Amphoterism
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"Amphoteric" redirects here. For other uses, see Amphoteric (disambiguation).
In chemistry, an amphoteric substance is one that can react as either an acid or base.
[edit] Examples
Examples include amino acids, proteins, and water. Many metals, such as zinc, tin, lead, aluminium, and beryllium, have amphoteric oxides.
For example, zinc oxide (ZnO) reacts differently depending on the pH of the solution:
In acids: ZnO + 2H+ → Zn2+ + H2O
In bases: ZnO + H2O + 2OH- → [Zn(OH)4]2-
This effect can be used to separate different cations, such as zinc from manganese.
There are many other examples of chemical compounds which are also amphoteric, for the simplest example water:
Acid: H2O + HCl → H3O+ + Cl−
Base: H2O + NH3 → NH4+ + OH−
- (Indeed, it can do both at once: 2H2O → H3O+ + OH−)
Aluminum hydroxide is as well:
Acid: Al(OH)3 + 3HCl → AlCl3 + 3H2O
Base: Al(OH)3 + NaOH → NaAl(OH)4
