AMPHOTERISM

"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 (more generally, the word describes something made of, or acting like, two components).

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.

Examples

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

See also

• Amphiprotic