Question
Explain the amphoteric nature of water.
✓
Answer
Water has the ability to act as an acid as well as a base. Such behaviour is known as amphoteric nature of water.
e.g.
$\underset{(\text { Acid) }}{ H _2 O _{( l )}}+ NH _{3( aq )} \rightleftharpoons OH _{( aq )}^{-}+ NH _{4( aq )}^{+}$
$\underset{(\text { Base })}{ H _2 O _{( l )}+ HCl _{( aq )}} \rightleftharpoons H _3 O _{( aq )}^{+}+ Cl _{( aq )}^{-}$
$H _2 O$ acts as an acid towards $NH _3$ and as a base towards $HCl$.
Therefore, $H _2 O$ is amphoteric.
e.g.
$\underset{(\text { Acid) }}{ H _2 O _{( l )}}+ NH _{3( aq )} \rightleftharpoons OH _{( aq )}^{-}+ NH _{4( aq )}^{+}$
$\underset{(\text { Base })}{ H _2 O _{( l )}+ HCl _{( aq )}} \rightleftharpoons H _3 O _{( aq )}^{+}+ Cl _{( aq )}^{-}$
$H _2 O$ acts as an acid towards $NH _3$ and as a base towards $HCl$.
Therefore, $H _2 O$ is amphoteric.
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