Question:

The reagent(s) that can selectively precipitate S²⁻ from a mixture of S²⁻ and SO₄²⁻ in aqueous solution is (are): BaCl₂, CuCl₂, Pb(OOCCH₃)₂, Na₂[Fe(CN)₅NO]

Pb(OOCCH3)2

CuCl2

Na2[Fe(CN)5NO]

BaCl2

A) CuCl₂ exists as Cu²⁺ and Cl⁻. Now CuSO₄ is highly soluble in water while, CuS forms a black ppt.