Inorganic ion colours and complexes

OCR A-level Chemistry

[Cu(H2O)6]2+

pale blue

NH3 added dropwise to Cu2+

pale blue precipitate

Excess NH3 to Cu2+

dark blue

CuCl4 2-

yellow

CuSO4

Blue solution

CuI

White precipitate

CoCl4 2-

Blue

[Cr(H2O)6]3+

pale purple

Cr(OH)3 with NH3 added dropwise

dark green precipitate

[Cr(NH3)6]3+ (NH3 added in excess to Cr3+)

Purple

[Cr(OH)6]3-

dark green

Cr2O7 2-

Orange

CrO4 2- (Cr3+ oxidised with hot H2O2)

yellow

[Mn(H2O)]2+

pale pink

Mn(OH)2

Pale brown precipitate

[Fe(H2O)6]2+

Pale green

Fe(OH)2 (NaOH added dropwise to Fe2+)

Dark green precipitate

[Fe(H2O)6]3+

yellow

Fe(OH)3 (NaOH added dropwise to Fe3+)

orange-brown precipitate

MnO4-/Fe2+ => Mn2+/Fe3+

Purple to pale pink

I-/Fe3+ => I2/Fe2+

Orange brown to brown