Cadmium Species in Basic Solution

The principal cadmium-containing species in basic solutions varies with the concentration of hydroxide ion such that the solubility of cadmium hydroxide can be satisfactorily expressed, in solutions of high ionic strength, in terms of [Cd(OH) + ] = 3.0 × 10 −9 [OH − ] −1 , [Cd(OH) 2 ] soln = 1.0 × 10 −6 , [Cd(OH) 3 − ] = 1.2 × 10 −6 [OH − ], and [Cd(OH) 4 2− ] = 3.1 × 10 −6 [OH − ]2. Since the solubility 10 varies from 10 −4 to 10 −6 M, the predominant species at high concentrations of hydroxide ion is Cd(OH) 4 2− ; at low concentrations of hydroxide ion Cd(OH) + is the principal cadmium-containing ion in solution. There is little free cadmium ion in solutions whose hydroxide ion concentration is greater than 10 -4 M.