Question

Analytical Chemists are charged with identifying chemicals in mixtures. Because one chemical often interferes with a test for another chemical, the first step is to isolate the chemicals from one another. You have been given a mixture that is reported to contain Iron, Mercury, Lead,Tin, Barium, and Sodium. Using precipitation reactions develop a method of first separating the metals. After the metals are separated define separate tests which will identify each of them.

Answer 1

Separation and identification of Hg, Sn, Pb, Ba and Na

First add dil HCl. Hg2Cl2 and PbCl2 precipitates out as white precipitate. Filter precipitate.

Precipitate analysis (Hg2^2+ and Pb2+)

Boil the solution. PbCl2 dissolves in hot water. Hg2Cl2 remined insoluble

Pb2+ is confirmed by adding K2CrO4 which gives yellow Pb(CrO4)2.

Passing excess ammonia gives Hg(l) formed as metallic gray.

Filtrate

Pass H2S gas. We get brown ppt of SnS. Filter.

Precipitate (Sn2+)

Add NH3 to dissolve and make solution neutral. Add HCl and K4Fe(CN)6. a gray white precipitate of K2Zn[Fe(CN)6]2

Filtrate

Add NH4OH, (NH4)2CO3. BaCO3 is formed as white precipitate. Filter

Precipitate

Add HNO3 and then K2CrO4. It forms BaCrO4 as yellow color precipitate

Filtrate contains sodium ions.

Flame test gives yellow flame.