Bases

Bases, oxides and hydroxides of elements that are cations in solutions of their salts (in contrast to elements that are anions in solutions of their salts and form acidic oxides). Hydroxides of K and Na (KOH, NaOH) and other metals of group 1 of the periodic table of elements are called alkalis. Aqueous solutions of hydroxides have a soapy taste and turn red litmus paper blue; however, very weak bases may not produce this coloring. Alkalis and their concentrated solutions have a cauterizing and corrosive effect on body tissues. When bases react with acids, they lose their basic properties; simultaneously, the acid loses its acidic properties; the reaction of interaction between bases and acids is called neutralization (see). Bases can also react with acid anhydrides, forming salts (in the case of hydroxides—also water): Ca(OH)₂ + CO₂ = CaCO₃ + H₂O; CaO + CO₂ = CaCO₃. Ammonia, NH₃, is also considered a base, forming ammonium hydroxide with water: NH₃ + H₂O = NH₄OH; with acids, ammonia forms salts: NH₃ + HCl = NH₄Cl; NH₄OH + HCl = NH₄Cl + H₂O. Many organic derivatives of ammonia are known, called amines (see). In the ammonium group (NH₄), all four hydrogens can be replaced by a radical to form tetra-substituted ammonium bases, such as the hydrate of tetramethylammonium (CH₃)₄N·OH. Such compounds are very strong bases, whereas methylamines and ammonia are weak bases. Organic bases are widespread in animals and plants, and some of them have strong pharmacodynamic action and important biological significance (see Alkaloids, Amines, Antagonistic amines, Hormones, Ptomaines).