Analysing Substances - C3 AQA

Flame tests can be used to identify metal ions. Lithium, sodium, potassium, calcium and barium compounds produce distinctive colours in flame tests:

*Lithium compounds result in a crimson flame

*Sodium compounds result in a yellow flame

*Potasium compounds result in a lilac flame

*Calcium compounds result in a red flame

*Barium compounds result in a green flame

Aluminium, calcium and magnesium ions form white precipitates with sodium hydroxide solution but only the aluminium hydroxide precipitate dissolves in excess sodiu hydroxide solution

Copper(II), iron(II) and iron(III) ions form coloured precipitates with sodium hydroxide solution. Copper forms a blue precipitate, iron(II) a green precipitate and iron(III) a brown precipitate.

Carbonates react with dilute acids to form carbon dioxide. Carbon dioxide produces a white precipitate with limewater. This turns limewater cloudy.

Halide ions in solution produce precipitates with silver nitrate solution in the presence of dilute nitric acid. Silver chloride is white, silver bromide is cream and silver iodide is yellow.

Sulfate ions in solution produce a white precipitate with barium chloride solution in the presence of dilute hydrochloric acid.

The volumes of acid and alkali solutions that react with each other can be measured by titration using a suitable indicator.

(The method of titration should be known)

Higher tier only

If the concentration of one of the reactants is known, the results of a titration can be used to find the concentration of the other reactant.

(This may have to be clalculated so the method of finding the alternative concentration should be known)