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Alkali

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For other uses, see Alkali (disambiguation).
Not to be confused with Alkalinity or alkali metal.
"Alkaline" redirects here. For other uses, see Alkaline (disambiguation).

In chemistry, an alkali (/ˈælkəlaɪ/ (Audio file "LL-Q1860 (eng)-Naomi Persephone Amethyst (NaomiAmethyst)-Alkali.wav" not found); from the Arabic word Template:Transliteration, القالِي "saltwort")[1] also base[2][1][3] is a hydroxide of any of either the alkali metal[4][5] which are Group I[6] s-block elements,[6][7] or the alkaline earth metal[5] which are Group II s-block.[6] Alkali can also be defined as a base that dissolves in water. A solution of a soluble base has a pH greater than 7.0. The adjectives alkaline and, less often, alkalescent are commonly used in English as a synonyms 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

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The word alkali is derived from Arabic al qalīy (or alkali),[8] meaning Template:Gloss (see calcination), referring to the original source of alkaline substances. A water-extract of burned plant ashes, called potash 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 soaps, 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, 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

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Alkalis are all Arrhenius bases, ones which form hydroxide 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, although some like barium carbonate are only soluble when reacting with an acidic aqueous solution.

Difference between alkali and base

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The terms "base" and "alkali" are often used interchangeably, particularly outside the context of chemistry and chemical engineering.

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[9] (this includes Mg(OH)2 (magnesium hydroxide) but excludes NH3 (ammonia)).
  • Any base that is soluble in water and forms hydroxide ions[10][11] or the solution of a base in water.[12] (This includes both Mg(OH)2 and NH3, which forms NH4OH.)

The second subset of bases is also called an "Arrhenius base".

Alkali salts

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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

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Main article: Alkali 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 mildly acidic soil (with pHs between 6.0 and 6.8), and alkaline soils can cause problems.[8]

Alkali lakes

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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:

See also

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References

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  1. ↑ 1.0 1.1 "An Etymological Dictionary of Astronomy and Astrophysics English-French-Persian فرهنگ ریشه‌شناختی اخترشناسی-اخترفیزیک - alkali qalyâ (#) قلیا". obspm.fr. Observatoire de Paris. Archived from the original on 5 May 2026. A substance that dissolves in water to give hydroxide ions. A generic name for → bases. Etymology (EN): M.E. alkaly, from M.fr. alcali, M.L. alkali, from Ar. al-qily (القلی) “salt wort,” a plant growing in alkaline soils.
  2. ↑ The Bodner Group. "Definitions of Acids and Bases and the Role of Water - Properties of Acids and Bases According to Boyle". Purdue University. Eventually alkalies became known as bases because they serve as the "base" for making certain salts.
  3. ↑ "Collection Strong and weak acids and bases". National STEM Learning Centre, University of York. Archived from the original on 5 October 2025. 3. A base/alkali inhibits the burning properties of an acid
  4. ↑ Virginia Anderson; Robert Burnham; Judy Cannon; et al. (1992). "A". In Christopher Morris; Daniel Hammer; Gail Rice; Elinor Williams; et al. (eds.). Academic Press Dictionary of Science and Technology. Academic Press. p. 75. ISBN 0122004000. alkali Chemistry. a hydroxide of one of the alkali metals, producing solutions with pH greater than 7, soluble in water, neutralizing acids to form salts, and turning red litmus paper blue...In aqueous solutions, the term is equivalent to base.
  5. ↑ 5.0 5.1 Stephen M Milner (10 November 2023). "Alkali Burns of the Skin". EPlasty. Johns Hopkins University School of Medicine, Baltimore: HMP Communications, LLC. 23 (QA12): QA12. ISSN 1937-5719. PMC 10715446 Check |pmc= value (help). PMID 38089840 Check |pmid= value (help) – via p.832 in; Journal of the Society of Chemical Industry (Volume 18), Watson Smith (ed.), Eyre & Spottiswoode: "The alkali metals are produced from their dry hydroxides by fusing them with" - The Light Metals (Potassium, Sodium), and Anhydrous Oxides and Peroxides and Cyanides of these Metals; a Process for the Production of; G.Wolfram, Rödelheim, 1898. What are the common causes of cutaneous alkali burns? Alkalis are soluble hydroxides of the alkali metals (eg, sodium, potassium, and lithium), the soluble hydroxides of the alkaline earth metals (eg, calcium, strontium, and barium
  6. ↑ 6.0 6.1 6.2 Michael Clugston; Rosalind Flemming (2000). "Chapter 16 The s-block elements". Advanced Chemistry. Oxford University Press. p. 280. ISBN 9780199146338. s-block elements concict of the metals contained in Groups I and II of the periodic table - because - have a valence-shell electronic structure of either ns1 (Group I) or ns2 (Group II)
  7. ↑ Abhik Ghosh; Steffen Berg (1 August 2014). "Chapter 2 The s-Block Elements: Alkali and Alkaline Earth Metals Summary". Arrow Pushing in Inorganic Chemistry: A Logical Approach to the Chemistry of the Main-Group Elements. John Wiley & Sons, Inc. doi:10.1002/9781118924525.ch2. ISBN 9781118924525. One of the key roles of s-block metals in chemistry
  8. ↑ 8.0 8.1 Chambers's encyclopaedia: a dictionary of universal knowledge, Volume 1. J.B. Lippincott & Co. 1888. p. 148.
  9. ↑ Alkali | Define Alkali at Dictionary.com. Dictionary.reference.com. Retrieved on 2012-04-18.
  10. ↑ alkali – definition of alkali by the Free Online Dictionary, Thesaurus and Encyclopedia. Thefreedictionary.com. Retrieved on 2012-04-18.
  11. ↑ Chung, L.H.M. (1997) "Characteristics of Alkali", pp. 363–365 in Integrated Chemistry Today. ISBN 9789623722520
  12. ↑ Acids, Bases and Salts. KryssTal. Retrieved on 2012-04-18.
  13. ↑ Davis, Jim and Milligan, Mark (2011). Why is Bear Lake so blue? Archived 2015-07-02 at the Wayback Machine Public Information Series 96. Utah Geological Survey, Department of Natural Resources
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