COMEDK2023Morning ShiftChemistryCoordination CompoundsActual
Aqueous CuSO ₄ changes its colour from sky blue to deep blue on addition of NH ₃ because
Options
- A[ Cu ( H ₂ O )₄ ]²⁺ is labile complex and changes to [ Cu ( NH ₃ )₄ ]²⁺ as NH ₃ is stronger ligand than H ₂ O
- BCu ²⁺ changes to Cu ⁺
- CCu ²⁺ forms hydrate
- DCu ⁺ changes to Cu ²⁺
Correct answer
A. [ Cu ( H ₂ O )₄ ]²⁺ is labile complex and changes to [ Cu ( NH ₃ )₄ ]²⁺ as NH ₃ is stronger ligand than H ₂ O
Step-by-step solution
Aqueous copper(II) sulfate exists as the complex ion [ Cu ( H ₂ O )₄ ]²⁺ (or more accurately [ Cu ( H ₂ O )₆ ]²⁺ ), which is sky blue in color. Upon the addition of ammonia ( NH ₃ ), the ammonia molecules act as stronger ligands than water molecules and displace them from the coordination sphere of the copper(II) ion. The reaction is represented as [ Cu ( H ₂ O )₄ ]²⁺ + 4 NH ₃ [ Cu ( NH ₃)₄ ]²⁺ + 4 H ₂ O . The resulting complex [ Cu ( NH ₃)₄ ]²⁺ (tetraamminecopper(II) ion) exhibits a deep blue color due to the chan