Test for Cations

• Aluminium Ion Al3+


  • aqueous sodium hydroxide : white precipitate of aluminium hydroxide formed, soluble in excess to form colourless solution
  • aqueous ammonia : white precipitate of aluminium hydroxide formed, insoluble in excess
• Ammonium ion NH4 +

  • Aqueous sodium hydroxide : no precipitate formed. Upon heating, gas evolved turns damp red litmus paper blue (ammonia gas)
• Calcium Ion Ca2+


  • aqueous sodium hydroxide : white precipitate of calcium hydroxide is formed, insoluble in excess
  • aqueous ammonia : no precipitate
• Copper (II) ion Cu2+


  • aqueous sodium hydroxide : light blue precipitate of copper (II) hydroxide formed, insoluble in excess
  • aqueous ammonia : light blue precipitate of copper (II) hydroxide formed, dissolves in excess to form a dark blue solution
• Iron (II) ion Fe2+

  • aqueous sodium hydroxide : green precipitate of iron (II) hydroxide formed, insoluble in excess and turns brown on standing
  • aqueous ammonia : green precipitate of iron (II) hydroxide formed, insoluble in excess and turns brown on standing
• Iron (III) Ion Fe3+


  • aqueous sodium hydroxide : red-brown precipitate of iron (III) hydroxide is formed, insoluble in excess
  • aqueous ammonia : red-brown precipitate of iron (III) hydroxide is formed, insoluble in excess
• Zinc Ion Zn2+


  • aqueous sodium hydroxide : white precipitate of zinc hydroxide, dissolves in excess to give colourless solution
  • aqueous ammonia : white precipitate of zinc hydroxide, dissolves in excess to give colourless solution