Editing Base (chemistry)

{{Short description|Type of chemical substance}}
{{other uses|Base (disambiguation)}}
{{See also|Alkali}}
{{Use dmy dates|date=September 2021}}
[[File:Handmade soap cropped and simplified.jpg|thumb|250px|right|[[Soap]]s are weak bases formed by the reaction of [[fatty acid]]s with [[sodium hydroxide]] or [[potassium hydroxide]].]]
{{Acids and bases}}

In [[chemistry]], there are three definitions in common use of the word "'''base'''": ''[[Arrhenius base]]s'', ''[[Brønsted base]]s'', and ''[[Lewis base]]s''. All definitions agree that bases are substances that react with [[acid]]s, as originally proposed by [[Guillaume-François Rouelle|G.-F. Rouelle]] in the mid-18th century.

In 1884, [[Svante Arrhenius]] proposed that a base is a substance which [[dissociate]]s in [[aqueous]] solution to form [[hydroxide]] ions OH<sup>−</sup>. These ions can react with [[Hydron (chemistry)|hydrogen ions]] (H<sup>+</sup> according to Arrhenius) from the dissociation of acids to form water in an [[acid–base reaction]]. A base was therefore a metal hydroxide such as [[NaOH]] or [[Calcium hydroxide|Ca(OH)<sub>2</sub>]]. Such [[aqueous]] hydroxide solutions were also described by certain characteristic properties. They are slippery to the touch, can taste [[Taste#Bitterness|bitter]]<ref>{{Cite book |title=Investigating chemistry: a forensic science perspective |last=Johlubl|first=Matthew E. |date=2009|publisher=W. H. Freeman and Co|isbn=978-1429209892 |edition=2nd |location=New York |oclc=392223218}}</ref> and change the color of [[pH indicator]]s (e.g., turn red [[litmus paper]] blue).

In water, by altering the [[self-ionization of water|autoionization]] [[Chemical equilibrium|equilibrium]], bases yield solutions in which the hydrogen ion [[Activity (chemistry)|activity]] is lower than it is in pure water, i.e., the water has a [[pH]] higher than 7.0 at standard conditions. A soluble base is called an [[alkali]] if it contains and releases OH<sup>−</sup> ions [[stoichiometry|quantitatively]]. [[Metal oxide]]s, [[hydroxide]]s, and especially [[alkoxide]]s are basic, and [[conjugate base]]s of [[acid strength|weak acid]]s are weak bases.

Bases and acids are seen as chemical opposites because the effect of an acid is to increase the [[hydronium]] (H<sub>3</sub>O<sup>+</sup>) concentration in water, whereas bases reduce this concentration. A reaction between aqueous solutions of an acid and a base is called [[Neutralization (chemistry)|neutralization]], producing a solution of water and a [[salt (chemistry)|salt]] in which the salt separates into its component ions. If the aqueous solution is [[saturated solution|saturated]] with a given salt [[Solvent|solute]], any additional such salt [[precipitate]]s out of the solution.

In the more general [[Brønsted–Lowry acid–base theory]] (1923), a base is a substance that can accept [[hydrogen cation]]s (H<sup>+</sup>)—otherwise known as [[proton]]s. This does include aqueous hydroxides since OH<sup>−</sup> does react with H<sup>+</sup> to form water, so that Arrhenius bases are a subset of Brønsted bases. However, there are also other Brønsted bases which accept protons, such as aqueous solutions of [[ammonia]] (NH<sub>3</sub>) or its organic [[Derivative (chemistry)|derivatives]] ([[amine]]s).{{sfnp|Whitten et al.|2009|page=363}} These bases do not contain a hydroxide ion but nevertheless react with water, resulting in an increase in the concentration of hydroxide ion.{{sfnp|Zumdahl|DeCoste|2013|page=257}} Also, some [[Inorganic nonaqueous solvent|non-aqueous solvents]] contain Brønsted bases which react with [[Solvation|solvated]] protons. For example, in [[liquid ammonia]], NH<sub>2</sub><sup>−</sup> is the basic ion species which accepts protons from NH<sub>4</sub><sup>+</sup>, the acidic species in this solvent.

[[G. N. Lewis]] realized that water, ammonia, and other bases can form a bond with a proton due to the [[unshared pair]] of [[electron]]s that the bases possess.{{sfnp|Zumdahl|DeCoste|2013|page=257}} In the [[Lewis theory]], a base is an [[electron pair]] donor which can share a pair of electrons with an electron acceptor which is described as a Lewis acid.{{sfnp|Whitten et al.|2009|page=349}} The Lewis theory is more general than the Brønsted model because the Lewis acid is not necessarily a proton, but can be another molecule (or ion) with a vacant low-lying [[atomic orbital|orbital]] which can accept a pair of electrons. One notable example is [[boron trifluoride]] (BF<sub>3</sub>).

Some [[Acid–base reaction#Acid–base definitions|other definitions]] of both bases and acids have been proposed in the past, but are not commonly used today.

==Properties==
General properties of bases include:

*Concentrated or strong bases are [[Causticity|caustic]] on organic matter and react violently with acidic substances.
*[[Aqueous solutions]] or molten bases dissociate in ions and conduct electricity.
*Reactions with [[PH indicator|indicators]]: bases turn red litmus paper blue, phenolphthalein pink, keep bromothymol blue in its natural colour of blue, and turn methyl orange-yellow.
*The [[pH]] of a basic solution at standard conditions is greater than seven.
*Bases are bitter.<ref>{{cite web|url=http://www.merriam-webster.com/dictionary/base|title=Definition of BASE|website=www.merriam-webster.com|access-date=3 May 2018|url-status=live|archive-url=https://web.archive.org/web/20180321215707/https://www.merriam-webster.com/dictionary/base|archive-date=21 March 2018}}</ref>

== Reactions between bases and water ==
The following reaction represents the general reaction between a base (B) and water to produce a conjugate acid (BH<sup>+</sup>) and a conjugate base (OH<sup>−</sup>):{{sfnp|Zumdahl|DeCoste|2013|page=257}}<chem display="block">{B}_{(aq)} + {H2O}_{(l)} <=> {BH+}_{(aq)} + {OH- }_{(aq)}</chem>The equilibrium constant, K<sub>b</sub>, for this reaction can be found using the following general equation:{{sfnp|Zumdahl|DeCoste|2013|page=257}}

: <math>K_b = \frac{[BH^+][OH^-]}{[B]}</math>

In this equation, the base (B) and the extremely [[strong base]] (the conjugate base OH<sup>−</sup>) compete for the proton.{{sfnp|Zumdahl|DeCoste|2013|page=258}} As a result, bases that react with water have relatively small equilibrium constant values.{{sfnp|Zumdahl|DeCoste|2013|page=258}} The base is weaker when it has a lower equilibrium constant value.{{sfnp|Zumdahl|DeCoste|2013|page=257}}

==Neutralization of acids==
[[File:Hydrochloric acid ammonia.jpg|thumb|[[Ammonia]] fumes from aqueous [[ammonium hydroxide]] (in test tube) reacting with [[hydrochloric acid]] (in [[beaker (glassware)|beaker]]) to produce [[ammonium chloride]] (white smoke).]]
Bases react with acids to neutralize each other at a fast rate both in water and in alcohol.<ref name=Gilbert /> When dissolved in water, the strong base [[sodium hydroxide]] ionizes into hydroxide and sodium ions:

:<chem>NaOH -> Na+ + OH-</chem>

and similarly, in water the acid [[hydrogen chloride]] forms hydronium and chloride ions:

:<chem>HCl + H2O -> H3O+ + Cl-</chem>

When the two solutions are mixed, the {{chem|H|3|O|+}} and {{chem|OH|-}} ions combine to form water molecules:

:<chem>H3O+ + OH- -> 2H2O</chem>

If equal quantities of NaOH and HCl are dissolved, the base and the acid neutralize exactly, leaving only NaCl, effectively [[table salt]], in solution.

Weak bases, such as baking soda or egg white, should be used to neutralize any acid spills. Neutralizing acid spills with strong bases, such as [[sodium hydroxide]] or [[potassium hydroxide]], can cause a violent exothermic reaction, and the base itself can cause just as much damage as the original acid spill.

==Alkalinity of non-hydroxides==
Bases are generally compounds that can neutralize an amount of acid. Both [[sodium carbonate]] and [[ammonia]] are bases, although neither of these substances contains {{chem|OH|-}} groups. Both compounds accept H<sup>+</sup> when dissolved in [[protic solvent]]s such as water:

:<chem>Na2CO3 + H2O -> 2Na+ + HCO3- + OH-</chem>
:<chem>NH3 + H2O -> NH4+ + OH-</chem>

From this, a [[pH]], or acidity, can be calculated for aqueous solutions of bases.

A base is also defined as a molecule that has the ability to accept an electron pair bond by entering another atom's valence shell through its possession of one electron pair.<ref name=Gilbert>{{cite journal|last1=Lewis|first1=Gilbert N.|author-link=Gilbert N. Lewis|title=Acids and Bases|volume=226|issue=3|date=September 1938|pages=293–313|journal=Journal of the Franklin Institute|doi=10.1016/S0016-0032(38)91691-6|url=https://www.sciencedirect.com/science/article/abs/pii/S0016003238916916|access-date=3 September 2020|archive-date=2 November 2021|archive-url=https://web.archive.org/web/20211102222025/https://www.sciencedirect.com/science/article/abs/pii/S0016003238916916|url-status=live}}</ref> There are a limited number of elements that have atoms with the ability to provide a molecule with basic properties.<ref name=Gilbert /> [[Carbon]] can act as a base as well as [[nitrogen]] and [[oxygen]]. Fluorine and sometimes rare gases possess this ability as well.<ref name=Gilbert /> This occurs typically in compounds such as [[N-Butyllithium|butyl lithium]], [[alkoxide]]s, and [[azanide|metal amide]]s such as [[sodium amide]]. Bases of carbon, nitrogen and oxygen without [[resonance (chemistry)|resonance]] stabilization are usually very strong, or [[superbase]]s, which cannot exist in a water solution due to the acidity of water. Resonance stabilization, however, enables weaker bases such as carboxylates; for example, [[sodium acetate]] is a [[weak base]].

==Strong bases==
A strong base is a basic chemical compound that can remove a proton (H<sup>+</sup>) from (or ''[[deprotonate]]'') a molecule of even a very weak acid (such as water) in an acid–base reaction. Common examples of strong bases include hydroxides of [[Alkali metal|alkali metals]] and [[Alkaline earth metal|alkaline earth metals]], like [[sodium hydroxide]] and [[calcium hydroxide]], respectively. Due to their low [[solubility]], some bases, such as alkaline earth hydroxides, can be used when the solubility factor is not taken into account.{{sfnp|Zumdahl|DeCoste|2013|page=255}}

One advantage of this low solubility is that "many [[Antacid|antacids]] were [[Suspension (chemistry)|suspensions]] of metal hydroxides such as [[aluminium hydroxide]] and [[magnesium hydroxide]]";{{sfnp|Zumdahl|DeCoste|2013|page=256}} compounds with low solubility and the ability to stop an increase in the concentration of the hydroxide ion, preventing the harm of the tissues in the mouth, oesophagus, and stomach.{{sfnp|Zumdahl|DeCoste|2013|page=256}} As the reaction continues and the salts dissolve, the [[stomach acid]] reacts with the hydroxide produced by the suspensions.{{sfnp|Zumdahl|DeCoste|2013|page=256}}

Strong bases hydrolyze in water almost completely, resulting in the [[leveling effect]].<ref name=Gilbert /> In this process, the water molecule combines with a strong base, due to the water's amphoteric ability; and, a hydroxide ion is released.<ref name=Gilbert /> Very strong bases can even deprotonate very weakly acidic C–H groups in the absence of water. Here is a list of several strong bases:

{|
|[[Lithium hydroxide]]||LiOH
|-
|[[Sodium hydroxide]]||NaOH
|-
|[[Potassium hydroxide]]||KOH
|-
|[[Rubidium hydroxide]]||RbOH
|-
|style="border-bottom-style:dashed;"|[[Cesium hydroxide]]||style="border-bottom-style:dashed;"|CsOH
|-
|[[Magnesium hydroxide]]||{{chem|Mg(OH)|2}}
|-
|[[Calcium hydroxide]]||{{chem|Ca(OH)|2}}
|-
|[[Strontium hydroxide]]||{{chem|Sr(OH)|2}}
|-
|style="border-bottom-style:dashed;"|[[Barium hydroxide]]||style="border-bottom-style:dashed;"|{{chem|Ba(OH)|2}}
|-
|[[Tetramethylammonium hydroxide]]||{{chem|N(CH|3|)|4|OH}}
|-
|[[Guanidine]]||{{chem|HNC(NH|2|)|2}}
|}

The cations of these strong bases appear in the first and second groups of the periodic table (alkali and earth alkali metals). Tetraalkylated ammonium hydroxides are also strong bases since they dissociate completely in water. [[Guanidine]] is a special case of a species that is exceptionally stable when protonated, analogously to the reason that makes [[perchloric acid]] and [[sulfuric acid]] very strong acids.

Acids with a p''K<sub>a</sub>'' of more than about 13 are considered very weak, and their [[conjugate base]]s are strong bases.

===Superbases===
{{Main|Superbase}}
Group 1 salts of [[carbanion]]s, [[azanide ion|amide ions]], and [[hydrides]] tend to be even stronger bases due to the extreme weakness of their conjugate acids, which are stable hydrocarbons, amines, and dihydrogen. Usually, these bases are created by adding pure alkali metals such as sodium into the conjugate acid. They are called ''[[superbase]]s'', and it is impossible to keep them in aqueous solutions because they are stronger bases than the [[hydroxide]] ion (See the [[leveling effect]].) For example, the ethoxide ion (conjugate base of ethanol) undergoes this reaction quantitatively in presence of water.<ref name="AlkoxideLibreText">{{cite web |title=10.4.1. Alkoxide Ions |url=https://chem.libretexts.org/Courses/Purdue/Purdue_Chem_26100%3A_Organic_Chemistry_I_(Wenthold)/Chapter_10%3A_Alcohols/10.4_Acidity_of_Alcohols/10.4.1._Alkoxide_Ions |website=Chemistry Libretexts |date=16 July 2015 |publisher=LibreText |access-date=28 October 2022}}</ref>

:<chem>CH3CH2O- + H2O -> CH3CH2OH + OH-</chem>

Examples of common superbases are:
*[[n-Butyllithium|Butyl lithium]] (n-C<sub>4</sub>H<sub>9</sub>Li)
*[[Lithium diisopropylamide]] (LDA) [(CH<sub>3</sub>)<sub>2</sub>CH]<sub>2</sub>NLi 
*[[Lithium diethylamide]] (LDEA) {{chem|(C|2|H|5|)|2|NLi}}
*[[Sodium amide]] (NaNH<sub>2</sub>)
*[[Sodium hydride]] (NaH)
*[[Lithium bis(trimethylsilyl)amide]] {{chem|[(CH|3|)|3|Si]|2|NLi}}

Strongest superbases are synthesised in only gas phase:
*[[Ortho-diethynylbenzene dianion]] (C<sub>6</sub>H<sub>4</sub>(C<sub>2</sub>)<sub>2</sub>)<sup>2−</sup> (the strongest superbase ever synthesized)  
*[[Meta-diethynylbenzene dianion]] (C<sub>6</sub>H<sub>4</sub>(C<sub>2</sub>)<sub>2</sub>)<sup>2−</sup> (second strongest superbase)
*[[Para-diethynylbenzene dianion]] (C<sub>6</sub>H<sub>4</sub>(C<sub>2</sub>)<sub>2</sub>)<sup>2−</sup> (third strongest superbase)
*[[Lithium monoxide anion]] (LiO<sup>−</sup>) was considered the strongest superbase before diethynylbenzene dianions were created.

== Weak bases ==
{{main|weak base}}
A weak base is one which does not fully ionize in an [[aqueous solution]], or in which [[protonation]] is incomplete. For example, [[ammonia]] transfers a proton to water according to the equation<ref>{{cite book |last1=Whitten |first1=Kenneth W. |last2=Gailey |first2=Kenneth D. |last3=Davis |first3=Raymond E. |title=General Chemistry |date=1992 |publisher=Saunders College Publishing |isbn=0-03-072373-6 |page=358 |edition=4th}}</ref>
:NH<sub>3</sub>(aq) + H<sub>2</sub>O(l) &rarr; NH{{su|b=4|p=+}}(aq) + OH<sup>−</sup>(aq)
The [[equilibrium constant]] for this reaction at 25&nbsp;°C is 1.8 x 10<sup>−5</sup>,<ref>{{cite book |last1=Petrucci |first1=Ralph H. |last2=Harwood |first2=William S. |last3=Herring |first3=F. Geoffrey |title=General Chemistry. Principles and Modern Applications |date=2002 |publisher=Prentice Hall |isbn=0-13-014329-4 |page=678 |edition=8th}}</ref> such that the extent of reaction or [[degree of ionization]] is quite small.

== Lewis bases ==
A [[Lewis acids and bases|Lewis base]] or ''electron-pair donor'' is a molecule with one or more high-energy [[lone pair]]s of electrons which can be shared with a low-energy vacant orbital in an acceptor molecule to form an [[adduct]]. In addition to H<sup>+</sup>, possible ''electron-pair acceptors'' (Lewis acids) include neutral molecules such as BF<sub>3</sub> and high oxidation state metal ions such as Ag<sup>2+</sup>, Fe<sup>3+</sup> and Mn<sup>7+</sup>. Adducts involving metal ions are usually described as [[coordination complex]]es.<ref>{{cite book |last1=Miessler |first1=Gary L. |last2=Tarr |first2=Donald A. |title=Inorganic Chemistry |date=1999 |publisher=Prentice-Hall |isbn=0-13-841891-8 |pages=157–159 |edition=2nd}}</ref>

According to the original formulation of [[Gilbert N. Lewis|Lewis]], when a neutral base forms a bond with a neutral acid, a condition of electric stress occurs.<ref name=Gilbert /> The acid and the base share the electron pair that formerly belonged to the base.<ref name=Gilbert /> As a result, a high dipole moment is created, which can only be decreased to zero by rearranging the molecules.<ref name=Gilbert />

== Solid bases ==
Examples of solid bases include:
* Oxide mixtures: SiO<sub>2</sub>, Al<sub>2</sub>O<sub>3</sub>; MgO, SiO<sub>2</sub>; CaO, SiO<sub>2</sub><ref name=Tanabe>{{cite book |last1=Tanabe |first1=Kozo |title=Solid Acids and Bases: their catalytic properties |publisher=Academic Press |year=1970 |page=2 |isbn=9780323160582 |url=https://books.google.com/books?id=tFfBYuHg4vAC&pg=PP1 |access-date=19 February 2015 |archive-date=8 October 2022 |archive-url=https://web.archive.org/web/20221008015036/https://books.google.com/books?id=tFfBYuHg4vAC&pg=PP1 |url-status=live }}</ref>
* Mounted bases: LiCO<sub>3</sub> on silica; NR<sub>3</sub>, NH<sub>3</sub>, KNH<sub>2</sub> on alumina; NaOH, KOH mounted on silica on alumina<ref name="Tanabe"/>
* Inorganic chemicals: BaO, KNaCO<sub>3</sub>, BeO, MgO, CaO, KCN<ref name="Tanabe"/>
* Anion exchange resins<ref name="Tanabe"/>
*Charcoal that has been treated at 900 degrees Celsius or activates with N<sub>2</sub>O, NH<sub>3</sub>, ZnCl<sub>2</sub>-NH<sub>4</sub>Cl-CO<sub>2</sub><ref name="Tanabe"/>

Depending on a solid surface's ability to successfully form a conjugate base by absorbing an electrically neutral acid, basic strength of the surface is determined.<ref name="books.google.com"/> The "number of basic sites per unit surface area of the solid" is used to express how much basic strength is found on a solid base catalyst.<ref name="books.google.com"/> Scientists have developed two methods to measure the amount of basic sites: one, titration with benzoic acid using indicators and gaseous acid adsorption.<ref name="books.google.com"/> A solid with enough basic strength will absorb an electrically neutral acidic indicator and cause the acidic indicator's color to change to the color of its conjugate base.<ref name="books.google.com"/> When performing the gaseous acid adsorption method, [[nitric oxide]] is used.<ref name="books.google.com"/> The basic sites are then determined by calculating the amount of carbon dioxide that is absorbed.<ref name="books.google.com"/>

==Bases as catalysts==
Basic substances can be used as [[insoluble]] heterogeneous [[catalyst]]s for [[chemical reaction]]s. Some examples are metal oxides such as [[magnesium oxide]], [[calcium oxide]], and [[barium oxide]] as well as [[potassium fluoride on alumina]] and some [[zeolite]]s. Many [[transition metal]]s make good catalysts, many of which form basic substances. Basic catalysts are used for [[hydrogenation]], the migration of [[double bond]]s, in the [[Meerwein-Ponndorf-Verley reduction]], the [[Michael reaction]], and many others. Both CaO and BaO can be highly active catalysts if they are heated to high temperatures.<ref name="books.google.com">{{cite book |last1=Tanabe |first1=K. |last2=Misono |first2=M. |last3=Ono |first3=Y. |last4=Hattori |first4=H. |title=New Solid Acids and Bases: their catalytic properties |publisher=Elsevier |year=1990 |page=14 |isbn=9780080887555 |url=https://books.google.com/books?id=Aq9cdug9hM0C&pg=PA14 |access-date=19 February 2015 |archive-date=8 October 2022 |archive-url=https://web.archive.org/web/20221008015036/https://books.google.com/books?id=Aq9cdug9hM0C&pg=PA14 |url-status=live }}</ref>

==Uses of bases==
*Sodium hydroxide is used in the manufacture of soap, paper, and the synthetic fiber [[rayon]].
*Calcium hydroxide (slaked lime) is used in the manufacture of bleaching powder.
*Calcium hydroxide is also used to clean the [[sulfur dioxide]], which is caused by the exhaust, that is found in power plants and factories.{{sfnp|Zumdahl|DeCoste|2013|page=256}}
*Magnesium hydroxide is used as an 'antacid' to neutralize excess acid in the stomach and cure indigestion.
*[[Sodium carbonate]] is used as washing soda and for softening hard water.
*[[Sodium bicarbonate]] (or sodium hydrogen carbonate) is used as baking soda in cooking food, for making baking powders, as an antacid to cure indigestion and in soda acid fire extinguisher.
*[[Ammonium hydroxide]] is used to remove grease stains from clothes

== Monoprotic and polyprotic bases ==
Bases with only one [[ionizable]] [[hydroxide]] (OH<sup>−</sup>) ion per formula unit are called '''monoprotic''' since they can accept one proton (H<sup>+</sup>). Bases with more than one OH- per formula unit are '''polyprotic'''.<ref>{{Cite web|date=2016-07-13|title=Polyprotic Acids & Bases|url=https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Acids_and_Bases/Monoprotic_Versus_Polyprotic_Acids_And_Bases/Polyprotic_Acids_and_Bases_1|access-date=2022-01-09|website=Chemistry LibreTexts|language=en|archive-date=9 January 2022|archive-url=https://web.archive.org/web/20220109005712/https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Acids_and_Bases/Monoprotic_Versus_Polyprotic_Acids_And_Bases/Polyprotic_Acids_and_Bases_1|url-status=live}}</ref>

The number of [[ionizable]] [[hydroxide]] (OH<sup>−</sup>) ions present in one formula unit of a base is also called the '''acidity''' of the base.<ref>{{Cite web |url=http://www.citycollegiate.com/acidbasesalt4.htm |title=Electrophile – Nucleophile – Basicity – Acidity – pH Scale |website=City Collegiate |access-date=20 June 2016 |url-status=usurped |archive-url=https://web.archive.org/web/20160630222902/http://www.citycollegiate.com/acidbasesalt4.htm |archive-date=30 June 2016 }}</ref><ref name=Toppr>{{Cite web|url=https://www.toppr.com/guides/chemistry/acids-bases-and-salts/introduction-to-bases/|title=Introduction to Bases: Classification, Examples with Questions & Videos|date=2 February 2018|website=Toppr-guides|language=en-US|access-date=14 March 2019|archive-date=26 July 2020|archive-url=https://web.archive.org/web/20200726153900/https://www.toppr.com/guides/chemistry/acids-bases-and-salts/introduction-to-bases/|url-status=dead}}</ref> On the basis of acidity bases can be classified into three types: monoacidic, diacidic and triacidic.

=== Monoacidic bases ===
[[File:Sodium hydroxide image .jpg|thumb|[[Sodium hydroxide]]]]
When one molecule of a base via complete [[ionization]] produces one [[hydroxide]] ion, the base is said to be a monoacidic or '''monoprotic''' base. Examples of monoacidic bases are:

[[Sodium hydroxide]], [[potassium hydroxide]], [[silver hydroxide]], [[ammonium hydroxide]], etc.

=== Diacidic bases ===
When one molecule of base via complete [[ionization]] produces two [[hydroxide]] ions, the base is said to be diacidic or '''diprotic'''. Examples of diacidic bases are:
[[File:BARIUM HYDROXIDE IMAGE.jpg|thumb|[[Barium hydroxide]]]]
[[Barium hydroxide]], [[magnesium hydroxide]], [[calcium hydroxide]], [[zinc hydroxide]], [[iron(II) hydroxide]], [[tin(II) hydroxide]], [[lead(II) hydroxide]], [[copper(II) hydroxide]], etc.

=== Triacidic bases ===
When one molecule of base via complete [[ionization]] produces three [[hydroxide]] ions, the base is said to be triacidic or '''triprotic'''. Examples of triacidic bases are:

[[Aluminium hydroxide]], [[ferrous hydroxide]], [[Hydroxide|Gold Trihydroxide]],<ref name=Toppr/>

==Etymology of the term==
The concept of base stems from an older [[alchemical]] notion of "the matrix":

{{Blockquote|The term "base" appears to have been first used in 1717 by the French chemist, [[Louis Lémery]], as a synonym for the older [[Paracelsus|Paracelsian]] term "matrix." In keeping with 16th-century [[animism]], Paracelsus had postulated that naturally occurring salts grew within the earth as a result of a universal acid or seminal principle having impregnated an earthy matrix or womb. ... Its modern meaning and general introduction into the chemical vocabulary, however, is usually attributed to the French chemist, [[Guillaume-François Rouelle]]. ... In 1754 Rouelle explicitly defined a neutral salt as the product formed by the union of an acid with any substance, be it a water-soluble alkali, a volatile alkali, an absorbent earth, a metal, or an oil, capable of serving as "a base" for the salt "by giving it a concrete or solid form." Most acids known in the 18th century were volatile liquids or "spirits" capable of distillation, whereas salts, by their very nature, were crystalline solids. Hence it was the substance that neutralized the acid which supposedly destroyed the volatility or spirit of the acid and which imparted the property of solidity (i.e., gave a concrete base) to the resulting salt. |[[William B. Jensen]]|The origin of the term "base"<ref name="Jensen">{{cite journal|author1-link=William B. Jensen |author=Jensen, William B. |title=The origin of the term 'base' |journal=The Journal of Chemical Education |year=2006 |volume=83 |page=1130 |url=http://www.che.uc.edu/Jensen/W.%20B.%20Jensen/Reprints/129.%20Base.pdf |issue=8 |url-status=dead |archive-url=https://web.archive.org/web/20160304023719/http://www.che.uc.edu/Jensen/W.%20B.%20Jensen/Reprints/129.%20Base.pdf |archive-date=4 March 2016 |df=dmy |bibcode=2006JChEd..83.1130J |doi=10.1021/ed083p1130 }}</ref>}}

==See also==
*[[Acid–base reaction]]s
*[[Acid]]s
*[[Base-richness]] (used in ecology, referring to environments)
*[[Conjugate base]]
*[[Lewis acids and bases]]
*[[Titration]]

==References==
{{Reflist}}
{{refbegin}}
* {{cite book|last1=Whitten|first1=Kenneth W.|first2=Larry|last2=Peck|first3=Raymond E.|last3=Davis|first4=Lisa|last4=Lockwood|first5=George G.|last5=Stanley|title=Chemistry|edition=9th|date=2009|publisher=Brooks/Cole Cengage Learning |isbn=978-0-495-39163-0|ref={{harvid|Whitten et al.|2009}}|url-access=registration|url=https://archive.org/details/chemistry0000unse_c3m0}}
* {{cite book|last1=Zumdahl|first1=Steven|last2=DeCoste|first2=Donald|title=Chemical Principles|date=2013|publisher=Mary Finch|edition=7th}}
{{refend}}

== External links ==
* {{Wiktionary inline|base}}

{{Authority control}}

{{DEFAULTSORT:Base (Chemistry)}}
[[Category:Bases (chemistry)| ]]
[[Category:Chemical compounds]]