Question:
Ammonia forms the complex ion [Cu(NH₃)₄]²⁺ with copper ions in alkaline solutions but not in acidic solutions. What is the reason for it?
Ammonia forms the complex ion [Cu(NH₃)₄]²⁺ with copper ions in alkaline solutions but not in acidic solutions. What is the reason for it?
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Ligands must be free to donate lone pairs.
Updated On: Mar 17, 2026
- In acidic solutions protons coordinate with ammonia molecules forming NH₄^+ ions and NH₃ molecules are not available.
- In alkaline solutions insoluble Cu(OH)₂ is precipitated which is soluble in excess of any alkali.
- Copper hydroxide is an amphoteric substance.
- In acidic solutions hydration protects copper ions.
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The Correct Option is A
Solution and Explanation
In acidic medium:
NH3 + H+ -> NH4+
Ammonia is protonated and cannot act as a ligand.
Hence complex formation does not occur.
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