Exercise 2 | Solubility and Precipitation Reactions

Calculate the solubility in g.L-1 of Ca(OH)2 (s) in pure water given that Ksp = 5.00 x 10-6 3

Chemical equation:

Ca(OH)2 (s)  Ca2+ (aq) + 2 HO- (aq)


Pure water: the only source of Ca2+ and HO- is Ca(OH)2

From the reaction stoichiometry: [HO-] = 2 [Ca2+]

s = solubility of Ca(OH)2 (s) in M = [Ca2+]


Ksp = [Ca2+][HO-]2

Ksp = 4 [Ca2+]3

Ksp = 4 s3

⇒ s = 1.08 x 10-2 M


S = solubility of Ca(OH)2 (s) in g.L-1 = s x MCa(OH)2

⇒ S = 7.98 x 10-1 g.L-1