CHEMISTRY · Multi-part · A Level · Chemistry · Reactions of ions in aqueous solution · Reactions of ions in aqueous solution
Problem
A mixture contains aqueous Ag+, Ba2+, and Zn2+ ions, each at an initial concentration of 0.020 M. A chemist wishes to separate all three ions by selective precipitation using a single anion, Xn−, that can be delivered in controlled amounts as a 0.10 M sodium salt solution.
(a) Propose an anion Xn− that will allow sequential precipitation of the cations in the order Ag+ → Ba2+ → Zn2+. Support your choice with appropriate chemical reasoning, including reference to accepted solubility tendencies.
(b) Describe in detail the procedure—including reagent additions, stirring, and filtration steps—that the chemist should follow to accomplish the separation. Indicate the observable changes at each stage.
(c) For each precipitation step, write the balanced net ionic equation and explain how competing equilibria or complex-ion formation could interfere with complete removal of the target ion.
(d) Suppose trace amounts of the earlier-precipitated ions remain adsorbed on later precipitates. Suggest one practical laboratory technique to minimize this contamination and justify how it improves purity.