Question

Give a chemical test to distinguish between the following pairs of chemicals.
(i) Lead nitrate solution and Zinc nitrate solution.
(ii) Sodium chloride solution and Sodium nitrate solution.

Answer 1

To distinguish between a pair of compounds, find out a suitable reagent that forms a precipitate with one of the compounds, but the same reagent should not form a precipitate with another compound. If the reagent forms precipitate with both compounds, then one of the precipitate should be soluble in the excess of the reagent, whereas other precipitate should not dissolve in the excess of the reagent.

Complete Step by step answer: (i) To distinguish between Lead nitrate solution and Zinc nitrate solution, you can add excess ammonium hydroxide solution. Zinc nitrate reacts with ammonium hydroxide solution to form white precipitate. This white precipitate dissolves in excess ammonium hydroxide. Lead nitrate reacts with ammonium hydroxide solution to form white precipitate. This white precipitate does not dissolve in excess ammonium hydroxide.

(ii) To distinguish between sodium chloride solution and Sodium nitrate solution, you can use a silver nitrate test. When you add silver nitrate reagent to a solution containing sodium chloride, you will obtain a white precipitate of silver chloride. When you add silver nitrate reagent to a solution containing sodium nitrate, you will NOT obtain any precipitate of silver chloride.

Note: A precipitate is obtained when the ionic product exceeds the solubility product. In qualitative analysis of inorganic ions, the formation of a particular precipitate usually indicates the presence of a particular ion. For example, when you obtain silver chloride precipitate by treating the unknown with silver nitrate, you can say that the unknown contains chloride ions.