Cr(s) –0.90

Cr2O72− + 14H+ + 6e\(\rightleftharpoons\) 2Cr3+ + 7H2O(l)

1.36

CrO42− + 4H2O(l) + 3e\(\rightleftharpoons\)2Cr(OH)4 + 4OH

–0.13 in 1 M NaOH
Cobalt  
Co2+ + 2e \(\rightleftharpoons\) Co(s) –0.277
Co3+ + e \(\rightleftharpoons\) Co2+ 1.92

Co(NH3)63+ +e  \(\rightleftharpoons\) Co(NH3)62+

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  
Cu+ + e \(\rightleftharpoons\) Cu(s) 0.520
Cu2+ + e \(\rightleftharpoons\) Cu+ 0.159
Cu2+ + 2e \(\rightleftharpoons\) Cu(s) 0.3419
Cu2+ + I +e \(\rightleftharpoons\) CuI(s) 0.86
Cu2+ + Cl + e \(\rightleftharpoons\) CuCl(s) 0.559
Fluorine  

F2(g) + 2H+ + 2e \(\rightleftharpoons\) 2HF

3.053

F2(g) + 2e \(\rightleftharpoons\) 2F

2.87
Gallium  

\[Ga^{3+} + 3e^− \rightleftharpoons Ga(s)\]

-0.56
Gold  
Au+ + e \(\rightleftharpoons\) Au(s) 1.83

Au3+ + 2e \(\rightleftharpoons\) Au+

1.36
Au3+ + 3e \(\rightleftharpoons\) Au(s) 1.52

AuCl4 + 3e \(\rightleftharpoons\) Au(s) + 4Cl

1.002
Hydrogen  

\[2H^+ + 2e^− \rightleftharpoons H_2(g) \]

0.00000

H2O + e \(\rightleftharpoons\) ½H2(g) + OH

–0.828
Iodine  

\[I_2(s) + 2e^− \rightleftharpoons 2I^−\]

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  
Fe2+ + 2e \(\rightleftharpoons\) Fe(s) –0.44
Fe3+ + 3e \(\rightleftharpoons\) Fe(s) –0.037

Fe3+ + e \(\rightleftharpoons\) Fe2+

0.771

Fe(CN)63− + e\(\rightleftharpoons\) Fe(CN)64−

0.356

Fe(phen)63+ +e\(\rightleftharpoons\)Fe(phen)62+

1.147
Lanthanum  
La3+ + 3e \(\rightleftharpoons\) La(s) –2.38
Lead  
Pb2+ + 2e \(\rightleftharpoons\) Pb(s) –0.126
PbO2(s) + 4H+ +2e- \(\rightleftharpoons\) Pb2+(aq) + 2H2O(l) 1.46

PbO2(s) + 4SO42− + 4H+ + 2e \(\rightleftharpoons\) PbSO4(s) + 2H2O(l)

1.690

PbSO4(s) + 2e \(\rightleftharpoons\) Pb(s) + SO42−

–0.356
Lithium  
Li+ + e \(\rightleftharpoons\) Li(s) –3.040
Magnesium  
Mg2+ + 2e \(\rightleftharpoons\) Mg(s) –2.356

Mg(OH)2(s) + 2e \(\rightleftharpoons\) Mg(s) + 2OH

–2.687
Manganese  
Mn2+ + 2e \(\rightleftharpoons\) Mn(s) –1.17

Mn3+ + e \(\rightleftharpoons\) Mn2+

1.5

MnO2(s) + 4H+ + 2e \(\rightleftharpoons\) Mn2+ + 2H2O(l)

1.23
MnO2(s) + 4H+ + e- \(\rightleftharpoons\) Mn3+ (aq) + H2O(I) 0.95

MnO4 + 4H+ +3e \(\rightleftharpoons\) MnO2(s) + 2H2O(l)

1.70

MnO4+ 8H+ + 5e \(\rightleftharpoons\) Mn2+ + 4H2O(l)

1.51
MnO4 + 2H2O(l) + 3e \(\rightleftharpoons\) MnO2(s) + 4OH 0.60
Mercury  
Hg2+ + 2e \(\rightleftharpoons\) Hg(l) 0.8535
2Hg2+ + 2e \(\rightleftharpoons\) Hg22+ 0.911

Hg22+ + 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  
Mo3+ + 3e \(\rightleftharpoons\) Mo(s) –0.2

MoO2(s) + 4H+ + 4e \(\rightleftharpoons\) Mo(s) + 2H2O(l)

–0.152

MoO42− + 4H2O(l) + 6e \(\rightleftharpoons\)Mo(s) + 8OH

–0.913
Nickel  
Ni2+ + 2e \(\rightleftharpoons\) Ni(s) –0.257

Ni(OH)2 + 2e \(\rightleftharpoons\) Ni(s) + 2OH

–0.72

Ni(NH3)62+ + 2e \(\rightleftharpoons\) Ni(s) + 6NH3

–0.49
Nitrogen  
\[N_2(g) + 5H^+ + 4e^− \rightleftharpoons N_2H_5^+\] –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  
\[ O_2(g) + 2H^+ + 2e^− \rightleftharpoons H_2O_2\] 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  
\[P(s,white) + 3H^+ + 3e^− \rightleftharpoons PH_3(g)\] 0.06

H3PO3+ 2H+ + 2e \(\rightleftharpoons\) H3PO2 + H2O(l)

-0.50

H3PO4 + 2H+ + 2e \(\rightleftharpoons\) H3PO3 + H2O(l)

-0.28

Platinum  
Pt2+ + 2e \(\rightleftharpoons\) Pt(s) 1.2
PtCl42− + 2e \(\rightleftharpoons\) Pt(s) + 4Cl 0.73
PtCl62− + 2e \(\rightleftharpoons\) PtCl42- + 2Cl 0.68
Potassium  
K+ + e \(\rightleftharpoons\) K(s) -2.93
Rubidium  
Rb+ + e- \(\rightleftharpoons\) Rb (s) -2.98
Ruthenium  
Ru3+ + e \(\rightleftharpoons\) Ru2+ 0.249

RuO2(s) + 4H+ + 4e \(\rightleftharpoons\) Ru(s) + 2H2O(l)

0.68

Ru(NH3)63+ + e \(\rightleftharpoons\) Ru(s) + Ru(NH3)62+

0.10

Ru(CN)63− +e \(\rightleftharpoons\) Ru(s) + Ru(CN)64−

0.86
Selenium  
\[Se(s) + 2e^−\rightleftharpoons Se^{2−}\] –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

SeO43− + 4H+ + e \(\rightleftharpoons\) H2SeO3 + H2O(l)

1.151
Silicon  
\[SiF_6^{2−} + 4e^− \rightleftharpoons Si(s) + 6F^−\] –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  
Ag+ + e \(\rightleftharpoons\) Ag(s) 0.7996
AgBr(s) + e \(\rightleftharpoons\) Ag(s) + Br 0.071

 Ag2C2O4(s) + 2e \(\rightleftharpoons\) 2Ag(s) + C2O42−

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) + S2−

–0.71

Ag(NH3)2+ + e \(\rightleftharpoons\) Ag(s) + 2NH3

–0.373
Sodium  
\[Na^+ + e^− \rightleftharpoons Na(s)\] –2.713
Strontium  
\[Sr^{2+} + 2e^− \rightleftharpoons Sr(s)\] –2.89
Sulfur  
\[S(s) + 2e^− \rightleftharpoons S^{2−}\] –0.407

S(s) + 2H+ + 2e \(\rightleftharpoons\) H2S

0.144

S2O62− + 4H+ + 2e \(\rightleftharpoons\) 2H2SO3

0.569

S2O82− + 2e \(\rightleftharpoons\)2SO42−

1.96

S4O62− + 2e \(\rightleftharpoons\)2S2O32−

0.080

2SO32− + 2H2O(l) + 2e\(\rightleftharpoons\) S2O42− + 4OH

–1.13

2SO32− + 3H2O(l) + 4e\(\rightleftharpoons\)S2O32− + 6OH

 

2SO42− + 4H+ + 2e\(\rightleftharpoons\) S2O62− + 2H2O(l)

–0.25

SO42− + H2O(l) + 2e\(\rightleftharpoons\) SO32−+ 2OH

–0.936

SO42− + 4H+ + 2e\(\rightleftharpoons\) H2SO32−+ H2O(l)

0.172
Thallium  
\[Tl^{3+} + 2e^− \rightleftharpoons Tl^+\] 0.77 in 1 M HCl
Tl3+ + 3e \(\rightleftharpoons\) Tl(s) 0.742
Tin  
Sn2+ + 2e\(\rightleftharpoons\) Sn(s) -0.14

Sn4+ + 2e \(\rightleftharpoons\) Sn2+

0.154
Titanium  
\[Ti^{2+} + 2e^− \rightleftharpoons Ti(s)\] –0.163

Ti3+ + e \(\rightleftharpoons\) Ti2+

–0.37
Tungsten  
\[WO_2(s) + 4H^+ + 4e^− \rightleftharpoons W(s) + 2H_2O(l)\] –0.119

WO3(s) + 6H+ + 6e \(\rightleftharpoons\) W(s) + 3H2O(l)

–0.090
Uranium  
U3+ + 3e \(\rightleftharpoons\) U(s) –1.66

U4+ + e \(\rightleftharpoons\) U3+

–0.52

UO2+ + 4H+ + e\(\rightleftharpoons\)U4+ + 2H2O(l)

0.27

UO22+ + e\(\rightleftharpoons\)UO2+

0.16

UO22+ + 4H+ + 2e\(\rightleftharpoons\) U4+ + 2H2O(l)

0.327
Vanadium  
\[V^{2+} + 2e^− \rightleftharpoons V(s)\] –1.13

V3+ + e \(\rightleftharpoons\) V2+

–0.255

VO2+ + 2H+ +e \(\rightleftharpoons\)V3+ + H2O(l)

0.337

VO22+ + 2H+  +e \(\rightleftharpoons\) VO2+ + H2O(l)

1.000
Zinc  

Zn2+(aq) + 2e− \(\rightleftharpoons\) Zn(s)

–0.7618

Zn(OH)42− + 2e \(\rightleftharpoons\) Zn(s) + 4OH

–1.285

Zn(NH3)42+ + 2e \(\rightleftharpoons\) Zn(s) + 4NH3

–1.04

Zn(CN)42− + 2e \(\rightleftharpoons\) Zn(s) + 4CN

–1.34