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.

Explanation

Aqueous `CuSO_(4)` solution exists as `[Cu(H_(2)O)_(4)]SO_(4)` which has blue colour due to `[Cu(H_(2)O)_(4)]^(2+)` ions. (i) When KF is added, the weak `H_(2)O` ligands are replaced by `F^(-)` ligands forming `[CuF_(4)]^(2-)` ions which is a green precipitate.
`[Cu(H_(2)O)_(4)]^(2+)+4F^(-)rarrunderset(("Green ppt."))underset("Tetrafluorocuprate(II)")([CuF_(4)]^(2-))+4H_(2)O`
(ii) When KCl is added, `Cl^(-)` ligands replace the weak `H_(2)O` ligands forming `[CuCl_(4)]^(2-)` ion which has bright green colour.
`[Cu(H_(2)O)_(4)]^(2+)+4Cl^(-)rarrunderset(("Green solution"))underset("Tetrachlorocuprate(II)")([CuCl_(4)]^(2-))+4H_(2)O`
Alternatively, directly we can write the reaction as :
`CuSO_(4)(aq)+4KF(aq)rarrK_(2)[CuF_(4)]+K_(2)SO_(4)`
`CuSO_(4)(aq)+4KCl(aq)rarrK_(2)[CuCl_(4)]+K_(2)SO_(4)`