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Explain why copper sulphate is blue in colour when dissolved in water but turns yellow when treated with concentrated HCl. |
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Answer» i. The electronic configuration of Cu: [Ar] 3d104s1 and Cu2+: [Ar] 3d9 ii. In the aqueous solution of copper sulphate, Cu2+ forms blue hydrated complex [Cu(H2O)6]2+ because it has one unpaired electron in 3d subshell. The complex has octahedral geometry. iii. When CuSO4 solution is treated with concentrated HCl solution, it forms a new complex [CuCl4]2- . [Cu(H2O)6]2+ + 4Cl- → [CuCl4]2- + 6H2O iv. The complex [CuCl4]2- has a tetrahedral geometry. Due to the change in geometry and hybridisation of the complex, the colour of the solution changes from blue to yellow. |
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