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 copper sulphate exists as `[Cu(H_2 O)_4 ] SO_4`. It is labile complex. The blue colour of the solution is due to `[Cu(H_2 O)_4]^(2+)` ion.
(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^(-) to [CuF_4]^(2-) + 4H_2 O`
Tetrafluorocuprate (II) (Green ppt.)
(ii) When KCl is added. `CI^-` ligands replace the weak `H_2 O` ligands forming `[CuCl_4]^(2-)` ion, which has bright green colour.
`[Cu(H_2 O)_4]^(2+) + 4 Cl^(-) to [CuCl_4]^(2-) + 4 H_2 O `
Tetrachlorocuprate (II) (Green solution).