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In chemistry, an alkali (; from ar, القلوي, al-qaly, lit=ashes of the saltwort) is a
basic BASIC (Beginners' All-purpose Symbolic Instruction Code) is a family of general-purpose, high-level programming languages designed for ease of use. The original version was created by John G. Kemeny and Thomas E. Kurtz at Dartmouth College ...
, ionic
salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quanti ...
of an alkali metal or an alkaline earth metal. An alkali can also be defined as a base that dissolves in
water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as ...
. A solution of a soluble base has a pH greater than 7.0. The
adjective In linguistics, an adjective ( abbreviated ) is a word that generally modifies a noun or noun phrase or describes its referent. Its semantic role is to change information given by the noun. Traditionally, adjectives were considered one of the ...
alkaline, and less often, alkalescent, is commonly used in English as a
synonym A synonym is a word, morpheme, or phrase that means exactly or nearly the same as another word, morpheme, or phrase in a given language. For example, in the English language, the words ''begin'', ''start'', ''commence'', and ''initiate'' are al ...
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.


Etymology

The word "alkali" is derived from Arabic ''al qalīy'' (or ''alkali''), meaning ''the calcined ashes'' (see calcination), referring to the original source of alkaline substances. A water-extract of burned plant ashes, called
potash Potash () includes various mined and manufactured salts that contain potassium in water- soluble form.
and composed mostly of potassium carbonate, was mildly basic. After heating this substance with calcium hydroxide (''slaked lime''), a far more strongly basic substance known as ''caustic potash'' ( potassium hydroxide) was produced. Caustic potash was traditionally used in conjunction with animal fats to produce soft
soap Soap is a salt of a fatty acid used in a variety of cleansing and lubricating products. In a domestic setting, soaps are surfactants usually used for washing, bathing, and other types of housekeeping. In industrial settings, soaps are used ...
s, one of the caustic processes that rendered soaps from fats in the process of saponification, one known since antiquity. Plant potash lent the name to the element
potassium Potassium is the chemical element with the symbol K (from Neo-Latin '' kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmosp ...
, which was first derived from caustic potash, and also gave potassium its chemical symbol K (from the German name ''Kalium''), which ultimately derived from alkali.


Common properties of alkalis and bases

Alkalis are all Arrhenius bases, ones which form
hydroxide Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and hydrogen atom held together by a single covalent bond, and carries a negative electric charge. It is an important but usually minor constituent of water ...
ions (OH) when dissolved in water. Common properties of alkaline aqueous solutions include: * Moderately concentrated solutions (over 10−3 M) have a pH of 10 or greater. This means that they will turn phenolphthalein from colorless to pink. * Concentrated solutions are caustic (causing chemical burns). * Alkaline solutions are slippery or soapy to the touch, due to the saponification of the fatty substances on the surface of the skin. * Alkalis are normally
water-soluble In chemistry, solubility is the ability of a substance Substance may refer to: * Matter, anything that has mass and takes up space Chemistry * Chemical substance, a material with a definite chemical composition * Drug substance ** Substan ...
, although some like barium carbonate are only soluble when reacting with an acidic aqueous solution.


Difference between alkali and base

The terms "base" and "alkali" are often used interchangeably, particularly outside the context of chemistry and
chemical engineering Chemical engineering is an engineering field which deals with the study of operation and design of chemical plants as well as methods of improving production. Chemical engineers develop economical commercial processes to convert raw materials in ...
. There are various, more specific definitions for the concept of an alkali. Alkalis are usually defined as a subset of the bases. One of two subsets is commonly chosen. * A basic salt of an alkali metal or alkaline earth metal (this includes Mg(OH)2 ( magnesium hydroxide) but excludes NH3 (
ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogeno ...
)). * Any base that is soluble in water and forms hydroxide ions or the solution of a base in water. (This includes both Mg(OH)2 and NH3, which forms NH4OH.) The second subset of bases is also called an " Arrhenius base".


Alkali salts

Alkali salts are soluble hydroxides of alkali metals and alkaline earth metals, of which common examples are: * Sodium hydroxide (NaOH) – often called "caustic soda" * Potassium hydroxide (KOH) – commonly called "caustic potash" * Lye – generic term for either of two previous salts or their mixture * Calcium hydroxide (Ca(OH)2) – saturated solution known as " limewater" * Magnesium hydroxide (Mg(OH)2) – an atypical alkali since it has low solubility in water (although the dissolved portion is considered a strong base due to complete dissociation of its ions)


Alkaline soil

Soils with pH values that are higher than 7.3 are usually defined as being alkaline. These soils can occur naturally, due to the presence of alkali salts. Although many plants do prefer slightly basic soil (including vegetables like cabbage and fodder like buffalo grass), most plants prefer a mildly acidic soil (with pHs between 6.0 and 6.8), and
alkaline soil Alkali, or Alkaline, soils are clay soils with high pH (greater than 8.5), a poor soil structure and a low infiltration capacity. Often they have a hard calcareous layer at 0.5 to 1 metre depth. Alkali soils owe their unfavorable physi ...
s can cause problems.


Alkali lakes

In alkali lakes (also called ''soda lakes''), evaporation concentrates the naturally occurring carbonate salts, giving rise to an alkalic and often saline lake. Examples of alkali lakes: * Alkali Lake, Lake County, Oregon * Baldwin Lake,
San Bernardino County, California San Bernardino County (), officially the County of San Bernardino, is a county located in the southern portion of the U.S. state of California, and is located within the Inland Empire area. As of the 2020 U.S. Census, the population was 2,18 ...
* Bear LakeDavis, Jim and Milligan, Mark (2011)
Why is Bear Lake so blue?
Public Information Series 96. Utah Geological Survey, Department of Natural Resources
on the Utah–Idaho border * Lake Magadi in Kenya * Lake Turkana in
Kenya ) , national_anthem = " Ee Mungu Nguvu Yetu"() , image_map = , map_caption = , image_map2 = , capital = Nairobi , coordinates = , largest_city = Nairobi , ...
* Mono Lake, near Owens Valley in
California California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the ...
* Redberry Lake, Saskatchewan * Summer Lake, Lake County, Oregon *
Tramping Lake, Saskatchewan Tramping Lake ( 2016 population: ) is a village in the Canadian province of Saskatchewan within the Rural Municipality of Tramping Lake No. 380 and Census Division No. 13. The village gets its name from nearby Tramping Lake, which is a lake ...


See also

* Alkali metals * Alkaline earth metals *
Base (chemistry) In chemistry, there are three definitions in common use of the word base, known as Arrhenius bases, Brønsted bases, and Lewis bases. All definitions agree that bases are substances that react with acids, as originally proposed by G.-F. R ...


References

{{Authority control Inorganic chemistry