A colourless gas 'A' with a pungent odour is highly soluble in water and its aqueous solution is weakly basic. As a weak base, it precipitates the hydroxides of many metals from their salt solution. Gas 'A' finds application in detection of metal ions. It gives a deep blue colouration with copper ions. Identify the gas 'A' and write the chemical equations involved in the following :
(i) Gas 'A' with copper ions
(ii) Solution of gas 'A' with `ZnSO_(4)` solution.

Explanation

The available data suggests that the colourless gas 'A' with apungent odour and highly water soluble is ammonia. It dissolves in water to form `NH_(4)OH` which is weakly basic and precipitates the hydroxides of many metals. For example,
`FeCl_(3) +3NH_(4)OH to underset(("Brown ppt."))(Fe(OH)_(3))+3NH_(4)Cl`
Ammonia gives deep blue colour with `Cu^(2+)` ions by forming a complex.
(i) `Cu^(2+)+4overset(* *)(N)H_(3) to underset("Tetramminecopper (II) ion")([Cu(NH_(3))_(4)]^(2+))`
`(ii) ZnSO_(4)+2NH_(4)OH to underset(("White ppt."))(Zn(OH)_(2))+(NH_(4))_(2)SO_(4)`