In coordination chemistry, the color changes observed when adding aqueous ammonia to a copper II sulfate solution can be explained by the formation of different copper-ammonia complexes.Initially, copper II sulfate CuSO4 is present in the solution as blue-colored hydrated copper II ions [Cu H2O 6]. When aqueous ammonia NH3 is added to the solution, it acts as a ligand and starts to replace the water molecules surrounding the copper II ion.The first step involves the deprotonation of water molecules by ammonia, forming hydroxide ions OH :NH3 + H2O NH4 + OHThe hydroxide ions then react with the copper II ions to form a light blue precipitate of copper II hydroxide Cu OH 2 :Cu + 2OH Cu OH 2 s As more ammonia is added to the solution, it starts to form a complex with the copper II ions by replacing the hydroxide ions in the copper II hydroxide precipitate. This forms a deep blue-colored tetraamminecopper II complex:Cu OH 2 s + 4NH3 [Cu NH3 4 H2O 2] + 2H2OThe deep blue color of the solution is due to the formation of this tetraamminecopper II complex. The ammonia molecules act as ligands and coordinate to the central copper II ion through their lone pair of electrons on the nitrogen atom.The color changes observed during this process are a result of the different electronic transitions occurring within the copper complexes. The energy of these transitions, which corresponds to the absorption of specific wavelengths of light, is influenced by the nature of the ligands surrounding the copper II ion. As the ligands change from water molecules to ammonia molecules, the energy of the electronic transitions and the absorbed wavelengths of light change, resulting in the observed color changes.