9.13 Aqueous copper sulphate solution (blue in colour) gives:

(i) a green precipitate with aqueous potassium fluoride and

(ii) a bright green solution with aqueous potassium chloride. Explain these experimental results.

Aqueous copper sulphate solution is blue due to the formation of [Cu(H2O)4]SO4

[Cu(H2O)4]SO4(aq) ⇌ [Cu(H2O)4]2++SO2−4

[Cu(H2O)4]2+ is a labile complex in which ligands H2O get easily replaced by  F  ion of KF (as in (i) part) and by  Cl ion of KCl (as in (ii) part).

(i). [Cu(H2O)4]2+(aq)+4F(aq)→[CuF4]2− Green ppt. + 4H2O

(ii).[Cu(H2O)4]2+(aq)+4Cl(aq)→[CuCl4]2−(aq) (Bright green solution) + 4H2O

In both these cases, the weak field ligand water is replaced by the  F  and  Cl ions.