(i) Physical properties : Ammonia molecule is a trigonal pyramidal with the nitrogen atom at apex. It has three bonding electron pairs and one non-bonding electron pair.
Ammonia is colourless gas with a pungent order. Its freezing and boiling points are 198.4 and 239.7 K respectively. In the solid an liquid states, it is associated through H-bonds as in the case of water and that accounts for its higher melting and boiling points than expected on basis of its molecular mass.
(ii) Chemical properties : Ammonia is highly soluble in water. Its aqueous solution is weakly basic due to formation of -OH ions.
`NH_(3)(g) + H_(2)O (l) It forms ammonium salts with acid e.g., `NH_(4)Cl`, `(NH_4)_2SO_(4)` etc. As a weak base, it precipitates hydroxides (hydrated oxides in case of some metals) of many metals from their salt.
For example:
`ZnSO_(4)(aq) + 2NH_(4)OH_(aq) to Zn(OH)_(2) + (NH_(4))_(2).SO_(4)(aq)`
`FeCl_(3) (aq) + NH_(4)OH(aq) to Fe_(2)O_(3).xH_(2)O(s) + NH_(4)Cl(aq)` (Brown ppt)
Ammonia act as a lewis base due to presence of lone pair of electrons on nitrogen atom.
It donates the electron pair and forms linkage with metal ions and the formation of such complex compounds find application in detection of metal ions such as `Cu^(2+), Ag^(+)` etc.
`underset("blue")(Cu_(aq)^(2+) + 4NH_(3)(aq) `underset("colourless")(Ag_(aq))^(+) + underset("white ppts")(AgCl(s)) overset(2NH_(3)(aq)) to underset("colourless")(Ag(NH_(3))_(2)]Cl(aq)`
