State which of the following species are amphiprotic and write chemical equations illustrating the amphiprotic character of these species.

\({\rm{\;(a)\;N}}{{\rm{H}}_3}\)

\({\rm{\;(b)\;HPO}}_4^ - \)

\({\rm{\;(c)\;B}}{{\rm{r}}^ - }\).

\({\rm{\;(d)\;N}}{{\rm{H}}_4} + \)

\({\rm{\;(e)\;ASO}}_4^{3 - }\).

Amphiprotic species can react as a Bronsted-Lowry's acid (proton donor) and as a base (proton acceptor).

a) Ammonia is amphiprotic. Here \({\rm{N}}{{\rm{H}}_3}\)acts as an acid:

\({\rm{N}}{{\rm{H}}_3}(aq) + {{\rm{H}}_2}{\rm{O}}({\rm{l}}) \to {\rm{NH}}_2^ - (aq) + {{\rm{H}}_3}{{\rm{O}}^ + }(aq)\)

In this equation acts as a base:

\({\rm{N}}{{\rm{H}}_3}(aq) + {{\rm{H}}_2}{\rm{O}}({\rm{l}}) \to {\rm{NH}}_4^ + (aq) + {\rm{O}}{{\rm{H}}^ - }(aq)\)

b) \({\rm{HPO}}_4^{2 - }\) is also amphiprotic and it can be seen in its reactions with water. Here acts like an acid:

.\({\rm{HPO}}_4^{2 - }(aq) + {{\rm{H}}_2}{\rm{O}}({\rm{l}}) \to {\rm{PO}}_4^{3 - }(aq) + {{\rm{H}}_3}{{\rm{O}}^ + }(aq)\).

In following equation acts as a base:

\({\rm{HPO}}_4^{2 - }(aq) + {{\rm{H}}_2}{\rm{O}}({\rm{l}}) \to {{\rm{H}}_2}{\rm{PO}}_4^ - (aq) + {\rm{O}}{{\rm{H}}^ - }(aq)\)

c) \(B{r^ - }\)is not amphiprotic. It can act like a base - proton acceptor, but it cannot be an acid because it does not have any proton to donate.

d) \({\rm{NH}}_4^ + \)is also not amphiprotic. It can act like an acid - proton donor, but it cannot accept any more protons, so it is not a base.

e) \({\rm{AsO}}_4^{3 - }\)is not amphiprotic. It can act like a base - proton acceptor, but it cannot be an acid because it does not have any proton to donate.