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. 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:
and the corresponding formation constant as:
and associated equilibria can be written as:

Aluminium

Hydrolysis constants 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 ⇌ Al₂⁺ + 2 H⁺	–9.3	−10.63 ± 0.09	−10.63 ± 0.09
Al³⁺ + 3 H₂O ⇌ Al₃ + 3 H⁺	–15.0	−15.66 ± 0.23	−15.99 ± 0.23
Al³⁺ + 4 H₂O ⇌ Al₄^– + 4 H⁺	–23.0	−22.91 ± 0.10	−22.91 ± 0.10
2 Al³⁺ + 2 H₂O ⇌ Al₂₂⁴⁺ + 2 H⁺	–7.7	−7.62 ± 0.11	−7.62 ± 0.11
3 Al³⁺ + 4 H₂O ⇌ Al₃₄⁵⁺ + 4 H⁺	–13.94	−14.06 ± 0.22	−13.90 ± 0.12
13 Al³⁺ + 28 H₂O ⇌ Al₁₃O₄₂₄⁷⁺ + 32 H⁺	–98.73	−100.03 ± 0.09	−100.03 ± 0.09
α-Al₃ + 3 H⁺ ⇌ Al³⁺ + 3 H₂O	8.5	7.75 ± 0.08	7.75 ± 0.08
γ-AlOOH + 3 H⁺ ⇌ Al³⁺ + 2 H₂O		7.69 ± 0.15	9.4 ± 0.4

Americium(III)

Hydrolysis constants in critical compilations at infinite dilution and T = 298.15 K:

Reaction	NIST46	Brown and Ekberg, 2016	Grenthe et al., 2020
Am³⁺ + H₂O ⇌ Am²⁺ + H⁺	–6.5 ± 0.1	–7.22 ± 0.03	–7.2 ± 0.5
Am³⁺ + 2 H₂O ⇌ Am₂⁺ + 2 H⁺	–14.1 ± 0.3	–14.9 ± 0.2	–15.1 ± 0.7
Am³⁺ + 3 H₂O ⇌ Am₃ + 3 H⁺	–25.7	–26.0 ± 0.2	–26.2 ± 0.5
Am³⁺ + 3 H₂O ⇌ Am₃ + 3 H⁺	–16.9 ± 0.1	–16.9 ± 0.8	–16.9 ± 0.8
Am³⁺ + 3 H₂O ⇌ Am₃ + 3 H⁺	–15.2	–15.62 ± 0.04	–15.6 ± 0.6

Americium(V)

Hydrolysis constants in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Brown and Ekberg, 2016	Grenthe et al., 2020
AmO₂⁺ + H₂O ⇌ AmO₂ + H⁺	–10.7 ± 0.2
AmO₂⁺ + 2 H₂O ⇌ AmO₂₂^– + 2 H⁺	–22.9 ± 0.7
AmO₂⁺ + H₂O ⇌ AmO₂ + H⁺	–5.4 ± 0.4	–5.3 ± 0.5

Antimony(III)

Hydrolysis constants 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
Sb₃ + H⁺ ⇌ Sb₂⁺ + H₂O	1.41	1.30	1.371
Sb₃ + H₂O ⇌ Sb₄^‒ + H⁺	‒11.82	‒11.93	‒11.70
0.5 Sb₂O₃ + 1.5 H₂O ⇌ Sb₃	‒4.24
Sb₂O₃ + 3 H₂O ⇌ 2 Sb₃		‒8.72	‒10.00
Sb₂O₃ + 3 H₂O ⇌ 2 Sb₃			‒11.40

Antimony(V)

Hydrolysis constants in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Lothenbach et al., 1999; Kitamura et al., 2010
Sb₅ + H₂O ⇌ Sb₆^‒ + H⁺	‒2.72	‒2.72
12 Sb₅ + 4 H₂O ⇌ Sb₁₂₆₄^4‒ + 4 H⁺	20.34	20.34
12 Sb₅ + 5 H₂O ⇌ Sb₁₂₆₅^5‒ + 5 H⁺	16.72	16.72
12 Sb₅ + 6 H₂O ⇌ Sb₁₂₆₆^6‒ + 6 H⁺	11.89	11.89
12 Sb₅ + 7 H₂O ⇌ Sb₁₂₆₇^7‒ + 7 H⁺	6.07	6.07
0.5 Sb₂O₅ + 2.5 H₂O ⇌ Sb₅	‒3.7
Sb₂O₅ + 5 H₂O ⇌ 2 Sb₅		‒7.400

Arsenic(III)

Hydrolysis constants in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Nordstrom and Archer, 2003	Nordstrom et al., 2014
As₄^‒ + H⁺ ⇌ As₃ + H₂O	9.29	9.17	9.24 ± 0.02

Arsenic(V)

Hydrolysis constants in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer	Khodakovsky et al.	Nordstrom and Archer, 2003	Nordstrom et al., 2014
H₂AsO₄^‒ + H⁺ ⇌ H₃AsO₄	2.24	2.21	2.26 ± 0.078	2.25 ± 0.04
HAsO₄^2‒ + H⁺ ⇌ H₂AsO₄^‒		6.93	6.99 ± 0.1	6.98 ± 0.11
AsO₄^3‒ + H⁺ ⇌ HAsO₄^2‒		11.51	11.80 ± 0.1	11.58 ± 0.05
HAsO₄^2‒ + 2 H⁺ ⇌H₃AsO₄	9.20
AsO₄^3‒ + 3 H⁺ ⇌ H₃AsO₄	20.70

Barium

Hydrolysis constants 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 in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Brown and Ekberg, 2016
Bk³⁺ + 3 H₂O ⇌ Bk₃ + 3 H⁺	–13.5 ± 1.0

Beryllium

Hydrolysis constants 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 ⇌ Be₂ + 2 H⁺	–23.65
Be²⁺ + 3 H₂O ⇌ Be₃^– + 3 H⁺	–23.25
Be²⁺ + 4 H₂O ⇌ Be₄^2– + 4 H⁺	–37.42
2 Be²⁺ + H₂O ⇌ Be₂OH³⁺ + H⁺	–3.97
3 Be²⁺ + 3 H₂O ⇌ Be₃₃³⁺ + 3 H⁺	–8.92
6 Be²⁺ + 8 H₂O ⇌ Be₆₈⁴⁺ + 8 H⁺	–27.2
α-Be₂ + 2 H⁺ ⇌ Be²⁺ + 2 H₂O	6.69

Bismuth

Hydrolysis constants 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 ⇌ Bi₂⁺ + 2 H⁺		–2.56	–4.5	–2.560 ± 1.000	–2.59 ± 0.26
Bi³⁺ + 3 H₂O ⇌ Bi₃ + 3 H⁺	–8.86	–5.31	–9.0	–8.940 ± 0.500	–8.78 ± 0.20
Bi³⁺ + 4 H₂O ⇌ Bi₄^– + 4 H⁺	–21.8	–18.71	–21.2	–21.660 ± 0.870	–22.06 ± 0.14
3 Bi³⁺ + 4 H₂O ⇌ Bi₃₄⁵⁺ + 4 H⁺		–0.80		–0.800
6 Bi³⁺ + 12 H₂O ⇌ Bi₆₁₂⁶⁺ + 12 H⁺		1.34		1.340	0.98 ± 0.13
9 Bi³⁺ + 20 H₂O = Bi₉₂₀⁷⁺ + 20 H⁺		–1.36		–1.360
9 Bi³⁺ + 21 H₂O = Bi₉₂₁⁶⁺ + 21 H⁺		–3.25		–3.250
9 Bi³⁺ + 22 H₂O = Bi₉₂₂⁵⁺ + 22 H⁺		–4.86		–4.860
Bi₃ + 3 H⁺ = Bi³⁺ + 3 H₂O				31.501 ± 0.927
α-Bi₂O₃ + 6 H⁺ = 2 Bi³⁺ + 3 H₂O		0.76
BiO_1.5 + 3 H⁺ = Bi³⁺ + 1.5 H₂O	3.46			31.501 ± 0.927	2.88 ± 0.64

Boron

Hydrolysis constants in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	NIST46
B₃ + H₂O ⇌ Be₄⁺ + H⁺	–9.236	–9.236 ± 0.002
2 B₃ ⇌ B₂₅^– + H⁺	–9.36	–9.306
3 B₃ ⇌ B₃O₃₄^– + H⁺ + 2 H₂O	–7.03	–7.306
4 B₃ ⇌ B₄O₅₄^2– + 2 H⁺ + 3 H₂O	–16.3	–15.032

Cadmium

Hydrolysis constants 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 ⇌ Cd₂ + 2 H⁺	–20.35	–20.19 ± 0.13	−20.6 ± 0.4
Cd²⁺ + 3 H₂O ⇌ Cd₃^– + 3 H⁺	<–33.3	–33.5 ± 0.5	−33.5 ± 0.5
Cd²⁺ + 4 H₂O ⇌ Cd₄^2– + 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 ⇌ Cd₄₄⁴⁺ + 4 H⁺	–32.85
Cd₂ ⇌ Cd²⁺ + 2 OH^–		–14.28 ± 0.12
Cd₂ + 2 H⁺ ⇌ Cd²⁺ + 2 H₂O	13.65	13.72 ± 0.12	13.71 ± 0.12

Calcium

Hydrolysis constants 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
Ca₂ + 2 H⁺ ⇌ Ca²⁺ + 2 H₂O	22.80	22.8	22.75 ± 0.02

Californium(III)

Hydrolysis constants in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Brown and Ekberg, 2016
Cf³⁺ + 3 H₂O ⇌ Cf₃ + 3 H⁺	–13.0 ± 1.0

Cerium(III)

Hydrolysis constants 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 ⇌ Ce₂₂⁴⁺ + 2 H⁺			–16.0 ± 0.2
3 Ce³⁺ + 5 H₂O ⇌ Ce₃₅⁴⁺ + 5 H⁺			–34.6 ± 0.3
Ce₃ + 3 H⁺ ⇌ Ce³⁺ + 3 H₂O			18.5 ± 0.5
Ce₃ ⇌ Ce³⁺ + 3 OH^–		–22.1 ± 0.9

Chromium(II)

Hydrolysis constants in critical compilations at infinite dilution and T = 298.15 K :

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

Chromium(III)

Hydrolysis constants 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 ⇌ Cr₂⁺ + 2 H⁺	–9.7	–9.84		–9.65 ± 0.20
Cr³⁺ + 3 H₂O ⇌ Cr₃ + 3 H⁺	–18	–16.19		–16.25 ± 0.19
Cr³⁺ + 4 H₂O ⇌ Cr₄⁻ + 4 H⁺	–27.4	–27.65 ± 0.12		–27.56 ± 0.21
2 Cr³⁺ + 2 H₂O ⇌ Cr₂₂⁴⁺ + 2 H⁺	–5.06	–5.0		–5.29 ± 0.16
3 Cr³⁺ + 4 H₂O ⇌ Cr₃₄⁵⁺ + 4 H⁺	–8.15	–10.75 ± 0.15		–9.10 ± 0.14
Cr₃ + 3 H⁺ ⇌ Cr³⁺ + 3 H₂O	12		9.35	9.41 ± 0.17
Cr₂O₃ + 6 H⁺ ⇌ 2 Cr³⁺ + 3 H₂O			8.52
CrO_1.5 + 3 H⁺ ⇌ Cr³⁺ + 1.5 H₂O				7.83 ± 0.10

Chromium(VI)

Hydrolysis constants in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Ball and Nordstrom, 1998
CrO₄^2– + H⁺ ⇌ HCrO₄^–	6.51	6.55 ± 0.04
HCrO₄^– + H⁺ ⇌ H₂CrO₄	–0.20
CrO₄²– + 2 H⁺ ⇌ H₂CrO₄		6.31
2 HCrO₄^– ⇌ Cr₂O₇^2– + H₂O	1.523
2 CrO₄^2– + 2 H⁺ ⇌ Cr₂O₇^2– + H₂O		14.7 ± 0.1

Cobalt(II)

Hydrolysis constants 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 ⇌ Co₂ + 2 H⁺	–18.8	−19.77 ± 0.11
Co²⁺ + 3 H₂O ⇌ Co₃^– + 3 H⁺	–31.5	−32.01 ± 0.33
Co²⁺ + 4 H₂O ⇌ Co₄^2– + 4 H⁺	–46.3
2 Co²⁺ + H₂O ⇌ Co₂³⁺ + H⁺	–11.2
4 Co²⁺ + 4 H₂O ⇌ Co₄₄⁴⁺ + 4H⁺	–30.53
Co₂ + 2 H⁺ ⇌ Co²⁺ + 2 H₂O	12.3	13.24 ± 0.12
CoO + 2 H⁺ ⇌ Co²⁺ + H₂O		13.71 ± 0.10

Cobalt(III)

Hydrolysis constants 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 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 ⇌ Cu₂^– + 2 H⁺	–18.6 ± 0.6

Copper(II)

Hydrolysis constants 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 ⇌ Cu₂ + 2 H⁺		–17.3	–16.23 ± 0.15	–16.2 ± 0.2	–16.24 ± 0.03
Cu²⁺ + 3 H₂O ⇌ Cu₃^– + 3 H⁺		–27.8	–26.63 ± 0.40	–26.60 ± 0.09	–26.65 ± 0.13
Cu²⁺ + 4 H₂O ⇌ Cu₄^2– + 4 H⁺	–39.6	–39.6	–39.73 ± 0.17	–39.74 ± 0.18	–39.70 ± 0.19
2 Cu²⁺ + H₂O ⇌ Cu₂₃⁺ + H⁺			–6.71 ± 0.30	–6.40 ± 0.12	–6.41 ± 0.17
2 Cu²⁺ + 2 H₂O ⇌ Cu₂₂²⁺ + 2 H⁺	–10.36	–10.3	–10.55 ± 0.17	–10.43 ± 0.07	–10.55 ± 0.02
3 Cu²⁺ + 4 H₂O ⇌ Cu₃₄²⁺ + 4 H⁺			–20.95 ± 0.30	–21.1 ± 0.2	–21.2 ± 0.4
CuO + 2 H⁺ ⇌ Cu²⁺ + H₂O	7.62		7.64 ± 0.06	7.64 ± 0.06	7.63 ± 0.05
Cu₂ + 2 H⁺ ⇌ Cu²⁺ + 2 H₂O				8.67 ± 0.05	8.68 ± 0.10

Curium

Hydrolysis constants in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Brown and Ekberg, 2016
Cm³⁺ + H₂O ⇌ Cm²⁺ + H⁺	−7.66 ± 0.07
Cm³⁺ + 2 H₂O ⇌ Cm₂⁺ + 2 H⁺	−15.9 ± 0.1
Cm³⁺ + 3 H₂O ⇌ Cm₃ + 3 H⁺	−13.9 ± 0.4

Dysprosium

Hydrolysis constants 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 ⇌ Dy₂⁺ + 2 H⁺
Dy³⁺ + 3 H₂O ⇌ Dy₃ + 3 H⁺
Dy³⁺ + 4 H₂O ⇌ Dy₄⁻ + 4 H⁺	–33.5
2 Dy³⁺ + 2 H₂O ⇌ Dy₂₂⁴⁺ + 2 H⁺		−13.76 ± 0.20
3 Dy³⁺ + 5 H₂O ⇌ Dy₃₅⁴⁺ + 5 H⁺		−30.6 ± 0.3
Dy₃ + 3 H⁺ ⇌ Dy³⁺ + 3 H₂O	15.9	16.26 ± 0.30
Dy₃ + OH⁻ ⇌ Dy₄⁻	−3.6
Dy₃ ⇌ Dy₃	−8.8

Erbium

Hydrolysis constants 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 ⇌ Er₂⁺ + 2 H⁺
Er³⁺ + 3 H₂O ⇌ Er₃ + 3 H⁺
Er³⁺ + 4 H₂O ⇌ Er₄⁻ + 4 H⁺	−32.6
2 Er³⁺ + 2 H₂O ⇌ Er₂₂⁴⁺ + 2 H⁺	−13.65	−13.50 ± 0.20
3 Er³⁺ + 5 H₂O ⇌ Er₃₅⁴⁺ + 5 H⁺	<−29.3	−31.0 ± 0.3
Er₃ + 3 H⁺ ⇌ Er³⁺ + 3 H₂O	15.0	15.79 ± 0.30
Er₃ + OH⁻ ⇌ Er₄⁻	−3.6
Er₃ ⇌ Er₃	~ −9.2

Europium

Hydrolysis constants 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 ⇌ Eu₂⁺ + 2 H⁺			–15.1 ± 0.2
Eu³⁺ + 3 H₂O ⇌ Eu₃ + 3 H⁺			–23.7 ± 0.1
Eu³⁺ + 4 H₂O ⇌ Eu₄⁻ + 4 H⁺			–36.2 ± 0.5
2 Eu³⁺ + 2 H₂O ⇌ Eu₂₂⁴⁺ + 2 H⁺			-	–14.1 ± 0.2
3 Eu³⁺ + 5 H₂O ⇌ Eu₃₅⁴⁺ + 5 H⁺			-	–32.0 ± 0.3
Eu₃ + 3 H⁺ ⇌ Eu³⁺ + 3 H₂O	17.5		17.6 ± 0.8 14.9 ± 0.3	16.48 ± 0.30
Eu₃ ⇌ Eu³⁺ + 3 OH^–		–24.5 ± 0.7 –26.5

Gadolinium

Hydrolysis constants 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 ⇌ Gd₂⁺ + 2 H⁺
Gd³⁺ + 3 H₂O ⇌ Gd₃ + 3 H⁺
Gd³⁺ + 4 H₂O ⇌ Gd₄^– + 4 H⁺	–34.4
2 Gd³⁺ + 2 H₂O ⇌ Gd₂₂⁴⁺ + 2 H⁺		–14.16 ± 0.20
3 Gd³⁺ + 5 H₂O ⇌ Gd₃₅⁴⁺ + 5 H⁺		–33.0 ± 0.3
Gd₃ + 3 H⁺ ⇌ Gd³⁺ + 3 H₂O	15.6	17.20 ± 0.48
Gd₃ + OH^– ⇌ Gd₄^–	–4.8
Gd₃ ⇌ Gd₃	–9.6

Gallium

Hydrolysis constants 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 ⇌ Ga₂⁺ + 2 H⁺	–5.9	–6.694	–7.0
Ga³⁺ + 3 H₂O ⇌ Ga₃ + 3 H⁺	–10.3		–11.96
Ga³⁺ + 4 H₂O ⇌ Ga₄^– + 4 H⁺	–16.6	–16.588	–15.52
Ga₃ ⇌ Ga³⁺ + 3 OH^–	–37	–37.0
GaO + H₂O ⇌ Ga³⁺ + 3 OH^–	–39.06	–39.1	–40.51

Germanium

Hydrolysis constants in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Wood and Samson, 2006	Filella and May, 2023
Ge₄ ⇌ GeO₃⁻ + H⁺	–9.31	–9.32 ± 0.05	–9.099
Ge₄ ⇌ GeO2₂²⁺ + 2 H⁺	–21.9
GeO₂₂^2– + H⁺ ⇌ GeO₃^–			12.76
8 Ge₄ ⇌ Ge₈O₁₆₃^3- + 13 H₂O + 3 H⁺	–14.24
8 Ge₄ + 3 OH^– ⇌ Ge₈₃₅^3–			28.33
GeO₂ + 2 H₂O ⇌ Ge₄		–1.35	–1.373
GeO₂ + 2 H₂O ⇌ Ge₄	-4.37	–5.02	–4.999

Gold(III)

Hydrolysis constants in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976
Au₃ +2 H⁺ ⇌ AuOH²⁺ + 2 H₂O	1.51
Au₃ + H⁺ ⇌ Au₂⁺ + H₂O	< 1.0
Au₃ + H₂O ⇌ Au₄^– + H⁺	–11.77
Au₃ + 2 H₂O ⇌ Au₅^2– + 2 H⁺	–25.13
Au₅^2– + 3 H₂O ⇌ Au₆³– + 3 H⁺	< –41.1
Au₃ ⇌ Au₃	–5.51

Hafnium

Hydrolysis constants 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 ⇌ Hf₂²⁺ + 2 H⁺
Hf⁴⁺ + 3 H₂O ⇌ Hf₃⁺ + 3 H⁺
Hf⁴⁺ + 4 H₂O ⇌ Hf₄ + 4 H⁺	–10.7*	−3.75 ± 0.34*
Hf⁴⁺ + 5 H₂O ⇌ Hf₅^– + 5 H⁺	–17.2
3 Hf⁴⁺ + 4 H₂O ⇌ Hf₃₄⁸⁺ + 4 H⁺		0.55 ± 0.30
4 Hf⁴⁺ + 8 H₂O ⇌ Hf₄₈⁸⁺ + 8 H⁺		6.00 ± 0.30
HfO₂ + 4 H⁺ ⇌ Hf⁴⁺ + 2 H₂O	–1.2*	–5.56 ± 0.15*
HfO_{2 + 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 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 ⇌ Ho₂₂⁴⁺ + 2 H⁺		−13.5 ± 0.2
3 Ho³⁺ + 5 H₂O ⇌ Ho₃₅⁴⁺ + 5 H⁺		−30.9 ± 0.3
Ho₃ + 3 H⁺ ⇌ Ho³⁺ + 3 H₂O	15.4	15.60 ± 0.30

Indium

Hydrolysis constants 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 ⇌ In₂⁺ + 2 H⁺	–7.82	–7.794	–9.16
In³⁺ + 3 H₂O ⇌ In₃ + 3 H⁺	–12.4	–12.391
In³⁺ + 4 H₂O ⇌ In₄^– + 4 H⁺	–22.07	–22.088	–22.05
In₃ ⇌ In³⁺ + 3 OH^–	–36.92	–36.9	–36.92
1/2 In₂O₃ + 3/2 H₂O ⇌ In³⁺ + 3 OH^–			–35.24

Iridium

Hydrolysis constants 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 ⇌ Ir₂⁺ + 2 H⁺	‒8.46 ± 0.20
Ir₃ + 3 H⁺ ⇌ Ir³⁺ + 3 H₂O	8.88 ± 0.20

Iron(II)

Hydrolysis constants 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 ⇌ Fe₂ + 2 H⁺	–20.5				−20.52 ± 0.08
Fe²⁺ + 3 H₂O ⇌ Fe₃⁻ + 3 H⁺	–29.4				−32.68 ± 0.15
Fe₂ +2 H⁺ ⇌ Fe²⁺ + 2 H₂O					12.27 ± 0.88

Iron(III)

Hydrolysis constants 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 ⇌ Fe₂⁺ + 2 H⁺	–5.67	−4.8 ± 0.4	–5.71 ± 0.10
Fe³⁺ + 3 H₂O ⇌ Fe₃ + 3 H⁺	<–12	<–14	–12.42 ± 0.20
Fe³⁺ + 4 H₂O ⇌ Fe₄^– + 4 H⁺	–21.6	−21.5 ± 0.5	–21.60 ± 0.23
2 Fe³⁺ + 2 H₂O ⇌ Fe₂₂⁴⁺ + 2 H⁺	–2.95	–2.91 ± 0.07	–2.91 ± 0.07
3 Fe³⁺ + 4 H₂O ⇌ Fe₃₄⁵⁺ + 4 H⁺	–6.3		−6.3 ± 0.1
Fe₃ +3 H⁺ ⇌ Fe3⁺ + 3 H₂O 2-line ferrihydrite	2.5	3.5	3.50 ± 0.20
Fe₃ ⇌ Fe³⁺ + 3 OH⁻ 6-line ferrihydrite		−38.97 ± 0.64
α-FeOOH+ 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+ 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 + 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+ 3 H⁺ ⇌ Fe³⁺ + 2 H₂O goethite			1.85 ± 0.37
γ-FeOOH + H₂O ⇌ Fe³⁺ + 3 OH⁻ lepidocrocite		−40.13 ± 0.37
Fe₃ + 3 H⁺ ⇌ Fe³⁺ + 3 H₂O magnetite			−12.26 ± 0.26

Lanthanum

Hydrolysis constants 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 ⇌ La₂₂⁴⁺ + 2 H⁺	≤ –17.5	–17.57 ± 0.20
3 La³⁺ + 5 H₂O ⇌ La₃₅⁴⁺ + 5 H⁺	≤ –38.3	–37.8 ± 0.3
5 La³⁺ + 9 H₂O ⇌ La₅₉⁶⁺ + 9 H⁺	–71.2
La₃ + 3 H⁺ ⇌ La³⁺ + 3 H₂O	20.3	19.72 ± 0.34

Lead(II)

Hydrolysis constants 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 ⇌ Pb₂ + 2 H⁺	–17.12	–17.1	–16.94 ± 0.09	–16.99 ± 0.06	–16.12 ± 0.01
Pb²⁺ + 3 H₂O ⇌ Pb^3- + 3 H⁺	–28.06	–28.1	–28.03± 0.06	–27.94 ± 0.21	–28.4 ± 0.1
Pb²⁺ + 4 H₂O ⇌ Pb₄^2- + 4 H⁺			–40.8
2 Pb²⁺ + H₂O ⇌ Pb₂₃⁺ + H⁺	–6.36	–6.4	–7.28± 0.09	–6.73 ± 0.31
3 Pb²⁺ + 4 H₂O ⇌ Pb_{3₄²⁺ + 4 H⁺}	–23.88	–23.9	–23.01 ± 0.07	–23.43 ± 0.10
3 Pb²⁺ + 5 H₂O ⇌ Pb₃₅⁺ + 5 H⁺				–31.11 ± 0.10
4 Pb²⁺ + 4 H₂O ⇌ Pb₄₄⁴⁺ + 4 H⁺	–20.88	–20.9	–20.57± 0.06	–20.71 ± 0.18
6 Pb²⁺ + 8 H₂O ⇌ Pb₆₈⁴⁺ + 8 H⁺	–43.61	–43.6	–42.89± 0.07	–43.27 ± 0.47
PbO + 2 H⁺ ⇌ Pb²⁺ + H₂O			12.62 12.90
PbO +H2O ⇌ Pb²⁺ + 2 OH^–	–15.28	-15.3	–15.3 –15.1	–15.37 ± 0.04 –15.1 ± 0.08
Pb₂O_{2 +H2O ⇌ 2 Pb²⁺ + 4 OH^–}			–14.9
PbO +H₂O ⇌ Pb₂			–4.4 –4.2
Pb₂O₂ +H₂O ⇌ 2 Pb₂			–4.0
PbO + 2 H₂O ⇌ Pb₃^– + H⁺			–1.4 –1.2
Pb₂O_{2 + 2 H₂O ⇌ 2 Pb₃^– + 2 H⁺}			–1.0

Lead(IV)

Hydrolysis constants 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^– ⇌ Pb₆^2–	–4.5

Lithium

Hydrolysis constants 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 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 ⇌ Mg₄₄⁴⁺ + 4 H⁺	–39.71
Mg₂ + 2 H⁺ ⇌ Mg²⁺ + 2 H₂O	16.84	16.84	17.11 ± 0.04

Manganese(II)

Hydrolysis constants 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 ⇌ Mn₂ + 2 H⁺		–22.2			−22.18 ± 0.20
Mn²⁺ + 3 H₂O ⇌ Mn₃^– + 3 H⁺		–34.8			−34.34 ± 0.45
Mn²⁺ + 4 H₂O ⇌ Mn₄^2– + 4 H⁺		–48.3			−48.28 ± 0.40
2 Mn²⁺ + H₂O ⇌ Mn₂OH³⁺ + H⁺		–10.56
2 Mn²⁺ + 3 H₂O ⇌ Mn₂₃⁺ + 6 H⁺		–23.90
Mn₂ + 2 H⁺ ⇌ Mn²⁺ + 2 H₂O	15.2	15.2	15.2		15.19 ± 0.10
MnO + 2 H⁺ ⇌ Mn²⁺ + H₂O					17.94 ± 0.12

Manganese(III)

Hydrolysis constants 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 in critical compilations at infinite dilution and T = 298.15 K:

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

0.5 M HClO₄

Mercury(II)

Hydrolysis constants 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 ⇌ Hg₂ + 2 H⁺	-6.17	–5.98 ± 0.06	−5.96 ± 0.07
Hg²⁺ + 3 H₂O ⇌ Hg₃^– + 3 H⁺	–21.1	–21.1 ± 0.3
HgO + 2 H⁺ ⇌ Hg²⁺ + H₂O	2.56	2.37 ± 0.08	2.37 ± 0.08

Molybdenum(VI)

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

Reaction	Baes and Mesmer, 1976	Jolivet, 2000	NIST46	Crea et al., 2017
MoO₄^2– + H⁺ ⇌ HMoO₄^–	3.89^a		4.24	4.47 ± 0.02
MoO₄^2– + 2 H⁺ ⇌ H₂MoO₄	7.50^a			8.12 ± 0.03
HMoO₄^– + H⁺ ⇌ H₂MoO₄			4.0
Mo₇O₂₄^6– + H⁺ ⇌ HMo₇O₂₄^5–		4.4
HMo₇O₂₄^5– + H⁺ ⇌ H₂Mo7O₂₄^4–		3.5
H₂Mo₇O₂₄^4– + H⁺ ⇌ H₃Mo₇O₂₄^3–		2.5
7 MoO₄^2-+ 8 H⁺ ⇌ Mo₇O₂₄^6– + 4 H₂O	57.74^a		52.99^b	51.93 ± 0.04
7 MoO₄^2– + 9 H⁺ ⇌ Mo₇O₂₃^5– + 4 H₂O	62.14^a			58.90 ± 0.02
7 MoO₄^2– + 10 H⁺ ⇌ Mo₇O₂₂₂^4– + 4 H₂O	65.68^a			64.63 ± 0.05
7 MoO₄^2– + 11 H⁺ ⇌ Mo₇O₂₁₃^3– + 4 H₂O	68.21^a			68.68 ± 0.06
19 MoO₄^2- + 34 H⁺ ⇌ Mo₁₉O₅₉^4– + 17 H₂O	196.3^a		196^a
MoO₃ + H₂O ⇌ MoO₄^2– + 2 H⁺	–12.06^a

Neodymium

Hydrolysis constants 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 ⇌ Nd₂⁺ + 2 H⁺			–15.7 ± 0.7
Nd³⁺ + 3 H₂O ⇌ Nd₃ + 3 H⁺			–26.2 ± 0.5
Nd³⁺ + 4 H₂O ⇌ Nd₄⁻ + 4 H⁺		–37.4	–40.7 ± 0.7
2 Nd³⁺ + 2 H₂O ⇌ Nd₂₂⁴⁺ + 2 H⁺	–13.86	–13.9		–15.56 ± 0.20
3 Nd³⁺ + 5 H₂O ⇌ Nd₃₅⁴⁺ + 5 H⁺	< –28.5			–34.2 ± 0.3
Nd₃ + 3 H⁺ ⇌ Nd³⁺ + 3 H₂O	18.6		17.2 ± 0.4	17.89 ± 0.09
Nd₃ ⇌ Nd³⁺ + 3 OH^–		–23.2 ± 0.9	–21.5 –23.1

Neptunium(III)

Hydrolysis constants 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 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 ⇌ Np₂²⁺ + 2 H⁺			–3.7 ± 0.3	0.3 ± 0.3
Np⁴⁺ + 4 H₂O ⇌ Np₄ + 4 H⁺			–10.0 ± 0.9	–8 ± 1
Np⁴⁺ + 4 OH⁻ ⇌ NpO₂ + 2 H₂O	52	54.9 ± 0.4	57.5 ± 0.3	56.7 ± 0.5

Neptunium(V)

Hydrolysis constants 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 + H⁺	–8.85	–10.7 ± 0.5	–11.3 ± 0.7
NpO₂⁺ + 2 H₂O ⇌ NpO₂₂⁻ + 2 H⁺		–22.8 ± 0.7	–23.6 ± 0.5
NpO₂⁺ + H₂O ⇌ NpO₂ + H⁺	≤ –4.7	–5.21 ± 0.05	–5.3 ± 0.2
NpO₂⁺ + H₂O ⇌ NpO₂ + H⁺		–4.53 ± 0.06	–4.7 ± 0.5

Neptunium(VI)

Hydrolysis constants 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⁺ + H⁺	–5.15	–5.12	–5.1 ± 0.2	–5.1 ± 0.4
NpO₂²⁺ + 3 H₂O ⇌ NpO₂₃⁻ + 3 H⁺			–21 ± 1
NpO₂²⁺ + 4 H₂O ⇌ NpO₂₄^2- + 4 H⁺			–32 ± 1
2 NpO₂²⁺ + 2 H₂O ⇌ ₂₂²⁺ + 2 H⁺	–6.39	–6.39	–6.2 ± 0.2	–6.2 ± 0.2
3 NpO₂²⁺ + 5 H₂O ⇌ ₃₅⁺ + 5 H⁺	–17.49	–17.49	–17.0 ± 0.2	–17.1 ± 0.2
NpO₂²⁺ + 2 H₂O ⇌ NpO₃.H₂O + 2 H⁺	≥-6.6		–5.4 ± 0.4	–5.4 ± 0.4

Nickel(II)

Hydrolysis constants 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 ⇌ Ni₂ + 2 H⁺		–19	–19		< –18	–21.15 ± 0.0
Ni²⁺ + 3 H₂O ⇌ Ni₃^– + 3 H⁺		–30	–30	–29.2 ± 1.7	–29.2 ± 1.7
Ni²⁺ + 4 H₂O ⇌ Ni₄^2– + 4 H⁺		< –44
2 Ni²⁺ + H₂O ⇌ Ni₂³⁺ + H⁺		–10.7		–10.6 ± 1.0	–10.6 ± 1.0	–10.6 ± 1.0
4 Ni²⁺ + 4 H₂O ⇌ Ni₄₄⁴⁺ + 4 H⁺		–27.74	–27.7	–27.52 ± 0.15	–27.52 ± 0.15	–27.9 ± 0.6
β-Ni₂ + 2 H⁺ ⇌ Ni²⁺ + 2 H₂O		10.8			11.02 ± 0.20	10.96 ± 0.20 11.75 ± 0.13
Ni₂ ⇌ Ni²⁺ + 2 OH^–	–17.2		–17.2	–16.97± 0.20 –17.2 ± 1.3
Ni₂ + OH^– ⇌ Ni₃^–	–4.2
NiO + 2 H⁺ ⇌ Ni²⁺ + H₂O				12.38 ± 0.06		12.48 ± 0.15

Niobium

Hydrolysis constants in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Filella and May, 2020
Nb₅ + H⁺ ⇌ Nb₄⁺ + H₂O	~ –0.6	1.603
Nb₅ + H₂O ⇌ Nb₆^– + H⁺	~ –4.8	–4.951
Nb₆O₁₉^8– + H⁺ ⇌ HNb₆O₁₉^7–		14.95
HNb₆O₁₉^7– + H⁺ ⇌ H₂Nb₆O₁₉^6–		13.23
H₂Nb₆O₁₉^6– + H⁺ ⇌ H₃Nb₆O₁₉^5–		11.73
1/2 Nb₂O₅ + 5/2 H₂O ⇌ Nb₅	~ –7.4
Nb₅ ⇌ Nb₅		–7.510
Nb₂O₅ + 5 H₂O ⇌ 2 Nb₅		–18.31

Osmium(VI)

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

Reaction	Galbács et al., 1983
OsO₂₄^2– + H⁺ ⇌ HOsO₂₄^–	10.4
HOsO₂₄^– + H⁺ ⇌ H₂OsO₂₄	8.5

Osmium(VIII)

Hydrolysis constants in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Galbács et al., 1983
OsO₂₃aq + H⁺ ⇌ OsO₂₄aq	12.2^a
OsO₂₂₂aq + H⁺ ⇌ OsO₂₃aq	14.4^b

At I = 0.1 M At I = 2.5 M

Palladium

Hydrolysis constants 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 ⇌ Pd₂ + 2 H⁺	−2.6	−4 ± 1	−3.11 ± 0.63	−3.07 ± 0.16
Pd²⁺ + 3 H₂O ⇌ Pd₃⁻ + 3 H⁺		−15.5 ± 1	−14.20 ± 0.63
Pd₂ + 2 H⁺ ⇌ Pd²⁺ + 2 H₂O		−3.3 ± 1		−3.4 ± 0.2

Plutonium(III)

Hydrolysis constants 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 ⇌ Pu₃ + 3 H⁺	–19.65		–15.8 ± 0.8	–15 ± 1

Plutonium(IV)

Hydrolysis constants 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 ⇌ Pu₂²⁺ + 2 H⁺				0.6 ± 0.3
Pu⁴⁺ + 3 H₂O ⇌ Pu₃⁺ + 3 H⁺				–2.3 ± 0.4
Pu⁴⁺ + 4 H₂O ⇌ Pu₄ + 4 H⁺	–9.5		–12.5 ± 0.7	–8.5 ± 0.5
Pu⁴⁺ + 4 OH⁻ ⇌ PuO₂ + 2 H₂O	49.5		47.9 ± 0.4 53.8 ± 0.5	58.3 ± 0.5

Plutonium(V)

Hydrolysis constants 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 + H⁺	–1.49	–1.5	–1.31 ± 0.05	0.5 ± 0.2
PuO2+ + H2O ⇌ PuO2 + H⁺			–3.7 ± 0.3	0.3 ± 0.3

Plutonium(VI)

Hydrolysis constants 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⁺ + H⁺	–5.6	–5.6	–5.36 ± 0.09	–5.5 ± 0.5
PuO₂²⁺ + 2 H₂O ⇌ PuO₂₂ + 2 H⁺			–12.9 ± 0.2	–13 ± 1
PuO₂²⁺ + 3 H₂O ⇌ PuO₂₃⁻ + 3 H+				–24 ± 1
2 PuO₂²⁺ + 2 H₂O ⇌ ₂₂²⁺ + 2 H⁺	–8.36	–8.36	–7.8 ± 0.5	–7 ± 1
3 PuO₂²⁺ + 5 H₂O ⇌ ₃₅⁺ + 5 H⁺	–21.65	–21.65
PuO₂²⁺ + 2 OH⁻ ⇌ PuO₂₂				22.8 ± 0.6

Potassium

Hydrolysis constants 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 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 ⇌ Pr₂₂⁴+ + 2 H⁺			–16.31 ± 0.20
3 Pr³⁺ + 5 H₂O ⇌ Pr₃₅⁴⁺ + 5 H⁺			–35.0 ± 0.3
Pr₃ + 3 H⁺ ⇌ Pr³⁺ + 3 H₂O	19.5		18.57 ± 0.20
Pr₃ ⇌ Pr³⁺ + 3 OH^–		–22.3 ± 1.0

Radium

Hydrolysis constants 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 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
Rh₃ + OH^‒ ⇌ Rh₄^‒		‒3.9

Samarium

Hydrolysis constants 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 ⇌ Sm₂₂⁴⁺ + 2 H⁺			–14.75 ± 0.20
3 Sm³⁺ + 5 H₂O ⇌ Sm₃₅⁴⁺ + 5 H⁺			–33.9 ± 0.3
Sm₃ + 3H⁺ ⇌ Sm³⁺ + 3H₂O	16.5		17.19 ± 0.30
Sm₃ ⇌ Sm³⁺ + 3 OH⁻		–23.9 ± 0.9 –25.9

Scandium

Hydrolysis constants 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 ⇌ Sc₂⁺ + 2 H⁺	–9.7	–9.71 ± 0.30
Sc³⁺ + 3 H₂O ⇌ Sc₃ + 3 H⁺	–16.1	–16.08 ± 0.30
Sc³⁺ + 4 H₂O ⇌ Sc₄^–+ 4 H⁺	–26	–26.7 ± 0.3
2 Sc³⁺ + 2 H₂O ⇌ Sc₂₂⁴⁺ + 2 H⁺	–6.0	–6.02 ± 0.10
3 Sc³⁺ + 5 H₂O ⇌ Sc₃₅⁴⁺ + 5 H⁺	–16.34	–16.33 ± 0.10
Sc₃ + 3 H⁺ ⇌ Sc³⁺ + 3 H₂O		9.17 ± 0.30
ScO_1.5 + 3 H⁺ ⇌ Sc³⁺ + 1.5 H₂O		5.53 ± 0.30
ScO + 3 H⁺ ⇌ Sc³⁺ + 2 H₂O	9.4
Sc₃ + OH^– ⇌ Sc₄		–3.5 ± 0.2

Selenium(–II)

Hydrolysis constants in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Olin et al., 2015	Thoenen et al., 2014
H₂Se ⇌ H₂Se	–1.10 ± 0.01	–1.10 ± 0.01
H₂Se ⇌ HSe^– + H⁺	–3.85 ± 0.05	–3.85 ± 0.05
HSe^– ⇌ Se^2– + H⁺	–14.91 ± 0.20

Selenium(IV)

Hydrolysis constants in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Olin et al., 2005	Thoenen et al., 2014
SeO₃^2– + 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 in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Olin et al., 2005	Thoenen et al., 2014
SeO₄^2‒ + H⁺ ⇌ HSeO₄^‒	1.360	1.75 ± 0.10	1.75 ± 0.10

Silicon

Hydrolysis constants in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Thoenen et al., 2014
Si₄ ⇌ SiO₃^– + H⁺	–9.86	–9.81 ± 0.02
Si₄ ⇌ SiO₂₂^2– + 2 H⁺	–22.92	–23.14 ± 0.09
4 Si₄ ⇌ Si₄O₆₆^4– + 2 H⁺ + 4 H₂O	–13.44
4 Si₄ ⇌ Si₄O₈₄^4– + 4 H⁺ + 4 H₂O	–35.80	–36.3 ± 0.2
SiO₂ + 2 H₂O ⇌ Si₄	–4.0	–3.739 ± 0.087
SiO₂ + 2 H₂O ⇌ Si₄		–2.714

Silver

Hydrolysis constants 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 ⇌ Ag₂⁻ + 2 H⁺	−24.0	−24.34 ± 0.14
0.5 Ag₂O + H⁺ ⇌ Ag⁺ + 0.5 H₂O	6.29	6.27 ± 0.05

Sodium

Hydrolysis constants 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 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 in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Filella and May, 2019^a
Ta₅ + H⁺ ⇌ Ta₄⁺ + H₂O	~1	0.7007
Ta₅ + H₂O ⇌ Ta₆^– + H⁺	~ –9.6
Ta₆O₁₉^8– + H⁺ ⇌ HTa₆O₁₉^7–		16.35
HTa₆O₁₉^7– + H⁺ ⇌ H₂Ta₆O₁₉^6–		14.00
1/2 Ta₂O₅ + 5/2 H₂O ⇌ Ta₅	~ –5.2
Ta₅ ⇌ Ta₅		–5.295
Ta₂O₅ + 5 H₂O ⇌ 2 Ta₅		–20.00

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 in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Filella and May, 2019^a
Te^2‒ + H⁺ ⇌ HTe^‒	11.81
HTe^‒ + H⁺ ⇌ H₂Te	2.476

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 in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Filella and May, 2019^a
TeO₃^2‒ + H⁺ ⇌ HTeO₃^‒		9.928
HTeO₃^‒ + H⁺ ⇌ H₂TeO₃		6.445
H₂TeO₃ ⇌ HTeO₃^‒ + H⁺	‒2.68
H₂TeO₃ ⇌ TeO₃^2‒ + 2 H⁺	‒12.5
H₂TeO₃ + H⁺ ⇌ Te₃⁺	3.13	2.415
TeO₂ + H₂O ⇌ H₂TeO₃		‒4.709

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 in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Filella and May, 2019^a
TeO₂₄^2‒ + H⁺ ⇌ TeO₅^‒		10.83
TeO₅^‒ + H⁺ ⇌ Te₆	7.68	7.696
TeO₂₄^2‒ + 2 H⁺ ⇌ Te₆	18.68
TeO₃₃^3‒ + 3 H⁺ ⇌ Te₆	34.3
2 Te₆ ⇌ Te₂O₁₁^‒ + H⁺		‒6.929

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 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 ⇌ Tb₂₂⁴⁺ + 2 H⁺		−13.9 ± 0.2
3 Tb³⁺ + 5 H₂O ⇌ Tb₃₅⁴⁺ + 5 H⁺		−31.7 ± 0.3
Tb₃ + 3 H⁺ ⇌ Tb³⁺ + 3 H₂O	16.5	16.33 ± 0.30

Thallium(I)

Hydrolysis constants 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^– ⇌ Tl₂^–		–0.7 ± 0.7
Tl₂O + H⁺ ⇌ Tl⁺ + H₂O		13.55 ± 0.20

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 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 ⇌ Tl₂⁺ + 2 H⁺	–1.57
Tl³⁺ + 3 H₂O ⇌ Tl₃ + 3 H⁺	–3.3
Tl³⁺ + 4 H₂O ⇌ Tl₄^– + 4 H⁺	–15.0
Tl₂O₃ + 3 H⁺ ⇌ Tl³⁺ + H₂O	–3.90	–3.90 ± 0.10

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 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 ⇌ Th₂²⁺ + 2 H⁺	–6.93	–6.2 ± 0.5	–6.2 ± 0.5	–6.2 ± 0.5
Th⁴⁺ + 3 H₂O ⇌ Th₃⁺ + 3 H⁺	< –11.7
Th⁴⁺ + 4 H₂O ⇌ Th₄ + 4 H⁺	–15.9	–17.4 ± 0.7	–17.4 ± 0.7	–17.4 ± 0.7
2Th⁴⁺ + 2 H₂O ⇌ Th₂₂⁶⁺ + 2 H⁺	–6.14	–5.9 ± 0.5	–5.9 ± 0.5	–5.9 ± 0.5
2Th⁴⁺ + 3 H₂O ⇌ Th₂₃⁵⁺ + 3 H⁺		–6.8 ± 0.2	–6.8 ± 0.2	–6.8 ± 0.2
4Th⁴⁺ + 8 H₂O ⇌ Th₄₈⁸⁺ + 8 H⁺	–21.1	–20.4 ± 0.4	–20.4 ± 0.4	–20.4 ± 0.4
4Th⁴⁺ + 12 H₂O ⇌ Th₄₁₂⁴⁺ + 12 H⁺		–26.6 ± 0.2	–26.6 ± 0.2	–26.6 ± 0.2
6Th⁴⁺ + 15 H₂O ⇌ Th₆₁₅⁹⁺ + 15 H⁺	–36.76	–36.8 ± 1.5	–36.8 ± 1.5	–36.8 ± 1.5
6Th⁴⁺ + 14 H₂O ⇌ Th₆₁₄¹⁰⁺ + 14 H⁺		–36.8 ± 1.2	–36.8 ± 1.2	–36.8 ± 1.2
ThO₂ + 4 H⁺ ⇌ Th⁴⁺ + 2 H₂O	6.3
ThO₂ + 4 H⁺ ⇌ Th⁴⁺ + 2 H₂O				8.8 ± 1.0
ThO₂ + 4 H⁺ ⇌ Th⁴⁺ + 2 H₂O			9.3 ± 0.9
ThO₂ + 4 H⁺ ⇌ Th⁴⁺ + 2 H₂O			8.5 ± 0.9
Th⁴⁺ + 4 OH⁻ ⇌ ThO₂ + 2 H₂O		46.7 ± 0.9
Th⁴⁺ + 4 OH⁻ ⇌ ThO₂ + 2 H₂O		47.5 ± 0.9

Thulium

Hydrolysis constants 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 ⇌ Tm₂₂⁴⁺ + 2 H⁺		−13.2 ± 0.2
3 Tm³⁺ + 5 H₂O ⇌ Tm₃₅⁴⁺ + 5 H⁺		−30.5 ± 0.3
Tm₃ + 3 H⁺ ⇌ Tm³⁺ + 3 H₂O	15.0	15.56 ± 0.40

Tin(II)

Hydrolysis constants 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 ⇌ Sn₂ + 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 ⇌ Sn₃^– + 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 ⇌ Sn₂₂²⁺ + 2 H⁺		–4.77		–4.8	–4.79 ± 0.05
3 Sn²⁺ + 4 H₂O ⇌ Sn₃₄²⁺ + 4 H⁺		–6.88	–5.6 ± 1.6	–6.88	–5.88 ± 0.05	–5.60 ± 0.47	−5.60 ± 0.47
Sn₂ ⇌ Sn²⁺ + 2 OH^–				–25.8	–26.28 ± 0.08
SnO + 2 H⁺ ⇌ Sn²⁺ + H₂O		1.76	2.5± 0.5				1.60 ± 0.15
SnO + H₂O ⇌ Sn²⁺ + 2 OH^–	–26.2
SnO + H₂O ⇌ Sn₂	–5.3
SnO + 2 H₂O ⇌ Sn₃^– + H⁺	–0.9

Tin(IV)

Hydrolysis constants 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 ⇌ Sn₄ + 4 H⁺			7.53 ± 0.12
Sn⁴⁺ + 5 H₂O ⇌ Sn₅^– + 5 H⁺			–1.07 ± 0.42
Sn⁴⁺ + 6 H₂O ⇌ Sn₆^2– + 6 H⁺			–1.07 ± 0.42
Sn₄ + H₂O ⇌ Sn₅^– + H⁺	–8.0 ± 0.3	–8.60 ± 0.40
Sn₄ + 2 H₂O ⇌ Sn₆^2– + 2 H⁺	–18.4 ± 0.3	–18.67 ± 0.30
SnO₂ + 2 H₂O ⇌ Sn₄	–8.0 ± 0.2	–8.06 ± 0.11
SnO₂ + 2 H₂O ⇌ Sn₄	–7.3 ± 0.3	–7.22 ± 0.08
SnO₂ + 4 H⁺ ⇌ Sn⁴⁺ + 2 H₂O			–15.59 ± 0.04

Tungsten

Hydrolysis constants in critical compilations at infinite dilution and T = 298.15 K:

Reaction	NIST46
WO₄^2– + H⁺ ⇌ HWO₄^–	3.6
WO₄^2– + 2 H⁺ ⇌ H₂WO₄	5.8
6 WO₄^2– + 7 H⁺ ⇌ HW₆O₂₁^5– + 3 H₂O	63.83

Titanium(III)

Hydrolysis constants 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 ⇌ Ti₂₂⁴⁺ + 2 H⁺		–3.6	–2.64 ± 0.10

Titanium(IV)

Hydrolysis constants in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Brown and Ekberg, 2016
Ti₂²⁺ + H₂O ⇌ Ti³⁺ + H⁺	⩽–2.3
Ti₂²⁺ + 2 H₂O ⇌ Ti₄ + 2 H⁺	–4.8
TiO²⁺ + H₂O ⇌ TiOOH⁺ + H⁺		–2.48 ± 0.10
TiO²⁺ + 2 H₂O ⇌ TiO₂ + 2 H⁺		–5.49 ± 0.14
TiO²⁺ + 3 H₂O ⇌ TiO₃^– + 3 H⁺		–17.4 ± 0.5
TiO₂ + H₂O ⇌ TiO₃^– + H⁺		–11.9 ±0.5
TiO₂ +2 H₂O ⇌ Ti₄	~ –4.8
TiO₂ + H⁺ ⇌ TiOOH⁺		–6.06 ± 0.30
TiO₂ + H₂O ⇌ TiO₂		–9.02 ± 0.02
TiO₂ x H₂O ⇌ Ti₂²⁺
TiO₂ + 4 H⁺ ⇌ Ti⁴⁺ + 2 H₂O		–3.56 ± 0.10

Uranium(IV)

Hydrolysis constants 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 ⇌ U₂²⁺ + 2 H⁺		–1.1 ± 1.0	–1.4 ± 0.2	–1.9 ± 0.2
U⁴⁺ + 3 H₂O ⇌ U₃⁺ + 3 H⁺		–4.7 ± 1.0	–5.1 ± 0.3	–5.2 ± 0.4
U⁴⁺ + 4 H₂O ⇌ U₄ + 4 H⁺		–10.0 ± 1.4	–10.4 ± 0.5	–10.0 ± 1.4
U⁴⁺ + 5 H₂O ⇌ U₅⁻ + 5 H⁺	–16.0
UO₂ + 4 H⁺ ⇌ U⁴⁺ + 2 H₂O		1.5 ± 1.0
UO₂ + 2 H₂O ⇌ U⁴⁺ + 4 OH^–			–54.500 ± 1.000	–54.500 ± 1.000
UO₂ + 4 H⁺ ⇌ U⁴⁺ + 2 H₂O	–1.8
UO₂ + 2 H₂O ⇌ U⁴⁺ + 4 OH^–				–60.860 ± 1.000

Uranium(VI)

Hydrolysis constants 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⁺ + H⁺	–5.8	–5.2 ± 0.3	–5.9 ± 0.1	–5.13 ± 0.04	–5.2₅ ± 0.2₄
UO₂²⁺ + 2 H₂O ⇌ UO₂₂ + 2 H⁺		≤-10.3		–12.1₅ ± 0.2₀	–12.15 ± 0.07
UO₂²⁺ + 3 H₂O ⇌ UO₂₃^– + 3 H⁺		–19.2 ± 0.4		–20.2₅ ± 0.4₂	–20.2₅ ± 0.4₂
UO₂²⁺ + 4 H₂O ⇌ UO₂₄^2– + 4 H⁺		–33 ± 2		–32.4₀ ± 0.6₈	–32.4₀ ± 0.6₈
2 UO₂²⁺ + 2 H₂O ⇌ ₂₂²⁺ + 2 H⁺	–5.62	–5.62 ± 0.04	–5.58 ± 0.04	–5.68 ± 0.05	–5.62 ± 0.08
3 UO₂²⁺ + 5 H₂O ⇌ ₃₅⁺ + 5 H+	–15.63	–15.5₅ ± 0.1₂	–15.6	–15.7₅ ± 0.1₂	–15.5₅ ± 0.1₂
3 UO₂²⁺ + 4 H₂O ⇌ ₃₄²⁺ + 4 H⁺		–11.9 ± 0.3		–11.78 ± 0.05	–11.9 ± 0.3
3 UO₂²⁺ + 7 H₂O ⇌ ₃₇^– + 7 H⁺		–31 ± 2.0		–32.2 ± 0.8	–32.2 ± 0.8
4 UO₂²⁺ + 7 H₂O ⇌ ₄₇+ + 7 H⁺		–21.9 ± 1.0		–22.1 ± 0.2	–21.9 ± 1.0
2 UO₂²⁺ + H₂O ⇌ ₂³⁺ + H⁺		–2.7 ± 1.0			–2.7 ± 1.0
UO₂₂ + 2H⁺ ⇌ UO₂²⁺ + 2 H₂O	5.6		6.0	4.81 ± 0.20
UO₃·2H₂O + 2H⁺ ⇌ UO₂²⁺ + 3 H₂O					5.350 ± 0.130

Vanadium(IV)

Hydrolysis constants in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Brown and Ekberg, 2016
VO²⁺ + H₂O ⇌ VO⁺ + H⁺	–5.30 ± 0.13
2 VO²⁺ + 2 H₂O ⇌ ₂₂²⁺ + 2 H⁺	–6.71 ± 0.10

Vanadium(V)

Hydrolysis constants in critical compilations at infinite dilution and T = 298.15 K:

Reaction	Baes and Mesmer, 1976	Brown and Ekberg, 2016
VO₂⁺ + 2 H₂O ⇌ VO3 + H⁺	–3.3
VO₂⁺ + 2 H₂O ⇌ VO₂₂^– + 2 H⁺	–7.3	–7.18 ± 0.12
10 VO₂⁺ + 8 H₂O ⇌ V₁₀O₂₆₂^4– + 14 H⁺	–10.7
VO₂₂^– ⇌ VO₃^2– + H⁺	–8.55
2 VO₂₂^– ⇌ V₂O₆₂^3– + H⁺ + H₂O	–6.53
VO₃^2– ⇌ VO₄^3– + H⁺	–14.26
2 VO₃^2– ⇌ V₂O₇^4– + H₂O	0.56
3 VO₃^2– + 3 H⁺⇌ V₃O₉^3– + 3 H₂O	31.81
V₁₀O₂₆₂^4– ⇌ V₁₀O₂₇^5– + 3 H⁺	–3.6
V₁₀O₂₇^5– ⇌ V₁₀O₂₈^6– + H⁺	–6.15
VO₂⁺ + H₂O ⇌ VO₂OH + H⁺		–3.25 ± 0.1
VO₂⁺ + 3 H₂O ⇌ VO₂₃^2- + 3 H⁺		–15.74 ± 0.19
VO₂⁺ + 4 H₂O ⇌ VO₂₄^3- + 4 H⁺		–30.03 ± 0.24
2 VO₂⁺ + 4 H₂O ⇌ ₂₄^2- + 4 H⁺		–11.66 ± 0.53
2 VO₂⁺ + 5 H₂O ⇌ ₂₅^3- + 5 H⁺		–20.91 ± 0.22
2 VO₂⁺ + 6 H₂O ⇌ ₂₆^4- + 6 H⁺		–32.43 ± 0.30
4 VO₂⁺ + 8 H₂O ⇌ ₄8^4- + 8 H⁺		–20.78 ± 0.33
4 VO₂⁺ + 9 H₂O ⇌ ₄₉^5- + 9 H⁺		–31.85 ± 0.26
4 VO₂⁺ + 10 H₂O ⇌ ₄₁₀^6- + 10 H⁺		–45.85 ± 0.26
5 VO₂⁺ + 10 H₂O ⇌ ₅₁₀^5- + 10 H⁺		–27.02 ± 0.34
10 VO₂⁺ + 14 H₂O ⇌ ₁₀₁₄^4- + 14 H⁺		–10.5 ± 0.3
10 VO₂⁺ + 15 H₂O ⇌ ₁₀₁₅^5- + 15 H⁺		–15.73 ± 0.33
10 VO₂⁺ + 16 H₂O ⇌ ₁₀₁₆^6- + 16 H⁺		–23.90 ± 0.35
V₂O₅ + H⁺ ⇌ VO₂⁺ + H₂O	–0.66
V₂O₅ + 2 H⁺ ⇌ 2 VO₂⁺ + H₂O		–0.64 ± 0.09

Ytterbium

Hydrolysis constants 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 ⇌ Yb₂⁺ + 2 H⁺
Yb³⁺ + 3 H₂O ⇌ Yb₃ + 3 H⁺
Yb³⁺ + 4 H₂O ⇌ Yb₄⁻ + 4 H⁺	−32.7
2 Yb³⁺ + 2 H₂O ⇌ Yb₂₂⁴⁺ + 2 H⁺		−13.76 ± 0.20
3 Yb³⁺ + 5 H₂O ⇌ Yb₃₅⁴⁺ + 5 H⁺		−30.6 ± 0.3
Yb₃ + 3 H⁺ ⇌ Yb³⁺ + 3 H₂O	14.7	15.35 ± 0.20

Yttrium

Hydrolysis constants 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 ⇌ Y₂⁺ + 2 H⁺
Y³⁺ + 3 H₂O ⇌ Y₃ + 3 H⁺
Y³⁺ + 4 H₂O ⇌ Y₄⁻+ 4 H⁺	–36.5
2 Y³⁺ + 2 H₂O ⇌ Y₂₂⁴⁺ + 2 H⁺	–14.23	–14.1 ± 0.2
3 Y³⁺ + 5 H₂O ⇌ Y₃₅⁴⁺ + 5 H⁺	–31.6	–32.7 ± 0.3
Y₃ + 3 H⁺ ⇌ Y³⁺ + 3 H₂O	17.5	17.32 ± 0.30

Zinc

Hydrolysis constants 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 ⇌ Zn₂ + 2 H⁺	−16.9	–17.82 ± 0.08	−17.89 ± 0.15
Zn²⁺ + 3 H₂O ⇌ Zn₃⁻ + 3 H⁺	−28.4	–28.05 ± 0.05	−27.98 ± 0.10
Zn²⁺ + 4 H₂O ⇌ Zn₄^2- + 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 ⇌ Zn₂₆^2- + 6 H⁺	−57.8
ZnO + 2 H⁺ ⇌ Zn²⁺ + H₂O	11.14	11.12 ± 0.05	11.11 ± 0.10
ε-Zn₂ + 2 H⁺ ⇌ Zn²⁺ + 2 H₂O		11.38 ± 0.20	11.38± 0.20
β₁-Zn₂ + 2 H⁺ ⇌ Zn²⁺ + 2 H₂O		11.72 ± 0.04
β₂-Zn₂ + 2 H⁺ ⇌ Zn²+ + 2 H₂O		11.76 ± 0.04
γ-Zn₂ + 2 H⁺ ⇌ Zn²⁺ + 2 H₂O		11.70 ± 0.04
δ-Zn₂ + 2 H⁺ ⇌ Zn²⁺ + 2 H₂O		11.81 ± 0.04

Zirconium

Hydrolysis constants 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 ⇌ Zr₂²⁺ + 2 H⁺	*	0.98 ± 1.06*	−0.18 ± 0.17*
Zr⁴⁺ + 3 H₂O ⇌ Zr₃⁺ + 3 H⁺
Zr⁴⁺ + 4 H₂O ⇌ Zr₄ + 4 H⁺	–9.7*	–2.19 ± 0.70*	−4.53 ± 0.37*
Zr⁴⁺ + 5 H₂O ⇌ Zr₅^– + 5 H⁺	–16.0
Zr⁴⁺ + 6 H₂O ⇌ Zr₆^2– + 6 H⁺		–29± 0.70	–30.5 ± 0.3
3 Zr⁴⁺ + 4 H₂O ⇌ Zr₃₄⁸⁺ + 4 H⁺	–0.6	0.4 ± 0.3	0.90 ± 0.18
3 Zr⁴⁺ + 5 H₂O ⇌ Zr₃₅⁷⁺ + 5 H⁺	3.70
3 Zr⁴⁺ + 9 H₂O ⇌ Zr₃₉³⁺ + 9 H⁺		12.19 ± 0.20	12.19 ± 0.20
4 Zr⁴⁺ + 8 H₂O ⇌ Zr₄₈⁸⁺ + 8 H⁺	6.0	6.52 ± 0.05	6.52 ± 0.05
4 Zr⁴⁺ + 15 H₂O ⇌ Zr₄₁₅⁺ + 15 H⁺		12.58± 0.24
4 Zr⁴⁺ + 16 H₂O ⇌ Zr₄₁₆ + 16 H⁺		8.39± 0.80
ZrO₂ + 4 H⁺ ⇌ Zr⁴⁺ + 2 H₂O	–1.9*		–5.37 ± 0.42*
ZrO₂ + 4 H⁺ ⇌ Zr⁴⁺ + 2 H₂O		–7 ± 1.6
ZrO₂ + 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.