A solution of tap water contains both Fe²⁺ and Pb²⁺. While small amounts of Fe²⁺ can be fine for human health, even small amounts of Pb²⁺ can be harmful. Based on the provided Ksp values, assuming equimolar concentrations of Fe²⁺ and Pb²⁺, which anions could be used to selectively precipitate out the Pb²⁺ (i.e., not the Fe²⁺)?
Circle all that apply.
I. CO₃²⁻ (Ksp FeCO₃ = 3.07 × 10⁻¹¹; Ksp PbCO₃ = 7.4 × 10⁻¹⁴)
II. OH⁻ (Ksp Fe(OH)₂ = 4.87 × 10⁻²⁰; Ksp Pb(OH)₂ = 1.43 × 10⁻¹⁷)
III. S²⁻ (Ksp FeS = 3.72 × 10⁻¹⁹; Ksp PbS = 9.04 × 10⁻²⁹)
IV. Cl⁻ (Ksp FeCl₂ = 3.45; Ksp PbCl₂ = 1.17 × 10⁻⁵)