Test for Aqueous Cations

• Cation: Aluminium (Al 3+)

  Aqueous Sodium Hydroxide: White precipitate forms, which is soluble in excess giving a colourless solution.

  Aqueous Ammonia: White precipitate forms, which is insoluble in excess.
• Cation: Zinc (Zn 2+)

  Aqueous Sodium Hydroxide: White precipitate forms, which is soluble in excess giving a colourless solution.

  Aqueous Ammonia: White precipitate forms, which is soluble in excess giving a colourless solution.
• Cation: Calcium (Ca 2+)

  Aqueous Sodium Hydroxide: White precipitate forms, which is insoluble in excess

  Aqueous Ammonia: No precipitate or very slight white precipitate. If a slight precipitate forms, It is insoluble in excess.
• Cation: Chromium (Cr 2+)

  Aqueous Sodium Hydroxide: Green precipitate forms, which is insoluble in excess

  Aqueous Ammonia: Green precipitate forms, which is insoluble in excess
• Cation: Copper (Cu 2+)

  Aqueous Sodium Hydroxide: Light blue precipitate forms, which is insoluble in excess

  Aqueous Ammonia: Light blue precipitate forms, which is soluble in excess, giving a dark blue solution.
• Cation: Iron(II) (Fe 2+)

  Aqueous Sodium Hydroxide: Green precipitate forms, which is insoluble in excess. On standing for 5 minutes, the surface turns brown.

  Aqueous Ammonia: Green precipitate forms, which is insoluble in excess. On standing for 5 minutes, the surface turns brown as (Fe 3+) is formed.
• Cation: Iron(III) (Fe 3+)

  Aqueous Sodium Hydroxide: Red-brown precipitate forms, which is insoluble in excess.

  Aqueous Ammonia: Red-brown precipitate forms, which is insoluble in excess.
• Cation: Ammonium (NH4+)

  Aqueous Sodium Hydroxide: Ammonia gas produced on warming which turns damp red litmus paper blue.