amfoteriset

Amfoteriset, or amphoteric substances, are chemical species that can act both as acids and as bases depending on the reaction partner and the conditions. In practice this means they can donate a proton to a stronger base or accept a proton from a stronger acid. This dual behavior is common among many metal oxides and hydroxides in inorganic chemistry.

Typical examples include water (H2O), aluminum oxide (Al2O3) and zinc oxide (ZnO), as well as hydroxides such as aluminum hydroxide (Al(OH)3) and zinc hydroxide (Zn(OH)2). Not all compounds are amphoteric; many substances are either strictly acidic or strictly basic under given conditions.

Amphoteric substances show pH-dependent solubility and reactivity. For example, Al2O3 dissolves in acidic solutions to form aluminum ions, and dissolves in strongly basic solutions to form aluminates such as [Al(OH)4]−. A representative set of reactions is: Al2O3 + 6 H+ → 2 Al3+ + 3 H2O, and Al2O3 + 2 OH− + 3 H2O → 2 [Al(OH)4]−. Similar behavior is observed for ZnO and Al(OH)3, which can form various salts or complex ions depending on the pH.

Applications of amphoteric materials include catalysis, corrosion science, soil and environmental chemistry, and materials science. Understanding amphotericity helps predict dissolution, precipitation, and complex formation in aqueous systems and industrial processes. The term derives from Greek roots meaning “two-faced” or “having two aspects,” reflecting the dual chemical behavior.