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

The chloride ions in this compound are not considered ligands because they do not donate a lone pair of electrons to the copper ion; rather, they are coordinating ions.

The ionic equation for the reaction is: $[Cu(H2O)6]^{2+} + 4NH_3 \rightarrow [Cu(NH_3)4]^{2+} + 6H_2O$

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

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

Reagent D is hydrochloric acid (HCl). The ionic equation for the reaction is: $[Cu(H2O)6]^{2+} + 4Cl^- \rightarrow [CuCl_4]^{2-} + 6H_2O$

Colorimetry cannot be used to determine the concentration of solutions containing [CuCl2] because it is colorless and does not absorb frequencies of visible light. Additionally, the electron configuration of the copper ion does not allow for the absorption of specific wavelengths of light.