Hydrolysis constant

Last updated November 22, 2024

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.

Contents

Metal hydrolysis and associated equilibrium constant values

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

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

and the corresponding formation constant as:

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

and associated equilibria can be written as:

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

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

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

Aluminium

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


Reaction	Baes and Mesmer, 1976^[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)₆₄^4‒ + 4 H⁺	20.34	20.34
12 Sb(OH)₅ + 5 H₂O ⇌ Sb₁₂(OH)₆₅^5‒ + 5 H⁺	16.72	16.72
12 Sb(OH)₅ + 6 H₂O ⇌ Sb₁₂(OH)₆₆^6‒ + 6 H⁺	11.89	11.89
12 Sb(OH)₅ + 7 H₂O ⇌ Sb₁₂(OH)₆₇^7‒ + 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
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 (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)₄^2– + 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
BiO_1.5(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)₄^2– + 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)₄^2– + 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 ⇌ 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
CrO_1.5(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]
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 (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)₄^2– + 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)₄^2– + 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^–	$\approx$ –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)₂^2– + H⁺ ⇌ GeO(OH)₃^–			12.76
8 Ge(OH)₄ ⇌ Ge₈O₁₆(OH)₃^3- + 13 H₂O + 3 H⁺	–14.24
8 Ge(OH)₄ + 3 OH^– ⇌ Ge₈(OH)₃₅^3–			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)₅^2– + 2 H⁺	–25.13
Au(OH)₅^2– + 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 lepidocrocite			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)₄^2- + 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)₆^2–	–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)₄^2– + 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⁺	−5.0^a	−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]
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(OH)^5– + 4 H₂O	62.14^a			58.90 ± 0.02
7 MoO₄^2– + 10 H⁺ ⇌ Mo₇O₂₂(OH)₂^4– + 4 H₂O	65.68^a			64.63 ± 0.05
7 MoO₄^2– + 11 H⁺ ⇌ Mo₇O₂₁(OH)₃^3– + 4 H₂O	68.21^a			68.68 ± 0.06
19 MoO₄^2- + 34 H⁺ ⇌ Mo₁₉O₅₉^4– + 17 H₂O	196.3^a		196^a
MoO₃(s) + H₂O ⇌ MoO₄^2– + 2 H⁺	–12.06^a

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)₄^2- + 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)₄^2– + 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
Nb₆O₁₉^8– + H⁺ ⇌ HNb₆O₁₉^7–		14.95
HNb₆O₁₉^7– + H⁺ ⇌ H₂Nb₆O₁₉^6–		13.23
H₂Nb₆O₁₉^6– + H⁺ ⇌ H₃Nb₆O₁₉^5–		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)₄^2– + 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	12.2^a
OsO₂(OH)₂(O^-)₂aq + H⁺ ⇌ OsO₂(OH)₃(O^-)aq	14.4^b

(^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
ScO_1.5(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^– ⇌ Se^2– + 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]
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 (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]
SeO₄^2‒ + 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)₂^2– + 2 H⁺	–22.92	–23.14 ± 0.09
4 Si(OH)₄ ⇌ Si₄O₆(OH)₆^4– + 2 H⁺ + 4 H₂O	–13.44
4 Si(OH)₄ ⇌ Si₄O₈(OH)₄^4– + 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, 2019^a^[123]
Ta(OH)₅ + H⁺ ⇌ Ta(OH)₄⁺ + H₂O	~1	0.7007
Ta(OH)₅ + H₂O ⇌ Ta(OH)₆^– + H⁺	~ –9.6
Ta₆O₁₉^8– + H⁺ ⇌ HTa₆O₁₉^7–		16.35
HTa₆O₁₉^7– + H⁺ ⇌ H₂Ta₆O₁₉^6–		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, 2019^a^[124]
Te^2‒ + 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, 2019^a^[124]
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⁺ ⇌ 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, 2019^a^[124]
TeO₂(OH)₄^2‒ + H⁺ ⇌ TeO(OH)₅^‒		10.83
TeO(OH)₅^‒ + H⁺ ⇌ Te(OH)₆	7.68	7.696
TeO₂(OH)₄^2‒ + 2 H⁺ ⇌ Te(OH)₆	18.68
TeO₃(OH)₃^3‒ + 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)₆^2– + 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)₆^2– + 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]
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 (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)₄^2– + 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)₂^4– + 14 H⁺	–10.7
VO₂(OH)₂^– ⇌ VO₃(OH)^2– + H⁺	–8.55
2 VO₂(OH)₂^– ⇌ V₂O₆(OH)₂^3– + H⁺ + H₂O	–6.53
VO₃(OH)^2– ⇌ VO₄^3– + H⁺	–14.26
2 VO₃(OH)^2– ⇌ V₂O₇^4– + H₂O	0.56
3 VO₃(OH)^2– + 3 H⁺⇌ V₃O₉^3– + 3 H₂O	31.81
V₁₀O₂₆(OH)₂^4– ⇌ V₁₀O₂₇(OH)^5– + 3 H⁺	–3.6
V₁₀O₂₇(OH)^5– ⇌ V₁₀O₂₈^6– + H⁺	–6.15
VO₂⁺ + H₂O ⇌ VO₂OH + H⁺		–3.25 ± 0.1
VO₂⁺ + 3 H₂O ⇌ VO₂(OH)₃^2- + 3 H⁺		–15.74 ± 0.19
VO₂⁺ + 4 H₂O ⇌ VO₂(OH)₄^3- + 4 H⁺		–30.03 ± 0.24
2 VO₂⁺ + 4 H₂O ⇌ (VO₂)₂(OH)₄^2- + 4 H⁺		–11.66 ± 0.53
2 VO₂⁺ + 5 H₂O ⇌ (VO₂)₂(OH)₅^3- + 5 H⁺		–20.91 ± 0.22
2 VO₂⁺ + 6 H₂O ⇌ (VO₂)₂(OH)₆^4- + 6 H⁺		–32.43 ± 0.30
4 VO₂⁺ + 8 H₂O ⇌ (VO₂)₄(OH)8^4- + 8 H⁺		–20.78 ± 0.33
4 VO₂⁺ + 9 H₂O ⇌ (VO₂)₄(OH)₉^5- + 9 H⁺		–31.85 ± 0.26
4 VO₂⁺ + 10 H₂O ⇌ (VO₂)₄(OH)₁₀^6- + 10 H⁺		–45.85 ± 0.26
5 VO₂⁺ + 10 H₂O ⇌ (VO₂)₅(OH)₁₀^5- + 10 H⁺		–27.02 ± 0.34
10 VO₂⁺ + 14 H₂O ⇌ (VO₂)₁₀(OH)₁₄^4- + 14 H⁺		–10.5 ± 0.3
10 VO₂⁺ + 15 H₂O ⇌ (VO₂)₁₀(OH)₁₅^5- + 15 H⁺		–15.73 ± 0.33
10 VO₂⁺ + 16 H₂O ⇌ (VO₂)₁₀(OH)₁₆^6- + 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)₄^2- + 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 ⇌ Zn₂(OH)₆^2- + 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)₆^2– + 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.

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Conductivity or specific conductance of an electrolyte solution is a measure of its ability to conduct electricity. The SI unit of conductivity is siemens per meter (S/m).

In theoretical chemistry, Specific ion Interaction Theory is a theory used to estimate single-ion activity coefficients in electrolyte solutions at relatively high concentrations. It does so by taking into consideration interaction coefficients between the various ions present in solution. Interaction coefficients are determined from equilibrium constant values obtained with solutions at various ionic strengths. The determination of SIT interaction coefficients also yields the value of the equilibrium constant at infinite dilution.

Equilibrium chemistry is concerned with systems in chemical equilibrium. The unifying principle is that the free energy of a system at equilibrium is the minimum possible, so that the slope of the free energy with respect to the reaction coordinate is zero. This principle, applied to mixtures at equilibrium provides a definition of an equilibrium constant. Applications include acid–base, host–guest, metal–complex, solubility, partition, chromatography and redox equilibria.

In chemistry, metal aquo complexes are coordination compounds containing metal ions with only water as a ligand. These complexes are the predominant species in aqueous solutions of many metal salts, such as metal nitrates, sulfates, and perchlorates. They have the general stoichiometry [M(H₂O)_n]^z+. Their behavior underpins many aspects of environmental, biological, and industrial chemistry. This article focuses on complexes where water is the only ligand, but of course many complexes are known to consist of a mix of aquo and other ligands.

A metal ion in aqueous solution or aqua ion is a cation, dissolved in water, of chemical formula [M(H₂O)_n]^z+. The solvation number, n, determined by a variety of experimental methods is 4 for Li⁺ and Be²⁺ and 6 for most elements in periods 3 and 4 of the periodic table. Lanthanide and actinide aqua ions have higher solvation numbers (often 8 to 9), with the highest known being 11 for Ac³⁺. The strength of the bonds between the metal ion and water molecules in the primary solvation shell increases with the electrical charge, z, on the metal ion and decreases as its ionic radius, r, increases. Aqua ions are subject to hydrolysis. The logarithm of the first hydrolysis constant is proportional to z²/r for most aqua ions.

Reed McNeil Izatt was an American chemist who was emeritus Charles E. Maw Professor of Chemistry at Brigham Young University in Provo, Utah. His field of research was macrocyclic chemistry and metal separation technologies.

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