10.3 AMPHOTERIC BEHAVIOR
When an aqueous solution containing Zn 2 _ or Al 3 _ has NaOH added, a precipitate of the metal
hydroxide forms. Upon continued addition of base, the precipitate dissolves just as it does when an
acid is added. In the fi rst case, the aluminum hydroxide is behaving as a base, and in the second it
behaves as an acid. This behavior, the ability to react as an acid or a base, is known as amphoterism . The
reaction of Zn 2 _ with a base and an acid can be shown as follows: