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

The chloride ions in this compound do not donate a lone pair of electrons to the copper ion; hence, they do not form a coordinate (dative) bond.

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 for solutions containing [CuCl2] because it is colorless and cannot absorb frequencies of visible light. Additionally, the electron configuration of the copper ion does not allow for colorimetric measurements.