1 any of various water-soluble compounds capable of turning litmus blue and reacting with an acid to form a salt and water; "bases include oxides and hydroxides of metals and ammonia" [syn: base]
2 a mixture of soluble salts found in arid soils and some bodies of water; detrimental to agriculture [also: alkalies (pl)]
EtymologyFrench alcali, ultimately fr. Ar. alqalī ashes of the plant saltwort, fr. qalay to roast in a pan, fry.
- , /ˈælkəlaɪ/, /"
In chemistry, an alkali (from Arabic: Al-Qaly القلي, القالي ) is a basic, ionic salt of an alkali metal or alkaline earth metal element. Alkalis are best known for being bases (compounds with pH greater than 7) that dissolve in water. 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. Since Brønsted-Lowry acid-base theory, the term alkali in chemistry is normally restricted to those salts containing alkali and alkaline earth metal elements.
Common propertiesAlkalines are all 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 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 acids on the surface of the skin.
- Alkalis are normally 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
Alkalis are opposite of acids.
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 metals are alkaline; this designation applies only to those salts that 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 http://en.wiktionary.org/wiki/alkalihttp://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.htmlhttp://www.thefreedictionary.com/alkali. This is more accurately called an Arrhenius base.
- The solution of a base in water http://www.krysstal.com/acidbase.html.
Most basic salts are alkali salts, of which common examples are:
- sodium hydroxide (often called "caustic soda")
- potassium hydroxide (commonly called "caustic potash")
- 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 soilSoil 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.
LakesIn 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:
EtymologyThe 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.
alkali in Arabic: قلوي
alkali in German: Alkalien
alkali in Esperanto: Alkalo
alkali in Spanish: Álcali
alkali in Estonian: Leelis
alkali in French: Alcali
alkali in Norwegian: Alkali
alkali in Novial: Alkali
alkali in Uzbek: Ishqor
alkali in Polish: Alkalia
alkali in Russian: Щёлочи
alkali in Simple English: Alkali
alkali in Thai: อัลคาไล
alkali in Turkish: Alkali
alkali in Chinese: 碱
acid, acidity, agent, alkalinity, alloisomer, anion, antacid, atom, base, biochemical, cation, chemical, chemical element, chromoisomer, compound, copolymer, dimer, element, heavy chemicals, high polymer, homopolymer, hydracid, inorganic chemical, ion, isomer, macromolecule, metamer, molecule, monomer, neutralizer, nonacid, organic chemical, oxyacid, polymer, pseudoisomer, radical, reagent, sulfacid, trimer