Question

Which of the following will occur when solutions of ZnSO4(aq) and MgCl2(aq) are mixed? A precipitate of MgSO4 will form; Zn and CI" will be spectator ions. A precipitate of ZnCl2 will form; Mg and SO4 will be spectator ions. O No precipitate will form. A precipitate of MgCl2 will form: Zn2 and SO4will be spectator ions. A precipitate of ZnSO4 will form ; Mg" and CIT will be spectator ions.

Answer 1

Through experiments, chemists have developed a set of general rules for the solubility of common salts. Such solubility rules are written in the format: "All x (x = hydroxides, chlorides, sulfates, etc) are (in)-soluble, except for y and z (where y and z are cations)." It is imperative to memorize these rules. When a salt is insoluble in water, combination of the constituent ions leads to the formation of a precipitate.

The anions involved are the sulfates and the chlorides. All sulfates are soluble except for Ba2+, Sr2+,Pb2+.All chlorides are soluble except those of Ag+, Hg2^2+, Pb2+.

Hence, our reaction, which leads to the formation of magnesium sulfate (soluble) and zinc chloride (also soluble), forms NO PRECIPITATE.

ZnSO4(aq) +MgCl2(aq) ->ZnCl2(aq) +MgSO4(aq)