Which of the following pairs of aqueous solutions will form a precipitate when mixed?

A) Pb (C2H3O2) 2+Li2SO4

B) KNO3 + NaOH

C) KOH + Na2S

D) (NH4) 2SO4 + Nal

E) None of the above

The correct answer is A) Pb (C₂H₃O₂) ₂ + Li₂SO₄

Explanation:

All salts of Na, K and ammonium are soluble. All nitrates are soluble. All chlorides are soluble, with the exception of AgCl, Hg₂Cl₂, PbCl₂ and CuCl. All sulfates are soluble, with the exception of CaSO₄, SrSO₄, BaSO₄, PbSO₄, HgSO₄, Hg₂SO₄ and Ag₂SO₄. All hydroxides are poorly soluble, with the exception of alkaline hydroxides, Sr (OH) ₂, Ba (OH) ₂ and NH4 (OH) All carbonates are poorly soluble, with the exception of alkaline carbonates and ammonium carbonate. All sulfides are poorly soluble, with the exception of alkaline sulfides, alkaline earth sulfides, and ammonium sulfide.

The reaction A is:

Pb (C₂H₃O₂) ₂ + Li₂SO₄ ⇒PbSO₄ + 2 LiC₂H₃O₂

Lead sulfate is a slightly soluble solid, therefore it precipitates.