Solubility of group-2 hydroxides and sulfates

Moles dissolved per kilogram of water in saturated solutions at 20 °C: the hydroxides become more soluble from Be to Ba, the sulfates less soluble.


$\ce{Be(OH)2}$	hydroxide	—	5.57 × 10⁻⁸	from Ksp
$\ce{Mg(OH)2}$	hydroxide	—	1.21 × 10⁻⁴	from Ksp
$\ce{Ca(OH)2}$	hydroxide	0.173	0.0233	weighed solubility
$\ce{Sr(OH)2}$	hydroxide	0.81	0.0666	weighed solubility
$\ce{Ba(OH)2}$	hydroxide	3.89	0.227	weighed solubility
$\ce{BeSO4}$	sulfate	40	3.81	weighed solubility
$\ce{MgSO4}$	sulfate	35.1	2.92	weighed solubility
$\ce{CaSO4}$	sulfate	0.205	0.0151	weighed solubility
$\ce{SrSO4}$	sulfate	0.0135	7.35 × 10⁻⁴	weighed solubility
$\ce{BaSO4}$	sulfate	2.45 × 10⁻⁴	1.05 × 10⁻⁵	weighed solubility

Be(OH)₂ and Mg(OH)₂ are too insoluble to weigh reliably and are computed as s = (Ksp/4)^(1/3); Be(OH)₂ forms hydroxo complexes and polymers, so its value is only an estimate. Values for the soluble salts are given to two or three figures.

Sources

W. M. Haynes (ed.), CRC Handbook of Chemistry and Physics, 97th ed. (2016), “Aqueous solubility of inorganic compounds at various temperatures” and “Physical constants of inorganic compounds” (anhydrous basis, 20 °C; SrSO₄ and BaSO₄ at 20–25 °C).
A. E. Martell, R. M. Smith, Critical Stability Constants, Vol. 4 (1976) (Ksp of Mg(OH)₂); CRC Handbook, “Solubility product constants” (Ksp of Be(OH)₂, 6.92 × 10⁻²²).

Used in these lessons

Hydrogen and the s-block