Question

Ammonia forms the complex ion $\left[\right.Cu\left(\right.NH_{3}\left(\left.\right)_{4}\left(\left]\right.\right)^{2 +}$ with copper ions in the alkaline solutions but not in acidic solutions. What is the reason for it?

• A. In acidic solutions, protons coordinate with ammonia molecules forming $NH_{4}^{+}$ ions and $NH_{3}$ molecules are not available
• B. In alkaline solutions insoluble $Cu\left(\right.OH\left(\left.\right)_{2}$ 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

Answer 1

Answer: (A)

Ammonia forms the complex ion $\left[\right.Cu\left(\right.NH_{3}\left(\left.\right)_{4}\left(\left]\right.\right)^{2 +}$ with copper ions in the alkaline solutions but not in acidic solutions as in acidic solutions, $NH_{3}$ forms a bond with $H^{+}$ to give $NH_{4}^{+}$ ion which does not have a lone pair on N to act as a ligand.