The terms “base” and “alkali” are often used interchangeably, because most common bases are alkalis. It is common to speak of “measuring the alkalinity of soil” when what is actually meant is the measurement of the pH (base property). Similarly, bases which are not alkalis, such as ammonia, are sometimes erroneously referred to as alkaline.
Note that not all or even most salts formed by alkali metals are alkaline; this designation applies only to those salts which are basic.
While most electropositive metal oxides are basic, only the soluble alkali metal and alkaline earth metal oxides can be correctly called alkalis.
This definition of an alkali as a basic salt of an alkali metal or alkaline earth metal does appear to be the most common, based on dictionary definitions, however, conflicting definitions of the term alkali do exist. These include:
- Any base that is water soluble Alkali, Farlex, 2008. Retrieved April 8, 2008. This is more accurately called an Arrhenius base.
- The solution of a base in water.