Testing for positive ions

• When sodium hydroxide is added to metal cation solutions:

  • White precipitate formed and becomes colourless in excess> Aluminium (Al3+)
  • White precipitate formed and stays the same in excess> Calcium (Ca2+) and Magnesium (Mg2+)
  • Blue precipitate formed> Copper (Cu2+)
  • Green precipitate formed> Iron (Fe2+)
  • Brown precipitate formed> Iron (Fe3+)