MARTYN F. CHILLMAID / SCIENCE PHOTO LIBRARY MARTYN F. CHILLMAID / SCIENCE PHOTO LIBRARY
Complex metal ions, colour changes. The colours of complex metal ions varies depending on a number of factors, mainly the oxidation state of the ion and the type and number of ligands. The two solutions here are complexes of the copper (II) ion. At left is a solution of copper (II) sulphate dissolved in water, with the hexaaquacopper (II) ion (six water ligands around the copper ion) producing a blue colour. At right, the addition of chloride ions replaces the water ligands to produce tetrachlorocuprate (II) ions and a green colour.
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