A solution contains 0.010 M Ag⁺ and 0.010 M Pb²⁺. Solid NaCl is added gradually. Given Ksp(AgCl) = 1.8 × 10⁻¹⁰ and Ksp(PbCl₂) = 1.7 × 10⁻⁵, which solid precipitates first?

Core Concept

Each salt starts precipitating once its ion product reaches its Ksp. Silver chloride requires [Cl⁻] = 1.8 × 10⁻¹⁰ ÷ 0.010 = 1.8 × 10⁻⁸ M, whereas lead chloride waits for [Cl⁻] = √(1.7 × 10⁻⁵ ÷ 0.010), about 4.1 × 10⁻² M. The silver threshold sits millions of times lower, so AgCl precipitates first and selectively. This contrast underlies classic ion-separation schemes.