Ammonia is added to solutions of cobalt, nickel, and copper 2+ cations. First formation of the hydroxide precipitate is seen, then of the ammonia complex. Pour 0.1M solutions of Cu2+, Co2+, and Ni2+ ...

the purple precipitate being the desired compound. When freshly precipitated it dissolves in ammonia, but by exposure to the light the solution gradually decomposes, becoming gradually blue and ...