174. 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 contains coordination entities [Cu(H₂O)₄]²⁺ which are blue in colour. Water molecule is a weaker ligand than Cl^– and F^–.
(a) On addition of aqueous KF solution, a new complex entity is formed which is of green colour.

${\left[\mathrm{Cu}({\mathrm{H}}_2\mathrm{O}{)}_4\right]}^2+\underset{(from KF aq.solution)}{4{\mathrm{F}}^{-}}\to {\left[Cu{F}_4\right]}^{2+} + 4{\mathrm{H}}_2\mathrm{O}$

(b) On addition of aqueous solution of KCl, an another complex entity is formed which is soluble in water.

${\left[\mathrm{Cu}({\mathrm{H}}_2\mathrm{O}{)}_4\right]}^{2+} + \underset{(\mathrm{from} \mathrm{KCl} \mathrm{aq}. \mathrm{solution})}{4{\mathrm{Cl}}^{-}} \to \underset{bright green solution (\mathrm{a} soluble complex entity)}{{\left[Cuc{l}_4\right]}^{2-}}+ 4\hspace{0.17em}{\mathrm{H}}_2\mathrm{O}$