Qualitative Analysis (OCR A Level Chemistry)

Revision Note

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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

anion-test-5-6-7

  • 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

5-6-4-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) → NH(g) + H2O (l)

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

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Sonny

Author: Sonny

Expertise: Chemistry

Sonny graduated from Imperial College London with a first-class degree in Biomedical Engineering. Turning from engineering to education, he has now been a science tutor working in the UK for several years. Sonny enjoys sharing his passion for science and producing engaging educational materials that help students reach their goals.