Hydrolysis constant

The word hydrolysis is applied to chemical reactions in which a substance reacts with water. In organic chemistry, the products of the reaction are usually molecular, being formed by combination with H and OH groups (e.g., hydrolysis of an ester to an alcohol and a carboxylic acid). In inorganic chemistry, the word most often applies to cations forming soluble hydroxide or oxide complexes with, in some cases, the formation of hydroxide and oxide precipitates.

Metal hydrolysis and associated equilibrium constant values

The hydrolysis reaction for a hydrated metal ion in aqueous solution can be written as:

p Mz+ + q H2O ⇌ Mp(OH) + q H+

and the corresponding formation constant as:

and associated equilibria can be written as:

MOx(OH)z–2x(s) + z H+ ⇌ Mz+ + (z–x) H2O

MOx(OH)z–2x(s) + x H2O ⇌ Mz+ + z OH−

p MOx(OH)z–2x(s) + (pz–q) H+ ⇌ Mp(OH) + (pz–px–q) H2O

Aluminium Hydrolysis constants (log values) in critical compilations at infinite dilution and : +ReactionBaes and Mesmer, 1976Brown and Ekberg, 2016Hummel and Thoenen, 2023Al3+ + H2O ⇌ AlOH2+ + H+–4.97−4.98 ± 0.02−4.98 ± 0.02Al3+ + 2 H2O ⇌ Al(OH)2+ + 2 H+–9.3−10.63 ± 0.09−10.63 ± 0.09Al3+ + 3 H2O ⇌ Al(OH)3 + 3 H+–15.0−15.66 ± 0.23−15.99 ± 0.23Al3+ + 4 H2O ⇌ Al(OH)4– + 4 H+–23.0−22.91 ± 0.10−22.91 ± 0.102 Al3+ + 2 H2O ⇌ Al2(OH)24+ + 2 H+–7.7−7.62 ± 0.11−7.62 ± 0.113 Al3+ + 4 H2O ⇌ Al3(OH)45+ + 4 H+–13.94−14.06 ± 0.22−13.90 ± 0.1213 Al3+ + 28 H2O ⇌ Al13O4(OH)247+ + 32 H+–98.73−100.03 ± 0.09−100.03 ± 0.09α-Al(OH)3(s) + 3 H+ ⇌ Al3+ + 3 H2O8.57.75 ± 0.087.75 ± 0.08γ-AlOOH(s) + 3 H+ ⇌ Al3+ + 2 H2O7.69 ± 0.159.4 ± 0.4

Americium(III) Hydrolysis constants (log values) in critical compilations at infinite dilution and : +ReactionNIST46Brown and Ekberg, 2016Grenthe et al., 2020Am3+ + H2O ⇌ Am(OH)2+ + H+–6.5 ± 0.1–7.22 ± 0.03–7.2 ± 0.5Am3+ + 2 H2O ⇌ Am(OH)2+ + 2 H+–14.1 ± 0.3–14.9 ± 0.2–15.1 ± 0.7Am3+ + 3 H2O ⇌ Am(OH)3 + 3 H+–25.7–26.0 ± 0.2–26.2 ± 0.5Am3+ + 3 H2O ⇌ Am(OH)3(am) + 3 H+–16.9 ± 0.1–16.9 ± 0.8–16.9 ± 0.8Am3+ + 3 H2O ⇌ Am(OH)3(cr) + 3 H+–15.2–15.62 ± 0.04–15.6 ± 0.6

Americium(V) Hydrolysis constants (log values) in critical compilations at infinite dilution and : +ReactionBrown and Ekberg, 2016Grenthe et al., 2020AmO2+ + H2O ⇌ AmO2(OH) + H+–10.7 ± 0.2AmO2+ + 2 H2O ⇌ AmO2(OH)2– + 2 H+–22.9 ± 0.7AmO2+ + H2O ⇌ AmO2(OH)(am) + H+–5.4 ± 0.4–5.3 ± 0.5

Antimony(III) Hydrolysis constants (log values) in critical compilations at infinite dilution and : +ReactionBaes and Mesmer, 1976Lothenbach et al., 1999;Kitamura et al., 2010Filella and May, 2003Sb(OH)3 + H+ ⇌ Sb(OH)2+ + H2O1.41 1.30 1.371Sb(OH)3 + H2O ⇌ Sb(OH)4‒ + H+‒11.82‒11.93‒11.70 Sb2O3(s) + H2O ⇌ Sb(OH)3‒4.24Sb2O3(rhombic,s) + 3 H2O ⇌ 2 Sb(OH)3‒8.72‒10.00Sb2O3(cubic,s) + 3 H2O ⇌ 2 Sb(OH)3‒11.40

Antimony(V) Hydrolysis constants (log values) in critical compilations at infinite dilution and : +ReactionBaes and Mesmer, 1976Lothenbach et al., 1999;Kitamura et al., 2010Sb(OH)5 + H2O ⇌ Sb(OH)6‒ + H+‒2.72 ‒2.7212 Sb(OH)5 + 4 H2O ⇌ Sb12(OH)644‒ + 4 H+20.3420.3412 Sb(OH)5 + 5 H2O ⇌ Sb12(OH)655‒ + 5 H+16.7216.7212 Sb(OH)5 + 6 H2O ⇌ Sb12(OH)666‒ + 6 H+11.8911.8912 Sb(OH)5 + 7 H2O ⇌ Sb12(OH)677‒ + 7 H+6.076.07 Sb2O5(s) + H2O ⇌ Sb(OH)5‒3.7Sb2O5(am) + 5 H2O ⇌ 2 Sb(OH)5‒7.400

Arsenic(III) Hydrolysis constants (log values) in critical compilations at infinite dilution and : +ReactionBaes and Mesmer, 1976Nordstrom and Archer, 2003Nordstrom et al., 2014As(OH)4‒ + H+ ⇌ As(OH)3 + H2O9.29 9.17 9.24 ± 0.02

Arsenic(V) Hydrolysis constants (log values) in critical compilations at infinite dilution and : +ReactionBaes and MesmerKhodakovsky et al. (1968)Nordstrom and Archer, 2003Nordstrom et al., 2014H2AsO4‒ + H+ ⇌ H3AsO42.242.21 2.26 ± 0.078 2.25 ± 0.04HAsO42‒ + H+ ⇌ H2AsO4‒6.936.99 ± 0.16.98 ± 0.11AsO43‒ + H+ ⇌ HAsO42‒11.5111.80 ± 0.111.58 ± 0.05HAsO42‒ + 2 H+ ⇌H3AsO49.20AsO43‒ + 3 H+ ⇌ H3AsO420.70

Barium Hydrolysis constants (log values) in critical compilations at infinite dilution and : +ReactionBaes and Mesmer, 1976Nordstrom et al., 1990Brown and Ekberg, 2016Ba2+ + H2O ⇌ BaOH+ + H+ –13.47 –13.47 –13.32 ± 0.07

Berkelium(III) Hydrolysis constants (log values) in critical compilations at infinite dilution and : +ReactionBrown and Ekberg, 2016Bk3+ + 3 H2O ⇌ Bk(OH)3(s) + 3 H+ –13.5 ± 1.0

Beryllium Hydrolysis constants (log values) in critical compilations at infinite dilution and : +ReactionBaes and Mesmer, 1976Be2+ + H2O ⇌ BeOH+ + H+ –5.10Be2+ + 2 H2O ⇌ Be(OH)2 + 2 H+–23.65Be2+ + 3 H2O ⇌ Be(OH)3– + 3 H+–23.25Be2+ + 4 H2O ⇌ Be(OH)42– + 4 H+–37.422 Be2+ + H2O ⇌ Be2OH3+ + H+–3.973 Be2+ + 3 H2O ⇌ Be3(OH)33+ + 3 H+–8.926 Be2+ + 8 H2O ⇌ Be6(OH)84+ + 8 H+–27.2α-Be(OH)2(cr) + 2 H+ ⇌ Be2+ + 2 H2O6.69

Bismuth Hydrolysis constants (log values) in critical compilations at infinite dilution and : +ReactionBaes and Mesmer, 1976Lothenbach et al., 1999NIST46Kitamura et al., 2010Brown and Ekberg, 2016Bi3+ + H2O ⇌ BiOH2+ + H+ –1.0–0.92–1.1–0.920–0.92 ± 0.15Bi3+ + 2 H2O ⇌ Bi(OH)2+ + 2 H+(–4)–2.56–4.5–2.560 ± 1.000–2.59 ± 0.26Bi3+ + 3 H2O ⇌ Bi(OH)3 + 3 H+–8.86 –5.31–9.0–8.940 ± 0.500–8.78 ± 0.20Bi3+ + 4 H2O ⇌ Bi(OH)4– + 4 H+–21.8 –18.71–21.2–21.660 ± 0.870–22.06 ± 0.143 Bi3+ + 4 H2O ⇌ Bi3(OH)45+ + 4 H+–0.80–0.8006 Bi3+ + 12 H2O ⇌ Bi6(OH)126+ + 12 H+1.341.3400.98 ± 0.139 Bi3+ + 20 H2O = Bi9(OH)207+ + 20 H+–1.36–1.3609 Bi3+ + 21 H2O = Bi9(OH)216+ + 21 H+–3.25–3.2509 Bi3+ + 22 H2O = Bi9(OH)225+ + 22 H+–4.86–4.860Bi(OH)3(am) + 3 H+ = Bi3+ + 3 H2O31.501 ± 0.927α-Bi2O3(cr) + 6 H+ = 2 Bi3+ + 3 H2O0.76BiO1.5(s, α) + 3 H+ = Bi3+ + 1.5 H2O3.4631.501 ± 0.9272.88 ± 0.64

Boron Hydrolysis constants (log values) in critical compilations at infinite dilution and : +ReactionBaes and Mesmer, 1976NIST46B(OH)3 + H2O ⇌ Be(OH)4+ + H+ –9.236–9.236 ± 0.0022 B(OH)3 ⇌ B2(OH)5– + H+–9.36–9.3063 B(OH)3 ⇌ B3O3(OH)4– + H+ + 2 H2O–7.03–7.3064 B(OH)3 ⇌ B4O5(OH)42– + 2 H+ + 3 H2O–16.3 –15.032

Cadmium Hydrolysis constants (log values) in critical compilations at infinite dilution and : +ReactionBaes and Mesmer, 1976Powell et al., 2011Brown and Ekberg, 2016Cd2+ + H2O ⇌ CdOH+ + H+ −10.08 –9.80 ± 0.10 −9.81 ± 0.10Cd2+ + 2 H2O ⇌ Cd(OH)2 + 2 H+–20.35–20.19 ± 0.13−20.6 ± 0.4Cd2+ + 3 H2O ⇌ Cd(OH)3– + 3 H+<–33.3–33.5 ± 0.5−33.5 ± 0.5Cd2+ + 4 H2O ⇌ Cd(OH)42– + 4 H+–47.35–47.28 ± 0.15−47.25 ± 0.152 Cd2+ + H2O ⇌ Cd2OH3+ + H+–9.390–8.73 ± 0.01−8.74 ± 0.104 Cd2+ + 4 H2O ⇌ Cd4(OH)44+ + 4 H+–32.85Cd(OH)2(s) ⇌ Cd2+ + 2 OH––14.28 ± 0.12Cd(OH)2(s) + 2 H+ ⇌ Cd2+ + 2 H2O13.6513.72 ± 0.1213.71 ± 0.12

Calcium Hydrolysis constants (log values) in critical compilations at infinite dilution and : +ReactionBaes and Mesmer, 1976Nordstrom et al., 1990Brown and Ekberg, 2016Ca2+ + H2O ⇌ CaOH+ + H+ –12.85 –12.78 –12.57 ± 0.03Ca(OH)2(cr) + 2 H+ ⇌ Ca2+ + 2 H2O22.8022.822.75 ± 0.02

Californium(III) Hydrolysis constants (log values) in critical compilations at infinite dilution and : +ReactionBrown and Ekberg, 2016Cf3+ + 3 H2O ⇌ Cf(OH)3(s) + 3 H+ –13.0 ± 1.0

Cerium(III) Hydrolysis constants (log values) in critical compilations at infinite dilution and : +ReactionBaes and Mesmer, 1976NIST46Brown and Ekberg, 2016Ce3+ + H2O ⇌ CeOH2+ + H+ –8.3 –8.3 –8.31 ± 0.032 Ce3+ + 2 H2O ⇌ Ce2(OH)24+ + 2 H+–16.0 ± 0.23 Ce3+ + 5 H2O ⇌ Ce3(OH)54+ + 5 H+–34.6 ± 0.3Ce(OH)3(s) + 3 H+ ⇌ Ce3+ + 3 H2O18.5 ± 0.5Ce(OH)3(s) ⇌ Ce3+ + 3 OH– –22.1 ± 0.9

Chromium(II) Hydrolysis constants (log values) in critical compilations at infinite dilution and (The divalent state is unstable in water, producing hydrogen whilst being oxidised to a higher valency state (Baes and Mesmer, 1976). The reliability of the data is in doubt.): +ReactionNIST46Ball and Nordstrom, 1988Cr2+ + H2O ⇌ CrOH+ + H+ –5.5Cr(OH)2(s) ⇌ Cr2+ + 2 OH– –17 ± 0.02

Chromium(III) Hydrolysis constants (log values) in critical compilations at infinite dilution and : +ReactionBaes and Mesmer, 1976Rai et al., 1987Ball and Nordstrom, 1988Brown and Ekberg, 2016Cr3+ + H2O ⇌ CrOH2+ + H+ –4.0 –3.57 ± 0.08 –3.60 ± 0.07Cr3+ + 2 H2O ⇌ Cr(OH)2+ + 2 H+–9.7–9.84–9.65 ± 0.20Cr3+ + 3 H2O ⇌ Cr(OH)3 + 3 H+–18–16.19–16.25 ± 0.19Cr3+ + 4 H2O ⇌ Cr(OH)4− + 4 H+–27.4–27.65 ± 0.12–27.56 ± 0.212 Cr3+ + 2 H2O ⇌ Cr2(OH)24+ + 2 H+–5.06 –5.0 –5.29 ± 0.163 Cr3+ + 4 H2O ⇌ Cr3(OH)45+ + 4 H+–8.15–10.75 ± 0.15–9.10 ± 0.14Cr(OH)3(s) + 3 H+ ⇌ Cr3+ + 3 H2O129.35 9.41 ± 0.17Cr2O3(s) + 6 H+ ⇌ 2 Cr3+ + 3 H2O8.52CrO1.5(s) + 3 H+ ⇌ Cr3+ + 1.5 H2O7.83 ± 0.10

Chromium(VI) Hydrolysis constants (log values) in critical compilations at infinite dilution and : +ReactionBaes and Mesmer, 1976Ball and Nordstrom, 1998CrO42– + H+ ⇌ HCrO4– 6.51 6.55 ± 0.04HCrO4– + H+ ⇌ H2CrO4–0.20CrO42– + 2 H+ ⇌ H2CrO46.312 HCrO4– ⇌ Cr2O72– + H2O1.5232 CrO42– + 2 H+ ⇌ Cr2O72– + H2O14.7 ± 0.1

Cobalt(II) Hydrolysis constants (log values) in critical compilations at infinite dilution and : +ReactionBaes and Mesmer, 1976Brown and Ekberg, 2016Co2+ + H2O ⇌ CoOH+ + H+ –9.65 −9.61 ± 0.17Co2+ + 2 H2O ⇌ Co(OH)2 + 2 H+–18.8−19.77 ± 0.11Co2+ + 3 H2O ⇌ Co(OH)3– + 3 H+–31.5 −32.01 ± 0.33Co2+ + 4 H2O ⇌ Co(OH)42– + 4 H+–46.32 Co2+ + H2O ⇌ Co2(OH)3+ + H+–11.24 Co2+ + 4 H2O ⇌ Co4(OH)44+ + 4 H+–30.53Co(OH)2(s) + 2 H+ ⇌ Co2+ + 2 H2O 12.313.24 ± 0.12CoO(s) + 2 H+ ⇌ Co2+ + H2O13.71 ± 0.10

Cobalt(III) Hydrolysis constants (log values) in critical compilations at infinite dilution and : +ReactionBrown and Ekberg, 2016Co3+ + H2O ⇌ CoOH2+ + H+ −1.07 ± 0.11

Copper(I) Hydrolysis constants (log values) in critical compilations at infinite dilution and : +ReactionBrown and Ekberg, 2016Cu+ + H2O ⇌ CuOH + H+ –7.8 ± 0.4Cu+ + 2 H2O ⇌ Cu(OH)2– + 2 H+–18.6 ± 0.6

Copper(II) Hydrolysis constants (log values) in critical compilations at infinite dilution and : +ReactionBaes and Mesmer, 1976NIST46Plyasunova et al., 1997Powell et al., 2007Brown and Ekberg, 2016Cu2+ + H2O ⇌ CuOH+ + H+< –8 –7.7–7.97 ± 0.09–7.95 ± 0.16 –7.64 ± 0.17Cu2+ + 2 H2O ⇌ Cu(OH)2 + 2 H+(< –17.3) –17.3–16.23 ± 0.15–16.2 ± 0.2 –16.24 ± 0.03Cu2+ + 3 H2O ⇌ Cu(OH)3– + 3 H+(< –27.8) –27.8 –26.63 ± 0.40 –26.60 ± 0.09 –26.65 ± 0.13Cu2+ + 4 H2O ⇌ Cu(OH)42– + 4 H+–39.6 –39.6 –39.73 ± 0.17 –39.74 ± 0.18–39.70 ± 0.192 Cu2+ + H2O ⇌ Cu2(OH)3+ + H+–6.71 ± 0.30–6.40 ± 0.12 –6.41 ± 0.172 Cu2+ + 2 H2O ⇌ Cu2(OH)22+ + 2 H+–10.36–10.3–10.55 ± 0.17 –10.43 ± 0.07–10.55 ± 0.023 Cu2+ + 4 H2O ⇌ Cu3(OH)42+ + 4 H+–20.95 ± 0.30–21.1 ± 0.2–21.2 ± 0.4CuO(s) + 2 H+ ⇌ Cu2+ + H2O7.62 7.64 ± 0.067.64 ± 0.067.63 ± 0.05Cu(OH)2(s) + 2 H+ ⇌ Cu2+ + 2 H2O8.67 ± 0.058.68 ± 0.10

Curium Hydrolysis constants (log values) in critical compilations at infinite dilution and : +ReactionBrown and Ekberg, 2016Cm3+ + H2O ⇌ Cm(OH)2+ + H+−7.66 ± 0.07Cm3+ + 2 H2O ⇌ Cm(OH)2+ + 2 H+−15.9 ± 0.1Cm3+ + 3 H2O ⇌ Cm(OH)3(s) + 3 H+−13.9 ± 0.4

Dysprosium Hydrolysis constants (log values) in critical compilations at infinite dilution and : +ReactionBaes and Mesmer, 1976Brown and Ekberg, 2016Dy3+ + H2O ⇌ DyOH2+ + H+−8.0−7.53 ± 0.14Dy3+ + 2 H2O ⇌ Dy(OH)2+ + 2 H+(–16.2)Dy3+ + 3 H2O ⇌ Dy(OH)3 + 3 H+(–24.7)Dy3+ + 4 H2O ⇌ Dy(OH)4− + 4 H+–33.52 Dy3+ + 2 H2O ⇌ Dy2(OH)24+ + 2 H+−13.76 ± 0.203 Dy3+ + 5 H2O ⇌ Dy3(OH)54+ + 5 H+−30.6 ± 0.3Dy(OH)3(s) + 3 H+ ⇌ Dy3+ + 3 H2O15.916.26 ± 0.30Dy(OH)3(c) + OH− ⇌ Dy(OH)4−−3.6Dy(OH)3(c) ⇌ Dy(OH)3−8.8

Erbium Hydrolysis constants (log values) in critical compilations at infinite dilution and : +ReactionBaes and Mesmer, 1976Brown and Ekberg, 2016Er3+ + H2O ⇌ ErOH2+ + H+−7.9−7.46 ± 0.09Er3+ + 2 H2O ⇌ Er(OH)2+ + 2 H+(−15.9)Er3+ + 3 H2O ⇌ Er(OH)3 + 3 H+(−24.2)Er3+ + 4 H2O ⇌ Er(OH)4− + 4 H+−32.62 Er3+ + 2 H2O ⇌ Er2(OH)24+ + 2 H+−13.65−13.50 ± 0.203 Er3+ + 5 H2O ⇌ Er3(OH)54+ + 5 H+<−29.3−31.0 ± 0.3Er(OH)3(s) + 3 H+ ⇌ Er3+ + 3 H2O15.015.79 ± 0.30Er(OH)3(c) + OH− ⇌ Er(OH)4−−3.6Er(OH)3(c) ⇌ Er(OH)3~ −9.2

Europium Hydrolysis constants (log values) in critical compilations at infinite dilution and :