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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.
(i) a green precipitate with aqueous potassium fluoride and
(ii) a bright green solution with aqueous potassium chloride. Explain these experimental results.
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Aqueous \(\mathrm{CuSO}_4\) solution exists as \(\left[\mathrm{Cu}\left(\mathrm{H}_2 \mathrm{O}\right)_4\right] \mathrm{SO}_4\) which has blue colour due to \(\left[\mathrm{Cu}\left(\mathrm{H}_2 \mathrm{O}\right)_4\right]^{2+}\) ions.
(i) When \(\mathrm{KF}\) is added, the weak \(\mathrm{H}_2 \mathrm{O}\) ligands are replaced by \(\mathrm{F}^{-}\)ligands forming \(\left[\mathrm{CuF}_4\right]^{2-}\) ions which is a green precipitate.
\(\left[\mathrm{Cu}\left(\mathrm{H}_2 \mathrm{O}\right)_4\right]^{2+}+4 \mathrm{~F}^{-} \longrightarrow \underset{\substack{\text { Tetrafluoridocuprate (II) } \\ \text { (Green ppt.) }}}{\left[\mathrm{CuF}_4\right]^{2-}}+4 \mathrm{H}_2 \mathrm{O}\)
(b) When \(\mathrm{KCl}\) is added, \(\mathrm{Cl}^{-}\)ligands replace the weak \(\mathrm{H}_2 \mathrm{O}\) ligands forming \(\left[\mathrm{CuCl}_4\right]^{2-}\) ion which has bright green colour.
\(\left[\mathrm{Cu}\left(\mathrm{H}_2 \mathrm{O}\right)_4\right]^{2+}+4 \mathrm{Cl}^{-} \longrightarrow\underset{\text{Tetrachloridocuprate(II)} \atop \text{(Bright green solution)}}{\left[\mathrm{CuCl}_4\right]^{2-}}+4 \mathrm{H}_2 \mathrm{O}\)
(i) When \(\mathrm{KF}\) is added, the weak \(\mathrm{H}_2 \mathrm{O}\) ligands are replaced by \(\mathrm{F}^{-}\)ligands forming \(\left[\mathrm{CuF}_4\right]^{2-}\) ions which is a green precipitate.
\(\left[\mathrm{Cu}\left(\mathrm{H}_2 \mathrm{O}\right)_4\right]^{2+}+4 \mathrm{~F}^{-} \longrightarrow \underset{\substack{\text { Tetrafluoridocuprate (II) } \\ \text { (Green ppt.) }}}{\left[\mathrm{CuF}_4\right]^{2-}}+4 \mathrm{H}_2 \mathrm{O}\)
(b) When \(\mathrm{KCl}\) is added, \(\mathrm{Cl}^{-}\)ligands replace the weak \(\mathrm{H}_2 \mathrm{O}\) ligands forming \(\left[\mathrm{CuCl}_4\right]^{2-}\) ion which has bright green colour.
\(\left[\mathrm{Cu}\left(\mathrm{H}_2 \mathrm{O}\right)_4\right]^{2+}+4 \mathrm{Cl}^{-} \longrightarrow\underset{\text{Tetrachloridocuprate(II)} \atop \text{(Bright green solution)}}{\left[\mathrm{CuCl}_4\right]^{2-}}+4 \mathrm{H}_2 \mathrm{O}\)
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