Alumina is purified away from aluminum salts containing this ion in the Bayer process. During saponification, this ion acts as a nucleophile at a carbonyl group to convert fats into soaps. Although this polyatomic (20[1])ion precipitates most metals, at very high concentrations it re-solubilizes zinc and aluminum because it forms amphoteric salts. This naked ion reacts with carbon dioxide to form (*) bicarbonate. The equilibrium constant K-sub-b equals the molarity of this ion times “HB over B minus.” The sodium salt of this ion is sold as pellets called “caustic soda.” The concentration (10[1])of this an·ion increases when ammonia is dissolved in water. For 10 points, all strong bases are salts of what polyatomic ion with formula “OH minus”? ■END■