Hydrolysis constant

Template:SHORTDESC: 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 M^z+ + q H₂O ⇌ M_p(OH)_q^(pz–q) + q H⁺

and the corresponding formation constant as:

${\beta }_{pq}=\frac{[M_p(OH{)}_q^{(pz-q)}][H^{+}{]}^q}{[M^{z+}{]}^p}$

and associated equilibria can be written as:

MO_x(OH)_z–2x(s) + z H⁺ ⇌ M^z+ + (z–x) H₂O

MO_x(OH)_z–2x(s) + x H₂O ⇌ M^z+ + z OH⁻

p MO_x(OH)_z–2x(s) + (pz–q) H⁺ ⇌ M_p(OH)_q^(pz–q) + (pz–px–q) H₂O

Aluminium

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Brown and Ekberg, 2016	Hummel and Thoenen, 2023
Al3+ + H2O ⇌ AlOH2+ + H+	–4.97	−4.98 ± 0.02	−4.98 ± 0.02
Al3+ + 2 H2O ⇌ Al(OH)2+ + 2 H+	–9.3	−10.63 ± 0.09	−10.63 ± 0.09
Al3+ + 3 H2O ⇌ Al(OH)3 + 3 H+	–15.0	−15.66 ± 0.23	−15.99 ± 0.23
Al3+ + 4 H2O ⇌ Al(OH)4– + 4 H+	–23.0	−22.91 ± 0.10	−22.91 ± 0.10
2 Al3+ + 2 H2O ⇌ Al2(OH)24+ + 2 H+	–7.7	−7.62 ± 0.11	−7.62 ± 0.11
3 Al3+ + 4 H2O ⇌ Al3(OH)45+ + 4 H+	–13.94	−14.06 ± 0.22	−13.90 ± 0.12
13 Al3+ + 28 H2O ⇌ Al13O4(OH)247+ + 32 H+	–98.73	−100.03 ± 0.09	−100.03 ± 0.09
α-Al(OH)3(s) + 3 H+ ⇌ Al3+ + 3 H2O	8.5	7.75 ± 0.08	7.75 ± 0.08
γ-AlOOH(s) + 3 H+ ⇌ Al3+ + 2 H2O		7.69 ± 0.15	9.4 ± 0.4

Americium(III)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	NIST46	Brown and Ekberg, 2016	Grenthe et al., 2020
Am3+ + H2O ⇌ Am(OH)2+ + H+	–6.5 ± 0.1	–7.22 ± 0.03	–7.2 ± 0.5
Am3+ + 2 H2O ⇌ Am(OH)2+ + 2 H+	–14.1 ± 0.3	–14.9 ± 0.2	–15.1 ± 0.7
Am3+ + 3 H2O ⇌ Am(OH)3 + 3 H+	–25.7	–26.0 ± 0.2	–26.2 ± 0.5
Am3+ + 3 H2O ⇌ Am(OH)3(am) + 3 H+	–16.9 ± 0.1	–16.9 ± 0.8	–16.9 ± 0.8
Am3+ + 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 T = 298.15 K:

Reaction	Brown and Ekberg, 2016	Grenthe et al., 2020
AmO2+ + H2O ⇌ AmO2(OH) + H+	–10.7 ± 0.2
AmO2+ + 2 H2O ⇌ AmO2(OH)2– + 2 H+	–22.9 ± 0.7
AmO2+ + 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 T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Lothenbach et al., 1999; Kitamura et al., 2010	Filella and May, 2003
Sb(OH)3 + H+ ⇌ Sb(OH)2+ + H2O	1.41	1.30	1.371
Sb(OH)3 + H2O ⇌ Sb(OH)4‒ + H+	‒11.82	‒11.93	‒11.70
0.5 Sb2O3(s) + 1.5 H2O ⇌ Sb(OH)3	‒4.24
Sb2O3(rhombic,s) + 3 H2O ⇌ 2 Sb(OH)3		‒8.72	‒10.00
Sb2O3(cubic,s) + 3 H2O ⇌ 2 Sb(OH)3			‒11.40

Antimony(V)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Lothenbach et al., 1999; Kitamura et al., 2010
Sb(OH)5 + H2O ⇌ Sb(OH)6‒ + H+	‒2.72	‒2.72
12 Sb(OH)5 + 4 H2O ⇌ Sb12(OH)644‒ + 4 H+	20.34	20.34
12 Sb(OH)5 + 5 H2O ⇌ Sb12(OH)655‒ + 5 H+	16.72	16.72
12 Sb(OH)5 + 6 H2O ⇌ Sb12(OH)666‒ + 6 H+	11.89	11.89
12 Sb(OH)5 + 7 H2O ⇌ Sb12(OH)677‒ + 7 H+	6.07	6.07
0.5 Sb2O5(s) + 2.5 H2O ⇌ Sb(OH)5	‒3.7
Sb2O5(am) + 5 H2O ⇌ 2 Sb(OH)5		‒7.400

Arsenic(III)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Nordstrom and Archer, 2003	Nordstrom et al., 2014
As(OH)4‒ + H+ ⇌ As(OH)3 + H2O	9.29	9.17	9.24 ± 0.02

Arsenic(V)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer	Khodakovsky et al. (1968)	Nordstrom and Archer, 2003	Nordstrom et al., 2014
H2AsO4‒ + H+ ⇌ H3AsO4	2.24	2.21	2.26 ± 0.078	2.25 ± 0.04
HAsO42‒ + H+ ⇌ H2AsO4‒		6.93	6.99 ± 0.1	6.98 ± 0.11
AsO43‒ + H+ ⇌ HAsO42‒		11.51	11.80 ± 0.1	11.58 ± 0.05
HAsO42‒ + 2 H+ ⇌H3AsO4	9.20
AsO43‒ + 3 H+ ⇌ H3AsO4	20.70

Barium

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Nordstrom et al., 1990	Brown and Ekberg, 2016
Ba2+ + H2O ⇌ BaOH+ + H+	–13.47	–13.47	–13.32 ± 0.07

Berkelium(III)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Brown and Ekberg, 2016
Bk3+ + 3 H2O ⇌ Bk(OH)3(s) + 3 H+	–13.5 ± 1.0

Beryllium

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976
Be2+ + H2O ⇌ BeOH+ + H+	–5.10
Be2+ + 2 H2O ⇌ Be(OH)2 + 2 H+	–23.65
Be2+ + 3 H2O ⇌ Be(OH)3– + 3 H+	–23.25
Be2+ + 4 H2O ⇌ Be(OH)42– + 4 H+	–37.42
2 Be2+ + H2O ⇌ Be2OH3+ + H+	–3.97
3 Be2+ + 3 H2O ⇌ Be3(OH)33+ + 3 H+	–8.92
6 Be2+ + 8 H2O ⇌ Be6(OH)84+ + 8 H+	–27.2
α-Be(OH)2(cr) + 2 H+ ⇌ Be2+ + 2 H2O	6.69

Bismuth

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Lothenbach et al., 1999	NIST46	Kitamura et al., 2010	Brown and Ekberg, 2016
Bi3+ + H2O ⇌ BiOH2+ + H+	–1.0	–0.92	–1.1	–0.920	–0.92 ± 0.15
Bi3+ + 2 H2O ⇌ Bi(OH)2+ + 2 H+	(–4)	–2.56	–4.5	–2.560 ± 1.000	–2.59 ± 0.26
Bi3+ + 3 H2O ⇌ Bi(OH)3 + 3 H+	–8.86	–5.31	–9.0	–8.940 ± 0.500	–8.78 ± 0.20
Bi3+ + 4 H2O ⇌ Bi(OH)4– + 4 H+	–21.8	–18.71	–21.2	–21.660 ± 0.870	–22.06 ± 0.14
3 Bi3+ + 4 H2O ⇌ Bi3(OH)45+ + 4 H+		–0.80		–0.800
6 Bi3+ + 12 H2O ⇌ Bi6(OH)126+ + 12 H+		1.34		1.340	0.98 ± 0.13
9 Bi3+ + 20 H2O = Bi9(OH)207+ + 20 H+		–1.36		–1.360
9 Bi3+ + 21 H2O = Bi9(OH)216+ + 21 H+		–3.25		–3.250
9 Bi3+ + 22 H2O = Bi9(OH)225+ + 22 H+		–4.86		–4.860
Bi(OH)3(am) + 3 H+ = Bi3+ + 3 H2O				31.501 ± 0.927
α-Bi2O3(cr) + 6 H+ = 2 Bi3+ + 3 H2O		0.76
BiO1.5(s, α) + 3 H+ = Bi3+ + 1.5 H2O	3.46			31.501 ± 0.927	2.88 ± 0.64

Boron

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	NIST46
B(OH)3 + H2O ⇌ Be(OH)4+ + H+	–9.236	–9.236 ± 0.002
2 B(OH)3 ⇌ B2(OH)5– + H+	–9.36	–9.306
3 B(OH)3 ⇌ B3O3(OH)4– + H+ + 2 H2O	–7.03	–7.306
4 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 T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Powell et al., 2011	Brown and Ekberg, 2016
Cd2+ + H2O ⇌ CdOH+ + H+	−10.08	–9.80 ± 0.10	−9.81 ± 0.10
Cd2+ + 2 H2O ⇌ Cd(OH)2 + 2 H+	–20.35	–20.19 ± 0.13	−20.6 ± 0.4
Cd2+ + 3 H2O ⇌ Cd(OH)3– + 3 H+	<–33.3	–33.5 ± 0.5	−33.5 ± 0.5
Cd2+ + 4 H2O ⇌ Cd(OH)42– + 4 H+	–47.35	–47.28 ± 0.15	−47.25 ± 0.15
2 Cd2+ + H2O ⇌ Cd2OH3+ + H+	–9.390	–8.73 ± 0.01	−8.74 ± 0.10
4 Cd2+ + 4 H2O ⇌ Cd4(OH)44+ + H+	–32.85
Cd(OH)2(s) ⇌ Cd2+ + 2 OH–		–14.28 ± 0.12
Cd(OH)2(s) + 2 H+ ⇌ Cd2+ + 2 H2O	13.65	13.72 ± 0.12	13.71 ± 0.12

Calcium

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Nordstrom et al., 1990	Brown and Ekberg, 2016
Ca2+ + H2O ⇌ CaOH+ + H+	–12.85	–12.78	–12.57 ± 0.03
Ca(OH)2(cr) + 2 H+ ⇌ Ca2+ + 2 H2O	22.80	22.8	22.75 ± 0.02

Californium(III)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Brown and Ekberg, 2016
Cf3+ + 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 T = 298.15 K:

Reaction	Baes and Mesmer, 1976	NIST46	Brown and Ekberg, 2016
Ce3+ + H2O ⇌ CeOH2+ + H+	–8.3	–8.3	–8.31 ± 0.03
2 Ce3+ + 2 H2O ⇌ Ce2(OH)24+ + 2 H+			–16.0 ± 0.2
3 Ce3+ + 5 H2O ⇌ Ce3(OH)54+ + 5 H+			–34.6 ± 0.3
Ce(OH)3(s) + 3 H+ ⇌ Ce3+ + 3 H2O			18.5 ± 0.5
Ce(OH)3(s) ⇌ Ce3+ + 3 OH–		–22.1 ± 0.9

Chromium(II)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K (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.):

Reaction	NIST46	Ball and Nordstrom, 1988
Cr2+ + H2O ⇌ CrOH+ + H+	–5.5
Cr(OH)2(s) ⇌ Cr2+ + 2 OH–		–17 ± 0.02

Chromium(III)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Rai et al., 1987	Ball and Nordstrom, 1988	Brown and Ekberg, 2016
Cr3+ + H2O ⇌ CrOH2+ + H+	–4.0	–3.57 ± 0.08		–3.60 ± 0.07
Cr3+ + 2 H2O ⇌ Cr(OH)2+ + 2 H+	–9.7	–9.84		–9.65 ± 0.20
Cr3+ + 3 H2O ⇌ Cr(OH)3 + 3 H+	–18	–16.19		–16.25 ± 0.19
Cr3+ + 4 H2O ⇌ Cr(OH)4− + 4 H+	–27.4	–27.65 ± 0.12		–27.56 ± 0.21
2 Cr3+ + 2 H2O ⇌ Cr2(OH)24+ + 2 H+	–5.06	–5.0		–5.29 ± 0.16
3 Cr3+ + 4 H2O ⇌ Cr3(OH)45+ + 4 H+	–8.15	–10.75 ± 0.15		–9.10 ± 0.14
Cr(OH)3(s) + 3 H+ ⇌ Cr3+ + 3 H2O	12		9.35	9.41 ± 0.17
Cr2O3(s) + 6 H+ ⇌ 2 Cr3+ + 3 H2O			8.52
CrO1.5(s) + 3 H+ ⇌ Cr3+ + 1.5 H2O				7.83 ± 0.10

Chromium(VI)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Ball and Nordstrom, 1998
CrO42– + H+ ⇌ HCrO4–	6.51	6.55 ± 0.04
HCrO4– + H+ ⇌ H2CrO4	–0.20
CrO42– + 2 H+ ⇌ H2CrO4		6.31
2 HCrO4– ⇌ Cr2O72– + H2O	1.523
2 CrO42– + 2 H+ ⇌ Cr2O72– + H2O		14.7 ± 0.1

Cobalt(II)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Brown and Ekberg, 2016
Co2+ + H2O ⇌ CoOH+ + H+	–9.65	−9.61 ± 0.17
Co2+ + 2 H2O ⇌ Co(OH)2 + 2 H+	–18.8	−19.77 ± 0.11
Co2+ + 3 H2O ⇌ Co(OH)3– + 3 H+	–31.5	−32.01 ± 0.33
Co2+ + 4 H2O ⇌ Co(OH)42– + 4 H+	–46.3
2 Co2+ + H2O ⇌ Co2(OH)3+ + H+	–11.2
4 Co2+ + 4 H2O ⇌ Co4(OH)44+ + 4H+	–30.53
Co(OH)2(s) + 2 H+ ⇌ Co2+ + 2 H2O	12.3	13.24 ± 0.12
CoO(s) + 2 H+ ⇌ Co2+ + H2O		13.71 ± 0.10

Cobalt(III)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Brown and Ekberg, 2016
Co3+ + H2O ⇌ CoOH2+ + H+	−1.07 ± 0.11

Copper(I)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Brown and Ekberg, 2016
Cu+ + H2O ⇌ CuOH + H+	–7.8 ± 0.4
Cu+ + 2 H2O ⇌ Cu(OH)2– + 2 H+	–18.6 ± 0.6

Copper(II)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	NIST46	Plyasunova et al., 1997	Powell et al., 2007	Brown and Ekberg, 2016
Cu2+ + H2O ⇌ CuOH+ + H+	< –8	–7.7	–7.97 ± 0.09	–7.95 ± 0.16	–7.64 ± 0.17
Cu2+ + 2 H2O ⇌ Cu(OH)2 + 2 H+	(< –17.3)	–17.3	–16.23 ± 0.15	–16.2 ± 0.2	–16.24 ± 0.03
Cu2+ + 3 H2O ⇌ Cu(OH)3– + 3 H+	(< –27.8)	–27.8	–26.63 ± 0.40	–26.60 ± 0.09	–26.65 ± 0.13
Cu2+ + 4 H2O ⇌ Cu(OH)42– + 4 H+	–39.6	–39.6	–39.73 ± 0.17	–39.74 ± 0.18	–39.70 ± 0.19
2 Cu2+ + H2O ⇌ Cu2(OH)3+ + H+			–6.71 ± 0.30	–6.40 ± 0.12	–6.41 ± 0.17
2 Cu2+ + 2 H2O ⇌ Cu2(OH)22+ + 2 H+	–10.36	–10.3	–10.55 ± 0.17	–10.43 ± 0.07	–10.55 ± 0.02
3 Cu2+ + 4 H2O ⇌ Cu3(OH)42+ + 4 H+			–20.95 ± 0.30	–21.1 ± 0.2	–21.2 ± 0.4
CuO(s) + 2 H+ ⇌ Cu2+ + H2O	7.62		7.64 ± 0.06	7.64 ± 0.06	7.63 ± 0.05
Cu(OH)2(s) + 2 H+ ⇌ Cu2+ + 2 H2O				8.67 ± 0.05	8.68 ± 0.10

Curium

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Brown and Ekberg, 2016
Cm3+ + H2O ⇌ Cm(OH)2+ + H+	−7.66 ± 0.07
Cm3+ + 2 H2O ⇌ Cm(OH)2+ + 2 H+	−15.9 ± 0.1
Cm3+ + 3 H2O ⇌ Cm(OH)3(s) + 3 H+	−13.9 ± 0.4

Dysprosium

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Brown and Ekberg, 2016
Dy3+ + H2O ⇌ DyOH2+ + H+	−8.0	−7.53 ± 0.14
Dy3+ + 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+	–33.5
2 Dy3+ + 2 H2O ⇌ Dy2(OH)24+ + 2 H+		−13.76 ± 0.20
3 Dy3+ + 5 H2O ⇌ Dy3(OH)54+ + 5 H+		−30.6 ± 0.3
Dy(OH)3(s) + 3 H+ ⇌ Dy3+ + 3 H2O	15.9	16.26 ± 0.30
Dy(OH)3(c) + OH− ⇌ Dy(OH)4−	−3.6
Dy(OH)3(c) ⇌ Dy(OH)3	−8.8

Erbium

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Brown and Ekberg, 2016
Er3+ + H2O ⇌ ErOH2+ + H+	−7.9	−7.46 ± 0.09
Er3+ + 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+	−32.6
2 Er3+ + 2 H2O ⇌ Er2(OH)24+ + 2 H+	−13.65	−13.50 ± 0.20
3 Er3+ + 5 H2O ⇌ Er3(OH)54+ + 5 H+	<−29.3	−31.0 ± 0.3
Er(OH)3(s) + 3 H+ ⇌ Er3+ + 3 H2O	15.0	15.79 ± 0.30
Er(OH)3(c) + OH− ⇌ Er(OH)4−	−3.6
Er(OH)3(c) ⇌ Er(OH)3	~ −9.2

Europium

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	NIST46	Hummel et al., 2002	Brown and Ekberg, 2016
Eu3+ + H2O ⇌ EuOH2+ + H+	–7.8		–7.64 ± 0.04	–7.66 ± 0.05
Eu3+ + 2 H2O ⇌ Eu(OH)2+ + 2 H+			–15.1 ± 0.2
Eu3+ + 3 H2O ⇌ Eu(OH)3 + 3 H+			–23.7 ± 0.1
Eu3+ + 4 H2O ⇌ Eu(OH)4− + 4 H+			–36.2 ± 0.5
2 Eu3+ + 2 H2O ⇌ Eu2(OH)24+ + 2 H+			-	–14.1 ± 0.2
3 Eu3+ + 5 H2O ⇌ Eu3(OH)54+ + 5 H+			-	–32.0 ± 0.3
Eu(OH)3(s) + 3 H+ ⇌ Eu3+ + 3 H2O	17.5		17.6 ± 0.8 (am) 14.9 ± 0.3 (cr)	16.48 ± 0.30
Eu(OH)3(s) ⇌ Eu3+ + 3 OH–		–24.5 ± 0.7 (am) –26.5 (cr)

Gadolinium

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Brown and Ekberg, 2016
Gd3+ + H2O ⇌ GdOH2+ + H+	–8.0	–7.87 ± 0.05
Gd3+ + 2 H2O ⇌ Gd(OH)2+ + 2 H+	(–16.4)
Gd3+ + 3 H2O ⇌ Gd(OH)3 + 3 H+	(–25.2)
Gd3+ + 4 H2O ⇌ Gd(OH)4– + 4 H+	–34.4
2 Gd3+ + 2 H2O ⇌ Gd2(OH)24+ + 2 H+		–14.16 ± 0.20
3 Gd3+ + 5 H2O ⇌ Gd3(OH)54+ + 5 H+		–33.0 ± 0.3
Gd(OH)3(s) + 3 H+ ⇌ Gd3+ + 3 H2O	15.6	17.20 ± 0.48
Gd(OH)3(c) + OH– ⇌ Gd(OH)4–	–4.8
Gd(OH)3(c) ⇌ Gd(OH)3	–9.6

Gallium

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Smith et al., 2003	Brown and Ekberg, 2016
Ga3+ + H2O ⇌ GaOH2+ + H+	–2.6	–2.897	–2.74
Ga3+ + 2 H2O ⇌ Ga(OH)2+ + 2 H+	–5.9	–6.694	–7.0
Ga3+ + 3 H2O ⇌ Ga(OH)3 + 3 H+	–10.3		–11.96
Ga3+ + 4 H2O ⇌ Ga(OH)4– + 4 H+	–16.6	–16.588	–15.52
Ga(OH)3(s) ⇌ Ga3+ + 3 OH–	$\approx$–37	–37.0
GaO(OH)(s) + H2O ⇌ Ga3+ + 3 OH–	–39.06	–39.1	–40.51

Germanium

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Wood and Samson, 2006	Filella and May, 2023
Ge(OH)4 ⇌ GeO(OH)3− + H+	–9.31	–9.32 ± 0.05	–9.099
Ge(OH)4 ⇌ GeO2(OH)22+ + 2 H+	–21.9
GeO2(OH)22– + H+ ⇌ GeO(OH)3–			12.76
8 Ge(OH)4 ⇌ Ge8O16(OH)33- + 13 H2O + 3 H+	–14.24
8 Ge(OH)4 + 3 OH– ⇌ Ge8(OH)353–			28.33
GeO2(s, hexa) + 2 H2O ⇌ Ge(OH)4		–1.35	–1.373
GeO2(s, tetra) + 2 H2O ⇌ Ge(OH)4	-4.37	–5.02	–4.999

Gold(III)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976
Au(OH)3 +2 H+ ⇌ AuOH2+ + 2 H2O	1.51
Au(OH)3 + H+ ⇌ Au(OH)2+ + H2O	< 1.0
Au(OH)3 + H2O ⇌ Au(OH)4– + H+	–11.77
Au(OH)3 + 2 H2O ⇌ Au(OH)52– + 2 H+	–25.13
Au(OH)52– + 3 H2O ⇌ Au(OH)63– + 3 H+	< –41.1
Au(OH)3(c) ⇌ Au(OH)3	–5.51

Hafnium

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Brown and Ekberg, 2016
Hf4+ + H2O ⇌ HfOH3+ + H+	–0.25	−0.26 ± 0.10
Hf4+ + 2 H2O ⇌ Hf(OH)22+ + 2 H+	(–2.4)
Hf4+ + 3 H2O ⇌ Hf(OH)3+ + 3 H+	(–6.0)
Hf4+ + 4 H2O ⇌ Hf(OH)4 + 4 H+	–10.7*	−3.75 ± 0.34*
Hf4+ + 5 H2O ⇌ Hf(OH)5– + 5 H+	–17.2
3 Hf4+ + 4 H2O ⇌ Hf3(OH)48+ + 4 H+		0.55 ± 0.30
4 Hf4+ + 8 H2O ⇌ Hf4(OH)88+ + 8 H+		6.00 ± 0.30
HfO2(s) + 4 H+ ⇌ Hf4+ + 2 H2O	–1.2*	–5.56 ± 0.15*
HfO2(am) + 4 H+ ⇌ Hf4+ + 2 H2O		–3.11 ± 0.20

*Errors in compilations concerning equilibrium and/or data elaboration. Data not recommended. Strongly suggested to refer to the original papers.

Holmium

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Brown and Ekberg, 2016
Ho3+ + H2O ⇌ HoOH2+ + H+	−8.0	−7.43 ± 0.05
2 Ho3+ + 2 H2O ⇌ Ho2(OH)24+ + 2 H+		−13.5 ± 0.2
3 Ho3+ + 5 H2O ⇌ Ho3(OH)54+ + 5 H+		−30.9 ± 0.3
Ho(OH)3(s) + 3 H+ ⇌ Ho3+ + 3 H2O	15.4	15.60 ± 0.30

Indium

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	NIST46	Brown and Ekberg, 2016
In3+ + H2O ⇌ InOH2+ + H+	–4.00	–3.927	–3.96
In3+ + 2 H2O ⇌ In(OH)2+ + 2 H+	–7.82	–7.794	–9.16
In3+ + 3 H2O ⇌ In(OH)3 + 3 H+	–12.4	–12.391
In3+ + 4 H2O ⇌ In(OH)4– + 4 H+	–22.07	–22.088	–22.05
In(OH)3(s) ⇌ In3+ + 3 OH–	–36.92	–36.9	–36.92
1/2 In2O3(s) + 3/2 H2O ⇌ In3+ + 3 OH–			–35.24

Iridium

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Brown and Ekberg, 2016
Ir3+ + H2O ⇌ IrOH2+ + H+	‒3.77 ± 0.10
Ir3+ + 2 H2O ⇌ Ir(OH)2+ + 2 H+	‒8.46 ± 0.20
Ir(OH)3(s) + 3 H+ ⇌ Ir3+ + 3 H2O	8.88 ± 0.20

Iron(II)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Nordstrom et al., 1990	Hummel et al., 2002	Lemire et al., 2013	Brown and Ekberg, 2016
Fe2+ + H2O ⇌ FeOH+ + H+	–9.3	–9.5	–9.5	–9.1 ± 0.4	−9.43 ± 0.10
Fe2+ + 2 H2O ⇌ Fe(OH)2 + 2 H+	–20.5				−20.52 ± 0.08
Fe2+ + 3 H2O ⇌ Fe(OH)3− + 3 H+	–29.4				−32.68 ± 0.15
Fe(OH)2(s) +2 H+ ⇌ Fe2+ + 2 H2O					12.27 ± 0.88

Iron(III)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Lemire et al., 2013	Brown and Ekberg, 2016
Fe3+ + H2O ⇌ FeOH2+ + H+	–2.19	−2.15 ± 0.07	–2.20 ± 0.02
Fe3+ + 2 H2O ⇌ Fe(OH)2+ + 2 H+	–5.67	−4.8 ± 0.4	–5.71 ± 0.10
Fe3+ + 3 H2O ⇌ Fe(OH)3 + 3 H+	<–12	<–14	–12.42 ± 0.20
Fe3+ + 4 H2O ⇌ Fe(OH)4– + 4 H+	–21.6	−21.5 ± 0.5	–21.60 ± 0.23
2 Fe3+ + 2 H2O ⇌ Fe2(OH)24+ + 2 H+	–2.95	–2.91 ± 0.07	–2.91 ± 0.07
3 Fe3+ + 4 H2O ⇌ Fe3(OH)45+ + 4 H+	–6.3		−6.3 ± 0.1
Fe(OH)3(s) +3 H+ ⇌ Fe3+ + 3 H2O 2-line ferrihydrite	2.5	3.5	3.50 ± 0.20
Fe(OH)3(s) ⇌ Fe3+ + 3 OH− 6-line ferrihydrite		−38.97 ± 0.64
α-FeOOH(s)+ 3 H+ ⇌ Fe3+ + 2 H2O goethite	0.5		0.33 ± 0.10
α-FeOOH + H2O ⇌ Fe3+ + 3 OH− goethite		−41.83 ± 0.37
0.5 α-Fe2O3(s)+ 3 H+ ⇌ Fe3+ + 1.5 H2O hematite			0.36 ± 0.40
0.5 α-Fe2O3 + 1.5 H2O ⇌ Fe3+ + 3 OH− hematite		−42.05 ± 0.26
0.5 γ-Fe2O3(s) + 3 H+ ⇌ Fe3+ + 1.5 H2O maghemite			1.61 ± 0.61
0.5 γ-Fe2O3 + 1.5 H2O ⇌ Fe3+ + 3 OH− maghemite		−40.59 ± 0.29
α-FeOOH(s)+ 3 H+ ⇌ Fe3+ + 2 H2O goethite			1.85 ± 0.37
γ-FeOOH + H2O ⇌ Fe3+ + 3 OH− lepidocrocite		−40.13 ± 0.37
Fe(OH)3(s) + 3 H+ ⇌ Fe3+ + 3 H2O magnetite			−12.26 ± 0.26

Lanthanum

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Brown and Ekberg, 2016
La3+ + H2O ⇌ LaOH2+ + H+	–8.5	–8.89 ± 0.10
2 La3+ + 2 H2O ⇌ La2(OH)24+ + 2 H+	≤ –17.5	–17.57 ± 0.20
3 La3+ + 5 H2O ⇌ La3(OH)54+ + 5 H+	≤ –38.3	–37.8 ± 0.3
5 La3+ + 9 H2O ⇌ La5(OH)96+ + 9 H+	–71.2
La(OH)3(s) + 3 H+ ⇌ La3+ + 3 H2O	20.3	19.72 ± 0.34

Lead(II)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	NIST46	Powell et al., 2009	Brown and Ekberg, 2016	Cataldo et al., 2018
Pb2+ + H2O ⇌ PbOH+ + H+	–7.71	–7.6	–7.46 ± 0.06	–7.49 ± 0.13	–6.47± 0.03
Pb2+ + 2 H2O ⇌ Pb(OH)2 + 2 H+	–17.12	–17.1	–16.94 ± 0.09	–16.99 ± 0.06	–16.12 ± 0.01
Pb2+ + 3 H2O ⇌ Pb(OH)3- + 3 H+	–28.06	–28.1	–28.03± 0.06	–27.94 ± 0.21	–28.4 ± 0.1
Pb2+ + 4 H2O ⇌ Pb(OH)42- + 4 H+			–40.8
2 Pb2+ + H2O ⇌ Pb2(OH)3+ + H+	–6.36	–6.4	–7.28± 0.09	–6.73 ± 0.31
3 Pb2+ + 4 H2O ⇌ Pb3(OH)42+ + 4 H+	–23.88	–23.9	–23.01 ± 0.07	–23.43 ± 0.10
3 Pb2+ + 5 H2O ⇌ Pb3(OH)5+ + 5 H+				–31.11 ± 0.10
4 Pb2+ + 4 H2O ⇌ Pb4(OH)44+ + 4 H+	–20.88	–20.9	–20.57± 0.06	–20.71 ± 0.18
6 Pb2+ + 8 H2O ⇌ Pb6(OH)84+ + 8 H+	–43.61	–43.6	–42.89± 0.07	–43.27 ± 0.47
PbO(s) + 2 H+ ⇌ Pb2+ + H2O			12.62 (red) 12.90 (yellow)
PbO(s) +H2O ⇌ Pb2+ + 2 OH–	–15.28 (red)	-15.3	–15.3 (red) –15.1 (yellow)	–15.37 ± 0.04 (red) –15.1 ± 0.08 (yellow)
Pb2O(OH)2(s) +H2O ⇌ 2 Pb2+ + 4 OH–			–14.9
PbO(s) +H2O ⇌ Pb(OH)2			–4.4 (red) –4.2 (yellow)
Pb2O(OH)2(s) +H2O ⇌ 2 Pb(OH)2			–4.0
PbO(s) + 2 H2O ⇌ Pb(OH)3– + H+			–1.4 (red) –1.2 (yellow)
Pb2O(OH)2(s) + 2 H2O ⇌ 2 Pb(OH)3– + 2 H+			–1.0

Lead(IV)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Feitknecht and Schindler, 1963
β-PbO2 + 2 H2O ⇌ Pb4+ + 4 OH–	–64
β-PbO2 + 2 H2O + 2 OH– ⇌ Pb(OH)62–	–4.5

Lithium

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Nordstrom et al., 1990	Brown and Ekberg, 2016
Li+ + H2O ⇌ LiOH + H+	–13.64	–13.64	–13.84 ± 0.14

Magnesium

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Nordstrom et al., 1990	Brown and Ekberg, 2016
Mg2+ + H2O ⇌ MgOH+ + H+	–11.44	–11.44	–11.70 ± 0.04
4 Mg2+ + 4 H2O ⇌ Mg4(OH)44+ + 4 H+	–39.71
Mg(OH)2(cr) + 2 H+ ⇌ Mg2+ + 2 H2O	16.84	16.84	17.11 ± 0.04

Manganese(II)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Perrin et al., 1969	Baes and Mesmer, 1976	Nordstrom et al., 1990	Hummel et al., 2002	Brown and Ekberg, 2016
Mn2+ + H2O ⇌ MnOH+ + H+	–10.59	–10.59	–10.59	–10.59	−10.58 ± 0.04
Mn2+ + 2 H2O ⇌ Mn(OH)2 + 2 H+		–22.2			−22.18 ± 0.20
Mn2+ + 3 H2O ⇌ Mn(OH)3– + 3 H+		–34.8			−34.34 ± 0.45
Mn2+ + 4 H2O ⇌ Mn(OH)42– + 4 H+		–48.3			−48.28 ± 0.40
2 Mn2+ + H2O ⇌ Mn2OH3+ + H+		–10.56
2 Mn2+ + 3 H2O ⇌ Mn2(OH)3+ + 6 H+		–23.90
Mn(OH)2(s) + 2 H+ ⇌ Mn2+ + 2 H2O	15.2	15.2	15.2		15.19 ± 0.10
MnO(s) + 2 H+ ⇌ Mn2+ + H2O					17.94 ± 0.12

Manganese(III)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Brown and Ekberg, 2016
Mn3+ + H2O ⇌ MnOH2+ + H+	–11.70 ± 0.04

Mercury(I)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Brown and Ekberg, 2016
Hg22+ + H2O ⇌ Hg2OH+ + H+	−5.0a	−4.45 ± 0.10

(^a) 0.5 M HClO₄

Mercury(II)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Powell et all, 2005	Brown and Ekberg, 2016
Hg2+ + H2O ⇌ HgOH+ + H+	−3.40	–3.40 ± 0.08	–3.40 ± 0.08
Hg2+ + 2 H2O ⇌ Hg(OH)2 + 2 H+	-6.17	–5.98 ± 0.06	−5.96 ± 0.07
Hg2+ + 3 H2O ⇌ Hg(OH)3– + 3 H+	–21.1	–21.1 ± 0.3
HgO(s) + 2 H+ ⇌ Hg2+ + H2O	2.56	2.37 ± 0.08	2.37 ± 0.08

Molybdenum(VI)

Hydrolysis constants (log values) in critical compilations at infinite dilution, T = 298.15 K and I = 3 M NaClO₄ (^a) or 0.1 M Na⁺ medium, Data at I = 0 are not available (^b):

Reaction	Baes and Mesmer, 1976	Jolivet, 2000	NIST46	Crea et al., 2017
MoO42– + H+ ⇌ HMoO4–	3.89a		4.24	4.47 ± 0.02
MoO42– + 2 H+ ⇌ H2MoO4	7.50a			8.12 ± 0.03
HMoO4– + H+ ⇌ H2MoO4			4.0
Mo7O246– + H+ ⇌ HMo7O245–		4.4
HMo7O245– + H+ ⇌ H2Mo7O244–		3.5
H2Mo7O244– + H+ ⇌ H3Mo7O243–		2.5
7 MoO42-+ 8 H+ ⇌ Mo7O246– + 4 H2O	57.74a		52.99b	51.93 ± 0.04
7 MoO42– + 9 H+ ⇌ Mo7O23(OH)5– + 4 H2O	62.14a			58.90 ± 0.02
7 MoO42– + 10 H+ ⇌ Mo7O22(OH)24– + 4 H2O	65.68a			64.63 ± 0.05
7 MoO42– + 11 H+ ⇌ Mo7O21(OH)33– + 4 H2O	68.21a			68.68 ± 0.06
19 MoO42- + 34 H+ ⇌ Mo19O594– + 17 H2O	196.3a		196a
MoO3(s) + H2O ⇌ MoO42– + 2 H+	–12.06a

Neodymium

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	NIST46	Neck et al., 2009	Brown and Ekberg, 2016
Nd3+ + H2O ⇌ NdOH2+ + H+	–8.0	–8.0	–7.4 ± 0.4	–8.13 ± 0.05
Nd3+ + 2 H2O ⇌ Nd(OH)2+ + 2 H+	(–16.9)		–15.7 ± 0.7
Nd3+ + 3 H2O ⇌ Nd(OH)3(aq) + 3 H+	(–26.5)		–26.2 ± 0.5
Nd3+ + 4 H2O ⇌ Nd(OH)4− + 4 H+	(–37.1)	–37.4	–40.7 ± 0.7
2 Nd3+ + 2 H2O ⇌ Nd2(OH)24+ + 2 H+	–13.86	–13.9		–15.56 ± 0.20
3 Nd3+ + 5 H2O ⇌ Nd3(OH)54+ + 5 H+	< –28.5			–34.2 ± 0.3
Nd(OH)3(s) + 3 H+ ⇌ Nd3+ + 3 H2O	18.6		17.2 ± 0.4	17.89 ± 0.09
Nd(OH)3(s) ⇌ Nd3+ + 3 OH–		–23.2 ± 0.9	–21.5 (act) –23.1(inact)

Neptunium(III)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Brown and Ekberg, 2016	Grenthe et al., 2020
Np3+ + H2O ⇌ NpOH2+ + H+	-7.3 ± 0.5	–6.8 ± 0.3

Neptunium(IV)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	NIST46	Brown and Ekberg, 2016	Grenthe et al., 2020
Np4+ + H2O ⇌ NpOH3+ + H+	–1.49	–1.5	–1.31 ± 0.05	0.5 ± 0.2
Np4+ + 2 H2O ⇌ Np(OH)22+ + 2 H+			–3.7 ± 0.3	0.3 ± 0.3
Np4+ + 4 H2O ⇌ Np(OH)4 + 4 H+			–10.0 ± 0.9	–8 ± 1
Np4+ + 4 OH− ⇌ NpO2(am, hyd) + 2 H2O	52	54.9 ± 0.4	57.5 ± 0.3	56.7 ± 0.5

Neptunium(V)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Brown and Ekberg, 2016	Grenthe et al., 2020
NpO2+ + + H2O ⇌ NpO2(OH) + H+	–8.85	–10.7 ± 0.5	–11.3 ± 0.7
NpO2+ + 2 H2O ⇌ NpO2(OH)2− + 2 H+		–22.8 ± 0.7	–23.6 ± 0.5
NpO2+ + H2O ⇌ NpO2(OH)(am, fresh) + H+	≤ –4.7	–5.21 ± 0.05	–5.3 ± 0.2
NpO2+ + H2O ⇌ NpO2(OH)(am, aged) + H+		–4.53 ± 0.06	–4.7 ± 0.5

Neptunium(VI)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	NIST46	Brown and Ekberg, 2016	Grenthe et al., 2020
NpO22+ + H2O ⇌ NpO2(OH)+ + H+	–5.15	–5.12	–5.1 ± 0.2	–5.1 ± 0.4
NpO22+ + 3 H2O ⇌ NpO2(OH)3− + 3 H+			–21 ± 1
NpO22+ + 4 H2O ⇌ NpO2(OH)42- + 4 H+			–32 ± 1
2 NpO22+ + 2 H2O ⇌ (NpO2)2(OH)22+ + 2 H+	–6.39	–6.39	–6.2 ± 0.2	–6.2 ± 0.2
3 NpO22+ + 5 H2O ⇌ (NpO2)3(OH)5+ + 5 H+	–17.49	–17.49	–17.0 ± 0.2	–17.1 ± 0.2
NpO22+ + 2 H2O ⇌ NpO3.H2O(cr) + 2 H+	≥-6.6		–5.4 ± 0.4	–5.4 ± 0.4

Nickel(II)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Feitknecht and Schindler, 1963	Baes and Messmer, 1976	NIST46	Gamsjäger et al., 2005	Thoenen et al., 2014	Brown and Ekberg, 2016
Ni2+ + H2O ⇌ NiOH+ + H+		–9.86	–9.9	–9.54 ± 0.14	–9.54 ± 0.14	–9.90 ± 0.03
Ni2+ + 2 H2O ⇌ Ni(OH)2 + 2 H+		–19	–19		< –18	–21.15 ± 0.0
Ni2+ + 3 H2O ⇌ Ni(OH)3– + 3 H+		–30	–30	–29.2 ± 1.7	–29.2 ± 1.7
Ni2+ + 4 H2O ⇌ Ni(OH)42– + 4 H+		< –44
2 Ni2+ + H2O ⇌ Ni2(OH)3+ + H+		–10.7		–10.6 ± 1.0	–10.6 ± 1.0	–10.6 ± 1.0
4 Ni2+ + 4 H2O ⇌ Ni4(OH)44+ + 4 H+		–27.74	–27.7	–27.52 ± 0.15	–27.52 ± 0.15	–27.9 ± 0.6
β-Ni(OH)2(s) + 2 H+ ⇌ Ni2+ + 2 H2O		10.8			11.02 ± 0.20	10.96 ± 0.20 11.75 ± 0.13 (microcr)
Ni(OH)2(s) ⇌ Ni2+ + 2 OH–	–17.2 (inactive)		–17.2	–16.97± 0.20 (β) –17.2 ± 1.3 (cr)
Ni(OH)2(s) + OH– ⇌ Ni(OH)3–	–4.2 (inactive)
NiO(cr) + 2 H+ ⇌ Ni2+ + H2O				12.38 ± 0.06		12.48 ± 0.15

Niobium

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Filella and May, 2020
Nb(OH)5 + H+ ⇌ Nb(OH)4+ + H2O	~ –0.6	1.603
Nb(OH)5 + H2O ⇌ Nb(OH)6– + H+	~ –4.8	–4.951
Nb6O198– + H+ ⇌ HNb6O197–		14.95
HNb6O197– + H+ ⇌ H2Nb6O196–		13.23
H2Nb6O196– + H+ ⇌ H3Nb6O195–		11.73
1/2 Nb2O5(act) + 5/2 H2O ⇌ Nb(OH)5	~ –7.4
Nb(OH)5(am,s) ⇌ Nb(OH)5		–7.510
Nb2O5(s) + 5 H2O ⇌ 2 Nb(OH)5		–18.31

Osmium(VI)

Hydrolysis constants (log values) in critical compilations at infinite dilution, I = 0.1 M and T = 298.15 K:

Reaction	Galbács et al., 1983
OsO2(OH)42– + H+ ⇌ HOsO2(OH)4–	10.4
HOsO2(OH)4– + H+ ⇌ H2OsO2(OH)4	8.5

Osmium(VIII)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Galbács et al., 1983
OsO2(OH)3(O−)aq + H+ ⇌ OsO2(OH)4aq	12.2a
OsO2(OH)2(O−)2aq + H+ ⇌ OsO2(OH)3(O−)aq	14.4b

(^a) At I = 0.1 M (^b) At I = 2.5 M

Palladium

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Perrin et al., 1969	Hummel et al., 2002	Kitamura and Yul, 2010	Brown and Ekberg, 2016
Pd2+ + H2O ⇌ PdOH+ + H+	−0.96		−0.65 ± 0.64	−1.16 ± 0.30
Pd2+ + 2 H2O ⇌ Pd(OH)2 + 2 H+	−2.6	−4 ± 1	−3.11 ± 0.63	−3.07 ± 0.16
Pd2+ + 3 H2O ⇌ Pd(OH)3− + 3 H+		−15.5 ± 1	−14.20 ± 0.63
Pd(OH)2(am) + 2 H+ ⇌ Pd2+ + 2 H2O		−3.3 ± 1		−3.4 ± 0.2

Plutonium(III)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	NIST46	Brown and Ekberg, 2016	Grenthe et al., 2020
Pu3+ + H2O ⇌ PuOH2+ + H+		–7.0	–6.9 ± 0.2	–6.9 ± 0.3
Pu3+ + 3 H2O ⇌ Pu(OH)3(cr) + 3 H+	–19.65		–15.8 ± 0.8	–15 ± 1

Plutonium(IV)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	NIST46	Brown and Ekberg, 2016	Grenthe et al., 2020
Pu4+ + H2O ⇌ PuOH 3+ + H+	–0.5	–0.5	–0.7 ± 0.1	0.6 ± 0.2
Pu4+ + 2 H2O ⇌ Pu(OH)22+ + 2 H+	(–2.3)			0.6 ± 0.3
Pu4+ + 3 H2O ⇌ Pu(OH)3+ + 3 H+	(–5.3)			–2.3 ± 0.4
Pu4+ + 4 H2O ⇌ Pu(OH)4 + 4 H+	–9.5		–12.5 ± 0.7	–8.5 ± 0.5
Pu4+ + 4 OH− ⇌ PuO2(am, hyd) + 2 H2O	49.5		47.9 ± 0.4 (0w) 53.8 ± 0.5 (1w)	58.3 ± 0.5

Plutonium(V)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	NIST46	Brown and Ekberg, 2016	Grenthe et al., 2020
PuO2+ + H2O ⇌ PuO2(OH) + H+	–1.49	–1.5	–1.31 ± 0.05	0.5 ± 0.2
PuO2+ + H2O ⇌ PuO2(OH)(am) + H+			–3.7 ± 0.3	0.3 ± 0.3

Plutonium(VI)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	NIST46	Brown and Ekberg, 2016	Grenthe et al., 2020
PuO22+ + H2O ⇌ PuO2(OH)+ + H+	–5.6	–5.6	–5.36 ± 0.09	–5.5 ± 0.5
PuO22+ + 2 H2O ⇌ PuO2(OH)2 + 2 H+			–12.9 ± 0.2	–13 ± 1
PuO22+ + 3 H2O ⇌ PuO2(OH)3− + 3 H+				–24 ± 1
2 PuO22+ + 2 H2O ⇌ (PuO2)2(OH)22+ + 2 H+	–8.36	–8.36	–7.8 ± 0.5	–7 ± 1
3 PuO22+ + 5 H2O ⇌ (PuO2)3(OH)5+ + 5 H+	–21.65	–21.65
PuO22+ + 2 OH− ⇌ PuO2(OH)2(am, hyd)				22.8 ± 0.6

Potassium

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Nordstrom et al., 1990	Brown and Ekberg, 2016
K+ + H2O ⇌ KOH + H+	–14.46	–14.46	–14.5 ± 0.4

Praseodymium

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	NIST46	Brown and Ekberg, 2016
Pr3+ + H2O ⇌ PrOH2+ + H+	–8.1		–8.30 ± 0.03
2 Pr3+ + 2 H2O ⇌ Pr2(OH)24+ + 2 H+			–16.31 ± 0.20
3 Pr3+ + 5 H2O ⇌ Pr3(OH)54+ + 5 H+			–35.0 ± 0.3
Pr(OH)3(s) + 3 H+ ⇌ Pr3+ + 3 H2O	19.5		18.57 ± 0.20
Pr(OH)3(s) ⇌ Pr3+ + 3 OH–		–22.3 ± 1.0

Radium

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Nordstrom et al., 1990
Ra2+ + H2O ⇌ RaOH+ + H+	–13.49

Rhodium

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Perrin et al., 1969	Baes and Mesmer, 1976	Brown and Ekberg
Rh3+ + H2O ⇌ RhOH2+ + H+	‒3.43	‒3.4	‒3.09 ± 0.1
Rh(OH)3(c) + OH‒ ⇌ Rh(OH)4‒		‒3.9

Samarium

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	NIST46	Brown and Ekberg
Sm3+ + H2O ⇌ SmOH2+ + H+	–7.9	–7.9	–7.84 ± 0.11
2 Sm3+ + 2 H2O ⇌ Sm2(OH)24+ + 2 H+			–14.75 ± 0.20
3 Sm3+ + 5 H2O ⇌ Sm3(OH)54+ + 5 H+			–33.9 ± 0.3
Sm(OH)3(s) + 3H+ ⇌ Sm3+ + 3H2O	16.5		17.19 ± 0.30
Sm(OH)3(s) ⇌ Sm3+ + 3 OH−		–23.9 ± 0.9 (am) –25.9 (cr)

Scandium

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Brown and Ekberg, 2016
Sc3+ + H2O ⇌ ScOH2+ + H+	–4.3	–4.16 ± 0.05
Sc3+ + 2 H2O ⇌ Sc(OH)2+ + 2 H+	–9.7	–9.71 ± 0.30
Sc3+ + 3 H2O ⇌ Sc(OH)3 + 3 H+	–16.1	–16.08 ± 0.30
Sc3+ + 4 H2O ⇌ Sc(OH)4–+ 4 H+	–26	–26.7 ± 0.3
2 Sc3+ + 2 H2O ⇌ Sc2(OH)24+ + 2 H+	–6.0	–6.02 ± 0.10
3 Sc3+ + 5 H2O ⇌ Sc3(OH)54+ + 5 H+	–16.34	–16.33 ± 0.10
Sc(OH)3(s) + 3 H+ ⇌ Sc3+ + 3 H2O		9.17 ± 0.30
ScO1.5(s) + 3 H+ ⇌ Sc3+ + 1.5 H2O		5.53 ± 0.30
ScO(OH)(c) + 3 H+ ⇌ Sc3+ + 2 H2O	9.4
Sc(OH)3(c) + OH– ⇌ Sc(OH)4		–3.5 ± 0.2

Selenium(–II)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Olin et al., 2015	Thoenen et al., 2014
H2Se(g) ⇌ H2Se(aq)	–1.10 ± 0.01	–1.10 ± 0.01
H2Se ⇌ HSe– + H+	–3.85 ± 0.05	–3.85 ± 0.05
HSe– ⇌ Se2– + H+	–14.91 ± 0.20

Selenium(IV)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Olin et al., 2005	Thoenen et al., 2014
SeO32– + H+ ⇌ HSeO3–	8.50	8.36 ± 0.23	8.36 ± 0.23
HSeO3– + H+ ⇌ H2SeO3	2.75	2.64 ± 0.14	2.64 ± 0.14

Selenium(VI)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Olin et al., 2005	Thoenen et al., 2014
SeO42‒ + H+ ⇌ HSeO4‒	1.360	1.75 ± 0.10	1.75 ± 0.10

Silicon

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Thoenen et al., 2014
Si(OH)4 ⇌ SiO(OH)3– + H+	–9.86	–9.81 ± 0.02
Si(OH)4 ⇌ SiO2(OH)22– + 2 H+	–22.92	–23.14 ± 0.09
4 Si(OH)4 ⇌ Si4O6(OH)64– + 2 H+ + 4 H2O	–13.44
4 Si(OH)4 ⇌ Si4O8(OH)44– + 4 H+ + 4 H2O	–35.80	–36.3 ± 0.2
SiO2(quartz) + 2 H2O ⇌ Si(OH)4	–4.0	–3.739 ± 0.087
SiO2(am) + 2 H2O ⇌ Si(OH)4		–2.714

Silver

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Brown and Ekberg, 2016
Ag+ + H2O ⇌ AgOH + H+	−12.0	−11.75 ± 0.14
Ag+ + 2 H2O ⇌ Ag(OH)2− + 2 H+	−24.0	−24.34 ± 0.14
0.5 Ag2O(am) + H+ ⇌ Ag+ + 0.5 H2O	6.29	6.27 ± 0.05

Sodium

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Nordstrom et al., 1990	Brown and Ekberg, 2016
Na+ + H2O ⇌ NaOH + H+	–14.18	–14.18	–14.4 ± 0.2

Strontium

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Nordstrom et al., 1990	Brown and Ekberg, 2016
Sr2+ + H2O ⇌ SrOH+ + H+	–13.29	–13.29	–13.15 ± 0.05

Tantalum

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Filella and May, 2019a
Ta(OH)5 + H+ ⇌ Ta(OH)4+ + H2O	~1	0.7007
Ta(OH)5 + H2O ⇌ Ta(OH)6– + H+	~ –9.6
Ta6O198– + H+ ⇌ HTa6O197–		16.35
HTa6O197– + H+ ⇌ H2Ta6O196–		14.00
1/2 Ta2O5(act) + 5/2 H2O ⇌ Ta(OH)5	~ –5.2
Ta(OH)5(s) ⇌ Ta(OH)5		–5.295
Ta2O5(s) + 5 H2O ⇌ 2 Ta(OH)5		–20.00

(^a) The number of significant figures are retained to minimise propagation of round-off errors; they should not be taken to indicate the relative uncertainty of the values, which is always at least one order of magnitude less than indicated.

Tellurium(-II)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Filella and May, 2019a
Te2‒ + H+ ⇌ HTe‒	11.81
HTe‒ + H+ ⇌ H2Te	2.476

(^a) The number of significant figures are retained to minimise propagation of round-off errors; they should not be taken to indicate the relative uncertainty of the values, which is always at least one order of magnitude less than indicated.

Tellurium(IV)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Filella and May, 2019a
TeO32‒ + H+ ⇌ HTeO3‒		9.928
HTeO3‒ + H+ ⇌ H2TeO3		6.445
H2TeO3 ⇌ HTeO3‒ + H+	‒2.68
H2TeO3 ⇌ TeO32‒ + 2 H+	‒12.5
H2TeO3 + H+ ⇌ Te(OH)3+	3.13	2.415
TeO2(s) + H2O ⇌ H2TeO3		‒4.709

(^a) The number of significant figures are retained to minimise propagation of round-off errors; they should not be taken to indicate the relative uncertainty of the values, which is always at least one order of magnitude less than indicated.

Tellurium(VI)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Filella and May, 2019a
TeO2(OH)42‒ + H+ ⇌ TeO(OH)5‒		10.83
TeO(OH)5‒ + H+ ⇌ Te(OH)6	7.68	7.696
TeO2(OH)42‒ + 2 H+ ⇌ Te(OH)6	18.68
TeO3(OH)33‒ + 3 H+ ⇌ Te(OH)6	34.3
2 Te(OH)6 ⇌ Te2O(OH)11‒ + H+		‒6.929

(^a) The number of significant figures are retained to minimise propagation of round-off errors; they should not be taken to indicate the relative uncertainty of the values, which is always at least one order of magnitude less than indicated.

Terbium

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Brown and Ekberg, 2016
Tb3+ + H2O ⇌ TbOH2+ + H+	−7.9	−7.60 ± 0.09
2 Tb3+ + 2 H2O ⇌ Tb2(OH)24+ + 2 H+		−13.9 ± 0.2
3 Tb3+ + 5 H2O ⇌ Tb3(OH)54+ + 5 H+		−31.7 ± 0.3
Tb(OH)3(s) + 3 H+ ⇌ Tb3+ + 3 H2O	16.5	16.33 ± 0.30

Thallium(I)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Brown and Ekberg, 2016
Tl+ + H2O ⇌ TlOH + H+	–13.21
Tl+ + OH– ⇌ TlOH		0.64 ± 0.05
Tl+ + 2 OH– ⇌ Tl(OH)2–		–0.7 ± 0.7
⁠1/2⁠ Tl2O(s) + H+ ⇌ Tl+ + ⁠1/2⁠ H2O		13.55 ± 0.20

(^a) The number of significant figures are retained to minimise propagation of round-off errors; they should not be taken to indicate the relative uncertainty of the values, which is always at least one order of magnitude less than indicated.

Thallium(III)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Brown and Ekberg, 2016
Tl3+ + H2O ⇌ TlOH2+ + H+	–0.62	–0.22 ± 0.19
Tl3+ + 2 H2O ⇌ Tl(OH)2+ + 2 H+	–1.57
Tl3+ + 3 H2O ⇌ Tl(OH)3 + 3 H+	–3.3
Tl3+ + 4 H2O ⇌ Tl(OH)4– + 4 H+	–15.0
⁠1/2⁠ Tl2O3(s) + 3 H+ ⇌ Tl3+ + ⁠3/2⁠ H2O	–3.90	–3.90 ± 0.10

(^a) The number of significant figures are retained to minimise propagation of round-off errors; they should not be taken to indicate the relative uncertainty of the values, which is always at least one order of magnitude less than indicated.

Thorium

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Rand et al., 2008	Thoenen et al., 014	Brown and Ekberg, 2016
Th4+ + H2O ⇌ ThOH3+ + H+	–3.20	–2.5 ± 0.5	–2.5 ± 0.5	–2.5 ± 0.5
Th4+ + 2 H2O ⇌ Th(OH)22+ + 2 H+	–6.93	–6.2 ± 0.5	–6.2 ± 0.5	–6.2 ± 0.5
Th4+ + 3 H2O ⇌ Th(OH)3+ + 3 H+	< –11.7
Th4+ + 4 H2O ⇌ Th(OH)4 + 4 H+	–15.9	–17.4 ± 0.7	–17.4 ± 0.7	–17.4 ± 0.7
2Th4+ + 2 H2O ⇌ Th2(OH)26+ + 2 H+	–6.14	–5.9 ± 0.5	–5.9 ± 0.5	–5.9 ± 0.5
2Th4+ + 3 H2O ⇌ Th2(OH)35+ + 3 H+		–6.8 ± 0.2	–6.8 ± 0.2	–6.8 ± 0.2
4Th4+ + 8 H2O ⇌ Th4(OH)88+ + 8 H+	–21.1	–20.4 ± 0.4	–20.4 ± 0.4	–20.4 ± 0.4
4Th4+ + 12 H2O ⇌ Th4(OH)124+ + 12 H+		–26.6 ± 0.2	–26.6 ± 0.2	–26.6 ± 0.2
6Th4+ + 15 H2O(l) ⇌ Th6(OH)159+ + 15 H+	–36.76	–36.8 ± 1.5	–36.8 ± 1.5	–36.8 ± 1.5
6Th4+ + 14 H2O(l) ⇌ Th6(OH)1410+ + 14 H+		–36.8 ± 1.2	–36.8 ± 1.2	–36.8 ± 1.2
ThO2(c) + 4 H+ ⇌ Th4+ + 2 H2O	6.3
ThO2(am) + 4 H+ ⇌ Th4+ + 2 H2O				8.8 ± 1.0
ThO2(am,hyd,fresh) + 4 H+ ⇌ Th4+ + 2 H2O			9.3 ± 0.9
ThO2(am,hyd,aged) + 4 H+ ⇌ Th4+ + 2 H2O			8.5 ± 0.9
Th4+ + 4 OH− ⇌ ThO2(am,hyd,fresh) + 2 H2O		46.7 ± 0.9
Th4+ + 4 OH− ⇌ ThO2(am,hyd,aged) + 2 H2O		47.5 ± 0.9

Thulium

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Brown and Ekberg, 2016
Tm3+ + H2O ⇌ TmOH2+ + H+	−7.7	−7.34 ± 0.09
2 Tm3+ + 2 H2O ⇌ Tm2(OH)24+ + 2 H+		−13.2 ± 0.2
3 Tm3+ + 5 H2O ⇌ Tm3(OH)54+ + 5 H+		−30.5 ± 0.3
Tm(OH)3(s) + 3 H+ ⇌ Tm3+ + 3 H2O	15.0	15.56 ± 0.40

Tin(II)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Feitknecht, 1963	Baes and Mesmer, 1976	Hummel et al., 2002	NIST46	Cigala et al., 2012	Gamsjäger et al., 2012	Brown and Ekberg, 2016
Sn2+ + H2O ⇌ SnOH+ + H+		–3.40	–3.8 ± 0.2	–3.4	–3.52 ± 0.05	–3.53 ± 0.40	–3.53 ± 0.40
Sn2+ + 2 H2O ⇌ Sn(OH)2 + 2 H+		–7.06	–7.7 ± 0.2	–7.1	–6.26 ± 0.06	–7.68 ± 0.40	–7.68 ± 0.40
Sn2+ + 3 H2O ⇌ Sn(OH)3– + 3 H+		–16.61	–17.5 ± 0.2	–16.6	–16.97 ± 0.17	–17.00 ± 0.60	–17.56 ± 0.40
2 Sn2+ + 2 H2O ⇌ Sn2(OH)22+ + 2 H+		–4.77		–4.8	–4.79 ± 0.05
3 Sn2+ + 4 H2O ⇌ Sn3(OH)42+ + 4 H+		–6.88	–5.6 ± 1.6	–6.88	–5.88 ± 0.05	–5.60 ± 0.47	−5.60 ± 0.47
Sn(OH)2(s) ⇌ Sn2+ + 2 OH–				–25.8	–26.28 ± 0.08
SnO(s) + 2 H+ ⇌ Sn2+ + H2O		1.76	2.5± 0.5				1.60 ± 0.15
SnO(s) + H2O ⇌ Sn2+ + 2 OH–	–26.2
SnO(s) + H2O ⇌ Sn(OH)2	–5.3
SnO(s) + 2 H2O ⇌ Sn(OH)3– + H+	–0.9

Tin(IV)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Hummel et al., 2002	Gamsjäger et al., 2012	Brown and Ekberg, 2016
Sn4+ + 4 H2O ⇌ Sn(OH)4 + 4 H+			7.53 ± 0.12
Sn4+ + 5 H2O ⇌ Sn(OH)5– + 5 H+			–1.07 ± 0.42
Sn4+ + 6 H2O ⇌ Sn(OH)62– + 6 H+			–1.07 ± 0.42
Sn(OH)4 + H2O ⇌ Sn(OH)5– + H+	–8.0 ± 0.3	–8.60 ± 0.40
Sn(OH)4 + 2 H2O ⇌ Sn(OH)62– + 2 H+	–18.4 ± 0.3	–18.67 ± 0.30
SnO2(cr) + 2 H2O ⇌ Sn(OH)4	–8.0 ± 0.2	–8.06 ± 0.11
SnO2(am) + 2 H2O ⇌ Sn(OH)4	–7.3 ± 0.3	–7.22 ± 0.08
SnO2(s) + 4 H+ ⇌ Sn4+ + 2 H2O			–15.59 ± 0.04

Tungsten

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	NIST46
WO42– + H+ ⇌ HWO4–	3.6
WO42– + 2 H+ ⇌ H2WO4	5.8
6 WO42– + 7 H+ ⇌ HW6O215– + 3 H2O	63.83

Titanium(III)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Perrin et al., 1969	Baes and Mesmer, 1976	Brown and Ekberg, 2016
Ti3+ + H2O ⇌ TiOH2+ + H+	–1.29	–2.2	–1.65 ± 0.11
2 Ti3+ + 2 H2O ⇌ Ti2(OH)24+ + 2 H+		–3.6	–2.64 ± 0.10

Titanium(IV)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Brown and Ekberg, 2016
Ti(OH)22+ + H2O ⇌ Ti(OH)3+ + H+	⩽–2.3
Ti(OH)22+ + 2 H2O ⇌ Ti(OH)4 + 2 H+	–4.8
TiO2+ + H2O ⇌ TiOOH+ + H+		–2.48 ± 0.10
TiO2+ + 2 H2O ⇌ TiO(OH)2 + 2 H+		–5.49 ± 0.14
TiO2+ + 3 H2O ⇌ TiO(OH)3– + 3 H+		–17.4 ± 0.5
TiO(OH)2 + H2O ⇌ TiO(OH)3– + H+		–11.9 ±0.5
TiO2(c) +2 H2O ⇌ Ti(OH)4	~ –4.8
TiO2(s) + H+ ⇌ TiOOH+		–6.06 ± 0.30
TiO2(s) + H2O ⇌ TiO(OH)2		–9.02 ± 0.02
TiO2 x H2O ⇌ Ti(OH)22+[OH–]
TiO2(s) + 4 H+ ⇌ Ti4+ + 2 H2O		–3.56 ± 0.10

Uranium(IV)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Thoenen et al., 2014	Brown and Ekberg, 2016	Grenthe et al., 2020
U4+ + H2O ⇌ UOH3+ + H+	–0.65	– 0.54 ± 0.06	–0.58 ± 0.08	– 0.54 ± 0.06
U4+ + 2 H2O ⇌ U(OH)22+ + 2 H+	(–2.6)	–1.1 ± 1.0	–1.4 ± 0.2	–1.9 ± 0.2
U4+ + 3 H2O ⇌ U(OH)3+ + 3 H+	(–5.8)	–4.7 ± 1.0	–5.1 ± 0.3	–5.2 ± 0.4
U4+ + 4 H2O ⇌ U(OH)4 + 4 H+	(–10.3)	–10.0 ± 1.4	–10.4 ± 0.5	–10.0 ± 1.4
U4+ + 5 H2O ⇌ U(OH)5− + 5 H+	–16.0
UO2(am, hyd) + 4 H+ ⇌ U4+ + 2 H2O		1.5 ± 1.0
UO2(am,hyd) + 2 H2O ⇌ U4+ + 4 OH–			–54.500 ± 1.000	–54.500 ± 1.000
UO2(c) + 4 H+ ⇌ U4+ + 2 H2O	–1.8
UO2(c) + 2 H2O ⇌ U4+ + 4 OH–				–60.860 ± 1.000

Uranium(VI)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Grenthe et al., 1992	NIST46	Brown and Ekberg, 2016	Grenthe et al., 2020
UO22+ + H2O ⇌ UO2(OH)+ + H+	–5.8	–5.2 ± 0.3	–5.9 ± 0.1	–5.13 ± 0.04	–5.25 ± 0.24
UO22+ + 2 H2O ⇌ UO2(OH)2 + 2 H+		≤-10.3		–12.15 ± 0.20	–12.15 ± 0.07
UO22+ + 3 H2O ⇌ UO2(OH)3– + 3 H+		–19.2 ± 0.4		–20.25 ± 0.42	–20.25 ± 0.42
UO22+ + 4 H2O ⇌ UO2(OH)42– + 4 H+		–33 ± 2		–32.40 ± 0.68	–32.40 ± 0.68
2 UO22+ + 2 H2O ⇌ (UO2)2(OH)22+ + 2 H+	–5.62	–5.62 ± 0.04	–5.58 ± 0.04	–5.68 ± 0.05	–5.62 ± 0.08
3 UO22+ + 5 H2O ⇌ (UO2)3(OH)5+ + 5 H+	–15.63	–15.55 ± 0.12	–15.6	–15.75 ± 0.12	–15.55 ± 0.12
3 UO22+ + 4 H2O ⇌ (UO2)3(OH)42+ + 4 H+	(–11.75)	–11.9 ± 0.3		–11.78 ± 0.05	–11.9 ± 0.3
3 UO22+ + 7 H2O ⇌ (UO2)3(OH)7– + 7 H+		–31 ± 2.0		–32.2 ± 0.8	–32.2 ± 0.8
4 UO22+ + 7 H2O ⇌ (UO2)4(OH)7+ + 7 H+		–21.9 ± 1.0		–22.1 ± 0.2	–21.9 ± 1.0
2 UO22+ + H2O ⇌ (UO2)2(OH)3+ + H+		–2.7 ± 1.0			–2.7 ± 1.0
UO2(OH)2(s) + 2H+ ⇌ UO22+ + 2 H2O	5.6		6.0	4.81 ± 0.20
UO3·2H2O(cr) + 2H+ ⇌ UO22+ + 3 H2O					5.350 ± 0.130

Vanadium(IV)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Brown and Ekberg, 2016
VO2+ + H2O ⇌ VO(OH)+ + H+	–5.30 ± 0.13
2 VO2+ + 2 H2O ⇌ (VO)2(OH)22+ + 2 H+	–6.71 ± 0.10

Vanadium(V)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Brown and Ekberg, 2016
VO2+ + 2 H2O ⇌ VO(OH)3 + H+	–3.3
VO2+ + 2 H2O ⇌ VO2(OH)2– + 2 H+	–7.3	–7.18 ± 0.12
10 VO2+ + 8 H2O ⇌ V10O26(OH)24– + 14 H+	–10.7
VO2(OH)2– ⇌ VO3(OH)2– + H+	–8.55
2 VO2(OH)2– ⇌ V2O6(OH)23– + H+ + H2O	–6.53
VO3(OH)2– ⇌ VO43– + H+	–14.26
2 VO3(OH)2– ⇌ V2O74– + H2O	0.56
3 VO3(OH)2– + 3 H+⇌ V3O93– + 3 H2O	31.81
V10O26(OH)24– ⇌ V10O27(OH)5– + 3 H+	–3.6
V10O27(OH)5– ⇌ V10O286– + H+	–6.15
VO2+ + H2O ⇌ VO2OH + H+		–3.25 ± 0.1
VO2+ + 3 H2O ⇌ VO2(OH)32- + 3 H+		–15.74 ± 0.19
VO2+ + 4 H2O ⇌ VO2(OH)43- + 4 H+		–30.03 ± 0.24
2 VO2+ + 4 H2O ⇌ (VO2)2(OH)42- + 4 H+		–11.66 ± 0.53
2 VO2+ + 5 H2O ⇌ (VO2)2(OH)53- + 5 H+		–20.91 ± 0.22
2 VO2+ + 6 H2O ⇌ (VO2)2(OH)64- + 6 H+		–32.43 ± 0.30
4 VO2+ + 8 H2O ⇌ (VO2)4(OH)84- + 8 H+		–20.78 ± 0.33
4 VO2+ + 9 H2O ⇌ (VO2)4(OH)95- + 9 H+		–31.85 ± 0.26
4 VO2+ + 10 H2O ⇌ (VO2)4(OH)106- + 10 H+		–45.85 ± 0.26
5 VO2+ + 10 H2O ⇌ (VO2)5(OH)105- + 10 H+		–27.02 ± 0.34
10 VO2+ + 14 H2O ⇌ (VO2)10(OH)144- + 14 H+		–10.5 ± 0.3
10 VO2+ + 15 H2O ⇌ (VO2)10(OH)155- + 15 H+		–15.73 ± 0.33
10 VO2+ + 16 H2O ⇌ (VO2)10(OH)166- + 16 H+		–23.90 ± 0.35
⁠1/2⁠ V2O5(c) + H+ ⇌ VO2+ + ⁠1/2⁠ H2O	–0.66
V2O5(s) + 2 H+ ⇌ 2 VO2+ + H2O		–0.64 ± 0.09

Ytterbium

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Brown and Ekberg, 2016
Yb3+ + H2O ⇌ YbOH2+ + H+	−7.7	−7.31 ± 0.18
Yb3+ + 2 H2O ⇌ Yb(OH)2+ + 2 H+	(−15.8)
Yb3+ + 3 H2O ⇌ Yb(OH)3 + 3 H+	(−24.1)
Yb3+ + 4 H2O ⇌ Yb(OH)4− + 4 H+	−32.7
2 Yb3+ + 2 H2O ⇌ Yb2(OH)24+ + 2 H+		−13.76 ± 0.20
3 Yb3+ + 5 H2O ⇌ Yb3(OH)54+ + 5 H+		−30.6 ± 0.3
Yb(OH)3(s) + 3 H+ ⇌ Yb3+ + 3 H2O	14.7	15.35 ± 0.20

Yttrium

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Brown and Ekberg, 2016
Y3+ + H2O ⇌ YOH2+ + H+	–7.7	–7.77 ± 0.06
Y3+ + 2 H2O ⇌ Y(OH)2+ + 2 H+	(–16.4) [Estimation]
Y3+ + 3 H2O ⇌ Y(OH)3 + 3 H+	(–26.0) [Estimation]
Y3+ + 4 H2O ⇌ Y(OH)4−+ 4 H+	–36.5
2 Y3+ + 2 H2O ⇌ Y2(OH)24+ + 2 H+	–14.23	–14.1 ± 0.2
3 Y3+ + 5 H2O ⇌ Y3(OH)54+ + 5 H+	–31.6	–32.7 ± 0.3
Y(OH)3(s) + 3 H+ ⇌ Y3+ + 3 H2O	17.5	17.32 ± 0.30

Zinc

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Powell and Brown, 2013	Brown and Ekberg, 2016
Zn2+ + H2O ⇌ ZnOH+ + H+	−8.96	−8.96 ± 0.05	−8.94 ± 0.06
Zn2+ + 2 H2O ⇌ Zn(OH)2 + 2 H+	−16.9	–17.82 ± 0.08	−17.89 ± 0.15
Zn2+ + 3 H2O ⇌ Zn(OH)3− + 3 H+	−28.4	–28.05 ± 0.05	−27.98 ± 0.10
Zn2+ + 4 H2O ⇌ Zn(OH)42- + 4 H+	−41.2	–40.41 ± 0.12	−40.35 ± 0.22
2 Zn2+ + H2O ⇌ Zn2OH3+ + H+	−9.0	–7.9 ± 0.2	−7.89 ± 0.31
2 Zn2+ + 6 H2O ⇌ Zn2(OH)62- + 6 H+	−57.8
ZnO(s) + 2 H+ ⇌ Zn2+ + H2O	11.14	11.12 ± 0.05	11.11 ± 0.10
ε-Zn(OH)2(s) + 2 H+ ⇌ Zn2+ + 2 H2O		11.38 ± 0.20	11.38± 0.20
β1-Zn(OH)2(s) + 2 H+ ⇌ Zn2+ + 2 H2O		11.72 ± 0.04
β2-Zn(OH)2(s) + 2 H+ ⇌ Zn2+ + 2 H2O		11.76 ± 0.04
γ-Zn(OH)2(s) + 2 H+ ⇌ Zn2+ + 2 H2O		11.70 ± 0.04
δ-Zn(OH)2(s) + 2 H+ ⇌ Zn2+ + 2 H2O		11.81 ± 0.04

Zirconium

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Thoenen et al., 2014	Brown and Ekberg, 2016
Zr4+ + H2O ⇌ ZrOH3+ + H+	0.32	0.32 ± 0.22	0.12 ± 0.12
Zr4+ + 2 H2O ⇌ Zr(OH)22+ + 2 H+	(−1.7)*	0.98 ± 1.06*	−0.18 ± 0.17*
Zr4+ + 3 H2O ⇌ Zr(OH)3+ + 3 H+	(−5.1)
Zr4+ + 4 H2O ⇌ Zr(OH)4 + 4 H+	–9.7*	–2.19 ± 0.70*	−4.53 ± 0.37*
Zr4+ + 5 H2O ⇌ Zr(OH)5– + 5 H+	–16.0
Zr4+ + 6 H2O ⇌ Zr(OH)62– + 6 H+		–29± 0.70	–30.5 ± 0.3
3 Zr4+ + 4 H2O ⇌ Zr3(OH)48+ + 4 H+	–0.6	0.4 ± 0.3	0.90 ± 0.18
3 Zr4+ + 5 H2O ⇌ Zr3(OH)57+ + 5 H+	3.70
3 Zr4+ + 9 H2O ⇌ Zr3(OH)93+ + 9 H+		12.19 ± 0.20	12.19 ± 0.20
4 Zr4+ + 8 H2O ⇌ Zr4(OH)88+ + 8 H+	6.0	6.52 ± 0.05	6.52 ± 0.05
4 Zr4+ + 15 H2O ⇌ Zr4(OH)15+ + 15 H+		12.58± 0.24
4 Zr4+ + 16 H2O ⇌ Zr4(OH)16 + 16 H+		8.39± 0.80
ZrO2(s) + 4 H+ ⇌ Zr4+ + 2 H2O	–1.9*		–5.37 ± 0.42*
ZrO2(s, baddeleyite) + 4 H+ ⇌ Zr4+ + 2 H2O		–7 ± 1.6
ZrO2(am) + 4 H+ ⇌ Zr4+ + 2 H2O		–3.24± 0.10	–2.97 ± 0.18

*Errors in compilations concerning equilibrium and/or data elaboration. Data not recommended. It is strongly suggested to refer to the original papers.