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

and the corresponding formation constant as:

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

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[1]	Brown and Ekberg, 2016[2]	Hummel and Thoenen, 2023[3]
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[4]	Brown and Ekberg, 2016[5]	Grenthe et al, 2020[6]
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[7]	Grenthe et al, 2020[6]
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[8]	Lothenbach et al., 1999;[9] Kitamura et al., 2010[10]	Filella and May, 2003[11]
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[8]	Lothenbach et al., 1999;[9] Kitamura et al., 2010[10]
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[12]	Nordstrom and Archer, 2003[13]	Nordstrom et al., 2014[14]
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[12]	Khodakovsky et al. (1968)[15]	Nordstrom and Archer, 2003[13]	Nordstrom et al., 2014[14]
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[16]	Nordstrom et al., 1990[17]	Brown and Ekberg, 2016[18]
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[19]
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[20]
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[21]	Lothenbach et al., 1999[9]	NIST46[4]	Kitamura et al., 2010[10]	Brown and Ekberg, 2016[22]
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[23]	NIST46[4]
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[24]	Powell et al., 2011[25]	Brown and Ekberg, 2016[26]
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[16]	Nordstrom et al., 1990[17]	Brown and Ekberg, 2016[27]
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[19]
Cf3+ + 3 H2O ⇌ Bk(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[28]	NIST46[4]	Brown and Ekberg, 2016[29]
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[4]	Ball and Nordstrom, 1988[30]
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[31]	Rai et al., 1987[32]	Ball and Nordstrom, 1988[30]	Brown and Ekberg, 2016[33]
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[34]	Ball and Nordstrom, 1998[30]
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[35]	Brown and Ekberg, 2016[36]
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[37]
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[38]
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[39]	NIST46[4]	Plyasunova et al., 1997[40]	Powell et al., 2007[41]	Brown and Ekberg, 2016[38]
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[42]
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[28]	Brown and Ekberg, 2016[43]
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[28]	Brown and Ekberg, 2016[44]
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[28]	NIST46[4]	Hummel et al., 2002[45]	Brown and Ekberg, 2016[29]
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[28]	Brown and Ekberg, 2016[46]
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[47]	Smith et al., 2003[48]	Brown and Ekberg, 2016[49]
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–	${\displaystyle \approx }$–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[50]	Wood and Samson, 2006[51]	Filella and May, 2023[52]
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[53]
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[54]	Brown and Ekberg, 2016[55]
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[28]	Brown and Ekberg, 2016[56]
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[57]	NIST46[4]	Brown and Ekberg, 2016[58]
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[59]
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[60]	Nordstrom et al., 1990[17]	Hummel et al., 2002[45]	Lemire et al., 2013[61]	Brown and Ekberg, 2016[62]
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[60]	Lemire et al., 2013[61]	Brown and Ekberg, 2016[63]
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[64]	Brown and Ekberg, 2016[29]
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[65]	NIST46[4]	Powell et al, 2009[66]	Brown and Ekberg, 2016[29]	Cataldo et al., 2018[67]
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[68]
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[69]	Nordstrom et al., 1990[17]	Brown and Ekberg, 2016[70]
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[71]	Nordstrom et al., 1990[17]	Brown and Ekberg, 2016[72]
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[73]	Baes and Mesmer, 1976[74]	Nordstrom et al., 1990[17]	Hummel et al., 2002[45]	Brown and Ekberg, 2016[75]
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[76]
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[77]	Brown and Ekberg, 2016[78]
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[79]	Powell et all, 2005[80]	Brown and Ekberg, 2016[76]
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[81]	Jolivet, 2000[82]	NIST46[4]	Crea et al., 2017[83]
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[28]	NIST46[4]	Neck et al., 2009[84]	Brown and Ekberg, 2016[29]
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[85]	Grenthe et al, 2020[6]
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[86]	NIST46[4]	Brown and Ekberg, 2016[87]	Grenthe et al, 2020[6]
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[86]	Brown and Ekberg, 2016[88]	Grenthe et al, 2020[6]
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[89]	NIST46[4]	Brown and Ekberg, 2016[90]	Grenthe et al, 2020[6]
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[68]	Baes and Messmer, 1976[91]	NIST46[4]	Gamsjäger et al., 2005[92]	Thoenen et al., 2014[93]	Brown and Ekberg, 2016[94]
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[69]	Filella and May, 2020[95]
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[96]
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[96]
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[97]	Hummel et al., 2002[45]	Kitamura and Yul, 2010[98]	Brown and Ekberg, 2016[99]
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[100]	NIST46[4]	Brown and Ekberg, 2016[101]	Grenthe et al, 2020[6]
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[102]	NIST46[4]	Brown and Ekberg, 2016[103]	Grenthe et al, 2020[6]
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[104]	NIST46[4]	Brown and Ekberg, 2016[105]	Grenthe et al, 2020[6]
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[106]	NIST46[4]	Brown and Ekberg, 2016[107]	Grenthe et al, 2020[6]
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[69]	Nordstrom et al., 1990[17]	Brown and Ekberg, 2016[108]
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[28]	NIST46[4]	Brown and Ekberg, 2016[29]
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[17]
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[109]	Baes and Mesmer, 1976[110]	Brown and Ekberg[111]
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[28]	NIST46[4]	Brown and Ekberg[29]
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[112]	Brown and Ekberg, 2016[113]
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[114]	Thoenen et al., 2014[93]
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[115]	Olin et al., 2005[114]	Thoenen et al., 2014[93]
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[116]	Olin et al., 2005[114]	Thoenen et al., 2014[93]
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[117]	Thoenen et al., 2014[93]
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[118]	Brown and Ekberg, 2016[119]
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[69]	Nordstrom et al., 1990[17]	Brown and Ekberg, 2016[120]
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[16]	Nordstrom et al., 1990[17]	Brown and Ekberg, 2016[121]
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[122]	Filella and May, 2019a[123]
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[124]
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[125]	Filella and May, 2019a[124]
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[125]	Filella and May, 2019a[124]
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[28]	Brown and Ekberg, 2016[126]
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[127]	Brown and Ekberg, 2016[128]
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[127]	Brown and Ekberg, 2016[128]
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[129]	Rand et al., 2008[130]	Thoenen et al, 014[131]	Brown and Ekberg, 2016[132]
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[28]	Brown and Ekberg, 2016[133]
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[68]	Baes and Mesmer, 1976[134]	Hummel et al., 2002[45]	NIST46[4]	Cigala et al, 2012[135]	Gamsjäger et al, 2012[136]	Brown and Ekberg, 2016[137]
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[45]	Gamsjäger et al, 2012[136]	Brown and Ekberg, 2016[137]
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[4]
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[138]	Baes and Mesmer, 1976[139]	Brown and Ekberg, 2016[140]
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[139]	Brown and Ekberg, 2016[140]
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[141]	Thoenen et al., 2014[142]	Brown and Ekberg, 2016[143]	Grenthe et al., 2020[6]
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[144]	Grenthe et al., 1992[145]	NIST46[4]	Brown and Ekberg, 2016[146]	Grenthe et al., 2020[6]
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[76]
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[147]	Brown and Ekberg, 2016[148]
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[28]	Brown and Ekberg, 2016[149]
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[28]	Brown and Ekberg, 2016[29]
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[150]	Powell and Brown, 2013[151]	Brown and Ekberg, 2016[152]
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[54]	Thoenen et al., 2014[93]	Brown and Ekberg, 2016[153]
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.