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Alkali

From Academic Kids

For the battery, see alkaline battery


The word alkali can mean:-

  • In chemistry, an alkali is a specific type of base, formed as a carbonate, hydroxide or other ionic salt of an alkali metal or alkali earth metal element. The word alkali or the adjective alkaline are frequently used to refer to all bases, since most common bases are alkalis, although such use is really a synecdoche.
  • In the western parts of the USA, natural soda or potash deposits (soda and potash themselves are both alkali salts).
  • Alkali Springs (http://www.tomlaidlaw.com/clickable/alkali.html) is a place in Oregon in the USA.
Contents

Common properties of alkalis

Alkalis 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 solutions include:

  • Alkalis all form aqueous solutions.
  • Alkalis are bitter to taste (compared with acid solutions which are described as sour).
  • Caustic (causing chemical burns).
  • Slippery or soapy to the touch (due to the caustic reaction dissolving the surface of the skin and fingerprint).
  • Alkalis have a pH greater than 7 and hence can be detected with litmus paper (litmus will turn blue on contact with an alkali).
  • Another common test for alkalis is the use of phenolphthalein since it turns from colourless to pink when the pH moves from 8 to 10 (making it suitable for detecting all but the most dilute solutions of alkalis).

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 you actually mean measuring the pH (base property). Similarly, bases which are not alkalis, like ammonia, are sometimes erroneously referred to as alkaline.

Alkali salts

Most basic salts are alkali salts.

Common alkali salts include:

Alkali soil

Soil with a pH above 7.4 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 cabbage family vegetables and buffalograss), most plant prefer a mildly acidic soil (pH between 6.0 and 6.8), and high pH levels can cause a problem.

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.

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.de:Alkali ru:Щёлочи

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