Alkali
In chemistry, an alkali (; from Arabic: "al-qaly" "ashes of the saltwort") is a basic, ionic salt of an alkali metal or alkaline earth metal chemical element. An alkali also can be defined as a base that dissolves in water. A solution of a soluble base has a pH greater than 7.0. The adjective alkaline is commonly, and alkalescent less often, used in English as a synonym for basic, especially for bases soluble in water. This broad use of the term is likely to have come about because alkalis were the first bases known to obey the Arrhenius definition of a base, and they are still among the most common bases.
Acid–base reaction
This causes the protonation of water, or the creation of the hydronium (HO) ion. Thus, in modern times, the symbol H is interpreted as a shorthand for HO, because it is now known that a bare proton does not exist as a free species in aqueous solution.
The Arrhenius definitions of acidity and alkalinity are restricted to aqueous solutions, and refer to the concentration of the solvent ions. Under this definition, pure HSO and HCl dissolved in toluene are not acidic, and molten NaOH and solutions of calcium amide in liquid ammonia are not alkaline. This led to the development of the Bronsted-Lowry theory and subsequent Lewis theory to account for these non-aqueous exceptions.