Precipitates and Complexes of Nickel (II)
Various chemicals in various amounts are added to a nickel (II) solution resulting in a variety of colors.
Ions of the transition elements exist in aqueous solution as complex ions. Transition-metal compounds are often colored. The color results from the transition of electrons between the two closely spaced d orbitals. The transitions are due to the electric field of the compound's ligands. For example, when water is the ligand the nickel complex has a green color, when ammonia is the ligand the color is blue.