In chemistry, an alkali (from Arabic: Al-Qaly القلي, القالي ) is a basic, ionic salt of an alkali metal or alkaline earth metal element. Some authors also define an alkali as a base that dissolves in water. A solution of a soluble base has a pH greater than 7. The adjective alkaline is commonly used in English as a synonym for base, especially for soluble bases. 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 are still among the more common bases.
Contents |
The word "alkali" is derived from Arabic al qalīy = the calcined ashes, referring to the original source of alkaline substance. Ashes were used in conjunction with animal fat to produce soap, a process known as saponification. Also used to process cereals.
Alkalis are all Arrhenius bases, which form hydroxide ions (OH-) when dissolved in water. Common properties of alkaline aqueous solutions include:
The terms "base" and "alkali" are often used interchangeably, particularly outside of a scientific context.
There are various definitions for alkali. Alkali is often defined as a subset of base. However, two subsets are commonly chosen.
The second subset of base is also called an Arrhenius base.
Most basic salts are alkali salts, of which common examples are:
Soil with a pH value higher than 7.3 is normally referred to as alkaline. This soil property can occur naturally, due to the presence of alkali salts. Although some plants do prefer slightly basic soil (including vegetables like cabbage and fodder like buffalograss), most plants prefer a mildly acidic soil (pH between 6.0 and 6.8), and alkaline soils can cause problems.
In alkali lakes (a type of salt lake), evaporation concentrates the naturally occurring alkali salts, often forming a crust of mildly basic salt across a large area.
Examples of alkali lakes: