Question

Ammonia forms the complex `[Cu(NH_3)_4]^(2+)` with copper ions in alkaline solution but not in acid solution. The reasons for it is:
A. In acidic solutions, hydration protects copper ions.
B. In acidic solutions, protons co-ordiante with ammonia molecules forming `NH_4^(+)` ions and `NH_3` molecules are not available.
C. In alkaline solutions, insoluble `Cu(OH)_2` is precipitated which is soluble in excess of any alkali.
D. Copper hydoxide is an amphoteric substance .

Answer 1

Correct Answer - B
In acidic medium , the electron pair on the N atom in `NH_3` molecule will be taken by `H^(+)` ion of the acid. It cannot co-ordinate with `Cu^(2+)` ion.