Hydrolysis constant explained

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

Metal hydrolysis and associated equilibrium constant values

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

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

and the corresponding formation constant as:

\beta _{pq} = ([M _{p(OH)} ^{(pz - q)} ^{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]

Al^3+ + H2O ⇌ AlOH^2+ + H^+	–4.97	−4.98 ± 0.02	−4.98 ± 0.02
Al^3+ + 2 H2O ⇌ Al(OH)2^+ + 2 H^+	–9.3	−10.63 ± 0.09	−10.63 ± 0.09
Al^3+ + 3 H2O ⇌ Al(OH)3 + 3 H^+	–15.0	−15.66 ± 0.23	−15.99 ± 0.23
Al^3+ + 4 H2O ⇌ Al(OH)4^– + 4 H^+	–23.0	−22.91 ± 0.10	−22.91 ± 0.10
2 Al^3+ + 2 H2O ⇌ Al2(OH)2^4+ + 2 H^+	–7.7	−7.62 ± 0.11	−7.62 ± 0.11
3 Al^3+ + 4 H2O ⇌ Al3(OH)4^5+ + 4 H^+	–13.94	−14.06 ± 0.22	−13.90 ± 0.12
13 Al^3+ + 28 H2O ⇌ Al13O4(OH)24^7+ + 32 H^+	–98.73	−100.03 ± 0.09	−100.03 ± 0.09
α-Al(OH)3(s) + 3 H^+ ⇌ Al^3+ + 3 H2O	8.5	7.75 ± 0.08	7.75 ± 0.08
γ-AlOOH(s) + 3 H^+ ⇌ Al^3+ + 2 H2O		7.69 ± 0.15	9.4 ± 0.4

Americium(III)

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

!Reaction!NIST46!Brown and Ekberg, 2016^[4] !Grenthe et al, 2020

Am^3+ + H2O ⇌ Am(OH)^2+ + H^+	–6.5 ± 0.1	–7.22 ± 0.03	–7.2 ± 0.5
Am^3+ + 2 H2O ⇌ Am(OH)2^+ + 2 H^+	–14.1 ± 0.3	–14.9 ± 0.2	–15.1 ± 0.7
Am^3+ + 3 H2O ⇌ Am(OH)3 + 3 H^+	–25.7	–26.0 ± 0.2	–26.2 ± 0.5
Am^3+ + 3 H2O ⇌ Am(OH)3(am) + 3 H^+	–16.9 ± 0.1	–16.9 ± 0.8	–16.9 ± 0.8
Am^3+ + 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^[5] !Grenthe et al, 2020

AmO2^+ + H2O ⇌ AmO2(OH) + H^+	–10.7 ± 0.2
AmO2^+ + 2 H2O ⇌ AmO2(OH)2^– + 2 H^+	–22.9 ± 0.7
AmO2^+ + H2O ⇌ AmO2(OH)(am) + H^+	–5.4 ± 0.4	–5.3 ± 0.5

Antimony(III)

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

!Reaction!Baes and Mesmer, 1976^[6] !Lothenbach et al., 1999;^[7] Kitamura et al., 2010^[8] !Filella and May, 2003^[9]

Sb(OH)3 + H^+ ⇌ Sb(OH)2^+ + H2O	1.41	1.30	1.371
Sb(OH)3 + H2O ⇌ Sb(OH)4^‒ + H^+	‒11.82	‒11.93	‒11.70
0.5 Sb2O3(s) + 1.5 H2O ⇌ Sb(OH)3	‒4.24
Sb2O3(rhombic,s) + 3 H2O ⇌ 2 Sb(OH)3		‒8.72	‒10.00
Sb2O3(cubic,s) + 3 H2O ⇌ 2 Sb(OH)3			‒11.40

Antimony(V)

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

!Reaction!Baes and Mesmer, 1976!Lothenbach et al., 1999; Kitamura et al., 2010

Sb(OH)5 + H2O ⇌ Sb(OH)6^‒ + H^+	‒2.72	‒2.72
12 Sb(OH)5 + 4 H2O ⇌ Sb12(OH)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^[10] !Nordstrom and Archer, 2003^[11] !Nordstrom et al., 2014^[12]

As(OH)4^‒ + H^+ ⇌ As(OH)3 + H2O

9.29

9.17

9.24 ± 0.02

Arsenic(V)

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

!Reaction!Baes and Mesmer!Khodakovsky et al. (1968)^[13] !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 (log values) in critical compilations at infinite dilution and T = 298.15 K:

!Reaction!Baes and Mesmer, 1976^[14] !Nordstrom et al., 1990^[15] !Brown and Ekberg, 2016^[16]

Ba^2+ + 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^[17]

Bk^3+ + 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^[18]

Be^2+ + H2O ⇌ BeOH^+ + H^+	–5.10
Be^2+ + 2 H2O ⇌ Be(OH)2 + 2 H^+	–23.65
Be^2+ + 3 H2O ⇌ Be(OH)3^– + 3 H^+	–23.25
Be^2+ + 4 H2O ⇌ Be(OH)4^2– + 4 H^+	–37.42
2 Be^2+ + H2O ⇌ Be2OH^3+ + H^+	–3.97
3 Be^2+ + 3 H2O ⇌ Be3(OH)3^3+ + 3 H^+	–8.92
6 Be^2+ + 8 H2O ⇌ Be6(OH)8^4+ + 8 H^+	–27.2
α-Be(OH)2(cr) + 2 H^+ ⇌ Be^2+ + 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^[19] !Lothenbach et al., 1999!NIST46^[20] !Kitamura et al., 2010!Brown and Ekberg, 2016^[21]

Bi^3+ + H2O ⇌ BiOH^2+ + H^+	–1.0	–0.92	–1.1	–0.920	–0.92 ± 0.15
Bi^3+ + 2 H2O ⇌ Bi(OH)2^+ + 2 H^+	(–4)	–2.56	–4.5	–2.560 ± 1.000	–2.59 ± 0.26
Bi^3+ + 3 H2O ⇌ Bi(OH)3 + 3 H^+	–8.86	–5.31	–9.0	–8.940 ± 0.500	–8.78 ± 0.20
Bi^3+ + 4 H2O ⇌ Bi(OH)4^– + 4 H^+	–21.8	–18.71	–21.2	–21.660 ± 0.870	–22.06 ± 0.14
3 Bi^3+ + 4 H2O ⇌ Bi3(OH)4^5+ + 4 H^+		–0.80		–0.800
6 Bi^3+ + 12 H2O ⇌ Bi6(OH)12^6+ + 12 H^+		1.34		1.340	0.98 ± 0.13
9 Bi^3+ + 20 H2O = Bi9(OH)20^7+ + 20 H^+		–1.36		–1.360
9 Bi^3+ + 21 H2O = Bi9(OH)21^6+ + 21 H^+		–3.25		–3.250
9 Bi^3+ + 22 H2O = Bi9(OH)22^5+ + 22 H^+		–4.86		–4.860
Bi(OH)3(am) + 3 H^+ = Bi^3+ + 3 H2O				31.501 ± 0.927
α-Bi2O3(cr) + 6 H^+ = 2 Bi^3+ + 3 H2O		0.76
BiO1.5(s, α) + 3 H^+ = Bi^3+ + 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^[22] !NIST46

B(OH)3 + H2O ⇌ Be(OH)4^+ + H^+	–9.236	–9.236 ± 0.002
2 B(OH)3 ⇌ B2(OH)5^– + H^+	–9.36	–9.306
3 B(OH)3 ⇌ B3O3(OH)4^– + H^+ + 2 H2O	–7.03	–7.306
4 B(OH)3 ⇌ B4O5(OH)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^[23] !Powell et al., 2011^[24] !Brown and Ekberg, 2016^[25]

Cd^2+ + H2O ⇌ CdOH^+ + H^+	−10.08	–9.80 ± 0.10	−9.81 ± 0.10
Cd^2+ + 2 H2O ⇌ Cd(OH)2 + 2 H^+	–20.35	–20.19 ± 0.13	−20.6 ± 0.4
Cd^2+ + 3 H2O ⇌ Cd(OH)3^– + 3 H^+	<–33.3	–33.5 ± 0.5	−33.5 ± 0.5
Cd^2+ + 4 H2O ⇌ Cd(OH)4^2– + 4 H^+	–47.35	–47.28 ± 0.15	−47.25 ± 0.15
2 Cd^2+ + H2O ⇌ Cd2OH^3+ + H^+	–9.390	–8.73 ± 0.01	−8.74 ± 0.10
4 Cd^2+ + 4 H2O ⇌ Cd4(OH)4^4+ + H^+	–32.85
Cd(OH)2(s) ⇌ Cd^2+ + 2 OH^–		–14.28 ± 0.12
Cd(OH)2(s) + 2 H^+ ⇌ Cd^2+ + 2 H2O	13.65	13.72 ± 0.12	13.71 ± 0.12

Calcium

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

!Reaction!Baes and Mesmer, 1976!Nordstrom et al., 1990!Brown and Ekberg, 2016^[26]

Ca^2+ + H2O ⇌ CaOH^+ + H^+	–12.85	–12.78	–12.57 ± 0.03
Ca(OH)2(cr) + 2 H^+ ⇌ Ca^2+ + 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

Cf^3+ + 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^[27] !NIST46!Brown and Ekberg, 2016^[28]

Ce^3+ + H2O ⇌ CeOH^2+ + H^+	–8.3	–8.3	–8.31 ± 0.03
2 Ce^3+ + 2 H2O ⇌ Ce2(OH)2^4+ + 2 H^+			–16.0 ± 0.2
3 Ce^3+ + 5 H2O ⇌ Ce3(OH)5^4+ + 5 H^+			–34.6 ± 0.3
Ce(OH)3(s) + 3 H^+ ⇌ Ce^3+ + 3 H2O			18.5 ± 0.5
Ce(OH)3(s) ⇌ Ce^3+ + 3 OH^–		–22.1 ± 0.9

Chromium(II)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K (The divalent state is unstable in water, producing hydrogen whilst being oxidised to a higher valency state (Baes and Mesmer, 1976). The reliability of the data is in doubt.):

!Reaction!NIST46!Ball and Nordstrom, 1988^[29]

Cr^2+ + H2O ⇌ CrOH^+ + H^+	–5.5
Cr(OH)2(s) ⇌ Cr^2+ + 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^[30] !Rai et al., 1987^[31] !Ball and Nordstrom, 1988!Brown and Ekberg, 2016^[32]

Cr^3+ + H2O ⇌ CrOH^2+ + H^+	–4.0	–3.57 ± 0.08		–3.60 ± 0.07
Cr^3+ + 2 H2O ⇌ Cr(OH)2^+ + 2 H^+	–9.7	–9.84		–9.65 ± 0.20
Cr^3+ + 3 H2O ⇌ Cr(OH)3 + 3 H^+	–18	–16.19		–16.25 ± 0.19
Cr^3+ + 4 H2O ⇌ Cr(OH)4^- + 4 H^+	–27.4	–27.65 ± 0.12		–27.56 ± 0.21
2 Cr^3+ + 2 H2O ⇌ Cr2(OH)2^4+ + 2 H^+	–5.06	–5.0		–5.29 ± 0.16
3 Cr^3+ + 4 H2O ⇌ Cr3(OH)4^5+ + 4 H^+	–8.15	–10.75 ± 0.15		–9.10 ± 0.14
Cr(OH)3(s) + 3 H^+ ⇌ Cr^3+ + 3 H2O	12		9.35	9.41 ± 0.17
Cr2O3(s) + 6 H^+ ⇌ 2 Cr^3+ + 3 H2O			8.52
CrO1.5(s) + 3 H^+ ⇌ Cr^3+ + 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^[33] !Ball and Nordstrom, 1998

CrO4^2– + H^+ ⇌ HCrO4^–	6.51	6.55 ± 0.04
HCrO4^– + H^+ ⇌ H2CrO4	–0.20
CrO4^2– + 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^[34] !Brown and Ekberg, 2016^[35]

Co^2+ + H2O ⇌ CoOH^+ + H^+	–9.65	−9.61 ± 0.17
Co^2+ + 2 H2O ⇌ Co(OH)2 + 2 H^+	–18.8	−19.77 ± 0.11
Co^2+ + 3 H2O ⇌ Co(OH)3^– + 3 H^+	–31.5	−32.01 ± 0.33
Co^2+ + 4 H2O ⇌ Co(OH)4^2– + 4 H^+	–46.3
2 Co^2+ + H2O ⇌ Co2(OH)3^+ + H^+	–11.2
4 Co^2+ + 4 H2O ⇌ Co4(OH)4^4+ + 4H^+	–30.53
Co(OH)2(s) + 2 H^+ ⇌ Co^2+ + 2 H2O	12.3	13.24 ± 0.12
CoO(s) + 2 H^+ ⇌ Co^2+ + 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^[36]

Co^3+ + H2O ⇌ CoOH^2+ + 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^[37]

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^[38] !NIST46!Plyasunova et al., 1997^[39] !Powell et al., 2007^[40] !Brown and Ekberg, 2016

Cu^2+ + H2O ⇌ CuOH^+ + H^+	< –8	–7.7	–7.97 ± 0.09	–7.95 ± 0.16	–7.64 ± 0.17
Cu^2+ + 2 H2O ⇌ Cu(OH)2 + 2 H^+	(< –17.3)	–17.3	–16.23 ± 0.15	–16.2 ± 0.2	–16.24 ± 0.03
Cu^2+ + 3 H2O ⇌ Cu(OH)3^– + 3 H^+	(< –27.8)	–27.8	–26.63 ± 0.40	–26.60 ± 0.09	–26.65 ± 0.13
Cu^2+ + 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 Cu^2+ + H2O ⇌ Cu2(OH)3^+ + H^+			–6.71 ± 0.30	–6.40 ± 0.12	–6.41 ± 0.17
2 Cu^2+ + 2 H2O ⇌ Cu2(OH)2^2+ + 2 H^+	–10.36	–10.3	–10.55 ± 0.17	–10.43 ± 0.07	–10.55 ± 0.02
3 Cu^2+ + 4 H2O ⇌ Cu3(OH)4^2+ + 4 H^+			–20.95 ± 0.30	–21.1 ± 0.2	–21.2 ± 0.4
CuO(s) + 2 H^+ ⇌ Cu^2+ + H2O	7.62		7.64 ± 0.06	7.64 ± 0.06	7.63 ± 0.05
Cu(OH)2(s) + 2 H^+ ⇌ Cu^2+ + 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^[41]

Cm^3+ + H2O ⇌ Cm(OH)^2+ + H^+	−7.66 ± 0.07
Cm^3+ + 2 H2O ⇌ Cm(OH)2^+ + 2 H^+	−15.9 ± 0.1
Cm^3+ + 3 H2O ⇌ Cm(OH)3(s) + 3 H^+	−13.9 ± 0.4

Dysprosium

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

!Reaction!Baes and Mesmer, 1976!Brown and Ekberg, 2016^[42]

Dy^3+ + H2O ⇌ DyOH^2+ + H^+	−8.0	−7.53 ± 0.14
Dy^3+ + 2 H2O ⇌ Dy(OH)2^+ + 2 H^+	(–16.2)
Dy^3+ + 3 H2O ⇌ Dy(OH)3 + 3 H^+	(–24.7)
Dy^3+ + 4 H2O ⇌ Dy(OH)4^− + 4 H^+	–33.5
2 Dy^3+ + 2 H2O ⇌ Dy2(OH)2^4+ + 2 H^+		−13.76 ± 0.20
3 Dy^3+ + 5 H2O ⇌ Dy3(OH)5^4+ + 5 H^+		−30.6 ± 0.3
Dy(OH)3(s) + 3 H^+ ⇌ Dy^3+ + 3 H2O	15.9	16.26 ± 0.30
Dy(OH)3(c) + OH^− ⇌ Dy(OH)4^−	−3.6
Dy(OH)3(c) ⇌ Dy(OH)3	−8.8

Erbium

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

!Reaction!Baes and Mesmer, 1976!Brown and Ekberg, 2016^[43]

Er^3+ + H2O ⇌ ErOH^2+ + H^+	−7.9	−7.46 ± 0.09
Er^3+ + 2 H2O ⇌ Er(OH)2^+ + 2 H^+	(−15.9)
Er^3+ + 3 H2O ⇌ Er(OH)3 + 3 H^+	(−24.2)
Er^3+ + 4 H2O ⇌ Er(OH)4^− + 4 H^+	−32.6
2 Er^3+ + 2 H2O ⇌ Er2(OH)2^4+ + 2 H^+	−13.65	−13.50 ± 0.20
3 Er^3+ + 5 H2O ⇌ Er3(OH)5^4+ + 5 H^+	<−29.3	−31.0 ± 0.3
Er(OH)3(s) + 3 H^+ ⇌ Er^3+ + 3 H2O	15.0	15.79 ± 0.30
Er(OH)3(c) + OH^− ⇌ Er(OH)4^−	−3.6
Er(OH)3(c) ⇌ Er(OH)3	~ −9.2

Europium

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

!Reaction!Baes and Mesmer, 1976!NIST46!Hummel et al., 2002!Brown and Ekberg, 2016

Eu^3+ + H2O ⇌ EuOH^2+ + H^+	–7.8		–7.64 ± 0.04	–7.66 ± 0.05
Eu^3+ + 2 H2O ⇌ Eu(OH)2^+ + 2 H^+			–15.1 ± 0.2
Eu^3+ + 3 H2O ⇌ Eu(OH)3 + 3 H^+			–23.7 ± 0.1
Eu^3+ + 4 H2O ⇌ Eu(OH)4^− + 4 H^+			–36.2 ± 0.5
2 Eu^3+ + 2 H2O ⇌ Eu2(OH)2^4+ + 2 H^+			-	–14.1 ± 0.2
3 Eu^3+ + 5 H2O ⇌ Eu3(OH)5^4+ + 5 H^+			-	–32.0 ± 0.3
Eu(OH)3(s) + 3 H^+ ⇌ Eu^3+ + 3 H2O	17.5		17.6 ± 0.8 (am)14.9 ± 0.3 (cr)	16.48 ± 0.30
Eu(OH)3(s) ⇌ Eu^3+ + 3 OH^–		–24.5 ± 0.7 (am)–26.5 (cr)

Gadolinium

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

!Reaction!Baes and Mesmer, 1976!Brown and Ekberg, 2016^[44]

Gd^3+ + H2O ⇌ GdOH^2+ + H^+	–8.0	–7.87 ± 0.05
Gd^3+ + 2 H2O ⇌ Gd(OH)2^+ + 2 H^+	(–16.4)
Gd^3+ + 3 H2O ⇌ Gd(OH)3 + 3 H^+	(–25.2)
Gd^3+ + 4 H2O ⇌ Gd(OH)4^– + 4 H^+	–34.4
2 Gd^3+ + 2 H2O ⇌ Gd2(OH)2^4+ + 2 H^+		–14.16 ± 0.20
3 Gd^3+ + 5 H2O ⇌ Gd3(OH)5^4+ + 5 H^+		–33.0 ± 0.3
Gd(OH)3(s) + 3 H^+ ⇌ Gd^3+ + 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^[45] !Smith et al., 2003^[46] !Brown and Ekberg, 2016^[47]

Ga^3+ + H2O ⇌ GaOH^2+ + H^+	–2.6	–2.897	–2.74
Ga^3+ + 2 H2O ⇌ Ga(OH)2^+ + 2 H^+	–5.9	–6.694	–7.0
Ga^3+ + 3 H2O ⇌ Ga(OH)3 + 3 H^+	–10.3		–11.96
Ga^3+ + 4 H2O ⇌ Ga(OH)4^– + 4 H^+	–16.6	–16.588	–15.52
Ga(OH)3(s) ⇌ Ga^3+ + 3 OH^–	≈ –37	–37.0
GaO(OH)(s) + H2O ⇌ Ga^3+ + 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^[48] !Wood and Samson, 2006^[49] !Filella and May, 2023^[50]

Ge(OH)4 ⇌ GeO(OH)3^- + H^+	–9.31	–9.32 ± 0.05	–9.099
Ge(OH)4 ⇌ GeO2(OH)2^2+ + 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^[51]

Au(OH)3 +2 H^+ ⇌ AuOH^2+ + 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)6^3– + 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^[52] !Brown and Ekberg, 2016^[53]

Hf^4+ + H2O ⇌ HfOH^3+ + H^+	–0.25	−0.26 ± 0.10
Hf^4+ + 2 H2O ⇌ Hf(OH)2^2+ + 2 H^+	(–2.4)
Hf^4+ + 3 H2O ⇌ Hf(OH)3^+ + 3 H^+	(–6.0)
Hf^4+ + 4 H2O ⇌ Hf(OH)4 + 4 H^+	–10.7*	−3.75 ± 0.34*
Hf^4+ + 5 H2O ⇌ Hf(OH)5^– + 5 H^+	–17.2
3 Hf^4+ + 4 H2O ⇌ Hf3(OH)4^8+ + 4 H^+		0.55 ± 0.30
4 Hf^4+ + 8 H2O ⇌ Hf4(OH)8^8+ + 8 H^+		6.00 ± 0.30
HfO2(s) + 4 H^+ ⇌ Hf^4+ + 2 H2O	–1.2*	–5.56 ± 0.15*
HfO2(am) + 4 H^+ ⇌ Hf^4+ + 2 H2O		–3.11 ± 0.20

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

Holmium

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

!Reaction!Baes and Mesmer, 1976!Brown and Ekberg, 2016^[54]

Ho^3+ + H2O ⇌ HoOH^2+ + H^+	−8.0	−7.43 ± 0.05
2 Ho^3+ + 2 H2O ⇌ Ho2(OH)2^4+ + 2 H^+		−13.5 ± 0.2
3 Ho^3+ + 5 H2O ⇌ Ho3(OH)5^4+ + 5 H^+		−30.9 ± 0.3
Ho(OH)3(s) + 3 H^+ ⇌ Ho^3+ + 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^[55] !NIST46!Brown and Ekberg, 2016^[56]

In^3+ + H2O ⇌ InOH^2+ + H^+	–4.00	–3.927	–3.96
In^3+ + 2 H2O ⇌ In(OH)2^+ + 2 H^+	–7.82	–7.794	–9.16
In^3+ + 3 H2O ⇌ In(OH)3 + 3 H^+	–12.4	–12.391
In^3+ + 4 H2O ⇌ In(OH)4^– + 4 H^+	–22.07	–22.088	–22.05
In(OH)3(s) ⇌ In^3+ + 3 OH^–	–36.92	–36.9	–36.92
1/2 In2O3(s) + 3/2 H2O ⇌ In^3+ + 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^[57]

Ir^3+ + H2O ⇌ IrOH^2+ + H^+	‒3.77 ± 0.10
Ir^3+ + 2 H2O ⇌ Ir(OH)2^+ + 2 H^+	‒8.46 ± 0.20
Ir(OH)3(s) + 3 H^+ ⇌ Ir^3+ + 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^[58] !Nordstrom et al., 1990!Hummel et al., 2002!Lemire et al., 2013^[59] !Brown and Ekberg, 2016^[60]

Fe^2+ + H2O ⇌ FeOH^+ + H^+	–9.3	–9.5	–9.5	–9.1 ± 0.4	−9.43 ± 0.10
Fe^2+ + 2 H2O ⇌ Fe(OH)2 + 2 H^+	–20.5				−20.52 ± 0.08
Fe^2+ + 3 H2O ⇌ Fe(OH)3^- + 3 H^+	–29.4				−32.68 ± 0.15
Fe(OH)2(s) +2 H^+ ⇌ Fe^2+ + 2 H2O					12.27 ± 0.88

Iron(III)

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

!Reaction!Baes and Mesmer, 1976!Lemire et al., 2013!Brown and Ekberg, 2016^[61]

Fe^3+ + H2O ⇌ FeOH^2+ + H^+	–2.19	−2.15 ± 0.07	–2.20 ± 0.02
Fe^3+ + 2 H2O ⇌ Fe(OH)2^+ + 2 H^+	–5.67	−4.8 ± 0.4	–5.71 ± 0.10
Fe^3+ + 3 H2O ⇌ Fe(OH)3 + 3 H^+	<–12	<–14	–12.42 ± 0.20
Fe^3+ + 4 H2O ⇌ Fe(OH)4^– + 4 H^+	–21.6	−21.5 ± 0.5	–21.60 ± 0.23
2 Fe^3+ + 2 H2O ⇌ Fe2(OH)2^4+ + 2 H^+	–2.95	–2.91 ± 0.07	–2.91 ± 0.07
3 Fe^3+ + 4 H2O ⇌ Fe3(OH)4^5+ + 4 H^+	–6.3		−6.3 ± 0.1
Fe(OH)3(s) +3 H^+ ⇌ Fe3^+ + 3 H2O2-line ferrihydrite	2.5	3.5	3.50 ± 0.20
Fe(OH)3(s) ⇌ Fe^3+ + 3 OH^−6-line ferrihydrite		−38.97 ± 0.64
α-FeOOH(s)+ 3 H^+ ⇌ Fe^3+ + 2 H2Ogoethite	0.5		0.33 ± 0.10
α-FeOOH + H2O ⇌ Fe^3+ + 3 OH^−goethite		−41.83 ± 0.37
0.5 α-Fe2O3(s)+ 3 H^+ ⇌ Fe^3+ + 1.5 H2Ohematite			0.36 ± 0.40
0.5 α-Fe2O3 + 1.5 H2O ⇌ Fe^3+ + 3 OH^−hematite		−42.05 ± 0.26
0.5 γ-Fe2O3(s) + 3 H^+ ⇌ Fe^3+ + 1.5 H2Omaghemite			1.61 ± 0.61
0.5 γ-Fe2O3 + 1.5 H2O ⇌ Fe^3+ + 3 OH^−maghemite		−40.59 ± 0.29
α-FeOOH(s)+ 3 H^+ ⇌ Fe^3+ + 2 H2Olepidocrocite			1.85 ± 0.37
γ-FeOOH + H2O ⇌ Fe^3+ + 3 OH^−lepidocrocite		−40.13 ± 0.37
Fe(OH)3(s) + 3 H^+ ⇌ Fe^3+ + 3 H2Omagnetite			−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^[62] !Brown and Ekberg, 2016

La^3+ + H2O ⇌ LaOH^2+ + H^+	–8.5	–8.89 ± 0.10
2 La^3+ + 2 H2O ⇌ La2(OH)2^4+ + 2 H^+	≤ –17.5	–17.57 ± 0.20
3 La^3+ + 5 H2O ⇌ La3(OH)5^4+ + 5 H^+	≤ –38.3	–37.8 ± 0.3
5 La^3+ + 9 H2O ⇌ La5(OH)9^6+ + 9 H^+	–71.2
La(OH)3(s) + 3 H^+ ⇌ La^3+ + 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^[63] !NIST46!Powell et al, 2009^[64] !Brown and Ekberg, 2016!Cataldo et al., 2018^[65]

Pb^2+ + H2O ⇌ PbOH+ + H^+	–7.71	–7.6	–7.46 ± 0.06	–7.49 ± 0.13	–6.47± 0.03
Pb^2+ + 2 H2O ⇌ Pb(OH)2 + 2 H^+	–17.12	–17.1	–16.94 ± 0.09	–16.99 ± 0.06	–16.12 ± 0.01
Pb^2+ + 3 H2O ⇌ Pb(OH)^3- + 3 H^+	–28.06	–28.1	–28.03± 0.06	–27.94 ± 0.21	–28.4 ± 0.1
Pb^2+ + 4 H2O ⇌ Pb(OH)4^2- + 4 H^+			–40.8
2 Pb^2+ + H2O ⇌ Pb2(OH)3^+ + H^+	–6.36	–6.4	–7.28± 0.09	–6.73 ± 0.31
3 Pb^2+ + 4 H2O ⇌ Pb3(OH)4^2+ + 4 H^+	–23.88	–23.9	–23.01 ± 0.07	–23.43 ± 0.10
3 Pb^2+ + 5 H2O ⇌ Pb3(OH)5^+ + 5 H^+				–31.11 ± 0.10
4 Pb^2+ + 4 H2O ⇌ Pb4(OH)4^4+ + 4 H^+	–20.88	–20.9	–20.57± 0.06	–20.71 ± 0.18
6 Pb^2+ + 8 H2O ⇌ Pb6(OH)8^4+ + 8 H^+	–43.61	–43.6	–42.89± 0.07	–43.27 ± 0.47
PbO(s) + 2 H^+ ⇌ Pb^2+ + H2O			12.62 (red)12.90 (yellow)
PbO(s) +H2O ⇌ Pb^2+ + 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 Pb^2+ + 4 OH^–			–14.9
PbO(s) +H2O ⇌ Pb(OH)2			–4.4 (red)–4.2 (yellow)
Pb2O(OH)2(s) +H2O ⇌ 2 Pb(OH)2			–4.0
PbO(s) + 2 H2O ⇌ Pb(OH)3^– + H^+			–1.4 (red)–1.2 (yellow)
Pb2O(OH)2(s) + 2 H2O ⇌ 2 Pb(OH)3^– + 2 H^+			–1.0

Lead(IV)

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

!Reaction!Feitknecht and Schindler, 1963

β-PbO2 + 2 H2O ⇌ Pb^4+ + 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^[66] !Nordstrom et al., 1990!Brown and Ekberg, 2016^[67]

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^[68] !Nordstrom et al., 1990!Brown and Ekberg, 2016^[69]

Mg^2+ + H2O ⇌ MgOH^+ + H^+	–11.44	–11.44	–11.70 ± 0.04
4 Mg^2+ + 4 H2O ⇌ Mg4(OH)4^4+ + 4 H^+	–39.71
Mg(OH)2(cr) + 2 H^+ ⇌ Mg^2+ + 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^[70] !Baes and Mesmer, 1976^[71] !Nordstrom et al., 1990!Hummel et al., 2002^[72] !Brown and Ekberg, 2016^[73]

Mn^2+ + H2O ⇌ MnOH^+ + H^+	–10.59	–10.59	–10.59	–10.59	−10.58 ± 0.04
Mn^2+ + 2 H2O ⇌ Mn(OH)2 + 2 H^+		–22.2			−22.18 ± 0.20
Mn^2+ + 3 H2O ⇌ Mn(OH)3^– + 3 H^+		–34.8			−34.34 ± 0.45
Mn^2+ + 4 H2O ⇌ Mn(OH)4^2– + 4 H^+		–48.3			−48.28 ± 0.40
2 Mn^2+ + H2O ⇌ Mn2OH^3+ + H^+		–10.56
2 Mn^2+ + 3 H2O ⇌ Mn2(OH)3^+ + 6 H^+		–23.90
Mn(OH)2(s) + 2 H^+ ⇌ Mn^2+ + 2 H2O	15.2	15.2	15.2		15.19 ± 0.10
MnO(s) + 2 H^+ ⇌ Mn^2+ + 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^[74]

Mn^3+ + H2O ⇌ MnOH^2+ + 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^[75] !Brown and Ekberg, 2016^[76]

Hg2^2+ + 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^[77] !Powell et all, 2005^[78] !Brown and Ekberg, 2016

Hg^2+ + H2O ⇌ HgOH+ + H^+	−3.40	–3.40 ± 0.08	–3.40 ± 0.08
Hg^2+ + 2 H2O ⇌ Hg(OH)2 + 2 H^+	-6.17	–5.98 ± 0.06	−5.96 ± 0.07
Hg^2+ + 3 H2O ⇌ Hg(OH)3^– + 3 H^+	–21.1	–21.1 ± 0.3
HgO(s) + 2 H^+ ⇌ Hg^2+ + 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^[79] !Jolivet, 2000^[80] !NIST46!Crea et al., 2017^[81]

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!NIST46!Neck et al., 2009^[82] !Brown and Ekberg, 2016

Nd^3+ + H2O ⇌ NdOH^2+ + H^+	–8.0	–8.0	–7.4 ± 0.4	–8.13 ± 0.05
Nd^3+ + 2 H2O ⇌ Nd(OH)2^+ + 2 H^+	(–16.9)		–15.7 ± 0.7
Nd^3+ + 3 H2O ⇌ Nd(OH)3(aq) + 3 H^+	(–26.5)		–26.2 ± 0.5
Nd^3+ + 4 H2O ⇌ Nd(OH)4^− + 4 H^+	(–37.1)	–37.4	–40.7 ± 0.7
2 Nd^3+ + 2 H2O ⇌ Nd2(OH)2^4+ + 2 H^+	–13.86	–13.9		–15.56 ± 0.20
3 Nd^3+ + 5 H2O ⇌ Nd3(OH)5^4+ + 5 H^+	< –28.5			–34.2 ± 0.3
Nd(OH)3(s) + 3 H^+ ⇌ Nd^3+ + 3 H2O	18.6		17.2 ± 0.4	17.89 ± 0.09
Nd(OH)3(s) ⇌ Nd^3+ + 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^[83] !Grenthe et al, 2020

Np^3+ + H2O ⇌ NpOH^2+ + 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^[84] !NIST46!Brown and Ekberg, 2016^[85] !Grenthe et al, 2020

Np^4+ + H2O ⇌ NpOH^3+ + H^+	–1.49	–1.5	–1.31 ± 0.05	0.5 ± 0.2
Np^4+ + 2 H2O ⇌ Np(OH)2^2+ + 2 H^+			–3.7 ± 0.3	0.3 ± 0.3
Np^4+ + 4 H2O ⇌ Np(OH)4 + 4 H^+			–10.0 ± 0.9	–8 ± 1
Np^4+ + 4 OH^- ⇌ NpO2(am, hyd) + 2 H2O	52	54.9 ± 0.4	57.5 ± 0.3	56.7 ± 0.5

Neptunium(V)

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

!Reaction!Baes and Mesmer, 1976!Brown and Ekberg, 2016^[86] !Grenthe et al, 2020

NpO2^+ + + H2O ⇌ NpO2(OH) + H^+	–8.85	–10.7 ± 0.5	–11.3 ± 0.7
NpO2^+ + 2 H2O ⇌ NpO2(OH)2^- + 2 H^+		–22.8 ± 0.7	–23.6 ± 0.5
NpO2^+ + H2O ⇌ NpO2(OH)(am, fresh) + H^+	≤ –4.7	–5.21 ± 0.05	–5.3 ± 0.2
NpO2^+ + H2O ⇌ NpO2(OH)(am, aged) + H^+		–4.53 ± 0.06	–4.7 ± 0.5

Neptunium(VI)

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

!Reaction!Baes and Mesmer,1976^[87] !NIST46!Brown and Ekberg,2016^[88] !Grenthe et al, 2020

NpO2^2+ + H2O ⇌ NpO2(OH)^+ + H^+	–5.15	–5.12	–5.1 ± 0.2	–5.1 ± 0.4
NpO2^2+ + 3 H2O ⇌ NpO2(OH)3^- + 3 H^+			–21 ± 1
NpO2^2+ + 4 H2O ⇌ NpO2(OH)4^2- + 4 H^+			–32 ± 1
2 NpO2^2+ + 2 H2O ⇌ (NpO2)2(OH)2^2+ + 2 H^+	–6.39	–6.39	–6.2 ± 0.2	–6.2 ± 0.2
3 NpO2^2+ + 5 H2O ⇌ (NpO2)3(OH)5^+ + 5 H^+	–17.49	–17.49	–17.0 ± 0.2	–17.1 ± 0.2
NpO2^2+ + 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^[89] !Baes and Messmer, 1976^[90] !NIST46!Gamsjäger et al., 2005^[91] !Thoenen et al., 2014!Brown and Ekberg, 2016^[92]

Ni^2+ + H2O ⇌ NiOH^+ + H^+		–9.86	–9.9	–9.54 ± 0.14	–9.54 ± 0.14	–9.90 ± 0.03
Ni^2+ + 2 H2O ⇌ Ni(OH)2 + 2 H^+		–19	–19		< –18	–21.15 ± 0.0
Ni^2+ + 3 H2O ⇌ Ni(OH)3^– + 3 H^+		–30	–30	–29.2 ± 1.7	–29.2 ± 1.7
Ni^2+ + 4 H2O ⇌ Ni(OH)4^2– + 4 H^+		< –44
2 Ni^2+ + H2O ⇌ Ni2(OH)^3+ + H^+		–10.7		–10.6 ± 1.0	–10.6 ± 1.0	–10.6 ± 1.0
4 Ni^2+ + 4 H2O ⇌ Ni4(OH)4^4+ + 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^+ ⇌ Ni^2+ + 2 H2O		10.8			11.02 ± 0.20	10.96 ± 0.2011.75 ± 0.13 (microcr)
Ni(OH)2(s) ⇌ Ni^2+ + 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^+ ⇌ Ni^2+ + H2O				12.38 ± 0.06		12.48 ± 0.15

Niobium

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

!Reaction!Baes and Mesmer, 1976!Filella and May, 2020^[93]

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^[94]

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

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^[95] !Hummel et al., 2002!Kitamura and Yul, 2010^[96] !Brown and Ekberg, 2016^[97]

Pd^2+ + H2O ⇌ PdOH^+ + H^+	−0.96		−0.65 ± 0.64	−1.16 ± 0.30
Pd^2+ + 2 H2O ⇌ Pd(OH)2 + 2 H^+	−2.6	−4 ± 1	−3.11 ± 0.63	−3.07 ± 0.16
Pd^2+ + 3 H2O ⇌ Pd(OH)3^− + 3 H^+		−15.5 ± 1	−14.20 ± 0.63
Pd(OH)2(am) + 2 H^+ ⇌ Pd^2+ + 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^[98] !NIST46!Brown and Ekberg, 2016^[99] !Grenthe et al, 2020

Pu^3+ + H2O ⇌ PuOH^2+ + H^+		–7.0	–6.9 ± 0.2	–6.9 ± 0.3
Pu^3+ + 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^[100] !NIST46!Brown and Ekberg, 2016^[101] !Grenthe et al, 2020

Pu^4+ + H2O ⇌ PuOH ^3+ + H^+	–0.5	–0.5	–0.7 ± 0.1	0.6 ± 0.2
Pu^4+ + 2 H2O ⇌ Pu(OH)2^2+ + 2 H^+	(–2.3)			0.6 ± 0.3
Pu^4+ + 3 H2O ⇌ Pu(OH)3^+ + 3 H^+	(–5.3)			–2.3 ± 0.4
Pu^4+ + 4 H2O ⇌ Pu(OH)4 + 4 H^+	–9.5		–12.5 ± 0.7	–8.5 ± 0.5
Pu^4+ + 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^[102] !NIST46!Brown and Ekberg, 2016^[103] !Grenthe et al, 2020

PuO2^+ + H2O ⇌ PuO2(OH) + H^+	–1.49	–1.5	–1.31 ± 0.05	0.5 ± 0.2
PuO2+ + H2O ⇌ PuO2(OH)(am) + H^+			–3.7 ± 0.3	0.3 ± 0.3

Plutonium(VI)

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

!Reaction!Baes and Mesmer,1976^[104] !NIST46!Brown and Ekberg, 2016^[105] !Grenthe et al, 2020

PuO2^2+ + H2O ⇌ PuO2(OH)^+ + H^+	–5.6	–5.6	–5.36 ± 0.09	–5.5 ± 0.5
PuO2^2+ + 2 H2O ⇌ PuO2(OH)2 + 2 H^+			–12.9 ± 0.2	–13 ± 1
PuO2^2+ + 3 H2O ⇌ PuO2(OH)3^- + 3 H+				–24 ± 1
2 PuO2^2+ + 2 H2O ⇌ (PuO2)2(OH)2^2+ + 2 H^+	–8.36	–8.36	–7.8 ± 0.5	–7 ± 1
3 PuO2^2+ + 5 H2O ⇌ (PuO2)3(OH)5^+ + 5 H^+	–21.65	–21.65
PuO2^2+ + 2 OH^- ⇌ PuO2(OH)2(am, hyd)				22.8 ± 0.6

Potassium

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

!Reaction!Baes and Mesmer, 1976!Nordstrom et al., 1990!Brown and Ekberg, 2016^[106]

K^+ + H2O ⇌ KOH + H^+

–14.46

–14.46

–14.5 ± 0.4

Praseodymium

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

!Reaction!Baes and Mesmer, 1976!NIST46!Brown and Ekberg, 2016

Pr^3+ + H2O ⇌ PrOH^2+ + H^+	–8.1		–8.30 ± 0.03
2 Pr^3+ + 2 H2O ⇌ Pr2(OH)2^4+ + 2 H^+			–16.31 ± 0.20
3 Pr^3+ + 5 H2O ⇌ Pr3(OH)5^4+ + 5 H^+			–35.0 ± 0.3
Pr(OH)3(s) + 3 H^+ ⇌ Pr^3+ + 3 H2O	19.5		18.57 ± 0.20
Pr(OH)3(s) ⇌ Pr^3+ + 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

Ra^2+ + 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^[107] !Baes and Mesmer, 1976^[108] !Brown and Ekberg^[109]

Rh^3+ + H2O ⇌ RhOH2^+ + H^+	‒3.43	‒3.4	‒3.09 ± 0.1
Rh(OH)3(c) + OH^‒ ⇌ Rh(OH)4^‒		‒3.9

Samarium

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

!Reaction!Baes and Mesmer, 1976!NIST46!Brown and Ekberg

Sm^3+ + H2O ⇌ SmOH^2+ + H^+	–7.9	–7.9	–7.84 ± 0.11
2 Sm^3+ + 2 H2O ⇌ Sm2(OH)2^4+ + 2 H^+			–14.75 ± 0.20
3 Sm^3+ + 5 H2O ⇌ Sm3(OH)5^4+ + 5 H^+			–33.9 ± 0.3
Sm(OH)3(s) + 3H^+ ⇌ Sm^3+ + 3H2O	16.5		17.19 ± 0.30
Sm(OH)3(s) ⇌ Sm^3+ + 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^[110] !Brown and Ekberg, 2016^[111]

Sc^3+ + H2O ⇌ ScOH^2+ + H^+	–4.3	–4.16 ± 0.05
Sc^3+ + 2 H2O ⇌ Sc(OH)2^+ + 2 H^+	–9.7	–9.71 ± 0.30
Sc^3+ + 3 H2O ⇌ Sc(OH)3 + 3 H^+	–16.1	–16.08 ± 0.30
Sc^3+ + 4 H2O ⇌ Sc(OH)4^–+ 4 H^+	–26	–26.7 ± 0.3
2 Sc^3+ + 2 H2O ⇌ Sc2(OH)2^4+ + 2 H^+	–6.0	–6.02 ± 0.10
3 Sc^3+ + 5 H2O ⇌ Sc3(OH)5^4+ + 5 H^+	–16.34	–16.33 ± 0.10
Sc(OH)3(s) + 3 H^+ ⇌ Sc^3+ + 3 H2O		9.17 ± 0.30
ScO1.5(s) + 3 H^+ ⇌ Sc^3+ + 1.5 H2O		5.53 ± 0.30
ScO(OH)(c) + 3 H^+ ⇌ Sc^3+ + 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^[112] !Thoenen et al., 2014

H2Se(g) ⇌ H2Se(aq)	–1.10 ± 0.01	–1.10 ± 0.01
H2Se ⇌ HSe^– + H^+	–3.85 ± 0.05	–3.85 ± 0.05
HSe^– ⇌ 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^[113] !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 (log values) in critical compilations at infinite dilution and T = 298.15 K:

!Reaction!Baes and Mesmer, 1976^[114] !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 (log values) in critical compilations at infinite dilution and T = 298.15 K:

!Reaction!Baes and Mesmer, 1976^[115] !Thoenen et al., 2014^[116]

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^[117] !Brown and Ekberg, 2016^[118]

Ag^+ + H2O ⇌ AgOH + H^+	−12.0	−11.75 ± 0.14
Ag^+ + 2 H2O ⇌ Ag(OH)2^− + 2 H^+	−24.0	−24.34 ± 0.14
0.5 Ag2O(am) + H^+ ⇌ Ag^+ + 0.5 H2O	6.29	6.27 ± 0.05

Sodium

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

!Reaction!Baes and Mesmer, 1976!Nordstrom et al., 1990!Brown and Ekberg, 2016^[119]

Na^+ + H2O ⇌ NaOH + H^+

–14.18

–14.18

–14.4 ± 0.2

Strontium

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

!Reaction!Baes and Mesmer, 1976!Nordstrom et al., 1990!Brown and Ekberg, 2016^[120]

Sr^2+ + 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^[121] !Filella and May, 2019^a[122]

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[123]

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^[124] !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^+ ⇌ Te(OH)3^+	3.13	2.415
TeO2(s) + H2O ⇌ H2TeO3		‒4.709

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

Tellurium(VI)

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

!Reaction!Baes and Mesmer, 1976!Filella and May, 2019^a

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!Brown and Ekberg, 2016^[125]

Tb^3+ + H2O ⇌ TbOH^2+ + H^+	−7.9	−7.60 ± 0.09
2 Tb^3+ + 2 H2O ⇌ Tb2(OH)2^4+ + 2 H^+		−13.9 ± 0.2
3 Tb^3+ + 5 H2O ⇌ Tb3(OH)5^4+ + 5 H^+		−31.7 ± 0.3
Tb(OH)3(s) + 3 H^+ ⇌ Tb^3+ + 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^[126] !Brown and Ekberg, 2016^[127]

Tl^+ + H2O ⇌ TlOH + H^+	–13.21
Tl^+ + OH^– ⇌ TlOH		0.64 ± 0.05
Tl^+ + 2 OH^– ⇌ Tl(OH)2^–		–0.7 ± 0.7
Tl2O(s) + H^+ ⇌ Tl^+ + H2O		13.55 ± 0.20

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

Thallium(III)

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

!Reaction!Baes and Mesmer, 1976!Brown and Ekberg, 2016

Tl^3+ + H2O ⇌ TlOH^2+ + H^+	–0.62	–0.22 ± 0.19
Tl^3+ + 2 H2O ⇌ Tl(OH)2^+ + 2 H^+	–1.57
Tl^3+ + 3 H2O ⇌ Tl(OH)3 + 3 H^+	–3.3
Tl^3+ + 4 H2O ⇌ Tl(OH)4^– + 4 H^+	–15.0
Tl2O3(s) + 3 H^+ ⇌ Tl^3+ + 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^[128] !Rand et al., 2008^[129] !Thoenen et al, 014^[130] !Brown and Ekberg,2016^[131]

Th^4+ + H2O ⇌ ThOH^3+ + H^+	–3.20	–2.5 ± 0.5	–2.5 ± 0.5	–2.5 ± 0.5
Th^4+ + 2 H2O ⇌ Th(OH)2^2+ + 2 H^+	–6.93	–6.2 ± 0.5	–6.2 ± 0.5	–6.2 ± 0.5
Th^4+ + 3 H2O ⇌ Th(OH)3^+ + 3 H^+	< –11.7
Th^4+ + 4 H2O ⇌ Th(OH)4 + 4 H^+	–15.9	–17.4 ± 0.7	–17.4 ± 0.7	–17.4 ± 0.7
2Th^4+ + 2 H2O ⇌ Th2(OH)2^6+ + 2 H^+	–6.14	–5.9 ± 0.5	–5.9 ± 0.5	–5.9 ± 0.5
2Th^4+ + 3 H2O ⇌ Th2(OH)3^5+ + 3 H^+		–6.8 ± 0.2	–6.8 ± 0.2	–6.8 ± 0.2
4Th^4+ + 8 H2O ⇌ Th4(OH)8^8+ + 8 H^+	–21.1	–20.4 ± 0.4	–20.4 ± 0.4	–20.4 ± 0.4
4Th^4+ + 12 H2O ⇌ Th4(OH)12^4+ + 12 H^+		–26.6 ± 0.2	–26.6 ± 0.2	–26.6 ± 0.2
6Th^4+ + 15 H2O(l) ⇌ Th6(OH)15^9+ + 15 H^+	–36.76	–36.8 ± 1.5	–36.8 ± 1.5	–36.8 ± 1.5
6Th^4+ + 14 H2O(l) ⇌ Th6(OH)14^10+ + 14 H^+		–36.8 ± 1.2	–36.8 ± 1.2	–36.8 ± 1.2
ThO2(c) + 4 H^+ ⇌ Th^4+ + 2 H2O	6.3
ThO2(am) + 4 H^+ ⇌ Th^4+ + 2 H2O				8.8 ± 1.0
ThO2(am,hyd,fresh) + 4 H^+ ⇌ Th^4+ + 2 H2O			9.3 ± 0.9
ThO2(am,hyd,aged) + 4 H^+ ⇌ Th^4+ + 2 H2O			8.5 ± 0.9
Th^4+ + 4 OH^- ⇌ ThO2(am,hyd,fresh) + 2 H2O		46.7 ± 0.9
Th^4+ + 4 OH^- ⇌ ThO2(am,hyd,aged) + 2 H2O		47.5 ± 0.9

Thulium

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

!Reaction!Baes and Mesmer, 1976!Brown and Ekberg, 2016^[132]

Tm^3+ + H2O ⇌ TmOH^2+ + H^+	−7.7	−7.34 ± 0.09
2 Tm^3+ + 2 H2O ⇌ Tm2(OH)2^4+ + 2 H^+		−13.2 ± 0.2
3 Tm^3+ + 5 H2O ⇌ Tm3(OH)5^4+ + 5 H^+		−30.5 ± 0.3
Tm(OH)3(s) + 3 H^+ ⇌ Tm^3+ + 3 H2O	15.0	15.56 ± 0.40

Tin(II)

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

!Reaction!Feitknecht, 1963!Baes and Mesmer, 1976^[133] !Hummel et al., 2002!NIST46!Cigala et al, 2012^[134] !Gamsjäger et al, 2012^[135] !Brown and Ekberg, 2016^[136]

Sn^2+ + H2O ⇌ SnOH^+ + H^+		–3.40	–3.8 ± 0.2	–3.4	–3.52 ± 0.05	–3.53 ± 0.40	–3.53 ± 0.40
Sn^2+ + 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
Sn^2+ + 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 Sn^2+ + 2 H2O ⇌ Sn2(OH)2^2+ + 2 H^+		–4.77		–4.8	–4.79 ± 0.05
3 Sn^2+ + 4 H2O ⇌ Sn3(OH)4^2+ + 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) ⇌ Sn^2+ + 2 OH^–				–25.8	–26.28 ± 0.08
SnO(s) + 2 H^+ ⇌ Sn^2+ + H2O		1.76	2.5± 0.5				1.60 ± 0.15
SnO(s) + H2O ⇌ Sn^2+ + 2 OH^–	–26.2
SnO(s) + H2O ⇌ Sn(OH)2	–5.3
SnO(s) + 2 H2O ⇌ Sn(OH)3^– + H^+	–0.9

Tin(IV)

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

!Reaction!Hummel et al., 2002!Gamsjäger et al, 2012!Brown and Ekberg, 2016

Sn^4+ + 4 H2O ⇌ Sn(OH)4 + 4 H^+			7.53 ± 0.12
Sn^4+ + 5 H2O ⇌ Sn(OH)5^– + 5 H^+			–1.07 ± 0.42
Sn^4+ + 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^+ ⇌ Sn^4+ + 2 H2O			–15.59 ± 0.04

Tungsten

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

!Reaction!Perrin et al., 1969^[137] !Baes and Mesmer, 1976^[138] !Brown and Ekberg, 2016^[139]

Ti^3+ + H2O ⇌ TiOH^2+ + H^+	–1.29	–2.2	–1.65 ± 0.11
2 Ti^3+ + 2 H2O ⇌ Ti2(OH)2^4+ + 2 H^+		–3.6	–2.64 ± 0.10

Titanium(IV)

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

!Reaction!Baes and Mesmer, 1976!Brown and Ekberg, 2016

Ti(OH)2^2+ + H2O ⇌ Ti(OH)^3+ + H^+	⩽–2.3
Ti(OH)2^2+ + 2 H2O ⇌ Ti(OH)4 + 2 H^+	–4.8
TiO^2+ + H2O ⇌ TiOOH^+ + H^+		–2.48 ± 0.10
TiO^2+ + 2 H2O ⇌ TiO(OH)2 + 2 H^+		–5.49 ± 0.14
TiO^2+ + 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)2^2+[OH<sup>–</sup>]
TiO2(s) + 4 H^+ ⇌ Ti^4+ + 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^[140] !Thoenen et al., 2014^[141] !Brown and Ekberg,2016^[142] !Grenthe et al.,2020^[143]

U^4+ + H2O ⇌ UOH^3+ + H^+	–0.65	– 0.54 ± 0.06	–0.58 ± 0.08	– 0.54 ± 0.06
U^4+ + 2 H2O ⇌ U(OH)2^2+ + 2 H^+	(–2.6)	–1.1 ± 1.0	–1.4 ± 0.2	–1.9 ± 0.2
U^4+ + 3 H2O ⇌ U(OH)3^+ + 3 H^+	(–5.8)	–4.7 ± 1.0	–5.1 ± 0.3	–5.2 ± 0.4
U^4+ + 4 H2O ⇌ U(OH)4 + 4 H^+	(–10.3)	–10.0 ± 1.4	–10.4 ± 0.5	–10.0 ± 1.4
U^4+ + 5 H2O ⇌ U(OH)5^- + 5 H^+	–16.0
UO2(am, hyd) + 4 H^+ ⇌ U^4+ + 2 H2O		1.5 ± 1.0
UO2(am,hyd) + 2 H2O ⇌ U^4+ + 4 OH^–			–54.500 ± 1.000	–54.500 ± 1.000
UO2(c) + 4 H^+ ⇌ U^4+ + 2 H2O	–1.8
UO2(c) + 2 H2O ⇌ U^4+ + 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!Brown and Ekberg,2016^[146] !Grenthe et al.,2020

UO2^2+ + H2O ⇌ UO2(OH)^+ + H^+	–5.8	–5.2 ± 0.3	–5.9 ± 0.1	–5.13 ± 0.04	–5.25 ± 0.24
UO2^2+ + 2 H2O ⇌ UO2(OH)2 + 2 H^+		≤-10.3		–12.15 ± 0.20	–12.15 ± 0.07
UO2^2+ + 3 H2O ⇌ UO2(OH)3^– + 3 H^+		–19.2 ± 0.4		–20.25 ± 0.42	–20.25 ± 0.42
UO2^2+ + 4 H2O ⇌ UO2(OH)4^2– + 4 H^+		–33 ± 2		–32.40 ± 0.68	–32.40 ± 0.68
2 UO2^2+ + 2 H2O ⇌ (UO2)2(OH)2^2+ + 2 H^+	–5.62	–5.62 ± 0.04	–5.58 ± 0.04	–5.68 ± 0.05	–5.62 ± 0.08
3 UO2^2+ + 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 UO2^2+ + 4 H2O ⇌ (UO2)3(OH)4^2+ + 4 H^+	(–11.75)	–11.9 ± 0.3		–11.78 ± 0.05	–11.9 ± 0.3
3 UO2^2+ + 7 H2O ⇌ (UO2)3(OH)7^– + 7 H^+		–31 ± 2.0		–32.2 ± 0.8	–32.2 ± 0.8
4 UO2^2+ + 7 H2O ⇌ (UO2)4(OH)7+ + 7 H^+		–21.9 ± 1.0		–22.1 ± 0.2	–21.9 ± 1.0
2 UO2^2+ + H2O ⇌ (UO2)2(OH)^3+ + H^+		–2.7 ± 1.0			–2.7 ± 1.0
UO2(OH)2(s) + 2H^+ ⇌ UO2^2+ + 2 H2O	5.6		6.0	4.81 ± 0.20
UO3·2H2O(cr) + 2H^+ ⇌ UO2^2+ + 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

VO^2+ + H2O ⇌ VO(OH)^+ + H^+	–5.30 ± 0.13
2 VO^2+ + 2 H2O ⇌ (VO)2(OH)2^2+ + 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
V2O5(c) + H^+ ⇌ VO2^+ + H2O	–0.66
V2O5(s) + 2 H^+ ⇌ 2 VO2^+ + H2O		–0.64 ± 0.09

Ytterbium

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

!Reaction!Baes and Mesmer, 1976!Brown and Ekberg, 2016^[149]

Yb^3+ + H2O ⇌ YbOH^2+ + H^+	−7.7	−7.31 ± 0.18
Yb^3+ + 2 H2O ⇌ Yb(OH)2^+ + 2 H^+	(−15.8)
Yb^3+ + 3 H2O ⇌ Yb(OH)3 + 3 H^+	(−24.1)
Yb^3+ + 4 H2O ⇌ Yb(OH)4^− + 4 H^+	−32.7
2 Yb^3+ + 2 H2O ⇌ Yb2(OH)2^4+ + 2 H^+		−13.76 ± 0.20
3 Yb^3+ + 5 H2O ⇌ Yb3(OH)5^4+ + 5 H^+		−30.6 ± 0.3
Yb(OH)3(s) + 3 H^+ ⇌ Yb^3+ + 3 H2O	14.7	15.35 ± 0.20

Yttrium

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

!Reaction!Baes and Mesmer, 1976!Brown and Ekberg, 2016

Y^3+ + H2O ⇌ YOH^2+ + H^+	–7.7	–7.77 ± 0.06
Y^3+ + 2 H2O ⇌ Y(OH)2^+ + 2 H^+	(–16.4) [Estimation]
Y^3+ + 3 H2O ⇌ Y(OH)3 + 3 H^+	(–26.0) [Estimation]
Y^3+ + 4 H2O ⇌ Y(OH)4^-+ 4 H^+	–36.5
2 Y^3+ + 2 H2O ⇌ Y2(OH)2^4+ + 2 H^+	–14.23	–14.1 ± 0.2
3 Y^3+ + 5 H2O ⇌ Y3(OH)5^4+ + 5 H^+	–31.6	–32.7 ± 0.3
Y(OH)3(s) + 3 H^+ ⇌ Y^3+ + 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]

Zn^2+ + H2O ⇌ ZnOH^+ + H^+	−8.96	−8.96 ± 0.05	−8.94 ± 0.06
Zn^2+ + 2 H2O ⇌ Zn(OH)2 + 2 H^+	−16.9	–17.82 ± 0.08	−17.89 ± 0.15
Zn^2+ + 3 H2O ⇌ Zn(OH)3^- + 3 H^+	−28.4	–28.05 ± 0.05	−27.98 ± 0.10
Zn^2+ + 4 H2O ⇌ Zn(OH)4^2- + 4 H^+	−41.2	–40.41 ± 0.12	−40.35 ± 0.22
2 Zn^2+ + H2O ⇌ Zn2OH^3+ + H^+	−9.0	–7.9 ± 0.2	−7.89 ± 0.31
2 Zn^2+ + 6 H2O ⇌ Zn2(OH)6^2- + 6 H^+	−57.8
ZnO(s) + 2 H^+ ⇌ Zn^2+ + H2O	11.14	11.12 ± 0.05	11.11 ± 0.10
ε-Zn(OH)2(s) + 2 H^+ ⇌ Zn^2+ + 2 H2O		11.38 ± 0.20	11.38± 0.20
β1-Zn(OH)2(s) + 2 H^+ ⇌ Zn^2+ + 2 H2O		11.72 ± 0.04
β2-Zn(OH)2(s) + 2 H^+ ⇌ Zn^2+ + 2 H2O		11.76 ± 0.04
γ-Zn(OH)2(s) + 2 H^+ ⇌ Zn^2+ + 2 H2O		11.70 ± 0.04
δ-Zn(OH)2(s) + 2 H^+ ⇌ Zn^2+ + 2 H2O		11.81 ± 0.04

Zirconium

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

!Reaction!Baes and Mesmer, 1976!Thoenen et al., 2014!Brown and Ekberg, 2016^[153]

Zr^4+ + H2O ⇌ ZrOH^3+ + H^+	0.32	0.32 ± 0.22	0.12 ± 0.12
Zr^4+ + 2 H2O ⇌ Zr(OH)2^2+ + 2 H^+	(−1.7)*	0.98 ± 1.06*	−0.18 ± 0.17*
Zr^4+ + 3 H2O ⇌ Zr(OH)3^+ + 3 H^+	(−5.1)
Zr^4+ + 4 H2O ⇌ Zr(OH)4 + 4 H^+	–9.7*	–2.19 ± 0.70*	−4.53 ± 0.37*
Zr^4+ + 5 H2O ⇌ Zr(OH)5^– + 5 H^+	–16.0
Zr^4+ + 6 H2O ⇌ Zr(OH)6^2– + 6 H^+		–29± 0.70	–30.5 ± 0.3
3 Zr^4+ + 4 H2O ⇌ Zr3(OH)4^8+ + 4 H^+	–0.6	0.4 ± 0.3	0.90 ± 0.18
3 Zr^4+ + 5 H2O ⇌ Zr3(OH)5^7+ + 5 H^+	3.70
3 Zr^4+ + 9 H2O ⇌ Zr3(OH)9^3+ + 9 H^+		12.19 ± 0.20	12.19 ± 0.20
4 Zr^4+ + 8 H2O ⇌ Zr4(OH)8^8+ + 8 H^+	6.0	6.52 ± 0.05	6.52 ± 0.05
4 Zr^4+ + 15 H2O ⇌ Zr4(OH)15^+ + 15 H^+		12.58± 0.24
4 Zr^4+ + 16 H2O ⇌ Zr4(OH)16 + 16 H^+		8.39± 0.80
ZrO2(s) + 4 H^+ ⇌ Zr^4+ + 2 H2O	–1.9*		–5.37 ± 0.42*
ZrO2(s, baddeleyite) + 4 H^+ ⇌ Zr^4+ + 2 H2O		–7 ± 1.6
ZrO2(am) + 4 H^+ ⇌ Zr^4+ + 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.

Notes and References

1. Book: Baes, C.F. . The Hydrolysis of Cations . Mesmer . R.E. . Wiley . 1976 . New York . 121.
2. Book: Brown, P.L. . Hydrolysis of Metal Ions . Ekberg . C. . Wiley . 2016 . 757–797.
3. Book: Hummel, W. . Technical Report 21-03. The PSI Chemical Thermodynamic Database 2020 . Thoenen . T. . NAGRA . 2023 . Wettingen . 252–259.
4. Book: Brown, P.L. . Hydrolysis of Metal Ions . Ekberg . C. . Wiley . 2016 . 407–414.
5. Book: Brown, P.L. . Hydrolysis of Metal Ions . Ekberg . C. . Wiley . 2016 . 414.
6. Book: Baes, C.F. . The Hydrolysis of Cations . Mesmer . R.E. . Wiley . 1976 . New York . 375.
7. Book: Lothenbach, B. . Thermodynamic Data for the Speciation and Solubility of Pd, Pb, Sn, Sb, Nb and Bi in Aqueous Solution. TN8400 99-011 . Ochs . M. . Wanner . H. . Yui . M. . Japan Nuclear Cycle Development Institute (JNC) . 1999.
8. Book: Kitamura, A. . JAEA Thermodynamic Database for Performance Assessment of Geological Disposal of High-Level Radioactive and TRU-Wastes. Report JAEA-Data/Code 2009-024 . Fujiwara . K. . Doi . R. . Yoshida . Y. . Mihara . M. . Terashima . M. . Yui . M. . Japan Atomic Energy Agency . 2010.
9. Filella . M. . May . P.M. . 2003 . Computer simulation of the low-molecular-weight inorganic species distribution of antimony(III) and antimony(V) in natural waters. . Geochim. Cosmochim. Acta . 67 . 4013–4031 . 10.1016/S0016-7037(03)00095-4.
10. Book: Baes, C.F. . The Hydrolysis of Cations . Mesmer . R.E. . Wiley . 1976 . New York . 370.
11. Book: Nordstrom, D.K. . Arsenic thermodynamic data and environmental geochemistry. In: Arsenic in Ground Water. . Archer . D. . Kluwer Academic Publishers . 2003 . Welch . AH . Amsterdam . 1‒25 . 10.1007/0-306-47956-7_1 . Stollenwerk . KG.
12. Nordstrom . D.K. . Majzlan . J. . Königsberger . E. . 2014 . Thermodynamic properties for As minerals & aqueous species . Reviews in Mineralogy & Geochemistry . 79 . 217‒255 . 10.2138/rmg.2014.79.4.
13. Khodakovsky . I.L. . Ryzhenko . B.N. . Naumov . G.B. . 1968 . Thermodynamics of aqueous electrolyte solutions at elevated temperatures (Temperature dependence of the heat capacities of ions in aqueous solution) . Geokhimiya . 12 . 1486‒ 1503, 1968.
14. Book: Baes, C.F. . The Hydrolysis of Cations . Mesmer . R.E. . Wiley . 1976 . New York . 103.
15. Book: Nordstrom, D.K. . Revised chemical equilibrium data for major water-mineral reactions and their limitations. In: Chemical Modeling of Aqueous Systems II . Plummer . L.N. . Langmuir . D. . Busenberg . E. . May . H.M. . Jones . B.F. . Parkhurst . D.L. . ACS . 1990 . Melchior . D.C. . Washington, DC . 398–446 . Basset . R.L..
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17. Book: Brown, P.L. . Hydrolysis of Metal Ions . Ekberg . C. . Wiley . 2016 . 419–422.
18. Book: Baes, C.F. . The Hydrolysis of Cations . Mesmer . R.E. . Wiley . 1976 . New York . 95.
19. Book: Baes, C.F. . The Hydrolysis of Cations . Mesmer . R.E. . Wiley . 1976 . New York . 383.
20. Book: NIST46 . NIST Critically Selected Stability Constants of Metal Complexes: Version 8.0..
21. Book: Brown, P.L. . Hydrolysis of Metal Ions . Ekberg . C. . Wiley . 2016 . 874–884.
22. Book: Baes, C.F. . The Hydrolysis of Cations . Mesmer . R.E. . Wiley . 1976 . New York . 111.
23. Book: Baes, C.F. . The Hydrolysis of Cations . Mesmer . R.E. . Wiley . 1976 . New York . 301.
24. Powell . K.J. . Brown . P.L. . Byrne . R.H. . Gajda . T. . Hefter . G. . Leuz . A.-K. . Sjöberg . S. . Wanner . H. . 2011 . Chemical speciation of environmentally significant metals with inorganic ligands. Part 4: The Cd²⁺ + OH^–, Cl^–, CO₃^2–, SO₄^2–, and PO₄^3– systems (IUPAC Technical Report) . Pure Appl. Chem. . 83 . 1163–1214 . 10.1351/PAC-REP-10-08-09. free .
25. Book: Brown, P.L. . Hydrolysis of Metal Ions . Ekberg . C. . Wiley . 2016 . 730–738.
26. Book: Brown, P.L. . Hydrolysis of Metal Ions . Ekberg . C. . Wiley . 2016 . Weinheim, Germany . 195–210.
27. Book: Baes, C.F. . The Hydrolysis of Cations . Mesmer . R.E. . Wiley . 1976 . New York . 137.
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33. Book: Baes, C.F. . The Hydrolysis of Cations . Mesmer . R.E. . Wiley . 1976 . New York . 216.
34. Book: Baes, C.F. . The Hydrolysis of Cations . Mesmer . R.E. . Wiley . 1976 . New York . 241.
35. Book: Brown, P.L. . Hydrolysis of Metal Ions . Ekberg . C. . Wiley . 2016 . 620–628.
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