Identification of Ions

• Aqueous cations


  • Aluminium
  • Ammonium
  • Calcium
  • Chromium(III)
  • Copper(II)
  • Iron(II)
  • Iron(III)
  • Zinc
• Identifying aqueous cations


  1. Add few drops NaOH

  2. Add excess NaOH
• Aqueous cations


  • Aluminium: White precipitate forms, precipitate re-dissolves
  • Ammonium: Ammonia gas given off, no change
  • Calcium: White precipitate forms, no change
  • Chromium(III): Grey-green precipitate forms, dark green solution forms
  • Copper(II): Blue precipitate forms, no change
  • Iron(II): Green precipitate forms, no change
  • Iron(III): Orange-brown precipitate forms, no change
  • Zinc: White precipitate forms, precipitate re-dissolves
• Identifying aqueous cations with ammonia

  1. Add few drops ammonia

  2. Add excess ammonia
• Aqueous cations with ammonia


  • Aluminium: White precipitate forms, no change
  • Calcium: No precipitate formed, no precipitate formed
  • Zinc: White precipitate forms, precipitate re-dissolves
• Flame test


  Used to identify lithium, sodium, potassium and copper(II) cations
• Anions


  • Carbonate
  • Chloride
  • Bromide
  • Iodide
  • Nitrate
  • Sulfate
  • Sulfite
• Identifying carbonates


  1. React with dilute acid to create carbon dioxide

  2. Bubble CO2 through limewater, turns cloudy
• Identifying halides


  1. Add dilute nitric acid, then silver nitrate solution

  2. Chloride: White precipitate

  3. Bromide: Cream precipitate

  4. Iodide: Yellow precipitate
• Identifying nitrates


  1. React copper/aluminium/zinc alloy with nitrate in sodium hydroxide, then add aluminium, ammonia is released

  2. Turns damp red litmus paper blue
• Identifying sulfates


  1. Add dilute hydrochloric acid, then barium chloride solution

  2. White precipitate forms
• Identifying sulfites


  1. React with dilute acids, sulfur dioxide gas given off

  2. Use aqueous potassium manganate(VII), colour changes from purple to colourless
• Gases


  • Ammonia
  • Carbon dioxide
  • Chlorine
  • Hydrogen
  • Oxygen
  • Sulfur dioxide
• Identifying ammonia


  Turns damp red litmus paper blue
• Identifying carbon dioxide


  Bubble gas through limewater, turns milky (cloudy)
• Identifying chlorine


  Damp litmus paper is bleached and turns white
• Identifying hydrogen


  Use a burning splint, creates a 'squeaky pop' sound
• Identifying oxygen


  Use a glowing splint, splint relights
• Identifying sulfur dioxide


  Use aqueous potassium manganate(VII), colour changes from purple to colourless