Solution A contains the compound [Cu(H2O)6]Cl2 - AQA - A-Level Chemistry - Question 7 - 2017 - Paper 1

The chloride ions are not considered to be ligands because they do not donate a lone pair to the copper atom; instead, they are coordinated ionically.

The ionic equation for the reaction is: $[Cu(H_2O)_6]^{2+} + 4NH_3 \rightarrow [Cu(NH_3)_4]^{2+} + 6H_2O$

The colour of solution B is deep blue or royal blue.

The blue-green solid C is copper carbonate (CuCO3) or basic copper carbonate.

Reagent D is hydrochloric acid (HCl). The ionic equation for the reaction is: $Cu^{2+} + 4Cl^- \rightarrow [CuCl_4]^{2-}$

Colorimetry cannot be used to determine the concentration of solutions containing [CuCl2] because the solution is colorless, which means it cannot absorb the visible light necessary for colorimetric analysis. Additionally, the electron configuration of the metal ion does not allow for any optical activity in this context.