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electrochemical series

Petr Vanýsek

There are three tables for this electrochemical series . Each table lists standard reduction potentials, E° values, at 298 .15 K (25 °C), and at a pressure of 101 .325 kPa (1 atm) . Table 1 is an alphabetical listing of the elements, according to the symbol of the elements . Thus, data for silver (Ag) precede those for aluminum (Al) . Table 2 lists only those reduction reactions that have E° values posi-tive in respect to the standard hydrogen electrode . In Table 2, the reactions are listed in the order of increasing positive potential, and they range from 0 .0000 V to + 3 .4 V . Table 3 lists only those reduction potentials which have E° negative with respect to the standard hydrogen electrode . In Table 3, the reactions are listed in the order of decreasing potential and range from 0 .0000 V to –4 .10 V . The reliability of the potentials is not the same for all the data . Typically, the values with fewer significant figures have lower

reliability . The values of reduction potentials, in particular those of less common reactions, are not definite; they are subject to oc-casional revisions .Abbreviations: ac = acetate; bipy = 2,2´-dipyridine, or bipyridine; en = ethylenediamine; phen = 1,10-phenanthroline .

references 1 . Milazzo, G ., Caroli, S ., and Sharma, V . K . Tables of Standard Electrode

Potentials, Wiley, Chichester, 1978 . 2 . Bard, A . J ., Parsons, R ., and Jordan, J . Standard Potentials in Aqueous

Solutions, Marcel Dekker, New York, 1985 . 3 . Bratsch, S . G . J. Phys. Chem. Ref. Data, 18, 1–21, 1989 .

Reaction E°/VAc3+ + 3 e ⇌ Ac –2 .20Ag+ + e ⇌ Ag 0 .7996Ag2+ + e ⇌ Ag+ 1 .980Ag(ac) + e ⇌ Ag + (ac)– 0 .643AgBr + e ⇌ Ag + Br– 0 .07133AgBrO3 + e ⇌ Ag + BrO3

– 0 .546Ag2C2O4 + 2 e ⇌ 2 Ag + C2O4

2– 0 .4647AgCl + e ⇌ Ag + Cl– 0 .22233AgCN + e ⇌ Ag + CN– –0 .017Ag2CO3 + 2 e ⇌ 2 Ag + CO3

2– 0 .47Ag2CrO4 + 2 e ⇌ 2 Ag + CrO4

2– 0 .4470AgF + e ⇌ Ag + F– 0 .779Ag4[Fe(CN)6] + 4 e ⇌ 4 Ag + [Fe(CN)6]

4– 0 .1478AgI + e ⇌ Ag + I– –0 .15224AgIO3 + e ⇌ Ag + IO3

– 0 .354Ag2MoO4 + 2 e ⇌ 2 Ag + MoO4

2– 0 .4573AgNO2 + e ⇌ Ag + 2 NO2

– 0 .564Ag2O + H2O + 2 e ⇌ 2 Ag + 2 OH– 0 .342Ag2O3 + H2O + 2 e ⇌ 2 AgO + 2 OH– 0 .739Ag3+ + 2 e ⇌ Ag+ 1 .9Ag3+ + e ⇌ Ag2+ 1 .8Ag2O2 + 4 H+ + e ⇌ 2 Ag + 2 H2O 1 .8022 AgO + H2O + 2 e ⇌ Ag2O + 2 OH– 0 .607AgOCN + e ⇌ Ag + OCN– 0 .41Ag2S + 2 e ⇌ 2 Ag + S2– –0 .691Ag2S + 2 H+ + 2 e ⇌ 2 Ag + H2S –0 .0366AgSCN + e ⇌ Ag + SCN– 0 .08951Ag2SeO3 + 2 e ⇌ 2 Ag + SeO4

2– 0 .3629Ag2SO4 + 2 e ⇌ 2 Ag + SO4

2– 0 .654Ag2WO4 + 2 e ⇌ 2 Ag + WO4

2– 0 .4660Al3+ + 3 e ⇌ Al –1 .662Al(OH)3 + 3 e ⇌ Al + 3 OH– –2 .31Al(OH)4

– + 3 e ⇌ Al + 4 OH– –2 .328H2AlO3

– + H2O + 3 e ⇌ Al + 4 OH– –2 .33AlF6

3– + 3 e ⇌ Al + 6 F– –2 .069Am4+ + e ⇌ Am3+ 2 .60Am2+ + 2 e ⇌ Am –1 .9Am3+ + 3 e ⇌ Am –2 .048Am3+ + e ⇌ Am2+ –2 .3

Reaction E°/VAs + 3 H+ + 3 e ⇌ AsH3 –0 .608As2O3 + 6 H+ + 6 e ⇌ 2 As + 3 H2O 0 .234HAsO2 + 3 H+ + 3 e ⇌ As + 2 H2O 0 .248AsO2

– + 2 H2O + 3 e ⇌ As + 4 OH– –0 .68H3AsO4 + 2 H+ + 2 e– ⇌ HAsO2 + 2 H2O 0 .560AsO4

3– + 2 H2O + 2 e ⇌ AsO2– + 4 OH– –0 .71

At2 + 2 e ⇌ 2 At– 0 .3Au+ + e ⇌ Au 1 .692Au3+ + 2 e ⇌ Au+ 1 .401Au3+ + 3 e ⇌ Au 1 .498Au2+ + e – ⇌ Au+ 1 .8AuOH2+ + H+ + 2 e ⇌ Au+ + H2O 1 .32AuBr2

– + e ⇌ Au + 2 Br– 0 .959AuBr4

– + 3 e ⇌ Au + 4 Br– 0 .854AuCl4

– + 3 e ⇌ Au + 4 Cl– 1 .002Au(OH)3 + 3 H+ + 3 e ⇌ Au + 3 H2O 1 .45H2BO3

– + 5 H2O + 8 e ⇌ BH4– + 8 OH– –1 .24

H2BO3– + H2O + 3 e ⇌ B + 4 OH– –1 .79

H3BO3 + 3 H+ + 3 e ⇌ B + 3 H2O –0 .8698B(OH)3 + 7 H+ + 8 e ⇌ BH4

– + 3 H2O –0 .481Ba2+ + 2 e ⇌ Ba –2 .912Ba2+ + 2 e ⇌ Ba(Hg) –1 .570Ba(OH)2 + 2 e ⇌ Ba + 2 OH– –2 .99Be2+ + 2 e ⇌ Be –1 .847Be2O3

2– + 3 H2O + 4 e ⇌ 2 Be + 6 OH– –2 .63p–benzoquinone + 2 H+ + 2 e ⇌

hydroquinone0 .6992

Bi+ + e ⇌ Bi 0 .5Bi3+ + 3 e ⇌ Bi 0 .308Bi3+ + 2 e ⇌ Bi+ 0 .2Bi + 3 H+ + 3 e ⇌ BiH3 –0 .8BiCl4

– + 3 e ⇌ Bi + 4 Cl– 0 .16Bi2O3 + 3 H2O + 6 e ⇌ 2 Bi + 6 OH– –0 .46Bi2O4 + 4 H+ + 2 e ⇌ 2 BiO+ + 2 H2O 1 .593BiO+ + 2 H+ + 3 e ⇌ Bi + H2O 0 .320BiOCl + 2 H+ + 3 e ⇌ Bi + Cl– + H2O 0 .1583Bk4+ + e ⇌ Bk3+ 1 .67Bk2+ + 2 e ⇌ Bk –1 .6Bk3+ + e ⇌ Bk2+ –2 .8

TABLE 1. Alphabetical Listing

5-80

Reaction E°/VBr2(aq) + 2 e ⇌ 2 Br– 1 .0873Br2(l) + 2 e ⇌ 2 Br– 1 .066HBrO + H+ + 2 e ⇌ Br– + H2O 1 .331HBrO + H+ + e ⇌ 1/2 Br2(aq) + H2O 1 .574HBrO + H+ + e ⇌ 1/2 Br2(l) + H2O 1 .596BrO– + H2O + 2 e ⇌ Br– + 2 OH– 0 .761BrO3

– + 6 H+ + 5 e ⇌ 1/2 Br2 + 3 H2O 1 .482BrO3

– + 6 H+ + 6 e ⇌ Br– + 3 H2O 1 .423BrO3

– + 3 H2O + 6 e ⇌ Br– + 6 OH– 0 .61(CN)2 + 2 H+ + 2 e ⇌ 2 HCN 0 .3732 HCNO + 2 H+ + 2 e ⇌ (CN)2 + 2 H2O 0 .330(CNS)2 + 2 e ⇌ 2 CNS– 0 .77CO2 + 2 H+ + 2 e ⇌ HCOOH –0 .199Ca+ + e ⇌ Ca –3 .80Ca2+ + 2 e ⇌ Ca –2 .868Ca(OH)2 + 2 e ⇌ Ca + 2 OH– –3 .02Calomel electrode, 1 molal KCl 0 .2800Calomel electrode, 1 molar KCl (NCE) 0 .2801Calomel electrode, 0 .1 molar KCl 0 .3337Calomel electrode, saturated KCl (SCE) 0 .2412Calomel electrode, saturated NaCl (SSCE) 0 .2360Cd2+ + 2 e ⇌ Cd –0 .4030Cd2+ + 2 e ⇌ Cd(Hg) –0 .3521Cd(OH)2 + 2 e ⇌ Cd(Hg) + 2 OH– –0 .809CdSO4 + 2 e ⇌ Cd + SO4

2– –0 .246Cd(OH)4

2– + 2 e ⇌ Cd + 4 OH– –0 .658CdO + H2O + 2 e ⇌ Cd + 2 OH– –0 .783Ce3+ + 3 e ⇌ Ce –2 .336Ce3+ + 3 e ⇌ Ce(Hg) –1 .4373Ce4+ + e ⇌ Ce3+ 1 .72CeOH3+ + H+ + e ⇌ Ce3+ + H2O 1 .715Cf4+ + e ⇌ Cf3+ 3 .3Cf3+ + e ⇌ Cf2+ –1 .6Cf3+ + 3 e ⇌ Cf –1 .94Cf2+ + 2 e ⇌ Cf –2 .12Cl2(g) + 2 e ⇌ 2 Cl– 1 .35827HClO + H + + e ⇌ 1/2 Cl2 + H2O 1 .611HClO + H+ + 2 e ⇌ Cl– + H2O 1 .482ClO– + H2O + 2 e ⇌ Cl– + 2 OH– 0 .81ClO2 + H+ + e ⇌ HClO2 1 .277HClO2 + 2 H+ + 2 e ⇌ HClO + H2O 1 .645HClO2 + 3 H+ + 3 e ⇌ 1/2 Cl2 + 2 H2O 1 .628HClO2 + 3 H+ + 4 e ⇌ Cl– + 2 H2O 1 .570ClO2

– + H2O + 2 e ⇌ ClO– + 2 OH– 0 .66ClO2

– + 2 H2O + 4 e ⇌ Cl– + 4 OH– 0 .76ClO2(aq) + e ⇌ ClO2

– 0 .954ClO3

– + 2 H+ + e ⇌ ClO2 + H2O 1 .152ClO3

– + 3 H+ + 2 e ⇌ HClO2 + H2O 1 .214ClO3

– + 6 H+ + 5 e ⇌ 1/2 Cl2 + 3 H2O 1 .47ClO3

– + 6 H+ + 6 e ⇌ Cl– + 3 H2O 1 .451ClO3

– + H2O + 2 e ⇌ ClO2– + 2 OH– 0 .33

ClO3– + 3 H2O + 6 e ⇌ Cl– + 6 OH– 0 .62

ClO4– + 2 H+ + 2 e ⇌ ClO3

– H2O 1 .189ClO4

– + 8 H+ + 7 e ⇌ 1/2 Cl2 + 4 H2O 1 .39ClO4

– + 8 H+ + 8 e ⇌ Cl– + 4 H2O 1 .389ClO4

– + H2O + 2 e ⇌ ClO3– + 2 OH– 0 .36

Cm4+ + e ⇌ Cm3+ 3 .0Cm3+ + 3 e ⇌ Cm –2 .04Co2+ + 2 e ⇌ Co –0 .28Co3+ + e ⇌ Co2+ 1 .92

Reaction E°/V[Co(NH3)6]

3+ + e ⇌ [Co(NH3)6]2+ 0 .108

Co(OH)2 + 2 e ⇌ Co + 2 OH– –0 .73Co(OH)3 + e ⇌ Co(OH)2 + OH– 0 .17Cr2+ + 2 e ⇌ Cr –0 .913Cr3+ + e ⇌ Cr2+ –0 .407Cr3+ + 3 e ⇌ Cr –0 .744Cr2O7

2– + 14 H+ + 6 e ⇌ 2 Cr3+ + 7 H2O 1 .36CrO2

– + 2 H2O + 3 e ⇌ Cr + 4 OH– –1 .2HCrO4

– + 7 H+ + 3 e ⇌ Cr3+ + 4 H2O 1 .350CrO2 + 4 H+ + e ⇌ Cr3+ + 2H2O 1 .48Cr(V) + e ⇌ Cr(IV) 1 .34CrO4

2– + 4 H2O + 3 e ⇌ Cr(OH)3 + 5 OH– –0 .13Cr(OH)3 + 3 e ⇌ Cr + 3 OH– –1 .48Cs+ + e ⇌ Cs –3 .026Cu+ + e ⇌ Cu 0 .521Cu2+ + e ⇌ Cu+ 0 .153Cu2+ + 2 e ⇌ Cu 0 .3419Cu2+ + 2 e ⇌ Cu(Hg) 0 .345Cu3+ + e ⇌ Cu2+ 2 .4Cu2O3 + 6 H+ + 2e ⇌ 2Cu2+ + 3 H2O 2 .0Cu2+ + 2 CN– + e ⇌ [Cu(CN)2]

– 1 .103CuI2

– + e ⇌ Cu + 2 I– 0 .00Cu2O + H2O + 2 e ⇌ 2 Cu + 2 OH– –0 .360Cu(OH)2 + 2 e ⇌ Cu + 2 OH– –0 .2222 Cu(OH)2 + 2 e ⇌ Cu2O + 2 OH– + H2O –0 .0802 D+ + 2 e ⇌ D2 –0 .013Dy2+ + 2 e ⇌ Dy –2 .2Dy3+ + 3 e ⇌ Dy –2 .295Dy3+ + e ⇌ Dy2+ –2 .6Er2+ + 2 e ⇌ Er –2 .0Er3+ + 3 e ⇌ Er –2 .331Er3+ + e ⇌ Er2+ –3 .0Es3+ + e ⇌ Es2+ –1 .3Es3+ + 3 e ⇌ Es –1 .91Es2+ + 2 e ⇌ Es –2 .23Eu2+ + 2 e ⇌ Eu –2 .812Eu3+ + 3 e ⇌ Eu –1 .991Eu3+ + e ⇌ Eu2+ –0 .36F2 + 2 H+ + 2 e ⇌ 2 HF 3 .053F2 + 2 e ⇌ 2 F– 2 .866F2O + 2 H+ + 4 e ⇌ H2O + 2 F– 2 .153Fe2+ + 2 e ⇌ Fe –0 .447Fe3+ + 3 e ⇌ Fe –0 .037Fe3+ + e ⇌ Fe2+ 0 .7712 HFeO4

– + 8 H+ + 6 e ⇌ Fe2O3 + 5 H2O 2 .09HFeO4

– + 4 H+ + 3 e ⇌ FeOOH + 2 H2O 2 .08HFeO4

– + 7 H+ + 3 e ⇌ Fe3+ + 4 H2O 2 .07Fe2O3 + 4 H+ + 2 e ⇌ 2 FeOH+ + H2O 0 .16[Fe(CN)6]

3– + e ⇌ [Fe(CN)6]4– 0 .358

FeO42– + 8 H+ + 3 e Fe3+ + 4 H2O 2 .20

[Fe(bipy)2]3+ + e ⇌ Fe(bipy)2]

2+ 0 .78[Fe(bipy)3]

3+ + e ⇌ Fe(bipy)3]2+ 1 .03

Fe(OH)3 + e ⇌ Fe(OH)2 + OH– –0 .56[Fe(phen)3]

3+ + e ⇌ [Fe(phen)3]2+ 1 .147

[Fe(phen)3]3+ + e ⇌ [Fe(phen)3]

2+ (1 molar H2SO4) 1 .06

[Ferricinium]+ + e ⇌ ferrocene 0 .400Fm3++ e ⇌ Fm2+ –1 .1Fm3+ + 3 e ⇌ Fm –1 .89Fm2+ + 2 e ⇌ Fm –2 .30

Electrochemical Series 5-81

Reaction E°/VFr+ + e ⇌ Fr –2 .9Ga3+ + 3 e ⇌ Ga –0 .549Ga+ + e ⇌ Ga –0 .2GaOH2+ + H+ + 3 e ⇌ Ga + H2O –0 .498H2GaO–

3 + H2O + 3 e ⇌ Ga + 4 OH– –1 .219Gd3+ + 3 e ⇌ Gd –2 .279Ge2+ + 2 e ⇌ Ge 0 .24Ge4+ + 4 e ⇌ Ge 0 .124Ge4+ + 2 e ⇌ Ge2+ 0 .00GeO2 + 2 H+ + 2 e ⇌ GeO + H2O –0 .118H2GeO3 + 4 H+ + 4 e ⇌ Ge + 3 H2O –0 .1822 H+ + 2 e ⇌ H2 0 .00000H2 + 2 e ⇌ 2 H– –2 .23HO2 + H+ + e ⇌ H2O2 1 .4952 H2O + 2 e ⇌ H2 + 2 OH– –0 .8277H2O2 + 2 H+ + 2 e ⇌ 2 H2O 1 .776Hf4+ + 4 e ⇌ Hf –1 .55HfO2+ + 2 H+ + 4 e ⇌ Hf + H2O –1 .724HfO2 + 4 H+ + 4 e ⇌ Hf + 2 H2O –1 .505HfO(OH)2 + H2O + 4 e ⇌ Hf + 4 OH– –2 .50Hg2+ + 2 e ⇌ Hg 0 .8512 Hg2+ + 2 e ⇌ Hg2

2+ 0 .920Hg2

2+ + 2 e ⇌ 2 Hg 0 .7973Hg2(ac)2 + 2 e ⇌ 2 Hg + 2(ac)– 0 .51163Hg2Br2 + 2 e ⇌ 2 Hg + 2 Br– 0 .13923Hg2Cl2 + 2 e ⇌ 2 Hg + 2 Cl– 0 .26808Hg2HPO4 + 2 e ⇌ 2 Hg + HPO4

2– 0 .6359Hg2I2 + 2 e ⇌ 2 Hg + 2 I– –0 .0405Hg2O + H2O + 2 e ⇌ 2 Hg + 2 OH– 0 .123HgO + H2O + 2 e ⇌ Hg + 2 OH– 0 .0977Hg(OH)2 + 2 H+ + 2 e ⇌ Hg + 2 H2O 1 .034Hg2SO4 + 2 e ⇌ 2 Hg + SO4

2– 0 .6125Ho2+ + 2 e ⇌ Ho –2 .1Ho3+ + 3 e ⇌ Ho –2 .33Ho3+ + e ⇌ Ho2+ –2 .8I2 + 2 e ⇌ 2 I– 0 .5355I3

– + 2 e ⇌ 3 I– 0 .536H3IO6

2– + 2 e ⇌ IO–3 + 3 OH– 0 .7

H5IO6 + H+ + 2 e ⇌ IO3– + 3 H2O 1 .601

2 HIO + 2 H+ + 2 e ⇌ I2 + 2 H2O 1 .439HIO + H+ + 2 e ⇌ I– + H2O 0 .987IO– + H2O + 2 e ⇌ I– + 2 OH– 0 .4852 IO3

– + 12 H+ + 10 e ⇌ I2 + 6 H2O 1 .195IO3

– + 6 H+ + 6 e ⇌ I– + 3 H2O 1 .085IO3

– + 2 H2O + 4 e ⇌ IO– + 4 OH– 0 .15IO3

– + 3 H2O + 6 e ⇌ IO– + 6 OH– 0 .26In+ + e ⇌ In –0 .14In2+ + e ⇌ In+ –0 .40In3+ + e ⇌ In2+ –0 .49In3+ + 2 e ⇌ In+ –0 .443In3+ + 3 e ⇌ In –0 .3382In(OH)3 + 3 e ⇌ In + 3 OH– –0 .99In(OH)4

– + 3 e ⇌ In + 4 OH– –1 .007In2O3 + 3 H2O + 6 e ⇌ 2 In + 6 OH– –1 .034Ir3+ + 3 e ⇌ Ir 1 .156[IrCl6]

2– + e ⇌ [IrCl6]3– 0 .8665

[IrCl6]3– + 3 e ⇌ Ir + 6 Cl– 0 .77

Ir2O3 + 3 H2O + 6 e ⇌ 2 Ir + 6 OH– 0 .098K+ + e ⇌ K –2 .931La3+ + 3 e ⇌ La –2 .379

Reaction E°/VLa(OH)3 + 3 e ⇌ La + 3 OH– –2 .90Li+ + e ⇌ Li –3 .0401Lr3+ + 3 e ⇌ Lr –1 .96Lu3+ + 3 e ⇌ Lu –2 .28Md3+ + e ⇌ Md2+ –0 .1Md3+ + 3 e ⇌ Md –1 .65Md2+ + 2 e ⇌ Md –2 .40Mg+ + e ⇌ Mg –2 .70Mg2+ + 2 e ⇌ Mg –2 .372Mg(OH)2 + 2 e ⇌ Mg + 2 OH– –2 .690Mn2+ + 2 e ⇌ Mn –1 .185Mn3+ + e ⇌ Mn2+ 1 .5415MnO2 + 4 H+ + 2 e ⇌ Mn2+ + 2 H2O 1 .224MnO4

– + e ⇌ MnO42– 0 .558

MnO4– + 4 H+ + 3 e ⇌ MnO2 + 2 H2O 1 .679

MnO4– + 8 H+ + 5 e ⇌ Mn2+ + 4 H2O 1 .507

MnO4– + 2 H2O + 3 e ⇌ MnO2 + 4 OH– 0 .595

MnO42– + 2 H2O + 2 e ⇌ MnO2 + 4 OH– 0 .60

Mn(OH)2 + 2 e ⇌ Mn + 2 OH– –1 .56Mn(OH)3 + e ⇌ Mn(OH)2 + OH– 0 .15Mn2O3 + 6 H+ + e ⇌ 2 Mn2+ + 3 H2O 1 .485Mo3+ + 3 e ⇌ Mo –0 .200MoO2 + 4 H+ + 4 e ⇌ Mo + 4 H2O –0 .152H3Mo7O24

3– + 45 H+ + 42 e ⇌ 7 Mo + 24 H2O 0 .082MoO3 + 6 H+ + 6 e ⇌ Mo + 3 H2O 0 .075N2 + 2 H2O + 6 H+ + 6 e ⇌ 2 NH4OH 0 .0923 N2 + 2 H+ + 2 e ⇌ 2 HN3 –3 .09N5

+ + 3 H+ + 2 e ⇌ 2 NH4+ 1 .275

N2O + 2 H+ + 2 e ⇌ N2 + H2O 1 .766H2N2O2 + 2 H+ + 2 e ⇌ N2 + 2 H2O 2 .65N2O4 + 2 e ⇌ 2 NO2

– 0 .867N2O4 + 2 H+ + 2 e ⇌ 2 NHO2 1 .065N2O4 + 4 H+ + 4 e ⇌ 2 NO + 2 H2O 1 .0352 NH3OH+ + H+ + 2 e ⇌ N2H5

+ + 2 H2O 1 .422 NO + 2 H+ + 2 e ⇌ N2O + H2O 1 .5912 NO + H2O + 2 e ⇌ N2O + 2 OH– 0 .76HNO2 + H+ + e ⇌ NO + H2O 0 .9832 HNO2 + 4 H+ + 4 e ⇌ H2N2O2 + 2 H2O 0 .862 HNO2 + 4 H+ + 4 e ⇌ N2O + 3 H2O 1 .297NO2

– + H2O + e ⇌ NO + 2 OH– –0 .462 NO2

– + 2 H2O + 4 e ⇌ N2O22– + 4 OH– –0 .18

2 NO2– + 3 H2O + 4 e ⇌ N2O + 6 OH– 0 .15

NO3– + 3 H+ + 2 e ⇌ HNO2 + H2O 0 .934

NO3– + 4 H+ + 3 e ⇌ NO + 2 H2O 0 .957

2 NO3– + 4 H+ + 2 e ⇌ N2O4 + 2 H2O 0 .803

NO3– + H2O + 2 e ⇌ NO2

– + 2 OH– 0 .012 NO3

– + 2 H2O + 2 e ⇌ N2O4 + 4 OH– –0 .85Na+ + e ⇌ Na –2 .71Nb3+ + 3 e ⇌ Nb –1 .099NbO2 + 2 H+ + 2 e ⇌ NbO + H2O –0 .646NbO2 + 4 H+ + 4 e ⇌ Nb + 2 H2O –0 .690NbO + 2 H+ + 2 e ⇌ Nb + H2O –0 .733Nb2O5 + 10 H+ + 10 e ⇌ 2 Nb + 5 H2O –0 .644Nd3+ + 3 e ⇌ Nd –2 .323Nd2+ + 2 e ⇌ Nd –2 .1Nd3+ + e ⇌ Nd2+ –2 .7Ni2+ + 2 e ⇌ Ni –0 .257Ni(OH)2 + 2 e ⇌ Ni + 2 OH– –0 .72NiO2 + 4 H+ + 2 e ⇌ Ni2+ + 2 H2O 1 .678NiO2 + 2 H2O + 2 e ⇌ Ni(OH)2 + 2 OH– –0 .490

5-82 Electrochemical Series

Reaction E°/VNo3+ + e ⇌ No2+ 1 .4No3+ + 3 e ⇌ No –1 .20No2+ + 2 e ⇌ No –2 .50Np3+ + 3 e ⇌ Np –1 .856Np4+ + e ⇌ Np3+ 0 .147NpO2 + H2O + H+ + e ⇌ Np(OH)3 –0 .962O2 + 2 H+ + 2 e ⇌ H2O2 0 .695O2 + 4 H+ + 4 e ⇌ 2 H2O 1 .229O2 + H2O + 2 e ⇌ HO2

– + OH– –0 .076O2 + 2 H2O + 2 e ⇌ H2O2 + 2 OH– –0 .146O2 + 2 H2O + 4 e ⇌ 4 OH– 0 .401O3 + 2 H+ + 2 e ⇌ O2 + H2O 2 .076O3 + H2O + 2 e ⇌ O2 + 2 OH– 1 .24O(g) + 2 H+ + 2 e ⇌ H2O 2 .421OH + e ⇌ OH– 2 .02HO2

– + H2O + 2 e ⇌ 3 OH– 0 .878OsO4 + 8 H+ + 8 e ⇌ Os + 4 H2O 0 .838OsO4 + 4 H+ + 4 e ⇌ OsO2 + 2 H2O 1 .02[Os(bipy)2]

3+ + e ⇌ [Os(bipy)2]2+ 0 .81

[Os(bipy)3]3+ + e ⇌ [Os(bipy)3]

2+ 0 .80P(red) + 3 H+ + 3 e ⇌ PH3(g) –0 .111P(white) + 3 H+ + 3 e ⇌ PH3(g) –0 .063P + 3 H2O + 3 e ⇌ PH3(g) + 3 OH– –0 .87H2P2

– + e ⇌ P + 2 OH– –1 .82H3PO2 + H+ + e ⇌ P + 2 H2O –0 .508H3PO3 + 2 H+ + 2 e ⇌ H3PO2 + H2O –0 .499H3PO3 + 3 H+ + 3 e ⇌ P + 3 H2O –0 .454HPO3

2– + 2 H2O + 2 e ⇌ H2PO2– + 3 OH– –1 .65

HPO32– + 2 H2O + 3 e ⇌ P + 5 OH– –1 .71

H3PO4 + 2 H+ + 2 e ⇌ H3PO3 + H2O –0 .276PO4

3– + 2 H2O + 2 e ⇌ HPO32– + 3 OH– –1 .05

Pa3+ + 3 e ⇌ Pa –1 .34Pa4+ + 4 e ⇌ Pa –1 .49Pa4+ + e ⇌ Pa3+ –1 .9Pb2+ + 2 e ⇌ Pb –0 .1262Pb2+ + 2 e ⇌ Pb(Hg) –0 .1205PbBr2 + 2 e ⇌ Pb + 2 Br– –0 .284PbCl2 + 2 e ⇌ Pb + 2 Cl– –0 .2675PbF2 + 2 e ⇌ Pb + 2 F– –0 .3444PbHPO4 + 2 e ⇌ Pb + HPO4

2– –0 .465PbI2 + 2 e ⇌ Pb + 2 I– –0 .365PbO + H2O + 2 e ⇌ Pb + 2 OH– –0 .580PbO2 + 4 H+ + 2 e ⇌ Pb2+ + 2 H2O 1 .455HPbO2

– + H2O + 2 e ⇌ Pb + 3 OH– –0 .537PbO2 + H2O + 2 e ⇌ PbO + 2 OH– 0 .247PbO2 + SO4

2– + 4 H+ + 2 e ⇌ PbSO4 + 2 H2O 1 .6913PbSO4 + 2 e ⇌ Pb + SO4

2– –0 .3588PbSO4 + 2 e ⇌ Pb(Hg) + SO4

2– –0 .3505Pd2+ + 2 e ⇌ Pd 0 .951[PdCl4]

2– + 2 e ⇌ Pd + 4 Cl– 0 .591[PdCl6]

2– + 2 e ⇌ [PdCl4]2– + 2 Cl– 1 .288

Pd(OH)2 + 2 e ⇌ Pd + 2 OH– 0 .07Pm2+ + 2 e ⇌ Pm –2 .2Pm3+ + 3 e ⇌ Pm –2 .30Pm3+ + e ⇌ Pm2+ –2 .6Po4+ + 2 e ⇌ Po2+ 0 .9Po4+ + 4 e ⇌ Po 0 .76Pr4+ + e ⇌ Pr3+ 3 .2Pr2+ + 2 e ⇌ Pr –2 .0Pr3+ + 3 e ⇌ Pr –2 .353

Reaction E°/VPr3+ + e ⇌ Pr2+ –3 .1Pt2+ + 2 e ⇌ Pt 1 .18[PtCl4]

2– + 2 e ⇌ Pt + 4 Cl– 0 .755[PtCl6]

2– + 2 e ⇌ [PtCl4]2– + 2 Cl– 0 .68

Pt(OH)2 + 2 e ⇌ Pt + 2 OH– 0 .14PtO3 + 2 H+ + 2 e ⇌ PtO2 + H2O 1 .7PtO3 + 4 H+ + 2 e ⇌ Pt(OH)2

2+ + H2O 1 .5PtOH+ + H+ + 2 e ⇌ Pt + H2O 1 .2PtO2 + 2 H+ + 2 e ⇌ PtO + H2O 1 .01PtO2 + 4 H+ + 4 e ⇌ Pt + 2 H2O 1 .00Pu3+ + 3 e ⇌ Pu –2 .031Pu4+ + e ⇌ Pu3+ 1 .006Pu5+ + e ⇌ Pu4+ 1 .099PuO2(OH)2 + 2 H+ + 2 e ⇌ Pu(OH)4 1 .325PuO2(OH)2 + H+ + e ⇌ PuO2OH + H2O 1 .062Ra2+ + 2 e ⇌ Ra –2 .8Rb+ + e ⇌ Rb –2 .98Re3+ + 3 e ⇌ Re 0 .300ReO4

– + 4 H+ + 3 e ⇌ ReO2 + 2 H2O 0 .510ReO2 + 4 H+ + 4 e ⇌ Re + 2 H2O 0 .2513ReO4

– + 2 H+ + e ⇌ ReO3 + H2O 0 .768ReO4

– + 4 H2O + 7 e ⇌ Re + 8 OH– –0 .584ReO4

– + 8 H+ + 7 e ⇀ Re + 4 H2O 0 .368Rh+ + e ⇌ Rh 0 .600Rh3+ + 3 e ⇌ Rh 0 .758[RhCl6]

3– + 3 e ⇌ Rh + 6 Cl– 0 .431RhOH2+ + H+ + 3 e ⇌ Rh + H2O 0 .83Ru2+ + 2 e ⇌ Ru 0 .455Ru3+ + e ⇌ Ru2+ 0 .2487RuO2 + 4 H+ + 2 e ⇌ Ru2+ + 2 H2O 1 .120RuO4

– + e ⇌ RuO42– 0 .59

RuO4 + e ⇌ RuO4– 1 .00

RuO4 + 6 H+ + 4 e ⇌ Ru(OH)22+ + 2 H2O 1 .40

RuO4 + 8 H+ + 8 e ⇌ Ru + 4 H2O 1 .038[Ru(bipy)3)

3+ + e– ⇌ [Ru(bipy)3]2+ 1 .24

[Ru(H2O)6]3+ + e– ⇌ [Ru(H2O)6]

2+ 0 .23[Ru(NH3)6]

3+ + e– ⇌ [Ru(NH3)6]2+ 0 .10

[Ru(en)3]3+ + e – ⇌ [Ru(en)3]

2+ 0 .210[Ru(CN)6]

3– + e– ⇌ [Ru(CN)6]4– 0 .86

S + 2 e ⇌ S2– –0 .47627S + 2H+ + 2 e ⇌ H2S(aq) 0 .142S + H2O + 2 e ⇌ SH– + OH– –0 .4782 S + 2 e ⇌ S2

2– –0 .42836S2O6

2– + 4 H+ + 2 e ⇌ 2 H2SO3 0 .564S2O8

2– + 2 e ⇌ 2 SO42– 2 .010

S2O82– + 2 H+ + 2 e ⇌ 2 HSO4

– 2 .123S4O6

2– + 2 e ⇌ 2 S2O32– 0 .08

2 H2SO3 + H+ + 2 e ⇌ HS2O4– + 2 H2O –0 .056

H2SO3 + 4 H+ + 4 e ⇌ S + 3 H2O 0 .4492 SO3

2– + 2 H2O + 2 e ⇌ S2O42– + 4 OH– –1 .12

2 SO32– + 3 H2O + 4 e ⇌ S2O3

2– + 6 OH– –0 .571SO4

2– + 4 H+ + 2 e ⇌ H2SO3 + H2O 0 .1722 SO4

2– + 4 H+ + 2 e ⇌ S2O62– + H2O –0 .22

SO42– + H2O + 2 e ⇌ SO3

2– + 2 OH– –0 .93Sb + 3 H+ + 3 e ⇌ SbH3 –0 .510Sb2O3 + 6 H+ + 6 e ⇌ 2 Sb + 3 H2O 0 .152Sb2O5 (senarmontite) + 4 H+ + 4 e ⇌ Sb2O3 +

2 H2O0 .671

Sb2O5 (valentinite) + 4 H+ + 4 e ⇌ Sb2O3 + 2 H2O

0 .649


Reaction E°/VSb2O5 + 6 H+ + 4 e ⇌ 2 SbO+ + 3 H2O 0 .581SbO+ + 2 H+ + 3 e ⇌ Sb + 2 H2O 0 .212SbO2

– + 2 H2O + 3 e ⇌ Sb + 4 OH– –0 .66SbO3

– + H2O + 2 e ⇌ SbO2– + 2 OH– –0 .59

Sc3+ + 3 e ⇌ Sc –2 .077Se + 2 e ⇌ Se2– –0 .924Se + 2 H+ + 2 e ⇌ H2Se(aq) –0 .399H2SeO3 + 4 H+ + 4 e ⇌ Se + 3 H2O 0 .74Se + 2 H+ + 2 e ⇌ H2Se –0 .082SeO3

2– + 3 H2O + 4 e ⇌ Se + 6 OH– –0 .366SeO4

2– + 4 H+ + 2 e ⇌ H2SeO3 + H2O 1 .151SeO4

2– + H2O + 2 e ⇌ SeO32– + 2 OH– 0 .05

SiF62– + 4 e ⇌ Si + 6 F– –1 .24

SiO + 2 H+ + 2 e ⇌ Si + H2O –0 .8SiO2 (quartz) + 4 H+ + 4 e ⇌ Si + 2 H2O 0 .857SiO3

2– + 3 H2O + 4 e ⇌ Si + 6 OH– –1 .697Sm3+ + e ⇌ Sm2+ –1 .55Sm3+ + 3 e ⇌ Sm –2 .304Sm2+ + 2 e ⇌ Sm –2 .68Sn2+ + 2 e ⇌ Sn –0 .1375Sn4+ + 2 e ⇀ Sn2+ 0 .151Sn(OH)3

+ + 3 H+ + 2 e ⇌ Sn2+ + 3 H2O 0 .142SnO2 + 4 H+ + 2 e– ⇌ Sn2+ + 2 H2O –0 .094SnO2 + 4 H+ + 4 e ⇌ Sn + 2 H2O –0 .117SnO2 + 3 H+ + 2 e ⇌ SnOH+ + H2O –0 .194SnO2 + 2 H2O + 4 e ⇌ Sn + 4 OH– –0 .945HSnO2

– + H2O + 2 e ⇌ Sn + 3 OH– –0 .909Sn(OH)6

2– + 2 e ⇌ HSnO2– + 3 OH– + H2O –0 .93

Sr+ + e ⇌ Sr –4 .10Sr2+ + 2 e ⇌ Sr –2 .899Sr2+ + 2 e ⇌ Sr(Hg) –1 .793Sr(OH)2 + 2 e ⇌ Sr + 2 OH– –2 .88Ta2O5 + 10 H+ + 10 e ⇌ 2 Ta + 5 H2O –0 .750Ta3+ + 3 e ⇌ Ta –0 .6Tc2+ + 2 e ⇌ Tc 0 .400TcO4

– + 4 H+ + 3 e ⇌ TcO2 + 2 H2O 0 .782Tc3+ + e ⇌ Tc2+ 0 .3TcO4

– + 8 H+ + 7 e ⇌ Tc + 4 H2O 0 .472Tb4+ + e ⇌ Tb3+ 3 .1Tb3+ + 3 e ⇌ Tb –2 .28Te + 2 e ⇌ Te2– –1 .143Te + 2 H+ + 2 e ⇌ H2Te –0 .793Te4+ + 4 e ⇌ Te 0 .568TeO2 + 4 H+ + 4 e ⇌ Te + 2 H2O 0 .593TeO3

2– + 3 H2O + 4 e ⇌ Te + 6 OH– –0 .57TeO4

– + 8 H+ + 7 e ⇌ Te + 4 H2O 0 .472H6TeO6 + 2 H+ + 2 e ⇌ TeO2 + 4 H2O 1 .02Th4+ + 4 e ⇌ Th –1 .899ThO2 + 4 H+ + 4 e ⇌ Th + 2 H2O –1 .789Th(OH)4 + 4 e ⇌ Th + 4 OH– –2 .48Ti2+ + 2 e ⇌ Ti –1 .630Ti3+ + e ⇌ Ti2+ –0 .9TiO2 + 4 H+ + 2 e ⇌ Ti2+ + 2 H2O –0 .502Ti3+ + 3 e ⇌ Ti –1 .37TiOH3+ + H+ + e ⇌ Ti3+ + H2O –0 .055

Reaction E°/VTl+ + e ⇌ Tl –0 .336Tl+ + e ⇌ Tl(Hg) –0 .3338Tl3+ + 2 e ⇌ Tl+ 1 .252Tl3+ + 3 e ⇌ Tl 0 .741TlBr + e ⇌ Tl + Br– –0 .658TlCl + e ⇌ Tl + Cl– –0 .5568TlI + e ⇌ Tl + I– –0 .752Tl2O3 + 3 H2O + 4 e ⇌ 2 Tl+ + 6 OH– 0 .02TlOH + e ⇌ Tl + OH– –0 .34Tl(OH)3 + 2 e ⇌ TlOH + 2 OH– –0 .05Tl2SO4 + 2 e ⇌ Tl + SO4

2– –0 .4360Tm3+ + e ⇌ Tm2+ –2 .2Tm3+ + 3 e ⇌ Tm –2 .319Tm2+ + 2 e ⇌ Tm –2 .4U3+ + 3 e ⇌ U –1 .798U4+ + e ⇌ U3+ –0 .607UO2

+ + 4 H+ + e ⇌ U4+ + 2 H2O 0 .612UO2

2+ + e ⇌ UO+2 0 .062

UO22+ + 4 H+ + 2 e ⇌ U4+ + 2 H2O 0 .327

UO22+ + 4 H+ + 6 e ⇌ U + 2 H2O –1 .444

V2+ + 2 e ⇌ V –1 .175V3+ + e ⇌ V2+ –0 .255VO2+ + 2 H+ + e ⇌ V3+ + H2O 0 .337VO2

+ + 2 H+ + e ⇌ VO2+ + H2O 0 .991V2O5 + 6 H+ + 2 e ⇌ 2 VO2+ + 3 H2O 0 .957V2O5 + 10 H+ + 10 e ⇌ 2 V + 5 H2O –0 .242V(OH)4

+ + 2 H+ + e ⇌ VO2+ + 3 H2O 1 .00V(OH)4

+ + 4 H+ + 5 e ⇌ V + 4 H2O –0 .254[V(phen)3]

3+ + e ⇌ [V(phen)3]2+ 0 .14

W3+ + 3 e ⇌ W 0 .1W2O5 + 2 H+ + 2 e ⇌ 2 WO2 + H2O –0 .031WO2 + 4 H+ + 4 e ⇌ W + 2 H2O –0 .119WO3 + 6 H+ + 6 e ⇌ W + 3 H2O –0 .090WO3 + 2 H+ + 2 e ⇌ WO2 + H2O 0 .0362 WO3 + 2 H+ + 2 e ⇌ W2O5 + H2O –0 .029H4XeO6 + 2 H+ + 2 e ⇌ XeO3 + 3 H2O 2 .42XeO3 + 6 H+ + 6 e ⇌ Xe + 3 H2O 2 .10XeF + e ⇌ Xe + F– 3 .4Y3+ + 3 e ⇌ Y –2 .372Yb3+ + e ⇌ Yb2+ –1 .05Yb3+ + 3 e ⇌ Yb –2 .19Yb2+ + 2 e ⇌ Yb –2 .76Zn2+ + 2 e ⇌ Zn –0 .7618Zn2+ + 2 e ⇌ Zn(Hg) –0 .7628ZnO2

2– + 2 H2O + 2 e ⇌ Zn + 4 OH– –1 .215ZnSO4 · 7 H2O + 2 e = Zn(Hg) + SO4

2– + 7 H2O (Saturated ZnSO4)

–0 .7993

ZnOH+ + H+ + 2 e ⇌ Zn + H2O –0 .497Zn(OH)4

2– + 2 e ⇌ Zn + 4 OH– –1 .199Zn(OH)2 + 2 e ⇌ Zn + 2 OH– –1 .249ZnO + H2O + 2 e ⇌ Zn + 2 OH– –1 .260ZrO2 + 4 H+ + 4 e ⇌ Zr + 2 H2O –1 .553ZrO(OH)2 + H2O + 4 e ⇌ Zr + 4 OH– –2 .36Zr4+ + 4 e ⇌ Zr –1 .45


TABLE 2. Reduction Reactions Having E° Values More Positive than That of the Standard Hydrogen Electrode

Reaction E°/V2 H+ + 2 e ⇌ H2 0 .00000CuI2

– + e ⇌ Cu + 2 I– 0 .00Ge4+ + 2 e ⇌ Ge2+ 0 .00NO3

– + H2O + 2 e ⇌ NO2– + 2 OH– 0 .01

Tl2O3 + 3 H2O + 4 e ⇌ 2 Tl+ + 6 OH– 0 .02SeO4

2– + H2O + 2 e ⇌ SeO32– + 2 OH– 0 .05

WO3 + 2 H+ + 2 e ⇌ WO2 + H2O 0 .036UO2

2+ + e = UO2+ 0 .062

Pd(OH)2 + 2 e ⇌ Pd + 2 OH– 0 .07AgBr + e ⇌ Ag + Br– 0 .07133MoO3 + 6 H+ + 6 e ⇌ Mo + 3 H2O 0 .075S4O6

2– + 2 e ⇌ 2 S2O32– 0 .08

H3Mo7O243– + 45 H+ + 42 e ⇌ 7 Mo + 24 H2O 0 .082

AgSCN + e ⇌ Ag + SCN– 0 .8951N2 + 2 H2O + 6 H+ + 6 e ⇌ 2 NH4OH 0 .092HgO + H2O + 2 e ⇌ Hg + 2 OH– 0 .0977Ir2O3 + 3 H2O + 6 e ⇌ 2 Ir + 6 OH– 0 .0982 NO + 2 e ⇌ N2O2

2– 0 .10[Ru(NH3)6]

3+ + e ⇌ [Ru(NH3)6]2+ 0 .10

W3+ + 3 e ⇌ W 0 .1[Co(NH3)6]

3+ + e ⇌ [Co(NH3)6]2+ 0 .108

Hg2O + H2O + 2 e ⇌ 2 Hg + 2 OH– 0 .123Ge4+ + 4 e ⇌ Ge 0 .124Hg2Br2 + 2 e ⇌ 2 Hg + 2 Br– 0 .13923Pt(OH)2 + 2 e ⇌ Pt + 2 OH– 0 .14[V(phen)3]

3+ + e ⇌ [V(phen)3]2+ 0 .14

S + 2H+ + 2 e ⇌ H2S(aq) 0 .142Sn(OH)3

+ + 3 H+ + 2 e ⇌ Sn2+ + 3 H2O 0 .142Np4+ + e ⇌ Np3+ 0 .147Ag4[Fe(CN)6] + 4 e ⇌ 4 Ag + [Fe(CN)6]

4– 0 .1478IO3

– + 2 H2O + 4 e ⇌ IO– + 4 OH– 0 .15Mn(OH)3 + e ⇌ Mn(OH)2 + OH– 0 .152 NO2

– + 3 H2O + 4 e ⇌ N2O + 6 OH– 0 .15Sn4+ + 2 e ⇌ Sn2+ 0 .151Sb2O3 + 6 H+ + 6 e ⇌ 2 Sb + 3 H2O 0 .152Cu2+ + e ⇌ Cu+ 0 .153BiOCl + 2 H+ + 3 e ⇌ Bi + Cl– + H2O 0 .1583BiCl4

– + 3 e ⇌ Bi + 4 Cl– 0 .16Fe2O3 + 4 H+ + 2 e ⇌ 2 FeOH+ + H2O 0 .16Co(OH)3 + e ⇌ Co(OH)2 + OH– 0 .17SO4

2– + 4 H+ + 2 e ⇌ H2SO3 + H2O 0 .172Bi3+ + 2 e ⇌ Bi+ 0 .2[Ru(en)3]

3+ + e ⇌ [Ru(en)3]2+ 0 .210

SbO+ + 2 H+ + 3 e ⇌ Sb + 2 H2O 0 .212AgCl + e ⇌ Ag + Cl– 0 .22233[Ru(H2O)6]

3+ + e ⇌ [Ru(H2O)6]2+ 0 .23

As2O3 + 6 H+ + 6 e ⇌ 2 As + 3 H2O 0 .234Calomel electrode, saturated NaCl (SSCE) 0 .2360Ge2+ + 2 e ⇌ Ge 0 .24Ru3+ + e ⇌ Ru2+ 0 .24Calomel electrode, saturated KCl 0 .2412PbO2 + H2O + 2 e ⇌ PbO + 2 OH– 0 .247HAsO2 + 3 H+ + 3 e ⇌ As + 2 H2O 0 .248Ru3+ + e ⇀ Ru2+ 0 .2487ReO2 + 4 H+ + 4 e ⇌ Re + 2 H2O 0 .2513IO3

– + 3 H2O + 6 e ⇌ I– + OH– 0 .26

Reaction E°/VHg2Cl2 + 2 e ⇌ 2 Hg + 2 Cl– 0 .26808Calomel electrode, 1 molal KCl 0 .2800Calomel electrode, 1 molar KCl (NCE) 0 .2801At2 + 2 e ⇌ 2 At– 0 .3Re3+ + 3 e ⇌ Re 0 .300Tc3+ + e ⇌ Tc2+ 0 .3Bi3+ + 3 e ⇌ Bi 0 .308BiO+ + 2 H+ + 3 e ⇌ Bi + H2O 0 .320UO2

2+ + 4 H+ + 2 e ⇌ U4+ + 2 H2O 0 .327ClO3

– + H2O + 2 e ⇌ ClO2– + 2 OH– 0 .33

2 HCNO + 2 H+ + 2 e ⇌ (CN)2 + 2 H2O 0 .330Calomel electrode, 0 .1 molar KCl 0 .3337VO2+ + 2 H+ + e ⇌ V3+ + H2O 0 .337Cu2+ + 2 e ⇌ Cu 0 .3419Ag2O + H2O + 2 e ⇌ 2 Ag + 2 OH– 0 .342Cu2+ + 2 e ⇌ Cu(Hg) 0 .345AgIO3 + e ⇌ Ag + IO3

– 0 .354[Fe(CN)6]

3– + e ⇌ [Fe(CN)6]4– 0 .358

ClO4– + H2O + 2 e ⇌ ClO–

3 + 2 OH– 0 .36Ag2SeO3 + 2 e ⇌ 2 Ag + SeO3

2– 0 .3629ReO4

– + 8 H+ + 7 e ⇌ Re + 4 H2O 0 .368(CN)2 + 2 H+ + 2 e ⇌ 2 HCN 0 .373[Ferricinium]+ + e ⇌ ferrocene 0 .400Tc2+ + 2 e ⇌ Tc 0 .400O2 + 2 H2O + 4 e ⇌ 4 OH– 0 .401AgOCN + e ⇌ Ag + OCN– 0 .41[RhCl6]

3– + 3 e ⇌ Rh + 6 Cl– 0 .431Ag2CrO4 + 2 e ⇌ 2 Ag + CrO4

2– 0 .4470H2SO3 + 4 H+ + 4 e ⇌ S + 3 H2O 0 .449Ru2+ + 2 e ⇌ Ru 0 .455Ag2MoO4 + 2 e ⇌ 2 Ag + MoO4

2– 0 .4573Ag2C2O4 + 2 e ⇌ 2 Ag + C2O4

2– 0 .4647Ag2WO4 + 2 e ⇌ 2 Ag + WO4

2– 0 .4660Ag2CO3 + 2 e ⇌ 2 Ag + CO3

2– 0 .47TcO4

– + 8 H+ + 7 e ⇌ Tc + 4 H2O 0 .472TeO4

– + 8 H+ + 7 e ⇌ Te + 4 H2O 0 .472IO– + H2O + 2 e ⇌ I– + 2 OH– 0 .485NiO2 + 2 H2O + 2 e ⇌ Ni(OH)2 + 2 OH– 0 .490Bi+ + e ⇌ Bi 0 .5ReO4

– + 4 H+ + 3 e ⇌ ReO2 + 2 H2O 0 .510Hg2(ac)2 + 2 e ⇌ 2 Hg + 2(ac)– 0 .51163Cu+ + e ⇌ Cu 0 .521I2 + 2 e ⇌ 2 I– 0 .5355I3

– + 2 e ⇌ 3 I– 0 .536AgBrO3 + e ⇌ Ag + BrO3

– 0 .546MnO4

– + e ⇌ MnO4– 0 .558

H3AsO4 + 2 H+ + 2 e ⇌ HAsO2 + 2 H2O 0 .560S2O6

2– + 4 H+ + 2 e ⇌ 2 H2SO3 0 .564AgNO2 + e ⇌ Ag + NO2

– 0 .564Te4+ + 4 e ⇌ Te 0 .568Sb2O5 + 6 H+ + 4 e ⇌ 2 SbO+ + 3 H2O 0 .581RuO4

– + e ⇌ RuO42– 0 .59

[PdCl4]2– + 2 e ⇌ Pd + 4 Cl– 0 .591

TeO2 + 4 H+ + 4 e ⇌ Te + 2 H2O 0 .593MnO4

– + 2 H2O + 3 e ⇌ MnO2 + 4 OH– 0 .595Rh2+ + 2 e ⇌ Rh 0 .600


Reaction E°/VRh+ + e ⇌ Rh 0 .600MnO4

2– + 2 H2O + 2 e ⇌ MnO2 + 4 OH– 0 .602 AgO + H2O + 2 e ⇌ Ag2O + 2 OH– 0 .607BrO3

– + 3 H2O + 6 e ⇌ Br– + 6 OH– 0 .61UO2

+ + 4 H+ + e ⇌ U4+ + 2 H2O 0 .612Hg2SO4 + 2 e ⇌ 2 Hg + SO4

2– 0 .6125ClO3

– + 3 H2O + 6 e ⇌ Cl– + 6 OH– 0 .62Hg2HPO4 + 2 e ⇌ 2 Hg + HPO4

2– 0 .6359Ag(ac) + e ⇌ Ag + (ac)– 0 .643Sb2O5(valentinite) + 4 H+ + 4 e ⇌ Sb2O3 + 2 H2O 0 .649Ag2SO4 + 2 e ⇌ 2 Ag + SO4

2– 0 .654ClO2

– + H2O + 2 e ⇌ ClO– + 2 OH– 0 .66Sb2O5(senarmontite) + 4 H+ + 4 e ⇌ Sb2O5 + 2

H2O 0 .671[PtCl6]

2– + 2 e ⇌ [PtCl4]2– + 2 Cl– 0 .68

O2 + 2 H+ + 2 e ⇌ H2O2 0 .695p–benzoquinone + 2 H+ + 2 e ⇌⇌ hydroquinone 0 .6992H3IO6

2– + 2 e ⇌ IO3– + 3 OH– 0 .7

Ag2O3+ H2O + 2 e ⇌ 2 AgO + 2 OH– 0 .739Tl3+ + 3 e ⇌ Tl 0 .741[PtCl4]

2– + 2 e ⇌ Pt + 4 Cl– 0 .755Rh3+ + 3 e ⇌ Rh 0 .758ClO2

– + 2 H2O + 4 e ⇌ Cl– + 4 OH– 0 .762 NO + H2O + 2 e ⇌ N2O + 2 OH– 0 .76Po4+ + 4 e ⇌ Po 0 .76BrO– + H2O + 2 e ⇌ Br– + 2 OH– 0 .761ReO4

– + 2 H+ +e ⇌ ReO3 + H2O 0 .768(CNS)2 + 2 e ⇌ 2 CNS– 0 .77[IrCl6]

3– + 3 e ⇌ Ir + 6 Cl– 0 .77Fe3+ + e ⇌ Fe2+ 0 .771AgF + e ⇌ Ag + F– 0 .779[Fe(bipy)2]

3+ + e ⇌ [Fe(bipy)2]2+ 0 .78

TcO4– + 4 H+ + 3 e ⇌ TcO2 + 2 H2O 0 .782

Hg22+ + 2 e ⇌ 2 Hg 0 .7973

Ag+ + e ⇌ Ag 0 .7996[Os(bipy)3]

3+ + e ⇌ [Os(bipy)3]2+ 0 .80

2 NO3– + 4 H+ + 2 e ⇌ N2O4 + 2 H2O 0 .803

[Os(bipy)2]3+ + e ⇌ [Os(bipy)2]

2+ 0 .81 RhOH2+ + H + 3 e ⇌ Rh + H2O 0 .83OsO4 + 8 H+ + 8 e ⇌ Os + 4 H2O 0 .838ClO– + H2O + 2 e ⇌ Cl– + 2 OH– 0 .841Hg2+ + 2 e ⇌ Hg 0 .851AuBr4

– + 3 e ⇌ Au + 4 Br– 0 .854SiO2(quartz) + 4 H+ + 4 e ⇌ Si + 2 H2O 0 .8572 HNO2 + 4 H+ + 4 e ⇌ H2N2O2 + H2O 0 .86[Ru(CN)6]

3– + e– ⇌ [Ru(CN)6]4– 0 .86

[IrCl6]2– + e ⇌ [IrCl6]

3– 0 .8665N2O4 + 2 e ⇌ 2 NO2

– 0 .867HO2

– + H2O + 2 e ⇌ 3 OH– 0 .878Po4+ + 2 e ⇌ Po2+ 0 .92 Hg2+ + 2 e ⇌ Hg2

2+ 0 .920NO3

– + 3 H+ + 2 e ⇌ HNO2 + H2O 0 .934Pd2+ + 2 e ⇌ Pd 0 .951ClO2(aq) + e ⇌ ClO2

– 0 .954NO3

– + 4 H+ + 3 e ⇌ NO + 2 H2O 0 .957V2O5 + 6 H+ + 2 e ⇌ 2 VO2+ + 3 H2O 0 .957AuBr2

– + e ⇌ Au + 2 Br– 0 .959HNO2 + H+ + e ⇌ NO + H2O 0 .983

Reaction E°/VHIO + H+ + 2 e ⇌ I– + H2O 0 .987VO2

+ + 2 H+ + e ⇌ VO2+ + H2O 0 .991PtO2 + 4 H+ + 4 e ⇌ Pt + 2 H2O 1 .00RuO4 + e ⇌ RuO4

– 1 .00V(OH)4

+ + 2 H+ + e ⇌ VO2+ + 3 H2O 1 .00AuCl4

– + 3 e ⇌ Au + 4 Cl– 1 .002Pu4+ + e ⇌ Pu3+ 1 .006PtO2 + 2 H+ + 2 e ⇌ PtO + H2O 1 .01OsO4 + 4 H + 4 e ⇌ OsO2 + 2 H2O 1 .02H6TeO6 + 2 H+ + 2 e ⇌ TeO2 + 4 H2O 1 .02[Fe(bipy)3]

3+ + e ⇌ [Fe(bipy)3]2+ 1 .03

Hg(OH)2 + 2 H+ + 2 e ⇌ Hg + 2 H2O 1 .034N2O4 + 4 H+ + 4 e ⇌ 2 NO + 2 H2O 1 .035RuO4 + 8 H+ + 8 e ⇌ Ru + 4H2O 1 .038[Fe(phen)3]

3+ + e ⇌ [Fe(phen)3]2+ (1 molar H2SO4) 1 .06

PuO2(OH)2 + H+ + e ⇌ PuO2OH + H2O 1 .062N2O4 + 2 H+ + 2 e ⇌ 2 HNO2 1 .065Br2(l) + 2 e ⇌ 2Br– 1 .066IO3

– + 6 H+ + 6 e ⇌ I– + 3 H2O 1 .085Br2(aq) + 2 e ⇌ 2Br– 1 .0873Pu5+ + e ⇌ Pu4+ 1 .099Cu2+ + 2 CN– + e ⇌ [Cu(CN)2]

– 1 .103RuO2 + 4 H+ + 2 e ⇌ Ru2+ + 2 H2O 1 .120[Fe(phen)3]

3+ + e ⇌⇀ [Fe(phen)3]2+ 1 .147

SeO42– + 4 H+ + 2 e ⇌ H2SeO3 + H2O 1 .151

ClO3– + 2 H+ + e ⇌ ClO2 + H2O 1 .152

Ir3+ + 3 e ⇀ Ir 1 .156Pt2+ + 2 e ⇌ Pt 1 .18ClO4

– + 2 H+ + 2 e ⇌ ClO3– + H2O 1 .189

2 IO3– + 12 H+ + 10 e ⇌ I2 + 6 H2O 1 .195

PtOH+ + H+ + 2 e ⇌ Pt + H2O 1 .2ClO3

– + 3 H+ + 2 e ⇌ HClO2 + H2O 1 .214MnO2 + 4 H+ + 2 e ⇌ Mn2+ + 2 H2O 1 .224O2 + 4 H+ + 4 e ⇌ 2 H2O 1 .229O3 + H2O + 2 e ⇌ O2 + 2 OH– 1 .24[Ru(bipy)3]

3+ + e ⇌ [Ru(bipy)3]2+ 1 .24

Tl3+ + 2 e ⇌ Tl+ 1 .252N2H5

+ + 3 H+ + 2 e ⇌ 2 NH4+ 1 .275

ClO2 + H+ + e ⇌ HClO2 1 .277[PdCl6]

2– + 2 e ⇌ [PdCl4]2– + 2 Cl– 1 .288

2 HNO2 + 4 H+ + 4 e ⇌ N2O + 3 H2O 1 .297AuOH2+ + H+ + 2 e ⇌ Au+ + H2O 1 .32PuO2(OH)2 + 2 H– + 2 e ⇌ Pu(OH)4 1 .325HBrO + H+ + 2 e ⇌ Br– + H2O 1 .331Cr(V) + e ⇌ Cr(IV) 1 .34HCrO4

– + 7 H+ + 3 e ⇌ Cr3+ + 4 H2O 1 .350Cl2(g) + 2 e ⇌ 2Cl– 1 .35827Cr2O7

2– + 14 H+ + 6 e ⇌ 2 Cr3+ + 7 H2O 1 .36ClO4

– + 8 H+ + 8 e ⇌ Cl– + 4 H2O 1 .389ClO4

– + 8 H+ + 7 e ⇌ 1/2 Cl2 + 4 H2O 1 .39No3+ + e ⇌ No2+ 1 .4RuO4 + 6 H+ + 4 e ⇌ Ru(OH)2

2+ + 2 H2O 1 .40Au3+ + 2 e ⇌ Au+ 1 .4012 NH3OH+ + H+ + 2 e ⇌ N2H5

+ + 2 H2O 1 .42BrO3

– + 6 H+ + 6 e ⇌ Br– + 3 H2O 1 .4232 HIO + 2 H+ + 2 e ⇌ I2 + 2 H2O 1 .439Au(OH)3 + 3 H+ + 3 e ⇌ Au– + 3 H2O 1 .45


Reaction E°/V3IO3

– + 6 H+ + 6 e ⇌ Cl– + 3 H2O 1 .451PbO2 +4 H+ + 2 e ⇌ Pb2+ + 2 H2O 1 .455ClO3

– + 6 H+ + 5 e ⇌ 1/2 Cl2 + 3 H2O 1 .47CrO2 + 4 H+ + e ⇌ Cr3+ + 2 H2O 1 .48BrO3

– + 6 H+ + 5 e ⇌ 1/2 Br2 + 3 H2O 1 .482HClO + H+ + 2 e ⇌ Cl– + H2O 1 .482Mn2O3 + 6 H+ + e ⇌ 2 Mn2+ + 3 H2O 1 .485HO2 + H+ + e ⇌ H2O2 1 .495Au3+ + 3 e ⇌ Au 1 .498PtO3 + 4 H+ + 2 e ⇌ Pt(OH)2

2+ + H2O 1 .5MnO4

– + 8 H+ + 5 e ⇌ Mn2+ + 4 H2O 1 .507Mn3+ + e ⇌ Mn2– 1 .5415HClO2 + 3 H+ + 4 e ⇌ Cl– + 2 H2O 1 .570HBrO + H+ + e ⇌ 1/2 Br2(aq) + H2O 1 .5742 NO + 2 H+ + 2 e ⇌ N2O + H2O 1 .591Bi2O4 + 4 H+ + 2 e ⇌ 2 BiO+ + 2 H2O 1 .593HBrO + H+ + e ⇌ 1/2 Br2(l) + H2O 1 .596H5IO6 + H+ + 2 e ⇌ IO3

– + 3 H2O 1 .601HClO + H+ + e ⇌ 1/2 Cl2 + H2O 1 .611HClO2 + 3 H+ + 3 e ⇌ 1/2 Cl2 + 2 H2O 1 .628HClO2 + 2 H+ + 2 e ⇌ HClO + H2O 1 .645Bk4+ + e ⇌ Bk3+ 1 .67NiO2 + 4 H+ + 2 e ⇌ Ni2+ + 2 H2O 1 .678MnO4

– + 4 H+ + 3 e ⇀ MnO2 + 2 H2O 1 .679PbO2 + SO4

2– + 4 H+ + 2 e ⇌ PbSO4 + 2 H2O 1 .6913Au+ + e ⇌ Au 1 .692PtO3 + 2 H+ + 2 e ⇌ PtO2 + H2O 1 .7CeOH3+ + H+ + e ⇌ Ce3+ + H2O 1 .715Ce4+ + e ⇌ Ce3+ 1 .72N2O + 2 H+ + 2 e⇌ N2 + H2O 1 .766H2O2 + 2 H+ + 2 e ⇌ 2 H2O 1 .776

Reaction E°/VAg3+ + e ⇌ Ag2+ 1 .8Au2+ + e– ⇌ Au+ 1 .8Ag2O2 + 4 H+ + e ⇌ 2 Ag + 2 H2O 1 .802Co3+ + e ⇌ Co2–(2 molar H2SO4) 1 .83Ag3+ + 2 e ⇌ Ag+ 1 .9Co3+ + e ⇌ Co2+ 1 .92Ag2+ + e ⇌ Ag+ 1 .980Cu2O3 + 6 H+ + 2 e ⇌ 2 Cu2+ + 3 H2O 2 .0S2O8

2– + 2 e ⇌ 2 SO42– 2 .010

OH + e ⇌ OH– 2 .02HFeO4

– + 7 H+ + 3 e ⇌ Fe3+ + 4 H2O 2 .07O3 + 2 H+ + 2 e ⇌ O2 + H2O 2 .076HFeO4

– + 4 H+ + 3 e ⇌ FeOOH + 2 H2O 2 .082 HFeO4

– + 8 H+ + 6 e ⇌ Fe2O3 + 5 H2O 2 .09XeO3 + 6 H+ + 6 e ⇌ Xe + 3 H2O 2 .10S2O8

2– + 2 H+ + 2 e ⇌ 2 HSO4– 2 .123

F2O + 2 H+ + 4 e ⇌ H2O + 2 F– 2 .153FeO4

2– + 8 H+ + 3 e ⇌ Fe3+ + 4 H2O 2 .20Cu3+ + e ⇌ Cu2+ 2 .4H4XeO6 + 2 H+ + 2 e ⇌ XeO3 + 3 H2O 2 .42O(g) + 2 H+ + 2 e ⇌ H2O 2 .421Am4+ + e ⇌ Am3+ 2 .60H2N2O2 + 2 H+ + 2 e ⇌ N2 + 2 H2O 2 .65F2 + 2 e ⇌ 2 F– 2 .866Cm4+ + e ⇌ Cm3+ 3 .0F2 + 2 H+ + 2 e ⇌ 2 HF 3 .053Tb4+ + e ⇌ Tb3+ 3 .1Pr4+ + e ⇌ Pr3+ 3 .2Cf4+ + e ⇌ Cf3+ 3 .3XeF + e ⇌ Xe + F– 3 .4

TABLE 3. Reduction Reactions Having E° Values More Negative than That of the Standard Hydrogen Electrode

Reaction E°/V2 H+ + 2 e ⇌ H2 0 .000002 D+ + 2 e ⇌ D2 –0 .013AgCN + e ⇌ Ag + CN– –0 .0172 WO3 + 2 H+ + 2 e ⇌ W2O5 + H2O –0 .029W2O5 + 2 H+ + 2 e ⇌ 2 WO2 + H2O –0 .031Ag2S + 2 H+ + 2 e ⇌ 2 Ag + H2S –0 .0366Fe3+ + 3 e ⇌ Fe –0 .037Hg2I2 + 2 e ⇌ 2 Hg + 2 I– –0 .0405Tl(OH)3 + 2 e ⇌ TlOH + 2 OH– –0 .05TiOH3+ + H+ + e ⇌ Ti3+ + H2O –0 .0552 H2SO3 + H+ + 2 e ⇌ HS2O4

– + 2 H2O –0 .056P(white) + 3 H+ + 3 e ⇌ PH3(g) –0 .063O2 + H2O + 2 e ⇌ HO2

– + OH– –0 .0762 Cu(OH)2 + 2 e ⇌ Cu2O + 2 OH– + H2O –0 .080Se + 2 H+ + 2 e ⇌ H2Se –0 .082WO3 + 6 H+ + 6 e ⇌ W + 3 H2O –0 .090SnO2 + 4 H+ + 2 e ⇌ Sn2+ + 2 H2O –0 .094Md3+ + e ⇌ Md2+ –0 .1P(red) + 3 H+ + 3 e ⇌ PH3(g) –0 .111SnO2 + 4 H+ + 4 e ⇌ Sn + 2 H2O –0 .117GeO2 + 2 H+ + 2 e ⇌ GeO + H2O –0 .118

Reaction E°/VWO2 + 4 H+ + 4 e ⇌ W + 2 H2O –0 .119Pb2+ + 2 e ⇌ Pb(Hg) –0 .1205Pb2+ + 2 e ⇌ Pb –0 .1262CrO4

2– + 4 H2O + 3 e ⇌ Cr(OH)3 + 5 OH– –0 .13Sn2– + 2 e ⇌ Sn –0 .1375In+ + e ⇌ In –0 .14O2 + 2 H2O + 2 e ⇌ H2O2 + 2 OH– –0 .146MoO2 + 4 H+ + 4 e ⇌ Mo + 4 H2O –0 .152AgI + e ⇌ Ag + I– –0 .152242 NO2

– + 2 H2O + 4 e ⇌ N2O22– + 4 OH– –0 .18

H2GeO3 + 4 H+ + 4 e ⇌ Ge + 3 H2O –0 .182SnO2 + 3 H+ + 2 e ⇌ SnOH+ + H2O –0 .194CO2 + 2 H+ + 2 e ⇌ HCOOH –0 .199Mo3+ + 3 e ⇌ Mo –0 .200Ga+ + e ⇌ Ga –0 .22 SO2

2– + 4 H+ + 2 e ⇌ S2O62– + H2O –0 .22

Cu(OH)2 + 2 e ⇌ Cu + 2 OH– –0 .222V2O5 + 10 H+ + 10 e ⇌ 2 V + 5 H2O –0 .242CdSO4 + 2 e ⇌ Cd + SO4

2– –0 .246V(OH)4

+ + 4 H+ + 5 e ⇌ V + 4 H2O –0 .254V3+ + e ⇌ V2+ –0 .255


Reaction E°/VNi2+ + 2 e ⇌ Ni –0 .257PbCl2 + 2 e ⇌ Pb + 2 Cl– –0 .2675H3PO4 + 2 H+ + 2 e ⇌ H3PO3 + H2O –0 .276Co2+ + 2 e ⇌ Co –0 .28PbBr2 + 2 e ⇌ Pb + 2 Br– –0 .284Tl+ + e ⇌ Tl(Hg) –0 .3338Tl+ + e ⇌ Tl –0 .336In3+ + 3 e ⇌ In –0 .3382TlOH + e ⇌ Tl + OH– –0 .34PbF2 + 2 e ⇌ Pb + 2 F– –0 .3444PbSO4 + 2 e ⇌ Pb(Hg) + SO4

2– –0 .3505Cd2+ + 2 e ⇌ Cd(Hg) –0 .3521PbSO4 + 2 e ⇌ Pb + SO4

2– –0 .3588Cu2O + H2O + 2 e ⇌ 2 Cu + 2 OH– –0 .360Eu3+ + e ⇌ Eu2+ –0 .36PbI2 + 2 e ⇌ Pb + 2 I– –0 .365SeO3

2– + 3 H2O + 4 e ⇌ Se + 6 OH– –0 .366Se + 2 H+ + 2 e ⇌ H2Se(aq) –0 .399In2+ + e ⇌ In+ –0 .40Cd2+ + 2 e ⇌ Cd –0 .4030Cr3+ + e ⇌ Cr2+ –0 .4072 S + 2 e ⇌ S2

2– –0 .42836Tl2SO4 + 2 e ⇌ Tl + SO4

2– –0 .4360In3+ + 2 e ⇌ In+ –0 .443Fe2+ + 2 e ⇌ Fe –0 .447H3PO3 + 3 H+ + 3 e ⇌ P + 3 H2O –0 .454Bi2O3 + 3 H2O + 6 e ⇌ 2 Bi + 6 OH– –0 .46NO2

– + H2O + e ⇌ NO + 2 OH –0 .46PbHPO4 + 2 e ⇌ Pb + HPO4

2– –0 .465S + 2 e ⇌ S2– –0 .47627S + H2O + 2 e ⇌ HS– + OH– –0 .478B(OH)3 + 7 H+ + 8 e ⇌ BH4

– + 3 H2O –0 .481In3+ + e ⇌ In2+ –0 .49ZnOH+ + H+ + 2 e ⇌ Zn + H2O –0 .497GaOH2+ + H+ + 3 e ⇌ Ga + H2O –0 .498H3PO3 + 2 H+ + 2 e ⇌ H3PO2 + H2O –0 .499TiO2 + 4 H+ + 2 e ⇌ Ti2+ + 2 H2O –0 .502H3PO2 + H+ + e ⇌ P + 2 H2O –0 .508Sb + 3 H+ + 3 e ⇌ SbH3 –0 .510HPbO2

– + H2O + 2 e ⇌ Pb + 3 OH– –0 .537Ga3+ + 3 e ⇌ Ga –0 .549TlCl + e ⇌ Tl + Cl– –0 .5568Fe(OH)3 + e ⇌ Fe(OH)2 + OH– –0 .56TeO3

2– + 3 H2O + 4 e ⇌ Te + 6 OH– –0 .572 SO3

2– + 3 H2O + 4 e ⇌ S2O32– + 6 OH– –0 .571

PbO + H2O + 2 e ⇌ Pb + 2 OH– –0 .580ReO2

– + 4 H2O + 7 e ⇌ Re + 8 OH– –0 .584SbO3

– + H2O + 2 e ⇌ SbO2– + 2 OH– –0 .59

Ta3+ + 3 e ⇌ Ta –0 .6U4+ + e ⇌ U3+ –0 .607As + 3 H+ + 3 e ⇌ AsH3 –0 .608Nb2O5 + 10 H+ + 10 e ⇌ 2 Nb + 5 H2O –0 .644NbO2 + 2 H+ + 2 e ⇌ NbO + H2O –0 .646Cd(OH)4

2– + 2 e ⇌ Cd + 4 OH– –0 .658TlBr + e ⇌ Tl + Br– –0 .658SbO2

– + 2 H2O + 3 e ⇌ Sb + 4 OH– –0 .66AsO2

– + 2 H2O + 3 e ⇌ As + 4 OH– –0 .68

Reaction E°/VNbO2 + 4 H+ + 4 e ⇌ Nb + 2 H2O –0 .690Ag2S + 2 e ⇌ 2 Ag + S2– –0 .691AsO4

3– + 2 H2O + 2 e ⇌ AsO2– + 4 OH– –0 .71

Ni(OH)2 + 2 e ⇌ Ni + 2 OH– –0 .72Co(OH)2 + 2 e ⇌ Co + 2 OH– –0 .73NbO + 2 H+ + 2 e ⇌ Nb + H2O –0 .733H2SeO3 + 4 H+ + 4 e ⇌ Se + 3 H2O –0 .74Cr3+ + 3 e ⇌ Cr –0 .744Ta2O5 + 10 H+ + 10 e ⇌ 2 Ta + 5 H2O –0 .750TlI + e ⇌ Tl + I– –0 .752Zn2+ + 2 e ⇌ Zn –0 .7618Zn2+ + 2 e ⇌ Zn(Hg) –0 .7628CdO + H2O + 2 e ⇌ Cd + 2 OH– –0 .783Te + 2 H+ + 2 e ⇌ H2Te –0 .793ZnSO4

.7H2O + 2 e ⇌ Zn(Hg) + SO42– + 7 H2O –0 .7993

(Saturated ZnSO4)Bi + 3 H+ + 3 e ⇌ BiH3 –0 .8SiO + 2 H+ + 2 e ⇌ Si + H2O –0 .8Cd(OH)2 + 2 e ⇌ Cd(Hg) + 2 OH– –0 .8092 H2O + 2 e ⇌ H2 + 2 OH– –0 .82772 NO–

3 + 2 H2O + 2 e ⇌ N2O4 + 4 OH– –0 .85H3BO3 + 3 H+ + 3 e ⇌ B + 3 H2O –0 .8698P + 3 H2O + 3 e ⇌ PH3(g) + 3 OH– –0 .87Ti3+ + e ⇌ Ti2+ –0 .9HSnO2

– + H2O + 2 e ⇌ Sn + 3 OH– –0 .909Cr2+ + 2 e ⇌ Cr –0 .913Se + 2 e ⇌ Se2– –0 .924SO4

2– + H2O + 2 e ⇌ SO32– + 2 OH– –0 .93

Sn(OH)62– + 2 e ⇌ HSnO2

– + 3 OH– + H2O –0 .93SnO2 + 2 H2O + 4 e ⇌ Sn + 4 OH– –0 .945In(OH)3 + 3 e ⇌ In + 3 OH– –0 .99NpO2 + H2O + H+ + e ⇌ Np(OH)3 –0 .962In(OH)4

– + 3 e ⇌ In + 4 OH– –1 .007In2O3 + 3 H2O + 6 e ⇌ 2 In + 6 OH– –1 .034PO4

3– + 2 H2O + 2 e ⇌ HPO32– + 3 OH– –1 .05

Yb3+ + e ⇌ Yb2+ –1 .05Nb3+ + 3 e ⇌ Nb –1 .099Fm3+ + e ⇌ Fm2+ –1 .12 SO3

2– + 2 H2O + 2 e ⇌ S2O42– + 4 OH– –1 .12

Te + 2 e ⇌ Te2– –1 .143V2+ + 2 e ⇌ V –1 .175Mn2+ + 2 e ⇌ Mn –1 .185Zn(OH)4

2– + 2 e ⇌ Zn + 4 OH– –1 .199CrO2 + 2 H2O + 3 e ⇌ Cr + 4 OH– –1 .2No3+ + 3 e ⇌ No –1 .20ZnO2

– + 2 H2O + 2 e ⇌ Zn + 4 OH– –1 .215H2GaO3

– + H2O + 3 e ⇌ Ga + 4 OH– –1 .219H2BO3

– + 5 H2O + 8 e ⇌ BH4– + 8 OH– –1 .24

SiF62– + 4 e ⇌ Si + 6 F– –1 .24

Zn(OH)2 + 2 e ⇌ Zn + 2 OH– –1 .249ZnO + H2O + 2 e ⇌ Zn + 2 OH– –1 .260Es3+ + e ⇌ Es2+ –1 .3Pa3+ + 3 e ⇌ Pa –1 .34 Ti3+ + 3 e ⇌ Ti –1 .37Ce3+ + 3 e ⇌ Ce(Hg) –1 .4373UO2

2+ + 4 H+ + 6 e ⇌ U + 2 H2O –1 .444Zr4+ + 4 e ⇌ Zr –1 .45


Reaction E°/VCr(OH)3 + 3 e ⇌ Cr + 3 OH– –1 .48Pa4+ + 4 e ⇌ Pa –1 .49HfO2 + 4 H+ + 4 e ⇌ Hf + 2 H2O –1 .505Hf4+ + 4 e ⇌ Hf –1 .55Sm3+ + e ⇌ Sm2+ –1 .55ZrO2 + 4 H+ + 4 e ⇌ Zr + 2 H2O –1 .553Mn(OH)2 + 2 e ⇌ Mn + 2 OH– –1 .56Ba2+ + 2 e ⇌ Ba(Hg) –1 .570Bk2+ + 2 e ⇌ Bk –1 .6Cf3+ + e ⇌ Cf2+ –1 .6Ti2+ + 2 e ⇌ Ti –1 .630Md3+ + 3 e ⇌ Md –1 .65HPO3

2– + 2 H2O + 2 e ⇌ H2PO2– + 3 OH– –1 .65

Al3+ + 3 e ⇌ Al –1 .662SiO3

2– + H2O + 4 e ⇌ Si + 6 OH– –1 .697HPO3

2– + 2 H2O + 3 e ⇌ P + 5 OH– –1 .71HfO2+ + 2 H+ + 4 e ⇌ Hf + H2O –1 .724ThO2 + 4 H+ + 4 e ⇌ Th + 2 H2O –1 .789H2BO3

– + H2O + 3 e ⇌ B + 4 OH– –1 .79Sr2+ + 2 e ⇌ Sr(Hg) –1 .793U3+ + 3 e ⇌ U –1 .798H2PO–

2 + e ⇌ P + 2 OH– –1 .82Be2+ + 2 e ⇌ Be –1 .847Np3+ + 3 e ⇌ Np –1 .856Fm3+ + 3 e ⇌ Fm –1 .89Th4+ + 4 e ⇌ Th –1 .899Am2+ + 2 e ⇌ Am –1 .9Pa4+ + e ⇌ Pa3+ –1 .9Es3+ + 3 e ⇌ Es –1 .91Cf3+ + 3 e ⇌ Cf –1 .94Lr3+ + 3 e ⇌ Lr –1 .96Eu3+ + 3 e ⇌ Eu –1 .991Er2+ + 2 e ⇌ Er –2 .0Pr2+ + 2 e ⇌ Pr –2 .0Pu3+ + 3 e ⇌ Pu –2 .031Cm3+ + 3 e ⇌ Cm –2 .04Am3+ + 3 e ⇌ Am –2 .048AlF6

3– + 3 e ⇌ Al + 6 F– –2 .069Sc3+ + 3 e ⇌ Sc –2 .077Ho2+ + 2 e ⇌ Ho –2 .1Nd2+ + 2 e ⇌ Nd –2 .1Cf2+ + 2 e ⇌ Cf –2 .12Yb3+ + 3 e ⇌ Yb –2 .19Ac3+ + 3 e ⇌ Ac –2 .20Dy2+ + 2 e ⇌ Dy –2 .2Tm3+ + e ⇌ Tm2+ –2 .2Pm2+ + 2 e ⇌ Pm –2 .2Es2+ + 2 e ⇌ Es –2 .23H2 + 2 e ⇌ 2 H– –2 .23Gd3+ + 3 e ⇌ Gd –2 .279Tb3+ + 3 e ⇌ Tb –2 .28Lu3+ + 3 e ⇌ Lu –2 .28Dy3+ + 3 e ⇌ Dy –2 .295

Reaction E°/VAm3+ + e ⇌ Am2+ –2 .3Fm2+ + 2 e ⇌ Fm –2 .30Pm3+ + 3 e ⇌ Pm –2 .30Sm3+ + 3 e ⇌ Sm –2 .304Al(OH)3 + 3 e ⇌ Al + 3 OH– –2 .31Tm3+ + 3 e ⇌ Tm –2 .319Nd3+ + 3 e ⇌ Nd –2 .323Al(OH)– + 3 e ⇌ Al + 4 OH– –2 .328H2AlO3

– + H2O + 3 e ⇌ Al + 4 OH– –2 .33Ho3+ + 3 e ⇌ Ho –2 .33Er3+ + 3 e ⇌ Er –2 .331Ce3+ + 3 e ⇌ Ce –2 .336Pr3+ + 3 e ⇌ Pr –2 .353ZrO(OH)2 + H2O + 4 e ⇌ Zr + 4 OH– –2 .36Mg2+ + 2 e ⇌ Mg –2 .372Y3+ + 3 e ⇌ Y –2 .372La3+ + 3 e ⇌ La –2 .379Tm2+ + 2 e ⇌ Tm –2 .4Md2+ + 2 e ⇌ Md –2 .40Th(OH)4 + 4 e ⇌ Th + 4 OH– –2 .48HfO(OH)2 + H2O + 4 e ⇌ Hf + 4 OH– –2 .50No2+ + 2 e ⇌ No –2 .50Dy3+ + e ⇌ Dy2+ –2 .6Pm3+ + e ⇌ Pm2+ –2 .6Be2O3

2– + 3 H2O + 4 e ⇌ 2 Be + 6 OH– –2 .63Sm2+ + 2 e ⇌ Sm –2 .68Mg(OH)2 + 2 e ⇌ Mg + 2 OH– –2 .690Nd3+ + e ⇌ Nd2+ –2 .7Mg+ + e ⇌ Mg –2 .70Na+ + e ⇌ Na –2 .71Yb2+ + 2 e ⇌ Yb –2 .76Bk3+ + e ⇌ Bk2+ –2 .8Ho3+ + e ⇌ Ho2+ –2 .8Ra2+ + 2 e ⇌ Ra –2 .8Eu2+ + 2 e ⇌ Eu –2 .812Ca2+ + 2 e ⇌ Ca –2 .868Sr(OH)2 + 2 e ⇌ Sr + 2 OH– –2 .88Sr2+ + 2 e ⇌ Sr –2 .899Fr+ + e ⇌ Fr –2 .9La(OH)3 + 3 e ⇌ La + 3 OH– –2 .90Ba2+ + 2 e ⇌ Ba –2 .912K+ + e ⇌ K –2 .931Rb+ + e ⇌ Rb –2 .98Ba(OH)2 + 2 e ⇌ Ba + 2 OH– –2 .99Er3+ + e ⇌ Er2+ –3 .0Ca(OH)2 + 2 e ⇌ Ca + 2 OH– –3 .02Cs+ + e ⇌ Cs –3 .026Li+ + e ⇌ Li –3 .04013 N2 + 2 H+ + 2 e ⇌ 2 HN3 –3 .09Pr3+ + e ⇌ Pr2+ –3 .1Ca+ + e ⇌ Ca –3 .80Sr+ + e ⇌ Sr –4 .10
