amphoterism

amphoterism , in chemistry, the property of certain substances of acting either as acids or as bases depending on the reaction in which they are involved. Many hydroxide compounds are amphoteric. For example, aluminum hydroxide, Al(OH) ₃ , reacts as a base with common acids to form salts, e.g., with sulfuric acid, H ₂ SO ₄ , to form aluminum sulfate, Al ₂ (SO ₄ ) ₃ . It reacts as an acid with strong bases to form aluminates, e.g., with sodium hydroxide, NaOH, to form sodium aluminate, Na[Al(OH) ₄ (OH ₂ ) ₂ ]. Organic molecules that contain both acidic (e.g., carboxyl) and basic (e.g., amino) functional groups are usually amphoteric.

amphoteric Describing a compound that can act as both an acid and a base. Amino acids, which contain both acidic and basic groups in their molecules, can be described as amphoteric. Solvents, such as water, that can both donate and accept protons are usually described as amphiprotic (see solvent).