# Hydrolysis constant

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

## Metal hydrolysis and associated equilibrium constant values

The hydrolysis reaction for a hydrated metal ion in aqueous solution can be written as:
    p M$^{z+}$ + q H$_2$O ⇌ M$_p$(OH)$_q$$^{(pz–q)}$ + q H$^+$
and the corresponding formation constant as:
    $\beta _{pq}={\frac {[M_{p}(OH)_{q}^{(pz-q)}][H^{+}]^{q}}{[M^{z+}]^{p}}}$
and associated equilibria can be written as:
    MO$_x$(OH)$_{z–2x}$(s) + z H$^+$ ⇌ M$^{z+}$ + (z–x) H$_2$O
    MO$_x$(OH)$_{z–2x}$(s) + x H$_2$O ⇌ M$^{z+}$ + z OH$^−$
    p MO$_x$(OH)$_{z–2x}$(s) + (pz–q) H$^+$ ⇌ M$_p$(OH)$_q$$^{(pz–q)}$ + (pz–px–q) H$_2$O

### Aluminium

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:
| Reaction | Baes and Mesmer, 1976 | Brown and Ekberg, 2016 | Hummel and Thoenen, 2023 |
| Al$^{3+}$ + H$_2$O ⇌ AlOH$^{2+}$ + H$^+$ | –4.97 | −4.98 ± 0.02 | −4.98 ± 0.02 |
| Al$^{3+}$ + 2 H$_2$O ⇌ Al(OH)$_2$$^+$ + 2 H$^+$ | –9.3 | −10.63 ± 0.09 | −10.63 ± 0.09 |
| Al$^{3+}$ + 3 H$_2$O ⇌ Al(OH)$_3$ + 3 H$^+$ | –15.0 | −15.66 ± 0.23 | −15.99 ± 0.23 |
| Al$^{3+}$ + 4 H$_2$O ⇌ Al(OH)$_4$$^–$ + 4 H$^+$ | –23.0 | −22.91 ± 0.10 | −22.91 ± 0.10 |
| 2 Al$^{3+}$ + 2 H$_2$O ⇌ Al$_2$(OH)$_2$$^{4+}$ + 2 H$^+$ | –7.7 | −7.62 ± 0.11 | −7.62 ± 0.11 |
| 3 Al$^{3+}$ + 4 H$_2$O ⇌ Al$_3$(OH)$_4$$^{5+}$ + 4 H$^+$ | –13.94 | −14.06 ± 0.22 | −13.90 ± 0.12 |
| 13 Al$^{3+}$ + 28 H$_2$O ⇌ Al$_{13}$O$_4$(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 H$_2$O | 8.5 | 7.75 ± 0.08 | 7.75 ± 0.08 |
| γ-AlOOH(s) + 3 H$^+$ ⇌ Al$^{3+}$ + 2 H$_2$O | | 7.69 ± 0.15 | 9.4 ± 0.4 |

### Americium(III)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:
| Reaction | NIST46 | Brown and Ekberg, 2016 | Grenthe et al, 2020 |
| Am$^{3+}$ + H$_2$O ⇌ Am(OH)$^{2+}$ + H$^+$ | –6.5 ± 0.1 | –7.22 ± 0.03 | –7.2 ± 0.5 |
| Am$^{3+}$ + 2 H$_2$O ⇌ Am(OH)$_2$$^+$ + 2 H$^+$ | –14.1 ± 0.3 | –14.9 ± 0.2 | –15.1 ± 0.7 |
| Am$^{3+}$ + 3 H$_2$O ⇌ Am(OH)$_3$ + 3 H$^+$ | –25.7 | –26.0 ± 0.2 | –26.2 ± 0.5 |
| Am$^{3+}$ + 3 H$_2$O ⇌ Am(OH)$_3$(am) + 3 H$^+$ | –16.9 ± 0.1 | –16.9 ± 0.8 | –16.9 ± 0.8 |
| Am$^{3+}$ + 3 H$_2$O ⇌ Am(OH)$_3$(cr) + 3 H$^+$ | –15.2 | –15.62 ± 0.04 | –15.6 ± 0.6 |

### Americium(V)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:
| Reaction | Brown and Ekberg, 2016 | Grenthe et al, 2020 |
| AmO$_2$$^+$ + H$_2$O ⇌ AmO$_2$(OH) + H$^+$ | –10.7 ± 0.2 | |
| AmO$_2$$^+$ + 2 H$_2$O ⇌ AmO$_2$(OH)$_2$$^–$ + 2 H$^+$ | –22.9 ± 0.7 | |
| AmO$_2$$^+$ + H$_2$O ⇌ AmO$_2$(OH)(am) + H$^+$ | –5.4 ± 0.4 | –5.3 ± 0.5 |

### Antimony(III)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:
| Reaction | Baes and Mesmer, 1976 | Lothenbach et al., 1999; Kitamura et al., 2010 | Filella and May, 2003 |
| Sb(OH)$_3$ + H$^+$ ⇌ Sb(OH)$_2$$^+$ + H$_2$O | 1.41 | 1.30 | 1.371 |
| Sb(OH)$_3$ + H$_2$O ⇌ Sb(OH)$_4$$^‒$ + H$^+$ | ‒11.82 | ‒11.93 | ‒11.70 |
| 0.5 Sb$_2$O$_3$(s) + 1.5 H$_2$O ⇌ Sb(OH)$_3$ | ‒4.24 | | |
| Sb$_2$O$_3$(rhombic,s) + 3 H$_2$O ⇌ 2 Sb(OH)$_3$ | | ‒8.72 | ‒10.00 |
| Sb$_2$O$_3$(cubic,s) + 3 H$_2$O ⇌ 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)$_5$ + H$_2$O ⇌ Sb(OH)$_6$$^‒$ + H$^+$ | ‒2.72 | ‒2.72 |
| 12 Sb(OH)$_5$ + 4 H$_2$O ⇌ Sb$_{12}$(OH)$_{64}$$^{4‒}$ + 4 H$^+$ | 20.34 | 20.34 |
| 12 Sb(OH)$_5$ + 5 H$_2$O ⇌ Sb$_{12}$(OH)$_{65}$$^{5‒}$ + 5 H$^+$ | 16.72 | 16.72 |
| 12 Sb(OH)$_5$ + 6 H$_2$O ⇌ Sb$_{12}$(OH)$_{66}$$^{6‒}$ + 6 H$^+$ | 11.89 | 11.89 |
| 12 Sb(OH)$_5$ + 7 H$_2$O ⇌ Sb$_{12}$(OH)$_{67}$$^{7‒}$ + 7 H$^+$ | 6.07 | 6.07 |
| 0.5 Sb$_2$O$_5$(s) + 2.5 H$_2$O ⇌ Sb(OH)$_5$ | ‒3.7 | |
| Sb$_2$O$_5$(am) + 5 H$_2$O ⇌ 2 Sb(OH)$_5$ | | ‒7.400 |

### Arsenic(III)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:
| Reaction | Baes and Mesmer, 1976 | Nordstrom and Archer, 2003 | Nordstrom et al., 2014 |
| As(OH)$_4$$^‒$ + H$^+$ ⇌ As(OH)$_3$ + H$_2$O | 9.29 | 9.17 | 9.24 ± 0.02 |

### Arsenic(V)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:
| Reaction | Baes and Mesmer | Khodakovsky et al. (1968) | Nordstrom and Archer, 2003 | Nordstrom et al., 2014 |
| H$_2$AsO$_4$$^‒$ + H$^+$ ⇌ H$_3$AsO$_4$ | 2.24 | 2.21 | 2.26 ± 0.078 | 2.25 ± 0.04 |
| HAsO$_4$$^{2‒}$ + H$^+$ ⇌ H$_2$AsO$_4$$^‒$ | | 6.93 | 6.99 ± 0.1 | 6.98 ± 0.11 |
| AsO$_4$$^{3‒}$ + H$^+$ ⇌ HAsO$_4$$^{2‒}$ | | 11.51 | 11.80 ± 0.1 | 11.58 ± 0.05 |
| HAsO$_4$$^{2‒}$ + 2 H$^+$ ⇌H$_3$AsO$_4$ | 9.20 | | | |
| AsO$_4$$^{3‒}$ + 3 H$^+$ ⇌ H$_3$AsO$_4$ | 20.70 | | | |

### Barium

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:
| Reaction | Baes and Mesmer, 1976 | Nordstrom et al., 1990 | Brown and Ekberg, 2016 |
| Ba$^{2+}$ + H$_2$O ⇌ 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 |
| Bk$^{3+}$ + 3 H$_2$O ⇌ 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 |
| Be$^{2+}$ + H$_2$O ⇌ BeOH$^+$ + H$^+$ | –5.10 |
| Be$^{2+}$ + 2 H$_2$O ⇌ Be(OH)$_2$ + 2 H$^+$ | –23.65 |
| Be$^{2+}$ + 3 H$_2$O ⇌ Be(OH)$_3$$^–$ + 3 H$^+$ | –23.25 |
| Be$^{2+}$ + 4 H$_2$O ⇌ Be(OH)$_4$$^{2–}$ + 4 H$^+$ | –37.42 |
| 2 Be$^{2+}$ + H$_2$O ⇌ Be$_2$OH$^{3+}$ + H$^+$ | –3.97 |
| 3 Be$^{2+}$ + 3 H$_2$O ⇌ Be$_3$(OH)$_3$$^{3+}$ + 3 H$^+$ | –8.92 |
| 6 Be$^{2+}$ + 8 H$_2$O ⇌ Be$_6$(OH)$_8$$^{4+}$ + 8 H$^+$ | –27.2 |
| α-Be(OH)$_2$(cr) + 2 H$^+$ ⇌ Be$^{2+}$ + 2 H$_2$O | 6.69 |

### Bismuth

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:
| Reaction | Baes and Mesmer, 1976 | Lothenbach et al., 1999 | NIST46 | Kitamura et al., 2010 | Brown and Ekberg, 2016 |
| Bi$^{3+}$ + H$_2$O ⇌ BiOH$^{2+}$ + H$^+$ | –1.0 | –0.92 | –1.1 | –0.920 | –0.92 ± 0.15 |
| Bi$^{3+}$ + 2 H$_2$O ⇌ Bi(OH)$_2$$^+$ + 2 H$^+$ | (–4) | –2.56 | –4.5 | –2.560 ± 1.000 | –2.59 ± 0.26 |
| Bi$^{3+}$ + 3 H$_2$O ⇌ Bi(OH)$_3$ + 3 H$^+$ | –8.86 | –5.31 | –9.0 | –8.940 ± 0.500 | –8.78 ± 0.20 |
| Bi$^{3+}$ + 4 H$_2$O ⇌ Bi(OH)$_4$$^–$ + 4 H$^+$ | –21.8 | –18.71 | –21.2 | –21.660 ± 0.870 | –22.06 ± 0.14 |
| 3 Bi$^{3+}$ + 4 H$_2$O ⇌ Bi3(OH)$_4$$^{5+}$ + 4 H$^+$ | | –0.80 | | –0.800 | |
| 6 Bi$^{3+}$ + 12 H$_2$O ⇌ Bi$_6$(OH)$_{12}$$^{6+}$ + 12 H$^+$ | | 1.34 | | 1.340 | 0.98 ± 0.13 |
| 9 Bi$^{3+}$ + 20 H$_2$O = Bi$_9$(OH)$_{20}$$^{7+}$ + 20 H$^+$ | | –1.36 | | –1.360 | |
| 9 Bi$^{3+}$ + 21 H$_2$O = Bi$_9$(OH)$_{21}$$^{6+}$ + 21 H$^+$ | | –3.25 | | –3.250 | |
| 9 Bi$^{3+}$ + 22 H$_2$O = Bi9(OH)$_{22}$$^{5+}$ + 22 H$^+$ | | –4.86 | | –4.860 | |
| Bi(OH)$_3$(am) + 3 H$^+$ = Bi$^{3+}$ + 3 H$_2$O | | | | 31.501 ± 0.927 | |
| α-Bi$_2$O$_3$(cr) + 6 H$^+$ = 2 Bi$^{3+}$ + 3 H$_2$O | | 0.76 | | | |
| BiO$_{1.5}$(s, α) + 3 H$^+$ = Bi$^{3+}$ + 1.5 H$_2$O | 3.46 | | | 31.501 ± 0.927 | 2.88 ± 0.64 |

### Boron

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:
| Reaction | Baes and Mesmer, 1976 | NIST46 |
| B(OH)$_3$ + H$_2$O ⇌ Be(OH)$_4$$^+$ + H$^+$ | –9.236 | –9.236 ± 0.002 |
| 2 B(OH)$_3$ ⇌ B$_2$(OH)$_5$$^–$ + H$^+$ | –9.36 | –9.306 |
| 3 B(OH)$_3$ ⇌ B$_3$O$_3$(OH)$_4$$^–$ + H$^+$ + 2 H$_2$O | –7.03 | –7.306 |
| 4 B(OH)$_3$ ⇌ B$_4$O$_5$(OH)$_4$$^{2–}$ + 2 H$^+$ + 3 H$_2$O | –16.3 | –15.032 |

### Cadmium

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:
| Reaction | Baes and Mesmer, 1976 | Powell et al., 2011 | Brown and Ekberg, 2016 |
| Cd$^{2+}$ + H$_2$O ⇌ CdOH$^+$ + H$^+$ | −10.08 | –9.80 ± 0.10 | −9.81 ± 0.10 |
| Cd$^{2+}$ + 2 H$_2$O ⇌ Cd(OH)$_2$ + 2 H$^+$ | –20.35 | –20.19 ± 0.13 | −20.6 ± 0.4 |
| Cd$^{2+}$ + 3 H$_2$O ⇌ Cd(OH)$_3$$^–$ + 3 H$^+$ | <–33.3 | –33.5 ± 0.5 | −33.5 ± 0.5 |
| Cd$^{2+}$ + 4 H$_2$O ⇌ Cd(OH)$_4$$^{2–}$ + 4 H$^+$ | –47.35 | –47.28 ± 0.15 | −47.25 ± 0.15 |
| 2 Cd$^{2+}$ + H$_2$O ⇌ Cd$_2$OH$^{3+}$ + H$^+$ | –9.390 | –8.73 ± 0.01 | −8.74 ± 0.10 |
| 4 Cd$^{2+}$ + 4 H$_2$O ⇌ Cd$_4$(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 H$_2$O | 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 |
| Ca$^{2+}$ + H$_2$O ⇌ CaOH$^+$ + H$^+$ | –12.85 | –12.78 | –12.57 ± 0.03 |
| Ca(OH)$_2$(cr) + 2 H$^+$ ⇌ Ca$^{2+}$ + 2 H$_2$O | 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 H$_2$O ⇌ 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 | NIST46 | Brown and Ekberg, 2016 |
| Ce$^{3+}$ + H$_2$O ⇌ CeOH$^{2+}$ + H$^+$ | –8.3 | –8.3 | –8.31 ± 0.03 |
| 2 Ce$^{3+}$ + 2 H$_2$O ⇌ Ce$_2$(OH)$_2$$^{4+}$ + 2 H$^+$ | | | –16.0 ± 0.2 |
| 3 Ce$^{3+}$ + 5 H$_2$O ⇌ Ce$_3$(OH)$_5$$^{4+}$ + 5 H$^+$ | | | –34.6 ± 0.3 |
| Ce(OH)$_3$(s) + 3 H$^+$ ⇌ Ce$^{3+}$ + 3 H$_2$O | | | 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 |
| Cr$^{2+}$ + H$_2$O ⇌ 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 | Rai et al., 1987 | Ball and Nordstrom, 1988 | Brown and Ekberg, 2016 |
| Cr$^{3+}$ + H$_2$O ⇌ CrOH$^{2+}$ + H$^+$ | –4.0 | –3.57 ± 0.08 | | –3.60 ± 0.07 |
| Cr$^{3+}$ + 2 H$_2$O ⇌ Cr(OH)$_2$$^+$ + 2 H$^+$ | –9.7 | –9.84 | | –9.65 ± 0.20 |
| Cr$^{3+}$ + 3 H$_2$O ⇌ Cr(OH)$_3$ + 3 H$^+$ | –18 | –16.19 | | –16.25 ± 0.19 |
| Cr$^{3+}$ + 4 H$_2$O ⇌ Cr(OH)$_4$$^−$ + 4 H$^+$ | –27.4 | –27.65 ± 0.12 | | –27.56 ± 0.21 |
| 2 Cr$^{3+}$ + 2 H$_2$O ⇌ Cr$_2$(OH)$_2$$^{4+}$ + 2 H$^+$ | –5.06 | –5.0 | | –5.29 ± 0.16 |
| 3 Cr$^{3+}$ + 4 H$_2$O ⇌ Cr$_3$(OH)$_4$$^{5+}$ + 4 H$^+$ | –8.15 | –10.75 ± 0.15 | | –9.10 ± 0.14 |
| Cr(OH)$_3$(s) + 3 H$^+$ ⇌ Cr$^{3+}$ + 3 H$_2$O | 12 | | 9.35 | 9.41 ± 0.17 |
| Cr$_2$O$_3$(s) + 6 H$^+$ ⇌ 2 Cr$^{3+}$ + 3 H$_2$O | | | 8.52 | |
| CrO$_{1.5}$(s) + 3 H$^+$ ⇌ Cr$^{3+}$ + 1.5 H$_2$O | | | | 7.83 ± 0.10 |

### Chromium(VI)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:
| Reaction | Baes and Mesmer, 1976 | Ball and Nordstrom, 1998 |
| CrO$_4$$^{2–}$ + H$^+$ ⇌ HCrO$_4$$^–$ | 6.51 | 6.55 ± 0.04 |
| HCrO$_4$$^–$ + H$^+$ ⇌ H$_2$CrO$_4$ | –0.20 | |
| CrO$_4$$^2$– + 2 H$^+$ ⇌ H$_2$CrO$_4$ | | 6.31 |
| 2 HCrO$_4$$^–$ ⇌ Cr$_2$O$_7$$^{2–}$ + H$_2$O | 1.523 | |
| 2 CrO$_4$$^{2–}$ + 2 H$^+$ ⇌ Cr$_2$O$_7$$^{2–}$ + H$_2$O | | 14.7 ± 0.1 |

### Cobalt(II)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:
| Reaction | Baes and Mesmer, 1976 | Brown and Ekberg, 2016 |
| Co$^{2+}$ + H$_2$O ⇌ CoOH$^+$ + H$^+$ | –9.65 | −9.61 ± 0.17 |
| Co$^{2+}$ + 2 H$_2$O ⇌ Co(OH)$_2$ + 2 H$^+$ | –18.8 | −19.77 ± 0.11 |
| Co$^{2+}$ + 3 H$_2$O ⇌ Co(OH)$_3$$^–$ + 3 H$^+$ | –31.5 | −32.01 ± 0.33 |
| Co$^{2+}$ + 4 H$_2$O ⇌ Co(OH)$_4$$^{2–}$ + 4 H$^+$ | –46.3 | |
| 2 Co$^{2+}$ + H$_2$O ⇌ Co$_2$(OH)$_3$$^+$ + H$^+$ | –11.2 | |
| 4 Co$^{2+}$ + 4 H$_2$O ⇌ Co$_4$(OH)$_4$$^{4+}$ + 4H$^+$ | –30.53 | |
| Co(OH)$_2$(s) + 2 H$^+$ ⇌ Co$^{2+}$ + 2 H$_2$O | 12.3 | 13.24 ± 0.12 |
| CoO(s) + 2 H$^+$ ⇌ Co$^{2+}$ + H$_2$O | | 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 |
| Co$^{3+}$ + H$_2$O ⇌ 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 |
| Cu$^+$ + H$_2$O ⇌ CuOH + H$^+$ | –7.8 ± 0.4 |
| Cu$^+$ + 2 H$_2$O ⇌ Cu(OH)$_2$$^–$ + 2 H$^+$ | –18.6 ± 0.6 |

### Copper(II)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:
| Reaction | Baes and Mesmer, 1976 | NIST46 | Plyasunova et al., 1997 | Powell et al., 2007 | Brown and Ekberg, 2016 |
| Cu$^{2+}$ + H$_2$O ⇌ CuOH$^+$ + H$^+$ | < –8 | –7.7 | –7.97 ± 0.09 | –7.95 ± 0.16 | –7.64 ± 0.17 |
| Cu$^{2+}$ + 2 H$_2$O ⇌ Cu(OH)$_2$ + 2 H$^+$ | (< –17.3) | –17.3 | –16.23 ± 0.15 | –16.2 ± 0.2 | –16.24 ± 0.03 |
| Cu$^{2+}$ + 3 H$_2$O ⇌ Cu(OH)$_3$$^–$ + 3 H$^+$ | (< –27.8) | –27.8 | –26.63 ± 0.40 | –26.60 ± 0.09 | –26.65 ± 0.13 |
| Cu$^{2+}$ + 4 H$_2$O ⇌ Cu(OH)$_4$$^{2–}$ + 4 H$^+$ | –39.6 | –39.6 | –39.73 ± 0.17 | –39.74 ± 0.18 | –39.70 ± 0.19 |
| 2 Cu$^{2+}$ + H$_2$O ⇌ Cu$_2$(OH)$_3$$^+$ + H$^+$ | | | –6.71 ± 0.30 | –6.40 ± 0.12 | –6.41 ± 0.17 |
| 2 Cu$^{2+}$ + 2 H$_2$O ⇌ Cu$_2$(OH)$_2$$^{2+}$ + 2 H$^+$ | –10.36 | –10.3 | –10.55 ± 0.17 | –10.43 ± 0.07 | –10.55 ± 0.02 |
| 3 Cu$^{2+}$ + 4 H$_2$O ⇌ Cu$_3$(OH)$_4$$^{2+}$ + 4 H$^+$ | | | –20.95 ± 0.30 | –21.1 ± 0.2 | –21.2 ± 0.4 |
| CuO(s) + 2 H$^+$ ⇌ Cu$^{2+}$ + H$_2$O | 7.62 | | 7.64 ± 0.06 | 7.64 ± 0.06 | 7.63 ± 0.05 |
| Cu(OH)$_2$(s) + 2 H$^+$ ⇌ Cu$^{2+}$ + 2 H$_2$O | | | | 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 |
| Cm$^{3+}$ + H$_2$O ⇌ Cm(OH)$^{2+}$ + H$^+$ | −7.66 ± 0.07 |
| Cm$^{3+}$ + 2 H$_2$O ⇌ Cm(OH)$_2$$^+$ + 2 H$^+$ | −15.9 ± 0.1 |
| Cm$^{3+}$ + 3 H$_2$O ⇌ 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 |
| Dy$^{3+}$ + H$_2$O ⇌ DyOH$^{2+}$ + H$^+$ | −8.0 | −7.53 ± 0.14 |
| Dy$^{3+}$ + 2 H$_2$O ⇌ Dy(OH)$_2$$^+$ + 2 H$^+$ | (–16.2) | |
| Dy$^{3+}$ + 3 H$_2$O ⇌ Dy(OH)$_3$ + 3 H$^+$ | (–24.7) | |
| Dy$^{3+}$ + 4 H$_2$O ⇌ Dy(OH)$_4$$^−$ + 4 H$^+$ | –33.5 | |
| 2 Dy$^{3+}$ + 2 H$_2$O ⇌ Dy$_2$(OH)$_2$$^{4+}$ + 2 H$^+$ | | −13.76 ± 0.20 |
| 3 Dy$^{3+}$ + 5 H$_2$O ⇌ Dy$_3$(OH)$_5$$^{4+}$ + 5 H$^+$ | | −30.6 ± 0.3 |
| Dy(OH)$_3$(s) + 3 H$^+$ ⇌ Dy$^{3+}$ + 3 H$_2$O | 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 |
| Er$^{3+}$ + H$_2$O ⇌ ErOH$^{2+}$ + H$^+$ | −7.9 | −7.46 ± 0.09 |
| Er$^{3+}$ + 2 H$_2$O ⇌ Er(OH)$_2$$^+$ + 2 H$^+$ | (−15.9) | |
| Er$^{3+}$ + 3 H$_2$O ⇌ Er(OH)$_3$ + 3 H$^+$ | (−24.2) | |
| Er$^{3+}$ + 4 H$_2$O ⇌ Er(OH)$_4$$^−$ + 4 H$^+$ | −32.6 | |
| 2 Er$^{3+}$ + 2 H$_2$O ⇌ Er$_2$(OH)$_2$$^{4+}$ + 2 H$^+$ | −13.65 | −13.50 ± 0.20 |
| 3 Er$^{3+}$ + 5 H$_2$O ⇌ Er$_3$(OH)$_5$$^{4+}$ + 5 H$^+$ | <−29.3 | −31.0 ± 0.3 |
| Er(OH)$_3$(s) + 3 H$^+$ ⇌ Er$^{3+}$ + 3 H$_2$O | 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$^{3+}$ + H$_2$O ⇌ EuOH$^{2+}$ + H$^+$ | –7.8 | | –7.64 ± 0.04 | –7.66 ± 0.05 |
| Eu$^{3+}$ + 2 H$_2$O ⇌ Eu(OH)$_2$$^+$ + 2 H$^+$ | | | –15.1 ± 0.2 | |
| Eu$^{3+}$ + 3 H$_2$O ⇌ Eu(OH)$_3$ + 3 H$^+$ | | | –23.7 ± 0.1 | |
| Eu$^{3+}$ + 4 H$_2$O ⇌ Eu(OH)$_4$$^−$ + 4 H$^+$ | | | –36.2 ± 0.5 | |
| 2 Eu$^{3+}$ + 2 H$_2$O ⇌ Eu$_2$(OH)$_2$$^{4+}$ + 2 H$^+$ | | | - | –14.1 ± 0.2 |
| 3 Eu$^{3+}$ + 5 H$_2$O ⇌ Eu$_3$(OH)$_5$$^{4+}$ + 5 H$^+$ | | | - | –32.0 ± 0.3 |
| Eu(OH)$_3$(s) + 3 H$^+$ ⇌ Eu$^{3+}$ + 3 H$_2$O | 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 |
| Gd$^{3+}$ + H$_2$O ⇌ GdOH$^{2+}$ + H$^+$ | –8.0 | –7.87 ± 0.05 |
| Gd$^{3+}$ + 2 H$_2$O ⇌ Gd(OH)$_2$$^+$ + 2 H$^+$ | (–16.4) | |
| Gd$^{3+}$ + 3 H$_2$O ⇌ Gd(OH)$_3$ + 3 H$^+$ | (–25.2) | |
| Gd$^{3+}$ + 4 H$_2$O ⇌ Gd(OH)$_4$$^–$ + 4 H$^+$ | –34.4 | |
| 2 Gd$^{3+}$ + 2 H$_2$O ⇌ Gd$_2$(OH)$_2$$^{4+}$ + 2 H$^+$ | | –14.16 ± 0.20 |
| 3 Gd$^{3+}$ + 5 H$_2$O ⇌ Gd$_3$(OH)$_5$$^{4+}$ + 5 H$^+$ | | –33.0 ± 0.3 |
| Gd(OH)$_3$(s) + 3 H$^+$ ⇌ Gd$^{3+}$ + 3 H$_2$O | 15.6 | 17.20 ± 0.48 |
| Gd(OH)$_3$(c) + OH$^–$ ⇌ Gd(OH)$_4$$^–$ | –4.8 | |
| Gd(OH)$_3$(c) ⇌ Gd(OH)$_3$ | –9.6 | |

### Gallium

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:
| Reaction | Baes and Mesmer, 1976 | Smith et al., 2003 | Brown and Ekberg, 2016 |
| Ga$^{3+}$ + H$_2$O ⇌ GaOH$^{2+}$ + H$^+$ | –2.6 | –2.897 | –2.74 |
| Ga$^{3+}$ + 2 H$_2$O ⇌ Ga(OH)$_2$$^+$ + 2 H$^+$ | –5.9 | –6.694 | –7.0 |
| Ga$^{3+}$ + 3 H$_2$O ⇌ Ga(OH)$_3$ + 3 H$^+$ | –10.3 | | –11.96 |
| Ga$^{3+}$ + 4 H$_2$O ⇌ Ga(OH)$_4$$^–$ + 4 H$^+$ | –16.6 | –16.588 | –15.52 |
| Ga(OH)$_3$(s) ⇌ Ga$^{3+}$ + 3 OH$^–$ | $\approx$–37 | –37.0 | |
| GaO(OH)(s) + H$_2$O ⇌ 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 | Wood and Samson, 2006 | Filella and May, 2023 |
| Ge(OH)$_4$ ⇌ GeO(OH)$_3$$^−$ + H$^+$ | –9.31 | –9.32 ± 0.05 | –9.099 |
| Ge(OH)$_4$ ⇌ GeO2(OH)$_2$$^{2+}$ + 2 H$^+$ | –21.9 | | |
| GeO$_2$(OH)$_2$$^{2–}$ + H$^+$ ⇌ GeO(OH)$_3$$^–$ | | | 12.76 |
| 8 Ge(OH)$_4$ ⇌ Ge$_8$O$_{16}$(OH)$_3$$^{3-}$ + 13 H$_2$O + 3 H$^+$ | –14.24 | | |
| 8 Ge(OH)$_4$ + 3 OH$^–$ ⇌ Ge$_8$(OH)$_{35}$$^{3–}$ | | | 28.33 |
| GeO$_2$(s, hexa) + 2 H$_2$O ⇌ Ge(OH)$_4$ | | –1.35 | –1.373 |
| GeO$_2$(s, tetra) + 2 H$_2$O ⇌ Ge(OH)$_4$ | -4.37 | –5.02 | –4.999 |

### Gold(III)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:
| Reaction | Baes and Mesmer, 1976 |
| Au(OH)$_3$ +2 H$^+$ ⇌ AuOH$^{2+}$ + 2 H$_2$O | 1.51 |
| Au(OH)$_3$ + H$^+$ ⇌ Au(OH)$_2$$^+$ + H$_2$O | < 1.0 |
| Au(OH)$_3$ + H$_2$O ⇌ Au(OH)$_4$$^–$ + H$^+$ | –11.77 |
| Au(OH)$_3$ + 2 H$_2$O ⇌ Au(OH)$_5$$^{2–}$ + 2 H$^+$ | –25.13 |
| Au(OH)$_5$$^{2–}$ + 3 H$_2$O ⇌ 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 | Brown and Ekberg, 2016 |
| Hf$^{4+}$ + H$_2$O ⇌ HfOH$^{3+}$ + H$^+$ | –0.25 | −0.26 ± 0.10 |
| Hf$^{4+}$ + 2 H$_2$O ⇌ Hf(OH)$_2$$^{2+}$ + 2 H$^+$ | (–2.4) | |
| Hf$^{4+}$ + 3 H$_2$O ⇌ Hf(OH)$_3$$^+$ + 3 H$^+$ | (–6.0) | |
| Hf$^{4+}$ + 4 H$_2$O ⇌ Hf(OH)$_4$ + 4 H$^+$ | –10.7* | −3.75 ± 0.34* |
| Hf$^{4+}$ + 5 H$_2$O ⇌ Hf(OH)$_5$$^–$ + 5 H$^+$ | –17.2 | |
| 3 Hf$^{4+}$ + 4 H$_2$O ⇌ Hf$_3$(OH)$_4$$^{8+}$ + 4 H$^+$ | | 0.55 ± 0.30 |
| 4 Hf$^{4+}$ + 8 H$_2$O ⇌ Hf$_4$(OH)$_8$$^{8+}$ + 8 H$^+$ | | 6.00 ± 0.30 |
| HfO$_2$(s) + 4 H$^+$ ⇌ Hf$^{4+}$ + 2 H$_2$O | –1.2* | –5.56 ± 0.15* |
| HfO$_{2$am) + 4 H$^+$ ⇌ Hf$^{4+}$ + 2 H$_2$O | | –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 |
| Ho$^{3+}$ + H$_2$O ⇌ HoOH$^{2+}$ + H$^+$ | −8.0 | −7.43 ± 0.05 |
| 2 Ho$^{3+}$ + 2 H$_2$O ⇌ Ho$_2$(OH)$_2$$^{4+}$ + 2 H$^+$ | | −13.5 ± 0.2 |
| 3 Ho$^{3+}$ + 5 H$_2$O ⇌ Ho$_3$(OH)$_5$$^{4+}$ + 5 H$^+$ | | −30.9 ± 0.3 |
| Ho(OH)$_3$(s) + 3 H$^+$ ⇌ Ho$^{3+}$ + 3 H$_2$O | 15.4 | 15.60 ± 0.30 |

### Indium

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:
| Reaction | Baes and Mesmer, 1976 | NIST46 | Brown and Ekberg, 2016 |
| In$^{3+}$ + H$_2$O ⇌ InOH$^{2+}$ + H$^+$ | –4.00 | –3.927 | –3.96 |
| In$^{3+}$ + 2 H$_2$O ⇌ In(OH)$_2$$^+$ + 2 H$^+$ | –7.82 | –7.794 | –9.16 |
| In$^{3+}$ + 3 H$_2$O ⇌ In(OH)$_3$ + 3 H$^+$ | –12.4 | –12.391 | |
| In$^{3+}$ + 4 H$_2$O ⇌ In(OH)$_4$$^–$ + 4 H$^+$ | –22.07 | –22.088 | –22.05 |
| In(OH)$_3$(s) ⇌ In$^{3+}$ + 3 OH$^–$ | –36.92 | –36.9 | –36.92 |
| 1/2 In$_2$O$_3$(s) + 3/2 H$_2$O ⇌ 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 |
| Ir$^{3+}$ + H$_2$O ⇌ IrOH$^{2+}$ + H$^+$ | ‒3.77 ± 0.10 |
| Ir$^{3+}$ + 2 H$_2$O ⇌ Ir(OH)$_2$$^+$ + 2 H$^+$ | ‒8.46 ± 0.20 |
| Ir(OH)$_3$(s) + 3 H$^+$ ⇌ Ir$^{3+}$ + 3 H$_2$O | 8.88 ± 0.20 |

### Iron(II)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:
| Reaction | Baes and Mesmer, 1976 | Nordstrom et al., 1990 | Hummel et al., 2002 | Lemire et al., 2013 | Brown and Ekberg, 2016 |
| Fe$^{2+}$ + H$_2$O ⇌ FeOH$^+$ + H$^+$ | –9.3 | –9.5 | –9.5 | –9.1 ± 0.4 | −9.43 ± 0.10 |
| Fe$^{2+}$ + 2 H$_2$O ⇌ Fe(OH)$_2$ + 2 H$^+$ | –20.5 | | | | −20.52 ± 0.08 |
| Fe$^{2+}$ + 3 H$_2$O ⇌ Fe(OH)$_3$$^−$ + 3 H$^+$ | –29.4 | | | | −32.68 ± 0.15 |
| Fe(OH)$_2$(s) +2 H$^+$ ⇌ Fe$^{2+}$ + 2 H$_2$O | | | | | 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 |
| Fe$^{3+}$ + H$_2$O ⇌ FeOH$^{2+}$ + H$^+$ | –2.19 | −2.15 ± 0.07 | –2.20 ± 0.02 |
| Fe$^{3+}$ + 2 H$_2$O ⇌ Fe(OH)$_2$$^+$ + 2 H$^+$ | –5.67 | −4.8 ± 0.4 | –5.71 ± 0.10 |
| Fe$^{3+}$ + 3 H$_2$O ⇌ Fe(OH)$_3$ + 3 H$^+$ | <–12 | <–14 | –12.42 ± 0.20 |
| Fe$^{3+}$ + 4 H$_2$O ⇌ Fe(OH)$_4$$^–$ + 4 H$^+$ | –21.6 | −21.5 ± 0.5 | –21.60 ± 0.23 |
| 2 Fe$^{3+}$ + 2 H$_2$O ⇌ Fe$_2$(OH)$_2$$^{4+}$ + 2 H$^+$ | –2.95 | –2.91 ± 0.07 | –2.91 ± 0.07 |
| 3 Fe$^{3+}$ + 4 H$_2$O ⇌ Fe$_3$(OH)$_4$$^{5+}$ + 4 H$^+$ | –6.3 | | −6.3 ± 0.1 |
| Fe(OH)$_3$(s) +3 H$^+$ ⇌ Fe3$^+$ + 3 H$_2$O 2-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 H$_2$O goethite | 0.5 | | 0.33 ± 0.10 |
| α-FeOOH + H$_2$O ⇌ Fe$^{3+}$ + 3 OH$^−$ goethite | | −41.83 ± 0.37 | |
| 0.5 α-Fe$_2$O$_3$(s)+ 3 H$^+$ ⇌ Fe$^{3+}$ + 1.5 H$_2$O hematite | | | 0.36 ± 0.40 |
| 0.5 α-Fe$_2$O$_3$ + 1.5 H$_2$O ⇌ Fe$^{3+}$ + 3 OH$^−$ hematite | | −42.05 ± 0.26 | |
| 0.5 γ-Fe$_2$O$_3$(s) + 3 H$^+$ ⇌ Fe$^{3+}$ + 1.5 H$_2$O maghemite | | | 1.61 ± 0.61 |
| 0.5 γ-Fe$_2$O$_3$ + 1.5 H$_2$O ⇌ Fe$^{3+}$ + 3 OH$^−$ maghemite | | −40.59 ± 0.29 | |
| α-FeOOH(s)+ 3 H$^+$ ⇌ Fe$^{3+}$ + 2 H$_2$O goethite | | | 1.85 ± 0.37 |
| γ-FeOOH + H$_2$O ⇌ Fe$^{3+}$ + 3 OH$^−$ lepidocrocite | | −40.13 ± 0.37 | |
| Fe(OH)$_3$(s) + 3 H$^+$ ⇌ Fe$^{3+}$ + 3 H$_2$O magnetite | | | −12.26 ± 0.26 |

### Lanthanum

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:
| Reaction | Baes and Mesmer, 1976 | Brown and Ekberg, 2016 |
| La$^{3+}$ + H$_2$O ⇌ LaOH$^{2+}$ + H$^+$ | –8.5 | –8.89 ± 0.10 |
| 2 La$^{3+}$ + 2 H$_2$O ⇌ La$_2$(OH)$_2$$^{4+}$ + 2 H$^+$ | ≤ –17.5 | –17.57 ± 0.20 |
| 3 La$^{3+}$ + 5 H$_2$O ⇌ La$_3$(OH)$_5$$^{4+}$ + 5 H$^+$ | ≤ –38.3 | –37.8 ± 0.3 |
| 5 La$^{3+}$ + 9 H$_2$O ⇌ La$_5$(OH)$_9$$^{6+}$ + 9 H$^+$ | –71.2 | |
| La(OH)$_3$(s) + 3 H$^+$ ⇌ La$^{3+}$ + 3 H$_2$O | 20.3 | 19.72 ± 0.34 |

### Lead(II)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:
| Reaction | Baes and Mesmer, 1976 | NIST46 | Powell et al, 2009 | Brown and Ekberg, 2016 | Cataldo et al., 2018 |
| Pb$^{2+}$ + H$_2$O ⇌ PbOH+ + H$^+$ | –7.71 | –7.6 | –7.46 ± 0.06 | –7.49 ± 0.13 | –6.47± 0.03 |
| Pb$^{2+}$ + 2 H$_2$O ⇌ Pb(OH)$_2$ + 2 H$^+$ | –17.12 | –17.1 | –16.94 ± 0.09 | –16.99 ± 0.06 | –16.12 ± 0.01 |
| Pb$^{2+}$ + 3 H$_2$O ⇌ Pb(OH)$^{3-}$ + 3 H$^+$ | –28.06 | –28.1 | –28.03± 0.06 | –27.94 ± 0.21 | –28.4 ± 0.1 |
| Pb$^{2+}$ + 4 H$_2$O ⇌ Pb(OH)$_4$$^{2-}$ + 4 H$^+$ | | | –40.8 | | |
| 2 Pb$^{2+}$ + H$_2$O ⇌ Pb$_2$(OH)$_3$$^+$ + H$^+$ | –6.36 | –6.4 | –7.28± 0.09 | –6.73 ± 0.31 | |
| 3 Pb$^{2+}$ + 4 H$_2$O ⇌ Pb$_{3$OH)$_4$$^{2+}$ + 4 H$^+$ | –23.88 | –23.9 | –23.01 ± 0.07 | –23.43 ± 0.10 | |
| 3 Pb$^{2+}$ + 5 H$_2$O ⇌ Pb$_3$(OH)$_5$$^+$ + 5 H$^+$ | | | | –31.11 ± 0.10 | |
| 4 Pb$^{2+}$ + 4 H$_2$O ⇌ Pb$_4$(OH)$_4$$^{4+}$ + 4 H$^+$ | –20.88 | –20.9 | –20.57± 0.06 | –20.71 ± 0.18 | |
| 6 Pb$^{2+}$ + 8 H$_2$O ⇌ Pb$_6$(OH)$_8$$^{4+}$ + 8 H$^+$ | –43.61 | –43.6 | –42.89± 0.07 | –43.27 ± 0.47 | |
| PbO(s) + 2 H$^+$ ⇌ Pb$^{2+}$ + H$_2$O | | | 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) | |
| Pb$_2$O(OH)$_{2$s) +H2O ⇌ 2 Pb$^{2+}$ + 4 OH$^–$ | | | –14.9 | | |
| PbO(s) +H$_2$O ⇌ Pb(OH)$_2$ | | | –4.4 (red) –4.2 (yellow) | | |
| Pb$_2$O(OH)$_2$(s) +H$_2$O ⇌ 2 Pb(OH)$_2$ | | | –4.0 | | |
| PbO(s) + 2 H$_2$O ⇌ Pb(OH)$_3$$^–$ + H$^+$ | | | –1.4 (red) –1.2 (yellow) | | |
| Pb$_2$O(OH)$_{2$s) + 2 H$_2$O ⇌ 2 Pb(OH)$_3$$^–$ + 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-PbO$_2$ + 2 H$_2$O ⇌ Pb$^{4+}$ + 4 OH$^–$ | –64 |
| β-PbO$_2$ + 2 H$_2$O + 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 | Nordstrom et al., 1990 | Brown and Ekberg, 2016 |
| Li$^+$ + H$_2$O ⇌ LiOH + H$^+$ | –13.64 | –13.64 | –13.84 ± 0.14 |

### Magnesium

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:
| Reaction | Baes and Mesmer, 1976 | Nordstrom et al., 1990 | Brown and Ekberg, 2016 |
| Mg$^{2+}$ + H$_2$O ⇌ MgOH$^+$ + H$^+$ | –11.44 | –11.44 | –11.70 ± 0.04 |
| 4 Mg$^{2+}$ + 4 H$_2$O ⇌ Mg$_4$(OH)$_4$$^{4+}$ + 4 H$^+$ | –39.71 | | |
| Mg(OH)$_2$(cr) + 2 H$^+$ ⇌ Mg$^{2+}$ + 2 H$_2$O | 16.84 | 16.84 | 17.11 ± 0.04 |

### Manganese(II)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:
| Reaction | Perrin et al., 1969 | Baes and Mesmer, 1976 | Nordstrom et al., 1990 | Hummel et al., 2002 | Brown and Ekberg, 2016 |
| Mn$^{2+}$ + H$_2$O ⇌ MnOH$^+$ + H$^+$ | –10.59 | –10.59 | –10.59 | –10.59 | −10.58 ± 0.04 |
| Mn$^{2+}$ + 2 H$_2$O ⇌ Mn(OH)$_2$ + 2 H$^+$ | | –22.2 | | | −22.18 ± 0.20 |
| Mn$^{2+}$ + 3 H$_2$O ⇌ Mn(OH)$_3$$^–$ + 3 H$^+$ | | –34.8 | | | −34.34 ± 0.45 |
| Mn$^{2+}$ + 4 H$_2$O ⇌ Mn(OH)$_4$$^{2–}$ + 4 H$^+$ | | –48.3 | | | −48.28 ± 0.40 |
| 2 Mn$^{2+}$ + H$_2$O ⇌ Mn$_2$OH$^{3+}$ + H$^+$ | | –10.56 | | | |
| 2 Mn$^{2+}$ + 3 H$_2$O ⇌ Mn$_2$(OH)$_3$$^+$ + 6 H$^+$ | | –23.90 | | | |
| Mn(OH)$_2$(s) + 2 H$^+$ ⇌ Mn$^{2+}$ + 2 H$_2$O | 15.2 | 15.2 | 15.2 | | 15.19 ± 0.10 |
| MnO(s) + 2 H$^+$ ⇌ Mn$^{2+}$ + H$_2$O | | | | | 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 |
| Mn$^{3+}$ + H$_2$O ⇌ 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 | Brown and Ekberg, 2016 |
| Hg$_2$$^{2+}$ + H$_2$O ⇌ Hg$_2$OH$^+$ + H$^+$ | −5.0$^a$ | −4.45 ± 0.10 |
($^a$) 0.5 M HClO$_4$

### Mercury(II)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:
| Reaction | Baes and Mesmer, 1976 | Powell et all, 2005 | Brown and Ekberg, 2016 |
| Hg$^2$+ + H$_2$O ⇌ HgOH+ + H$^+$ | −3.40 | –3.40 ± 0.08 | –3.40 ± 0.08 |
| Hg$^{2+}$ + 2 H$_2$O ⇌ Hg(OH)$_2$ + 2 H$^+$ | -6.17 | –5.98 ± 0.06 | −5.96 ± 0.07 |
| Hg$^{2+}$ + 3 H$_2$O ⇌ Hg(OH)$_3$$^–$ + 3 H$^+$ | –21.1 | –21.1 ± 0.3 | |
| HgO(s) + 2 H$^+$ ⇌ Hg$^{2+}$ + H$_2$O | 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 NaClO$_4$ ($^a$) or 0.1 M Na$^+$ medium, Data at I = 0 are not available ($^b$):
| Reaction | Baes and Mesmer, 1976 | Jolivet, 2000 | NIST46 | Crea et al., 2017 |
| MoO$_4$$^{2–}$ + H$^+$ ⇌ HMoO$_4$$^–$ | 3.89$^a$ | | 4.24 | 4.47 ± 0.02 |
| MoO$_4$$^{2–}$ + 2 H$^+$ ⇌ H$_2$MoO$_4$ | 7.50$^a$ | | | 8.12 ± 0.03 |
| HMoO$_4$$^–$ + H$^+$ ⇌ H$_2$MoO$_4$ | | | 4.0 | |
| Mo$_7$O$_{24}$$^{6–}$ + H$^+$ ⇌ HMo$_7$O$_{24}$$^{5–}$ | | 4.4 | | |
| HMo$_7$O$_{24}$$^{5–}$ + H$^+$ ⇌ H$_2$Mo7O$_{24}$$^{4–}$ | | 3.5 | | |
| H$_2$Mo$_7$O$_{24}$$^{4–}$ + H$^+$ ⇌ H$_3$Mo$_7$O$_{24}$$^{3–}$ | | 2.5 | | |
| 7 MoO$_4$$^{2-}$+ 8 H$^+$ ⇌ Mo$_7$O$_{24}$$^{6–}$ + 4 H$_2$O | 57.74$^a$ | | 52.99$^b$ | 51.93 ± 0.04 |
| 7 MoO$_4$$^{2–}$ + 9 H$^+$ ⇌ Mo$_7$O$_{23}$(OH)$^{5–}$ + 4 H$_2$O | 62.14$^a$ | | | 58.90 ± 0.02 |
| 7 MoO$_4$$^{2–}$ + 10 H$^+$ ⇌ Mo$_7$O$_{22}$(OH)$_2$$^{4–}$ + 4 H$_2$O | 65.68$^a$ | | | 64.63 ± 0.05 |
| 7 MoO$_4$$^{2–}$ + 11 H$^+$ ⇌ Mo$_7$O$_{21}$(OH)$_3$$^{3–}$ + 4 H$_2$O | 68.21$^a$ | | | 68.68 ± 0.06 |
| 19 MoO$_4$$^{2-}$ + 34 H$^+$ ⇌ Mo$_{19}$O$_{59}$$^{4–}$ + 17 H$_2$O | 196.3$^a$ | | 196$^a$ | |
| MoO$_3$(s) + H$_2$O ⇌ MoO$_4$$^{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 | Brown and Ekberg, 2016 |
| Nd$^{3+}$ + H$_2$O ⇌ NdOH$^{2+}$ + H$^+$ | –8.0 | –8.0 | –7.4 ± 0.4 | –8.13 ± 0.05 |
| Nd$^{3+}$ + 2 H$_2$O ⇌ Nd(OH)$_2$$^+$ + 2 H$^+$ | (–16.9) | | –15.7 ± 0.7 | |
| Nd$^{3+}$ + 3 H$_2$O ⇌ Nd(OH)$_3$(aq) + 3 H$^+$ | (–26.5) | | –26.2 ± 0.5 | |
| Nd$^{3+}$ + 4 H$_2$O ⇌ Nd(OH)$_4$$^−$ + 4 H$^+$ | (–37.1) | –37.4 | –40.7 ± 0.7 | |
| 2 Nd$^{3+}$ + 2 H$_2$O ⇌ Nd$_2$(OH)$_2$$^{4+}$ + 2 H$^+$ | –13.86 | –13.9 | | –15.56 ± 0.20 |
| 3 Nd$^{3+}$ + 5 H$_2$O ⇌ Nd$_3$(OH)$_5$$^{4+}$ + 5 H$^+$ | < –28.5 | | | –34.2 ± 0.3 |
| Nd(OH)$_3$(s) + 3 H$^+$ ⇌ Nd$^{3+}$ + 3 H$_2$O | 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 | Grenthe et al, 2020 |
| Np$^{3+}$ + H$_2$O ⇌ 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 | NIST46 | Brown and Ekberg, 2016 | Grenthe et al, 2020 |
| Np$^{4+}$ + H$_2$O ⇌ NpOH$^{3+}$ + H$^+$ | –1.49 | –1.5 | –1.31 ± 0.05 | 0.5 ± 0.2 |
| Np$^{4+}$ + 2 H$_2$O ⇌ Np(OH)$_2$$^{2+}$ + 2 H$^+$ | | | –3.7 ± 0.3 | 0.3 ± 0.3 |
| Np$^{4+}$ + 4 H$_2$O ⇌ Np(OH)$_4$ + 4 H$^+$ | | | –10.0 ± 0.9 | –8 ± 1 |
| Np$^{4+}$ + 4 OH$^−$ ⇌ NpO$_2$(am, hyd) + 2 H$_2$O | 52 | 54.9 ± 0.4 | 57.5 ± 0.3 | 56.7 ± 0.5 |

### Neptunium(V)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:
| Reaction | Baes and Mesmer, 1976 | Brown and Ekberg, 2016 | Grenthe et al, 2020 |
| NpO$_2$$^+$ + + H$_2$O ⇌ NpO$_2$(OH) + H$^+$ | –8.85 | –10.7 ± 0.5 | –11.3 ± 0.7 |
| NpO$_2$$^+$ + 2 H$_2$O ⇌ NpO$_2$(OH)$_2$$^−$ + 2 H$^+$ | | –22.8 ± 0.7 | –23.6 ± 0.5 |
| NpO$_2$$^+$ + H$_2$O ⇌ NpO$_2$(OH)(am, fresh) + H$^+$ | ≤ –4.7 | –5.21 ± 0.05 | –5.3 ± 0.2 |
| NpO$_2$$^+$ + H$_2$O ⇌ NpO$_2$(OH)(am, aged) + H$^+$ | | –4.53 ± 0.06 | –4.7 ± 0.5 |

### Neptunium(VI)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:
| Reaction | Baes and Mesmer, 1976 | NIST46 | Brown and Ekberg, 2016 | Grenthe et al, 2020 |
| NpO$_2$$^{2+}$ + H$_2$O ⇌ NpO$_2$(OH)$^+$ + H$^+$ | –5.15 | –5.12 | –5.1 ± 0.2 | –5.1 ± 0.4 |
| NpO$_2$$^{2+}$ + 3 H$_2$O ⇌ NpO$_2$(OH)$_3$$^−$ + 3 H$^+$ | | | –21 ± 1 | |
| NpO$_2$$^{2+}$ + 4 H$_2$O ⇌ NpO$_2$(OH)$_4$$^{2-}$ + 4 H$^+$ | | | –32 ± 1 | |
| 2 NpO$_2$$^{2+}$ + 2 H$_2$O ⇌ (NpO$_2$)$_2$(OH)$_2$$^{2+}$ + 2 H$^+$ | –6.39 | –6.39 | –6.2 ± 0.2 | –6.2 ± 0.2 |
| 3 NpO$_2$$^{2+}$ + 5 H$_2$O ⇌ (NpO$_2$)$_3$(OH)$_5$$^+$ + 5 H$^+$ | –17.49 | –17.49 | –17.0 ± 0.2 | –17.1 ± 0.2 |
| NpO$_2$$^{2+}$ + 2 H$_2$O ⇌ NpO$_3$.H$_2$O(cr) + 2 H$^+$ | ≥-6.6 | | –5.4 ± 0.4 | –5.4 ± 0.4 |

### Nickel(II)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:
| Reaction | Feitknecht and Schindler, 1963 | Baes and Messmer, 1976 | NIST46 | Gamsjäger et al., 2005 | Thoenen et al., 2014 | Brown and Ekberg, 2016 |
| Ni$^{2+}$ + H$_2$O ⇌ NiOH$^+$ + H$^+$ | | –9.86 | –9.9 | –9.54 ± 0.14 | –9.54 ± 0.14 | –9.90 ± 0.03 |
| Ni$^{2+}$ + 2 H$_2$O ⇌ Ni(OH)$_2$ + 2 H$^+$ | | –19 | –19 | | < –18 | –21.15 ± 0.0 |
| Ni$^{2+}$ + 3 H$_2$O ⇌ Ni(OH)$_3$$^–$ + 3 H$^+$ | | –30 | –30 | –29.2 ± 1.7 | –29.2 ± 1.7 | |
| Ni$^{2+}$ + 4 H$_2$O ⇌ Ni(OH)$_4$$^{2–}$ + 4 H$^+$ | | < –44 | | | | |
| 2 Ni$^{2+}$ + H$_2$O ⇌ Ni$_2$(OH)$^{3+}$ + H$^+$ | | –10.7 | | –10.6 ± 1.0 | –10.6 ± 1.0 | –10.6 ± 1.0 |
| 4 Ni$^{2+}$ + 4 H$_2$O ⇌ Ni$_4$(OH)$_4$$^{4+}$ + 4 H$^+$ | | –27.74 | –27.7 | –27.52 ± 0.15 | –27.52 ± 0.15 | –27.9 ± 0.6 |
| β-Ni(OH)$_2$(s) + 2 H$^+$ ⇌ Ni$^{2+}$ + 2 H$_2$O | | 10.8 | | | 11.02 ± 0.20 | 10.96 ± 0.20 11.75 ± 0.13 (microcr) |
| Ni(OH)$_2$(s) ⇌ Ni$^{2+}$ + 2 OH$^–$ | –17.2 (inactive) | | –17.2 | –16.97± 0.20 (β) –17.2 ± 1.3 (cr) | | |
| Ni(OH)$_2$(s) + OH$^–$ ⇌ Ni(OH)$_3$$^–$ | –4.2 (inactive) | | | | | |
| NiO(cr) + 2 H$^+$ ⇌ Ni$^{2+}$ + H$_2$O | | | | 12.38 ± 0.06 | | 12.48 ± 0.15 |

### Niobium

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:
| Reaction | Baes and Mesmer, 1976 | Filella and May, 2020 |
| Nb(OH)$_5$ + H$^+$ ⇌ Nb(OH)$_4$$^+$ + H$_2$O | ~ –0.6 | 1.603 |
| Nb(OH)$_5$ + H$_2$O ⇌ Nb(OH)$_6$$^–$ + H$^+$ | ~ –4.8 | –4.951 |
| Nb$_6$O$_{19}$$^{8–}$ + H$^+$ ⇌ HNb$_6$O$_{19}$$^{7–}$ | | 14.95 |
| HNb$_6$O$_{19}$$^{7–}$ + H$^+$ ⇌ H$_2$Nb$_6$O$_{19}$$^{6–}$ | | 13.23 |
| H$_2$Nb$_6$O$_{19}$$^{6–}$ + H$^+$ ⇌ H$_3$Nb$_6$O$_{19}$$^{5–}$ | | 11.73 |
| 1/2 Nb$_2$O$_5$(act) + 5/2 H$_2$O ⇌ Nb(OH)$_5$ | ~ –7.4 | |
| Nb(OH)$_5$(am,s) ⇌ Nb(OH)$_5$ | | –7.510 |
| Nb$_2$O$_5$(s) + 5 H$_2$O ⇌ 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 |
| OsO$_2$(OH)$_4$$^{2–}$ + H$^+$ ⇌ HOsO$_2$(OH)$_4$$^–$ | 10.4 |
| HOsO$_2$(OH)$_4$$^–$ + H$^+$ ⇌ H$_2$OsO$_2$(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 |
| OsO$_2$(OH)$_3$(O$^−$)aq + H$^+$ ⇌ OsO$_2$(OH)$_4$aq | 12.2$^a$ |
| OsO$_2$(OH)$_2$(O$^−$)$_2$aq + H$^+$ ⇌ OsO$_2$(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 | Hummel et al., 2002 | Kitamura and Yul, 2010 | Brown and Ekberg, 2016 |
| Pd$^{2+}$ + H$_2$O ⇌ PdOH$^+$ + H$^+$ | −0.96 | | −0.65 ± 0.64 | −1.16 ± 0.30 |
| Pd$^{2+}$ + 2 H$_2$O ⇌ Pd(OH)$_2$ + 2 H$^+$ | −2.6 | −4 ± 1 | −3.11 ± 0.63 | −3.07 ± 0.16 |
| Pd$^{2+}$ + 3 H$_2$O ⇌ Pd(OH)$_3$$^−$ + 3 H$^+$ | | −15.5 ± 1 | −14.20 ± 0.63 | |
| Pd(OH)$_2$(am) + 2 H$^+$ ⇌ Pd$^{2+}$ + 2 H$_2$O | | −3.3 ± 1 | | −3.4 ± 0.2 |

### Plutonium(III)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:
| Reaction | Baes and Mesmer, 1976 | NIST46 | Brown and Ekberg, 2016 | Grenthe et al, 2020 |
| Pu$^{3+}$ + H$_2$O ⇌ PuOH$^{2+}$ + H$^+$ | | –7.0 | –6.9 ± 0.2 | –6.9 ± 0.3 |
| Pu$^{3+}$ + 3 H$_2$O ⇌ Pu(OH)$_3$(cr) + 3 H$^+$ | –19.65 | | –15.8 ± 0.8 | –15 ± 1 |

### Plutonium(IV)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:
| Reaction | Baes and Mesmer, 1976 | NIST46 | Brown and Ekberg, 2016 | Grenthe et al, 2020 |
| Pu$^{4+}$ + H$_2$O ⇌ PuOH $^{3+}$ + H$^+$ | –0.5 | –0.5 | –0.7 ± 0.1 | 0.6 ± 0.2 |
| Pu$^{4+}$ + 2 H$_2$O ⇌ Pu(OH)$_2$$^{2+}$ + 2 H$^+$ | (–2.3) | | | 0.6 ± 0.3 |
| Pu$^{4+}$ + 3 H$_2$O ⇌ Pu(OH)$_3$$^+$ + 3 H$^+$ | (–5.3) | | | –2.3 ± 0.4 |
| Pu$^{4+}$ + 4 H$_2$O ⇌ Pu(OH)$_4$ + 4 H$^+$ | –9.5 | | –12.5 ± 0.7 | –8.5 ± 0.5 |
| Pu$^{4+}$ + 4 OH$^−$ ⇌ PuO$_2$(am, hyd) + 2 H$_2$O | 49.5 | | 47.9 ± 0.4 (0w) 53.8 ± 0.5 (1w) | 58.3 ± 0.5 |

### Plutonium(V)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:
| Reaction | Baes and Mesmer, 1976 | NIST46 | Brown and Ekberg, 2016 | Grenthe et al, 2020 |
| PuO$_2$$^+$ + H$_2$O ⇌ PuO$_2$(OH) + H$^+$ | –1.49 | –1.5 | –1.31 ± 0.05 | 0.5 ± 0.2 |
| PuO2+ + H2O ⇌ PuO2(OH)(am) + H$^+$ | | | –3.7 ± 0.3 | 0.3 ± 0.3 |

### Plutonium(VI)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:
| Reaction | Baes and Mesmer, 1976 | NIST46 | Brown and Ekberg, 2016 | Grenthe et al, 2020 |
| PuO$_2$$^{2+}$ + H$_2$O ⇌ PuO$_2$(OH)$^+$ + H$^+$ | –5.6 | –5.6 | –5.36 ± 0.09 | –5.5 ± 0.5 |
| PuO$_2$$^{2+}$ + 2 H$_2$O ⇌ PuO$_2$(OH)$_2$ + 2 H$^+$ | | | –12.9 ± 0.2 | –13 ± 1 |
| PuO$_2$$^{2+}$ + 3 H$_2$O ⇌ PuO$_2$(OH)$_3$$^−$ + 3 H+ | | | | –24 ± 1 |
| 2 PuO$_2$$^{2+}$ + 2 H$_2$O ⇌ (PuO$_2$)$_2$(OH)$_2$$^{2+}$ + 2 H$^+$ | –8.36 | –8.36 | –7.8 ± 0.5 | –7 ± 1 |
| 3 PuO$_2$$^{2+}$ + 5 H$_2$O ⇌ (PuO$_2$)$_3$(OH)$_5$$^+$ + 5 H$^+$ | –21.65 | –21.65 | | |
| PuO$_2$$^{2+}$ + 2 OH$^−$ ⇌ PuO$_2$(OH)$_2$(am, hyd) | | | | 22.8 ± 0.6 |

### Potassium

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:
| Reaction | Baes and Mesmer, 1976 | Nordstrom et al., 1990 | Brown and Ekberg, 2016 |
| K$^+$ + H$_2$O ⇌ 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$^{3+}$ + H$_2$O ⇌ PrOH$^{2+}$ + H$^+$ | –8.1 | | –8.30 ± 0.03 |
| 2 Pr$^{3+}$ + 2 H$_2$O ⇌ Pr$_2$(OH)$_2$$^4$+ + 2 H$^+$ | | | –16.31 ± 0.20 |
| 3 Pr$^{3+}$ + 5 H$_2$O ⇌ Pr$_3$(OH)$_5$$^{4+}$ + 5 H$^+$ | | | –35.0 ± 0.3 |
| Pr(OH)$_3$(s) + 3 H$^+$ ⇌ Pr$^{3+}$ + 3 H$_2$O | 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$^{2+}$ + H$_2$O ⇌ RaOH$^+$ + H$^+$ | –13.49 |

### Rhodium

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:
| Reaction | Perrin et al., 1969 | Baes and Mesmer, 1976 | Brown and Ekberg |
| Rh$^{3+}$ + H$_2$O ⇌ RhOH$_2$$^+$ + H$^+$ | ‒3.43 | ‒3.4 | ‒3.09 ± 0.1 |
| Rh(OH)$_3$(c) + OH$^‒$ ⇌ Rh(OH)$_4$$^‒$ | | ‒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$^{3+}$ + H$_2$O ⇌ SmOH$^{2+}$ + H$^+$ | –7.9 | –7.9 | –7.84 ± 0.11 |
| 2 Sm$^{3+}$ + 2 H$_2$O ⇌ Sm$_2$(OH)$_2$$^{4+}$ + 2 H$^+$ | | | –14.75 ± 0.20 |
| 3 Sm$^{3+}$ + 5 H$_2$O ⇌ Sm$_3$(OH)$_5$$^{4+}$ + 5 H$^+$ | | | –33.9 ± 0.3 |
| Sm(OH)$_3$(s) + 3H$^+$ ⇌ Sm$^{3+}$ + 3H$_2$O | 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 | Brown and Ekberg, 2016 |
| Sc$^{3+}$ + H$_2$O ⇌ ScOH$^{2+}$ + H$^+$ | –4.3 | –4.16 ± 0.05 |
| Sc$^{3+}$ + 2 H$_2$O ⇌ Sc(OH)$_2$$^+$ + 2 H$^+$ | –9.7 | –9.71 ± 0.30 |
| Sc$^{3+}$ + 3 H$_2$O ⇌ Sc(OH)$_3$ + 3 H$^+$ | –16.1 | –16.08 ± 0.30 |
| Sc$^{3+}$ + 4 H$_2$O ⇌ Sc(OH)$_4$$^–$+ 4 H$^+$ | –26 | –26.7 ± 0.3 |
| 2 Sc$^{3+}$ + 2 H$_2$O ⇌ Sc$_2$(OH)$_2$$^{4+}$ + 2 H$^+$ | –6.0 | –6.02 ± 0.10 |
| 3 Sc$^{3+}$ + 5 H$_2$O ⇌ Sc$_3$(OH)$_5$$^{4+}$ + 5 H$^+$ | –16.34 | –16.33 ± 0.10 |
| Sc(OH)$_3$(s) + 3 H$^+$ ⇌ Sc$^{3+}$ + 3 H$_2$O | | 9.17 ± 0.30 |
| ScO$_{1.5}$(s) + 3 H$^+$ ⇌ Sc$^{3+}$ + 1.5 H$_2$O | | 5.53 ± 0.30 |
| ScO(OH)(c) + 3 H$^+$ ⇌ Sc$^{3+}$ + 2 H$_2$O | 9.4 | |
| Sc(OH)$_3$(c) + OH$^–$ ⇌ Sc(OH)$_4$ | | –3.5 ± 0.2 |

### Selenium(–II)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:
| Reaction | Olin et al., 2015 | Thoenen et al., 2014 |
| H$_2$Se(g) ⇌ H$_2$Se(aq) | –1.10 ± 0.01 | –1.10 ± 0.01 |
| H$_2$Se ⇌ 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 | Olin et al., 2005 | Thoenen et al., 2014 |
| SeO$_3$$^{2–}$ + H$^+$ ⇌ HSeO$_3$$^–$ | 8.50 | 8.36 ± 0.23 | 8.36 ± 0.23 |
| HSeO$_3$$^–$ + H$^+$ ⇌ H$_2$SeO$_3$ | 2.75 | 2.64 ± 0.14 | 2.64 ± 0.14 |

### Selenium(VI)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:
| Reaction | Baes and Mesmer, 1976 | Olin et al., 2005 | Thoenen et al., 2014 |
| SeO$_4$$^{2‒}$ + H$^+$ ⇌ HSeO$_4$$^‒$ | 1.360 | 1.75 ± 0.10 | 1.75 ± 0.10 |

### Silicon

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:
| Reaction | Baes and Mesmer, 1976 | Thoenen et al., 2014 |
| Si(OH)$_4$ ⇌ SiO(OH)$_3$$^–$ + H$^+$ | –9.86 | –9.81 ± 0.02 |
| Si(OH)$_4$ ⇌ SiO$_2$(OH)$_2$$^{2–}$ + 2 H$^+$ | –22.92 | –23.14 ± 0.09 |
| 4 Si(OH)$_4$ ⇌ Si$_4$O$_6$(OH)$_6$$^{4–}$ + 2 H$^+$ + 4 H$_2$O | –13.44 | |
| 4 Si(OH)$_4$ ⇌ Si$_4$O$_8$(OH)$_4$$^{4–}$ + 4 H$^+$ + 4 H$_2$O | –35.80 | –36.3 ± 0.2 |
| SiO$_2$(quartz) + 2 H$_2$O ⇌ Si(OH)$_4$ | –4.0 | –3.739 ± 0.087 |
| SiO$_2$(am) + 2 H$_2$O ⇌ Si(OH)$_4$ | | –2.714 |

### Silver

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:
| Reaction | Baes and Mesmer, 1976 | Brown and Ekberg, 2016 |
| Ag$^+$ + H$_2$O ⇌ AgOH + H$^+$ | −12.0 | −11.75 ± 0.14 |
| Ag$^+$ + 2 H$_2$O ⇌ Ag(OH)$_2$$^−$ + 2 H$^+$ | −24.0 | −24.34 ± 0.14 |
| 0.5 Ag$_2$O(am) + H$^+$ ⇌ Ag$^+$ + 0.5 H$_2$O | 6.29 | 6.27 ± 0.05 |

### Sodium

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:
| Reaction | Baes and Mesmer, 1976 | Nordstrom et al., 1990 | Brown and Ekberg, 2016 |
| Na$^+$ + H$_2$O ⇌ 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 |
| Sr$^{2+}$ + H$_2$O ⇌ SrOH$^+$ + H$^+$ | –13.29 | –13.29 | –13.15 ± 0.05 |

### Tantalum

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:
| Reaction | Baes and Mesmer, 1976 | Filella and May, 2019$^a$ |
| Ta(OH)$_5$ + H$^+$ ⇌ Ta(OH)$_4$$^+$ + H$_2$O | ~1 | 0.7007 |
| Ta(OH)$_5$ + H$_2$O ⇌ Ta(OH)$_6$$^–$ + H$^+$ | ~ –9.6 | |
| Ta$_6$O$_{19}$$^{8–}$ + H$^+$ ⇌ HTa$_6$O$_{19}$$^{7–}$ | | 16.35 |
| HTa$_6$O$_{19}$$^{7–}$ + H$^+$ ⇌ H$_2$Ta$_6$O$_{19}$$^{6–}$ | | 14.00 |
| 1/2 Ta$_2$O$_5$(act) + 5/2 H$_2$O ⇌ Ta(OH)$_5$ | ~ –5.2 | |
| Ta(OH)$_5$(s) ⇌ Ta(OH)$_5$ | | –5.295 |
| Ta$_2$O$_5$(s) + 5 H$_2$O ⇌ 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$^a$ |
| Te$^{2‒}$ + H$^+$ ⇌ HTe$^‒$ | 11.81 |
| HTe$^‒$ + H$^+$ ⇌ H$_2$Te | 2.476 |
($^a$) The number of significant figures are retained to minimise propagation of round-off errors; they should not be taken to indicate the relative uncertainty of the values, which is always at least one order of magnitude less than indicated.

### Tellurium(IV)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:
| Reaction | Baes and Mesmer, 1976 | Filella and May, 2019$^a$ |
| TeO$_3$$^{2‒}$ + H$^+$ ⇌ HTeO$_3$$^‒$ | | 9.928 |
| HTeO$_3$$^‒$ + H$^+$ ⇌ H$_2$TeO$_3$ | | 6.445 |
| H$_2$TeO$_3$ ⇌ HTeO$_3$$^‒$ + H$^+$ | ‒2.68 | |
| H$_2$TeO$_3$ ⇌ TeO$_3$$^{2‒}$ + 2 H$^+$ | ‒12.5 | |
| H$_2$TeO$_3$ + H$^+$ ⇌ Te(OH)$_3$$^+$ | 3.13 | 2.415 |
| TeO$_2$(s) + H$_2$O ⇌ H$_2$TeO$_3$ | | ‒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$^a$ |
| TeO$_2$(OH)$_4$$^{2‒}$ + H$^+$ ⇌ TeO(OH)$_5$$^‒$ | | 10.83 |
| TeO(OH)$_5$$^‒$ + H$^+$ ⇌ Te(OH)$_6$ | 7.68 | 7.696 |
| TeO$_2$(OH)$_4$$^{2‒}$ + 2 H$^+$ ⇌ Te(OH)$_6$ | 18.68 | |
| TeO$_3$(OH)$_3$$^{3‒}$ + 3 H$^+$ ⇌ Te(OH)$_6$ | 34.3 | |
| 2 Te(OH)$_6$ ⇌ Te$_2$O(OH)$_{11}$$^‒$ + 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 |
| Tb$^{3+}$ + H$_2$O ⇌ TbOH$^{2+}$ + H$^+$ | −7.9 | −7.60 ± 0.09 |
| 2 Tb$^{3+}$ + 2 H$_2$O ⇌ Tb$_2$(OH)$_2$$^{4+}$ + 2 H$^+$ | | −13.9 ± 0.2 |
| 3 Tb$^{3+}$ + 5 H$_2$O ⇌ Tb$_3$(OH)$_5$$^{4+}$ + 5 H$^+$ | | −31.7 ± 0.3 |
| Tb(OH)$_3$(s) + 3 H$^+$ ⇌ Tb$^{3+}$ + 3 H$_2$O | 16.5 | 16.33 ± 0.30 |

### Thallium(I)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:
| Reaction | Baes and Mesmer, 1976 | Brown and Ekberg, 2016 |
| Tl$^+$ + H$_2$O ⇌ TlOH + H$^+$ | –13.21 | |
| Tl$^+$ + OH$^–$ ⇌ TlOH | | 0.64 ± 0.05 |
| Tl$^+$ + 2 OH$^–$ ⇌ Tl(OH)$_2$$^–$ | | –0.7 ± 0.7 |
| ⁠1/2⁠ Tl$_2$O(s) + H$^+$ ⇌ Tl$^+$ + ⁠1/2⁠ H$_2$O | | 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$^{3+}$ + H$_2$O ⇌ TlOH$^{2+}$ + H$^+$ | –0.62 | –0.22 ± 0.19 |
| Tl$^{3+}$ + 2 H$_2$O ⇌ Tl(OH)$_2$$^+$ + 2 H$^+$ | –1.57 | |
| Tl$^{3+}$ + 3 H$_2$O ⇌ Tl(OH)$_3$ + 3 H$^+$ | –3.3 | |
| Tl$^{3+}$ + 4 H$_2$O ⇌ Tl(OH)$_4$$^–$ + 4 H$^+$ | –15.0 | |
| ⁠1/2⁠ Tl$_2$O$_3$(s) + 3 H$^+$ ⇌ Tl$^{3+}$ + ⁠3/2⁠ H$_2$O | –3.90 | –3.90 ± 0.10 |
($^a$) The number of significant figures are retained to minimise propagation of round-off errors; they should not be taken to indicate the relative uncertainty of the values, which is always at least one order of magnitude less than indicated.

### Thorium

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:
| Reaction | Baes and Mesmer, 1976 | Rand et al., 2008 | Thoenen et al, 014 | Brown and Ekberg, 2016 |
| Th$^{4+}$ + H$_2$O ⇌ ThOH$^{3+}$ + H$^+$ | –3.20 | –2.5 ± 0.5 | –2.5 ± 0.5 | –2.5 ± 0.5 |
| Th$^{4+}$ + 2 H$_2$O ⇌ Th(OH)$_2$$^{2+}$ + 2 H$^+$ | –6.93 | –6.2 ± 0.5 | –6.2 ± 0.5 | –6.2 ± 0.5 |
| Th$^{4+}$ + 3 H$_2$O ⇌ Th(OH)$_3$$^+$ + 3 H$^+$ | < –11.7 | | | |
| Th$^{4+}$ + 4 H$_2$O ⇌ Th(OH)$_4$ + 4 H$^+$ | –15.9 | –17.4 ± 0.7 | –17.4 ± 0.7 | –17.4 ± 0.7 |
| 2Th$^{4+}$ + 2 H$_2$O ⇌ Th$_2$(OH)$_2$$^{6+}$ + 2 H$^+$ | –6.14 | –5.9 ± 0.5 | –5.9 ± 0.5 | –5.9 ± 0.5 |
| 2Th$^{4+}$ + 3 H$_2$O ⇌ Th$_2$(OH)$_3$$^{5+}$ + 3 H$^+$ | | –6.8 ± 0.2 | –6.8 ± 0.2 | –6.8 ± 0.2 |
| 4Th$^{4+}$ + 8 H$_2$O ⇌ Th$_4$(OH)$_8$$^{8+}$ + 8 H$^+$ | –21.1 | –20.4 ± 0.4 | –20.4 ± 0.4 | –20.4 ± 0.4 |
| 4Th$^{4+}$ + 12 H$_2$O ⇌ Th$_4$(OH)$_{12}$$^{4+}$ + 12 H$^+$ | | –26.6 ± 0.2 | –26.6 ± 0.2 | –26.6 ± 0.2 |
| 6Th$^{4+}$ + 15 H$_2$O(l) ⇌ Th$_6$(OH)$_{15}$$^{9+}$ + 15 H$^+$ | –36.76 | –36.8 ± 1.5 | –36.8 ± 1.5 | –36.8 ± 1.5 |
| 6Th$^{4+}$ + 14 H$_2$O(l) ⇌ Th$_6$(OH)$_{14}$$^{10+}$ + 14 H$^+$ | | –36.8 ± 1.2 | –36.8 ± 1.2 | –36.8 ± 1.2 |
| ThO$_2$(c) + 4 H$^+$ ⇌ Th$^{4+}$ + 2 H$_2$O | 6.3 | | | |
| ThO$_2$(am) + 4 H$^+$ ⇌ Th$^{4+}$ + 2 H$_2$O | | | | 8.8 ± 1.0 |
| ThO$_2$(am,hyd,fresh) + 4 H$^+$ ⇌ Th$^{4+}$ + 2 H$_2$O | | | 9.3 ± 0.9 | |
| ThO$_2$(am,hyd,aged) + 4 H$^+$ ⇌ Th$^{4+}$ + 2 H$_2$O | | | 8.5 ± 0.9 | |
| Th$^{4+}$ + 4 OH$^−$ ⇌ ThO$_2$(am,hyd,fresh) + 2 H$_2$O | | 46.7 ± 0.9 | | |
| Th$^{4+}$ + 4 OH$^−$ ⇌ ThO$_2$(am,hyd,aged) + 2 H$_2$O | | 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 |
| Tm$^{3+}$ + H$_2$O ⇌ TmOH$^{2+}$ + H$^+$ | −7.7 | −7.34 ± 0.09 |
| 2 Tm$^{3+}$ + 2 H$_2$O ⇌ Tm$_2$(OH)$_2$$^{4+}$ + 2 H$^+$ | | −13.2 ± 0.2 |
| 3 Tm$^{3+}$ + 5 H$_2$O ⇌ Tm$_3$(OH)$_5$$^{4+}$ + 5 H$^+$ | | −30.5 ± 0.3 |
| Tm(OH)$_3$(s) + 3 H$^+$ ⇌ Tm$^{3+}$ + 3 H$_2$O | 15.0 | 15.56 ± 0.40 |

### Tin(II)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:
| Reaction | Feitknecht, 1963 | Baes and Mesmer, 1976 | Hummel et al., 2002 | NIST46 | Cigala et al, 2012 | Gamsjäger et al, 2012 | Brown and Ekberg, 2016 |
| Sn$^{2+}$ + H$_2$O ⇌ 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 H$_2$O ⇌ 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 H$_2$O ⇌ Sn(OH)$_3$$^–$ + 3 H$^+$ | | –16.61 | –17.5 ± 0.2 | –16.6 | –16.97 ± 0.17 | –17.00 ± 0.60 | –17.56 ± 0.40 |
| 2 Sn$^{2+}$ + 2 H$_2$O ⇌ Sn$_2$(OH)$_2$$^{2+}$ + 2 H$^+$ | | –4.77 | | –4.8 | –4.79 ± 0.05 | | |
| 3 Sn$^{2+}$ + 4 H$_2$O ⇌ Sn$_3$(OH)$_4$$^{2+}$ + 4 H$^+$ | | –6.88 | –5.6 ± 1.6 | –6.88 | –5.88 ± 0.05 | –5.60 ± 0.47 | −5.60 ± 0.47 |
| Sn(OH)$_2$(s) ⇌ Sn$^{2+}$ + 2 OH$^–$ | | | | –25.8 | –26.28 ± 0.08 | | |
| SnO(s) + 2 H$^+$ ⇌ Sn$^{2+}$ + H$_2$O | | 1.76 | 2.5± 0.5 | | | | 1.60 ± 0.15 |
| SnO(s) + H$_2$O ⇌ Sn$^{2+}$ + 2 OH$^–$ | –26.2 | | | | | | |
| SnO(s) + H$_2$O ⇌ Sn(OH)$_2$ | –5.3 | | | | | | |
| SnO(s) + 2 H$_2$O ⇌ Sn(OH)$_3$$^–$ + 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 H$_2$O ⇌ Sn(OH)$_4$ + 4 H$^+$ | | | 7.53 ± 0.12 |
| Sn$^{4+}$ + 5 H$_2$O ⇌ Sn(OH)$_5$$^–$ + 5 H$^+$ | | | –1.07 ± 0.42 |
| Sn$^{4+}$ + 6 H$_2$O ⇌ Sn(OH)$_6$$^{2–}$ + 6 H$^+$ | | | –1.07 ± 0.42 |
| Sn(OH)$_4$ + H$_2$O ⇌ Sn(OH)$_5$$^–$ + H$^+$ | –8.0 ± 0.3 | –8.60 ± 0.40 | |
| Sn(OH)$_4$ + 2 H$_2$O ⇌ Sn(OH)$_6$$^{2–}$ + 2 H$^+$ | –18.4 ± 0.3 | –18.67 ± 0.30 | |
| SnO$_2$(cr) + 2 H$_2$O ⇌ Sn(OH)$_4$ | –8.0 ± 0.2 | –8.06 ± 0.11 | |
| SnO$_2$(am) + 2 H$_2$O ⇌ Sn(OH)$_4$ | –7.3 ± 0.3 | –7.22 ± 0.08 | |
| SnO$_2$(s) + 4 H$^+$ ⇌ Sn$^{4+}$ + 2 H$_2$O | | | –15.59 ± 0.04 |

### Tungsten

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:
| Reaction | NIST46 |
| WO$_4$$^{2–}$ + H$^+$ ⇌ HWO$_4$$^–$ | 3.6 |
| WO$_4$$^{2–}$ + 2 H$^+$ ⇌ H$_2$WO$_4$ | 5.8 |
| 6 WO$_4$$^{2–}$ + 7 H$^+$ ⇌ HW$_6$O$_{21}$$^{5–}$ + 3 H$_2$O | 63.83 |

### Titanium(III)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:
| Reaction | Perrin et al., 1969 | Baes and Mesmer, 1976 | Brown and Ekberg, 2016 |
| Ti$^{3+}$ + H$_2$O ⇌ TiOH$^{2+}$ + H$^+$ | –1.29 | –2.2 | –1.65 ± 0.11 |
| 2 Ti$^{3+}$ + 2 H$_2$O ⇌ Ti$_2$(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$$^{2+}$ + H$_2$O ⇌ Ti(OH)$^{3+}$ + H$^+$ | ⩽–2.3 | |
| Ti(OH)$_2$$^{2+}$ + 2 H$_2$O ⇌ Ti(OH)$_4$ + 2 H$^+$ | –4.8 | |
| TiO$^{2+}$ + H$_2$O ⇌ TiOOH$^+$ + H$^+$ | | –2.48 ± 0.10 |
| TiO$^{2+}$ + 2 H$_2$O ⇌ TiO(OH)$_2$ + 2 H$^+$ | | –5.49 ± 0.14 |
| TiO$^{2+}$ + 3 H$_2$O ⇌ TiO(OH)$_3$$^–$ + 3 H$^+$ | | –17.4 ± 0.5 |
| TiO(OH)$_2$ + H$_2$O ⇌ TiO(OH)$_3$$^–$ + H$^+$ | | –11.9 ±0.5 |
| TiO$_2$(c) +2 H$_2$O ⇌ Ti(OH)$_4$ | ~ –4.8 | |
| TiO$_2$(s) + H$^+$ ⇌ TiOOH$^+$ | | –6.06 ± 0.30 |
| TiO$_2$(s) + H$_2$O ⇌ TiO(OH)$_2$ | | –9.02 ± 0.02 |
| TiO$_2$ x H$_2$O ⇌ Ti(OH)$_2$$^{2+}$[OH$^–$] | | |
| TiO$_2$(s) + 4 H$^+$ ⇌ Ti$^{4+}$ + 2 H$_2$O | | –3.56 ± 0.10 |

### Uranium(IV)

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:
| Reaction | Baes and Mesmer, 1976 | Thoenen et al., 2014 | Brown and Ekberg, 2016 | Grenthe et al., 2020 |
| U$^{4+}$ + H$_2$O ⇌ UOH$^{3+}$ + H$^+$ | –0.65 | – 0.54 ± 0.06 | –0.58 ± 0.08 | – 0.54 ± 0.06 |
| U$^{4+}$ + 2 H$_2$O ⇌ U(OH)$_2$$^{2+}$ + 2 H$^+$ | (–2.6) | –1.1 ± 1.0 | –1.4 ± 0.2 | –1.9 ± 0.2 |
| U$^{4+}$ + 3 H$_2$O ⇌ U(OH)$_3$$^+$ + 3 H$^+$ | (–5.8) | –4.7 ± 1.0 | –5.1 ± 0.3 | –5.2 ± 0.4 |
| U$^{4+}$ + 4 H$_2$O ⇌ U(OH)$_4$ + 4 H$^+$ | (–10.3) | –10.0 ± 1.4 | –10.4 ± 0.5 | –10.0 ± 1.4 |
| U$^{4+}$ + 5 H$_2$O ⇌ U(OH)$_5$$^−$ + 5 H$^+$ | –16.0 | | | |
| UO$_2$(am, hyd) + 4 H$^+$ ⇌ U$^{4+}$ + 2 H$_2$O | | 1.5 ± 1.0 | | |
| UO$_2$(am,hyd) + 2 H$_2$O ⇌ U$^{4+}$ + 4 OH$^–$ | | | –54.500 ± 1.000 | –54.500 ± 1.000 |
| UO$_2$(c) + 4 H$^+$ ⇌ U$^{4+}$ + 2 H$_2$O | –1.8 | | | |
| UO$_2$(c) + 2 H$_2$O ⇌ 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 | Grenthe et al., 1992 | NIST46 | Brown and Ekberg, 2016 | Grenthe et al., 2020 |
| UO$_2$$^{2+}$ + H$_2$O ⇌ UO$_2$(OH)$^+$ + H$^+$ | –5.8 | –5.2 ± 0.3 | –5.9 ± 0.1 | –5.13 ± 0.04 | –5.2$_5$ ± 0.2$_4$ |
| UO$_2$$^{2+}$ + 2 H$_2$O ⇌ UO$_2$(OH)$_2$ + 2 H$^+$ | | ≤-10.3 | | –12.1$_5$ ± 0.2$_0$ | –12.15 ± 0.07 |
| UO$_2$$^{2+}$ + 3 H$_2$O ⇌ UO$_2$(OH)$_3$$^–$ + 3 H$^+$ | | –19.2 ± 0.4 | | –20.2$_5$ ± 0.4$_2$ | –20.2$_5$ ± 0.4$_2$ |
| UO$_2$$^{2+}$ + 4 H$_2$O ⇌ UO$_2$(OH)$_4$$^{2–}$ + 4 H$^+$ | | –33 ± 2 | | –32.4$_0$ ± 0.6$_8$ | –32.4$_0$ ± 0.6$_8$ |
| 2 UO$_2$$^{2+}$ + 2 H$_2$O ⇌ (UO$_2$)$_2$(OH)$_2$$^{2+}$ + 2 H$^+$ | –5.62 | –5.62 ± 0.04 | –5.58 ± 0.04 | –5.68 ± 0.05 | –5.62 ± 0.08 |
| 3 UO$_2$$^{2+}$ + 5 H$_2$O ⇌ (UO$_2$)$_3$(OH)$_5$$^+$ + 5 H+ | –15.63 | –15.5$_5$ ± 0.1$_2$ | –15.6 | –15.7$_5$ ± 0.1$_2$ | –15.5$_5$ ± 0.1$_2$ |
| 3 UO$_2$$^{2+}$ + 4 H$_2$O ⇌ (UO$_2$)$_3$(OH)$_4$$^{2+}$ + 4 H$^+$ | (–11.75) | –11.9 ± 0.3 | | –11.78 ± 0.05 | –11.9 ± 0.3 |
| 3 UO$_2$$^{2+}$ + 7 H$_2$O ⇌ (UO$_2$)$_3$(OH)$_7$$^–$ + 7 H$^+$ | | –31 ± 2.0 | | –32.2 ± 0.8 | –32.2 ± 0.8 |
| 4 UO$_2$$^{2+}$ + 7 H$_2$O ⇌ (UO$_2$)$_4$(OH)$_7$+ + 7 H$^+$ | | –21.9 ± 1.0 | | –22.1 ± 0.2 | –21.9 ± 1.0 |
| 2 UO$_2$$^{2+}$ + H$_2$O ⇌ (UO$_2$)$_2$(OH)$^{3+}$ + H$^+$ | | –2.7 ± 1.0 | | | –2.7 ± 1.0 |
| UO$_2$(OH)$_2$(s) + 2H$^+$ ⇌ UO$_2$$^{2+}$ + 2 H$_2$O | 5.6 | | 6.0 | 4.81 ± 0.20 | |
| UO$_3$·2H$_2$O(cr) + 2H$^+$ ⇌ UO$_2$$^{2+}$ + 3 H$_2$O | | | | | 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$^{2+}$ + H$_2$O ⇌ VO(OH)$^+$ + H$^+$ | –5.30 ± 0.13 |
| 2 VO$^{2+}$ + 2 H$_2$O ⇌ (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 | Brown and Ekberg, 2016 |
| VO$_2$$^+$ + 2 H$_2$O ⇌ VO(OH$_3}$ + H$^+$ | –3.3 | |
| VO$_2$$^+$ + 2 H$_2$O ⇌ VO$_2$(OH)$_2$$^–$ + 2 H$^+$ | –7.3 | –7.18 ± 0.12 |
| 10 VO$_2$$^+$ + 8 H$_2$O ⇌ V$_{10}$O$_{26}$(OH)$_2$$^{4–}$ + 14 H$^+$ | –10.7 | |
| VO$_2$(OH)$_2$$^–$ ⇌ VO$_3$(OH)$^{2–}$ + H$^+$ | –8.55 | |
| 2 VO$_2$(OH)$_2$$^–$ ⇌ V$_2$O$_6$(OH)$_2$$^{3–}$ + H$^+$ + H$_2$O | –6.53 | |
| VO$_3$(OH)$^{2–}$ ⇌ VO$_4$$^{3–}$ + H$^+$ | –14.26 | |
| 2 VO$_3$(OH)$^{2–}$ ⇌ V$_2$O$_7$$^{4–}$ + H$_2$O | 0.56 | |
| 3 VO$_3$(OH)$^{2–}$ + 3 H$^+$⇌ V$_3$O$_9$$^{3–}$ + 3 H$_2$O | 31.81 | |
| V$_{10}$O$_{26}$(OH)$_2$$^{4–}$ ⇌ V$_{10}$O$_{27}$(OH)$^{5–}$ + 3 H$^+$ | –3.6 | |
| V$_{10}$O$_{27}$(OH)$^{5–}$ ⇌ V$_{10}$O$_{28}$$^{6–}$ + H$^+$ | –6.15 | |
| VO$_2$$^+$ + H$_2$O ⇌ VO$_2$OH + H$^+$ | | –3.25 ± 0.1 |
| VO$_2$$^+$ + 3 H$_2$O ⇌ VO$_2$(OH)$_3$$^{2-}$ + 3 H$^+$ | | –15.74 ± 0.19 |
| VO$_2$$^+$ + 4 H$_2$O ⇌ VO$_2$(OH)$_4$$^{3-}$ + 4 H$^+$ | | –30.03 ± 0.24 |
| 2 VO$_2$$^+$ + 4 H$_2$O ⇌ (VO$_2$)$_2$(OH)$_4$$^{2-}$ + 4 H$^+$ | | –11.66 ± 0.53 |
| 2 VO$_2$$^+$ + 5 H$_2$O ⇌ (VO$_2$)$_2$(OH)$_5$$^{3-}$ + 5 H$^+$ | | –20.91 ± 0.22 |
| 2 VO$_2$$^+$ + 6 H$_2$O ⇌ (VO$_2$)$_2$(OH)$_6$$^{4-}$ + 6 H$^+$ | | –32.43 ± 0.30 |
| 4 VO$_2$$^+$ + 8 H$_2$O ⇌ (VO$_2$)$_4$(OH)8$^{4-}$ + 8 H$^+$ | | –20.78 ± 0.33 |
| 4 VO$_2$$^+$ + 9 H$_2$O ⇌ (VO$_2$)$_4$(OH)$_9$$^{5-}$ + 9 H$^+$ | | –31.85 ± 0.26 |
| 4 VO$_2$$^+$ + 10 H$_2$O ⇌ (VO$_2$)$_4$(OH)$_{10}$$^{6-}$ + 10 H$^+$ | | –45.85 ± 0.26 |
| 5 VO$_2$$^+$ + 10 H$_2$O ⇌ (VO$_2$)$_5$(OH)$_{10}$$^{5-}$ + 10 H$^+$ | | –27.02 ± 0.34 |
| 10 VO$_2$$^+$ + 14 H$_2$O ⇌ (VO$_2$)$_{10}$(OH)$_{14}$$^{4-}$ + 14 H$^+$ | | –10.5 ± 0.3 |
| 10 VO$_2$$^+$ + 15 H$_2$O ⇌ (VO$_2$)$_{10}$(OH)$_{15}$$^{5-}$ + 15 H$^+$ | | –15.73 ± 0.33 |
| 10 VO$_2$$^+$ + 16 H$_2$O ⇌ (VO$_2$)$_{10}$(OH)$_{16}$$^{6-}$ + 16 H$^+$ | | –23.90 ± 0.35 |
| ⁠1/2⁠ V$_2$O$_5$(c) + H$^+$ ⇌ VO$_2$$^+$ + ⁠1/2⁠ H$_2$O | –0.66 | |
| V$_2$O$_5$(s) + 2 H$^+$ ⇌ 2 VO$_2$$^+$ + H$_2$O | | –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 |
| Yb$^{3+}$ + H$_2$O ⇌ YbOH$^{2+}$ + H$^+$ | −7.7 | −7.31 ± 0.18 |
| Yb$^{3+}$ + 2 H$_2$O ⇌ Yb(OH)$_2$$^+$ + 2 H$^+$ | (−15.8) | |
| Yb$^{3+}$ + 3 H$_2$O ⇌ Yb(OH)$_3$ + 3 H$^+$ | (−24.1) | |
| Yb$^{3+}$ + 4 H$_2$O ⇌ Yb(OH)$_4$$^−$ + 4 H$^+$ | −32.7 | |
| 2 Yb$^{3+}$ + 2 H$_2$O ⇌ Yb$_2$(OH)$_2$$^{4+}$ + 2 H$^+$ | | −13.76 ± 0.20 |
| 3 Yb$^{3+}$ + 5 H$_2$O ⇌ Yb$_3$(OH)$_5$$^{4+}$ + 5 H$^+$ | | −30.6 ± 0.3 |
| Yb(OH)$_3$(s) + 3 H$^+$ ⇌ Yb$^{3+}$ + 3 H$_2$O | 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$^{3+}$ + H$_2$O ⇌ YOH$^{2+}$ + H$^+$ | –7.7 | –7.77 ± 0.06 |
| Y$^{3+}$ + 2 H$_2$O ⇌ Y(OH)$_2$$^+$ + 2 H$^+$ | (–16.4) [Estimation] | |
| Y$^{3+}$ + 3 H$_2$O ⇌ Y(OH)$_3$ + 3 H$^+$ | (–26.0) [Estimation] | |
| Y$^{3+}$ + 4 H$_2$O ⇌ Y(OH)$_4$$^−$+ 4 H$^+$ | –36.5 | |
| 2 Y$^{3+}$ + 2 H$_2$O ⇌ Y$_2$(OH)$_2$$^{4+}$ + 2 H$^+$ | –14.23 | –14.1 ± 0.2 |
| 3 Y$^{3+}$ + 5 H$_2$O ⇌ Y$_3$(OH)$_5$$^{4+}$ + 5 H$^+$ | –31.6 | –32.7 ± 0.3 |
| Y(OH)$_3$(s) + 3 H$^+$ ⇌ Y$^{3+}$ + 3 H$_2$O | 17.5 | 17.32 ± 0.30 |

### Zinc

Hydrolysis constants (log values) in critical compilations at infinite dilution and T = 298.15 K:
| Reaction | Baes and Mesmer, 1976 | Powell and Brown, 2013 | Brown and Ekberg, 2016 |
| Zn$^{2+}$ + H$_2$O ⇌ ZnOH$^+$ + H$^+$ | −8.96 | −8.96 ± 0.05 | −8.94 ± 0.06 |
| Zn$^{2+}$ + 2 H$_2$O ⇌ Zn(OH)$_2$ + 2 H$^+$ | −16.9 | –17.82 ± 0.08 | −17.89 ± 0.15 |
| Zn$^{2+}$ + 3 H$_2$O ⇌ Zn(OH)$_3$$^−$ + 3 H$^+$ | −28.4 | –28.05 ± 0.05 | −27.98 ± 0.10 |
| Zn$^{2+}$ + 4 H$_2$O ⇌ Zn(OH)$_4$$^{2-}$ + 4 H$^+$ | −41.2 | –40.41 ± 0.12 | −40.35 ± 0.22 |
| 2 Zn$^{2+}$ + H$_2$O ⇌ Zn$_2$OH$^{3+}$ + H$^+$ | −9.0 | –7.9 ± 0.2 | −7.89 ± 0.31 |
| 2 Zn$^{2+}$ + 6 H$_2$O ⇌ Zn$_2$(OH)$_6$$^{2-}$ + 6 H$^+$ | −57.8 | | |
| ZnO(s) + 2 H$^+$ ⇌ Zn$^{2+}$ + H$_2$O | 11.14 | 11.12 ± 0.05 | 11.11 ± 0.10 |
| ε-Zn(OH)$_2$(s) + 2 H$^+$ ⇌ Zn$^{2+}$ + 2 H$_2$O | | 11.38 ± 0.20 | 11.38± 0.20 |
| β$_1$-Zn(OH)$_2$(s) + 2 H$^+$ ⇌ Zn$^{2+}$ + 2 H$_2$O | | 11.72 ± 0.04 | |
| β$_2$-Zn(OH)$_2$(s) + 2 H$^+$ ⇌ Zn$^2$+ + 2 H$_2$O | | 11.76 ± 0.04 | |
| γ-Zn(OH)$_2$(s) + 2 H$^+$ ⇌ Zn$^{2+}$ + 2 H$_2$O | | 11.70 ± 0.04 | |
| δ-Zn(OH)$_2$(s) + 2 H$^+$ ⇌ Zn$^{2+}$ + 2 H$_2$O | | 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 |
| Zr$^{4+}$ + H$_2$O ⇌ ZrOH$^{3+}$ + H$^+$ | 0.32 | 0.32 ± 0.22 | 0.12 ± 0.12 |
| Zr$^{4+}$ + 2 H$_2$O ⇌ Zr(OH)$_2$$^{2+}$ + 2 H$^+$ | (−1.7)* | 0.98 ± 1.06* | −0.18 ± 0.17* |
| Zr$^{4+}$ + 3 H$_2$O ⇌ Zr(OH)$_3$$^+$ + 3 H$^+$ | (−5.1) | | |
| Zr$^{4+}$ + 4 H$_2$O ⇌ Zr(OH)$_4$ + 4 H$^+$ | –9.7* | –2.19 ± 0.70* | −4.53 ± 0.37* |
| Zr$^{4+}$ + 5 H$_2$O ⇌ Zr(OH)$_5$$^–$ + 5 H$^+$ | –16.0 | | |
| Zr$^{4+}$ + 6 H$_2$O ⇌ Zr(OH)$_6$$^{2–}$ + 6 H$^+$ | | –29± 0.70 | –30.5 ± 0.3 |
| 3 Zr$^{4+}$ + 4 H$_2$O ⇌ Zr$_3$(OH)$_4$$^{8+}$ + 4 H$^+$ | –0.6 | 0.4 ± 0.3 | 0.90 ± 0.18 |
| 3 Zr$^{4+}$ + 5 H$_2$O ⇌ Zr$_3$(OH)$_5$$^{7+}$ + 5 H$^+$ | 3.70 | | |
| 3 Zr$^{4+}$ + 9 H$_2$O ⇌ Zr$_3$(OH)$_9$$^{3+}$ + 9 H$^+$ | | 12.19 ± 0.20 | 12.19 ± 0.20 |
| 4 Zr$^{4+}$ + 8 H$_2$O ⇌ Zr$_4$(OH)$_8$$^{8+}$ + 8 H$^+$ | 6.0 | 6.52 ± 0.05 | 6.52 ± 0.05 |
| 4 Zr$^{4+}$ + 15 H$_2$O ⇌ Zr$_4$(OH)$_{15}$$^+$ + 15 H$^+$ | | 12.58± 0.24 | |
| 4 Zr$^{4+}$ + 16 H$_2$O ⇌ Zr$_4$(OH)$_{16}$ + 16 H$^+$ | | 8.39± 0.80 | |
| ZrO$_2$(s) + 4 H$^+$ ⇌ Zr$^{4+}$ + 2 H$_2$O | –1.9* | | –5.37 ± 0.42* |
| ZrO$_2$(s, baddeleyite) + 4 H$^+$ ⇌ Zr$^{4+}$ + 2 H$_2$O | | –7 ± 1.6 | |
| ZrO$_2$(am) + 4 H$^+$ ⇌ Zr$^{4+}$ + 2 H$_2$O | | –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.