Warning: Copper salts are toxic. Do not eat or drink.
We have already seen the copper(I) ammine complex, which is colorless. It was formed when copper(I) oxide dissolves in ammonia. When it was oxidized, a blue solution of the copper(II) ammine complex was formed. Here, though, you will create a concentrated copper(II) ammine complex and see its real appearance.
You will need:
Copper(II) chloride or copper sulfate
Dissolve copper(II) chloride in water. The color from the hydrated copper(II) ions is blue for dilute solutions and green for concentrated solutions. Add ammonia. First, the hydroxide ions react to make a blue precipitate of copper(II) hydroxide. Then, the ammonia molecule itself removes the water molecules from the hydrated copper(II) ions, making the copper(II) ammine complex. This is indicated by a dramatic darkening of the solution to a navy blue.
Here is a relatively dilute solution of tetramminecopper(II). It is dark blue, almost black in the thick parts. The blue can be seen in the thin parts.