Cation & Anion Tests

• Cation: Aluminium

  • With aqueous sodium hydroxide: white ppt, soluble in excess - colourless solution
  • With aqueous ammonia: white ppt, insoluble in excess
• Cation: Ammonium

  • With aqueous sodium hydroxide: ammonia produced on warming
• Cation: Calcium

  • With aqueous sodium hydroxide: white ppt, insoluble in excess
  • With aqueous ammonia: no ppt or very slight white ppt
• Cation: Chromium(III)

  • With aqueous sodium hydroxide: green ppt, soluble in excess
  • With aqueous ammonia: green ppt, insoluble in excess
• Cation: Copper (II)

  • With aqueous sodium hydroxide: light blue ppt, insoluble in excess
  • With aqueous ammonia: light blue ppt, soluble in excess - dark blue solution
• Cation: Iron (II)

  • With aqueous sodium hydroxide: green ppt, insoluble in excess, brown near surface on standing
  • With aqueous ammonia: green ppt, insoluble in excess, brown near surface on standing
• Cation: Iron (III)

  • With aqueous sodium hydroxide: red-brown ppt, insoluble in excess
  • With aqueous ammonia: red-brown ppt, insoluble in excess
• Cation: Zinc

  • With aqueous sodium hydroxide: white ppt, soluble in excess - colourless solution
  • With aqueous ammonia: white ppt, soluble in excess - colourless solutino
• Anion: Carbonate

  • Test: add dilute acid, then test for carbon dioxide gas
  • Result: effervescence, carbon dioxide produced
• Effervescence - bubbles in a liquid
• Anion: Chloride

  Test: acidify with dilute nitric acid, then add aqueous silver nitrate

  Result: white ppt
• Anion: Bromide

  Test: acidify with dilute nitric acid, then add aqueous silver nitrate

  Result: cream ppt
• Anion: Iodide

  Test: acidify with dilute nitric acid, then add aqueous silver nitrate

  Result: yellow ppt
• Anion: Nitrate

  Test: add aqueous sodium hydroxide, then aluminium, warm carefully

  Result: ammonia produced
• Anion: Sulfate

  Test: acidify with dilute nitric acid, then add aqueous barium nitrate

  Result: white ppt
• Anion: Sulfite

  Test: add a small volume of acidified potassium manganate

  Result: acidified aqueous potassium manganate changes colour from purple to colourless
• Solving cation testing questions:

  • check for key words involving reagents (chemicals/solutions used to do with the experiment e.g. sodium hydroxide, ammonia) and also highlight defining words e.g. excess, aqueous
• Solving anion testing questions:

  • find reagents relation to the question e.g. barium nitrate, nitric acid
• Never use abbreviation, write 'precipitate' in full
• Solving observation questions:

  • write notes on all the observations given - make sure to utilise all the evidence given in the question
  • answer the question using notes given
• "What conclusions can you draw about solid N" - write down everything you know from your observations
• When there's no reaction, don't write 'nothing' or 'nothing happened. Write 'no reaction'
• Any ionic compound that is coloured is a transition metal except for zinc as it's usually colourless
• If it is mentioned that a substance is a solution, say that it's a solution. Don't say liquid!
• The appearance of a substance before the test is the same as the appearance after the reaction
• 'Test the gas' - always write bubbles for an observation involving this statement
• In a question asking you to 'test the gas' and 'record observations', include how to do the gas test, the result, and observations
• Liquid is a melted solid while solution is a dissolved solid
• Silver nitrate tests for halogens aka chlorides, iodides and brromides
• You can make an experiment more accurate by repeating it
• What is filtrate?

  Dissolved solid
• What is residue?


  Not dissolved solid
• Copper (II) oxide is a black solid
• What is the test for sulphate?

  add barium nitrate and white ppt formed