Alkali
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225579161
2008-07-14T11:58:30Z
VASANTH S.N.
7154392
{{Unreferenced|date=June 2008}}
{{dablink|"Alkaline" redirects here. For the power cell, see [[Alkaline battery]]. For other uses of the word "alkali" see [[Alkali (disambiguation)]].}}
In [[chemistry]], an '''alkali''' (from [[Arabic language|Arabic]]: ''Al-Qaly'' القلي, القالي ) is a [[Base (chemistry)|basic]], [[Ionic compound|ionic]] [[salt (chemistry)|salt]] of an [[alkali metal]] or [[alkaline earth metal]] [[Chemical element|element]]. Alkalis are best known for being [[Base (chemistry)|base]]s (compounds with [[pH]] greater than 7) that dissolve in [[water]]. The [[adjective]] '''alkaline''' is commonly used in [[English language|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 [[Acid-base reaction theories|Arrhenius]] definition of a base and are still among the more common bases. Since [[Acid-base reaction theories#The protonic (Brønsted-Lowry) definition|Brønsted-Lowry acid-base theory]], the term alkali in chemistry is normally restricted to those salts containing alkali and alkaline earth metal elements.
== Common properties ==
Alkalines are all [[Acid-base reaction theories|Arrhenius]] bases and share many properties with other chemicals in this group (Arrhenius bases form hydroxide ions when dissolved in water). Common properties of alkaline aqueous [[solution]]s include:
* Moderately-concentrated solutions (over 10<sup>-3</sup> M) have a pH of 10 or greater. This means that they will turn [[phenolphthalein]] from colorless to pink.
* Concentrated solutions are [[Caustic (substance)|caustic]] (causing chemical burns).
* Alkaline solutions are slippery or soapy to the touch, due to the [[saponification]] of the fatty acids on the surface of the skin.
* Alkalis are normally [[solubility|water soluble]], although some like [[barium carbonate]] are only soluble when reacting with an acidic aqueous solution.
Alkalis are very reactive because they are very close to having a full valence electron shell and so will react with many nonmetals to gain those electrons
== Confusion between base and alkali ==
The terms "base" and "alkali" are often used interchangeably, since 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). In a similar manner, bases that are not alkalis, such as [[ammonia]], are sometimes erroneously referred to as alkaline.
Note that not all or even most salts formed by [[alkali metal]]s are alkaline; this designation applies only to those salts that are basic.
While most [[electropositive]] metal [[oxide]]s 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 [http://en.wiktionary.org/wiki/alkali][http://dictionary.reference.com/search?q=alkali], however conflicting definitions of the term alkali do exist. These include:
* Any base that is water-soluble and [http://www.tiscali.co.uk/reference/encyclopaedia/hutchinson/m0029936.html][http://www.thefreedictionary.com/alkali]. This is more accurately called an [[Acid-base reaction theories|Arrhenius base]].
* The solution of a base in water [http://www.krysstal.com/acidbase.html].
== Salts ==
Most [[basic salts]] are alkali salts, of which common examples are:
* [[sodium hydroxide]] (often called "caustic soda")
* [[potassium hydroxide]] (commonly called "caustic potash")
* [[wikt:lye|lye]] (generic term, for either of the previous two, or even for a mixture)
* [[calcium carbonate]] (sometimes called "free lime")
* [[magnesium hydroxide]] is an example of an atypical alkali: it is a weak base (cannot be detected by phenolphthalein) and it has low solubility in water
== Alkaline soil ==
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 soil]]s can cause problems.
== Lakes ==
In alkali lakes (a type of [[salt lake (geography)|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:
*Redberry Lake, [[Saskatchewan]], [[Canada]]. <!-- Not Blueberry lake, ref see http://www.pnr-rpn.ec.gc.ca/nature/whp/sanctuaries/dc01s12.en.html -->
*Tramping Lake, Saskatchewan, Canada.
*[[Mono lake]], [[California]], [[United States]]
*Summer Lake, Summer Lake, Oregon
==Etymology==
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]].
[[Category:Inorganic chemistry]]
[[Category:Arabic words and phrases]]
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[[et:Leelis]]
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[[eo:Alkalo]]
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[[kn:ಕ್ಷಾರ]]