Core practical 5 - Analyse organic and inorganic unknowns

When testing an inorganic compound for the presence of halide ions, why is nitric acid added before adding silver nitrate?

It removes anions such as carbonate ions; that would form a precipitate with silver nitrate.

What further test could you do to distinguish between sulfate(VI) ions and sulfate(IV) ions?

Add dilute hydrochloric acid; sulfate(IV) ions will dissolve but sulfate(VI) ions will not.

Outline a further test that you could use to identify the presence of an aldehyde group.

Heat with Fehling’s or Benedict’s solution; the formation of a red precipitate indicates the presence of an aldehyde group

Safety

● Wear goggles.

● Concentrated hydrochloric acid, sodium hydroxide and concentrated sulfuric acid are corrosive.

● Nitric acid, hydrochloric acid and limewater are irritants.

● Barium chloride and bromine water are toxic and irritants.

● Ethanol is flammable – do not use it near a lit Bunsen burner.

● Pay attention to the hazard warnings on the tubs and bottles of unknown substances. In particular, if anything is marked flammable, do not use anywhere near a lit Bunsen burner. If heating a flammable substance is required then it must be heated by standing it in a beaker of hot water.