Transition metal salts. Transition metal salts are often coloured. Photographed here, left to right, front row: iron (II) sulphate heptahydrate (FeSO4 7H2O, pale green, in a Petri dish), copper (II) sulphate pentahydrate (CuSO4 5H2O, blue, in a beaker); middle row: nickel (II) sulphate hexahydrate (NiSO4 6H2O, green-blue, in a beaker), cobalt (II) chloride hexahydrate (CoCl2 6H2O, purple, in a vial), copper (II) carbonate (CuCO3, blue-green, in an evaporation dish); back row: chromium (III) potassium sulphate dodecahydrate (KCr (SO4)2 12H2O, dark red, in a beaker), potassium chromate (VI) (K2CrO4, yellow, in a vial), manganese (II) carbonate (MnCO3, pale pink, in a beaker). |