Consider a solution containing three metal cations;    [Pb²⁺] = [Ag⁺] = [Hg₂²⁺ ] = 0.0015M. 

At what concentration of Cl^–(aq) will each salt just begin to precipitate (be at equilibrium)?

K_sp of PbCl₂ = 1.7×10^-5        K_sp of AgCl = 1.8×10^-10      K_sp of Hg₂Cl₂ = 1.4×10^-18   

What concentration of chloride ion must be present to precipitate as much of the Hg₂²⁺ (as Hg₂Cl₂) as possible without precipitating the chlorides of Ag⁺, and Pb²⁺?