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?

• A. In acidic solutions protons coordinate with ammonia molecules forming NH₄^+ ions and NH₃ molecules are not available.
• B. In alkaline solutions insoluble Cu(OH)₂ is precipitated which is soluble in excess of any alkali.
• C. Copper hydroxide is an amphoteric substance.
• D. In acidic solutions hydration protects copper ions.

Hint:

Ligands must be free to donate lone pairs.

Answer 1

The Correct Option is A

In acidic medium: NH3 + H+ -> NH4+ Ammonia is protonated and cannot act as a ligand. Hence complex formation does not occur.