Qualitative Analysis (OCR A Level Chemistry A): Revision Note

Testing for Anions

• Tests can be used to identify anions in solutions of unknown compounds.

• If multiple tests are being carried out on the same solution it is important to carry them out in the same order as in the table below

Tests for solutions containing one or more unknown anions

• Ammonia can help distinguish between the silver halide precipitates

  • Silver chloride dissolves in dilute ammonia

  • Silver bromide dissolves in concentrated ammonia

  • Silver iodide is insoluble in concentrated ammonia

Testing for Cations

Testing for transition metal ions

• Adding aqueous sodium hydroxide to various transition metal ions produces precipitates.

• These reactions can be used for identifying transition metal ions in an unknown solution

The reactions of aqueous transition metal ions with aqueous sodium hydroxide

Testing for ammonium ions

• When heated with hydroxide ions ammonium ions react to produce ammonia gas

   NH₄⁺ (aq) + OH^- (aq) → NH₃ (g) + H₂O (l)

• Any ammonia produced will turn damp red litmus paper blue confirming the presence of ammonium ions in the original solution