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NCERT Class XII Chemistry
Chapter - Coordination Compounds
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Question : 13 of 43
Marks: +1, -0
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.
Solution:  
(i) Aqueous CuSO4\mathrm{uSO}_4 solution contains [Cu(H2O)4]2+[\mathrm{Cu}(\mathrm{H}_2\mathrm{O})_4]^{2+} ions whichimpart blue colour. When KF is added, H2O\mathrm{H}_2\mathrm{O} being weak field ligand canbe replaced by F−^{-}forming [CuF4]2−[\mathrm{CuF}_4]^{2-} ions which impart green colour.
[Cu(H2O)4]2++4F−[F]→[CuF4]2−+4H2O[\mathrm{Cu}(\mathrm{H}_2\mathrm{O})_4]^{2+} + 4\mathrm{F}^- [\mathrm{F}] \rightarrow [\mathrm{CuF}_4]^{2-} + 4\mathrm{H}_2\mathrm{O}
[From KF ] (Green ppt.)\begin{array}{cccccccc} & & & & & & & \text{[From KF ] (Green ppt.)} \end{array}
(ii) When KCl is added, Cl−^{-}ligand replaces H2O\mathrm{H}_2\mathrm{O} forming [CuCl4]2−[\mathrm{CuCl}_4]^{2-} ionswhich has bright green colour.
[Cu(H2O)4]2++4Cl−→[CuCl4]−6HO+4H2O[\mathrm{Cu}(\mathrm{H}_2\mathrm{O})_4]^{2+} + 4\mathrm{Cl}^{-} \rightarrow [\mathrm{CuCl}_4]^{-6}\mathrm{H O} + 4\mathrm{H}_2\mathrm{O}
[From KCl ] (Brightgreen solution)\begin{array}{c c c c c c} & & & & & \text{[From KCl ] (Brightgreen solution)} \end{array}
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