alkali

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)]

English

Etymology

French alcali, ultimately fr. Ar. alqalī ashes of the plant saltwort, fr. qalay to roast in a pan, fry.

Pronunciation

• , /ˈælkəlaɪ/, /"

Common properties

Alkalines 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.

Confusion between base and alkali

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.

Salts

• 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 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 soils can cause problems.

Lakes

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:

• Redberry Lake, Saskatchewan, Canada.
• Tramping Lake, Saskatchewan, Canada.
• Mono lake, California, United States of America
• 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.