Four glass bottles containg clear colorless solutions needs to be tested for ions. Bottles 1 and 3 contains cations and other two contains anions.
Nearby thse bottles four labels reading Pb, Cl, Ag and SO4 are lying in a jumble pile.A student tried test them by mixing them in pairs but there are only three empty beakers. When the solutions are mixed in pairs three combinations give white precipetates: Bottle 1+ bottle 2, Bottle 1+ bottle 4, Bottle 2+ bottle 3
From the labels lying near the bottles we know that the cations to be tested are Pb2+ and Ag+ and they are contained in bottles 1 and 3. The labels also identify the anions to be tested as Cl- and SO42- which are contained in bottles 2 and 4.
When the solutions in bottle 1 and bottle 2 is mixed, the precitipate is white in color. As Ag2SO4 is colorless, it implies that bottle 1 does not contain Ag+ and bottle 2 does not contain SO42- ions.
As there are 2 bottles with anions, the solution in bottle 1 should have the Pb2+ ions and the solution in bottle 3 should have the Ag+ ions. Similarly the solution in bottle 2 has Cl- cations and the solution in bottle 4 has the SO42- ions.
This is verified by the fact that when the solutions in bottle 1 and bottle 4 are mixed, we get a white precipitate which is PbSO4. When the solution in bottle 2 and bottle 3 is mixed we get a white precipitate which is AgCl.
The ion in the solution in bottle 1 is Pb2+, the solution in bottle 2 has Cl- ions, the solution in bottle 3 has Ag+ ions and that in bottle 4 has SO42- ions.