Question #82d07

1 Answer
Feb 2, 2017


Best and simple reaction that illustrates this topic is:

#2 color(white) "." H_2O rightleftharpoons H_3O^+ + OH^-#


The autoionization of water is the best example illustrating the amphoteric behavior of the #H_2O# molecule in a single chemical reaction. One of the reactant molecules acts as a base, thanks to the presence of the two pairs of non-shared electrons of the oxygen atom, while the other molecule behaves like an acid when releasing a hydrogen ion.

If we want to see this behavior against other substances, water can act as an acid when it has a base in front, as would be the case of ammonia:

#NH_3 + H_2O rightleftharpoons NH_4^+ + OH^-#,

or it can act as a base in the presence of an acid, such as ethanoic acid:

#CH_3COOH + H_2O rightleftharpoons CH_3COO^{-} + H_3O^+#.