A salt formed when aluminium hydroxide or γ-alumina is dissolved in solutions of strong bases, such as sodium hydroxide. Aluminates exist in solutions containing the aluminate ion, commonly written [Al(OH)4]−. In fact the ion probably is a complex hydrated ion and can be regarded as formed from a hydrated Al3+ ion by removal of four hydrogen ions:[Al(H2O)6]3++4OH− → 4H2O+[Al(OH)4(H2O)2]− Other aluminates and polyaluminates, such as [Al(OH)6]3− and [(HO)3AlOAl(OH)3]2−, are also present. See also aluminium hydroxide.
[Al(H2O)6]3++4OH− → 4H2O+[Al(OH)4(H2O)2]−