Question

Should Mg(OH)₂ precipitate from a solution that is 0.001 M MgCl₂ if the solution is also made 0.10 M in NH₃ [K_sp[Mg(OH)2] = 1.8 X 10^-11, K_b(NH4OH) = 1.8 X 10^-5].

Answer 1

⇒ [Mg²⁺] = 0.001 M 

Ionic product = [Mg²⁺] [OH^–]² = (0.001) × (1.34 × 10^–3)² 

= 1.8 × 10^–9 > K_sp 

As, Ionic product is greater than K_sp of Mg (OH)₂ , hence precipitation should occur.