Brønsted-Lowry acid-base theory
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In [[chemistry]], the '''Brønsted-Lowry acid-base theory''' or '''Brønsted-Lowry concept''' is an [[Acid-base reaction theories|acid-base theory]] describing the reaction mechanism between [[acid]]s and [[base (chemistry)|base]]s, and was independently proposed by [[Johannes Nicolaus Brønsted]] and [[Thomas Martin Lowry]] in [[1923]]. In this system, a Brønsted-Lowry acid is defined as any species that has the tendency to lose, or "donate" a [[hydrogen]] ion ([[proton]]), and a Brønsted-Lowry base as a substance with a tendency to gain or "accept" a hydrogen ion (proton). Thus, under this concept, an ''acid'' is synonymous with proton donor, or hydrogen donor, while base means a proton acceptor.
A wide range of compounds fall within this category of acids, from simple [[mineral acid]]s to ordinary [[acid]]s, [[carboxylic acid]]s, [[amine]]s, [[sulfonic acid]]s to less obvious ones like [[carbon acid]]s such as [[ethyl acetoacetate]] or [[Meldrum's acid]]. The [[pKa]] is a measure of the strength of a proton donor.
In the reaction between [[acetic acid]] and water, acetic acid acts as an acid by donating a proton to water, which acts as a base. The equation given is:
:<math>\mbox{CH}_3\mbox{COOH} + \mbox{H}_2\mbox{O} \longrightarrow{} \mbox{H}_3\mbox{O}^\mbox{+} + \mbox{CH}_3\mbox{COO}^-</math>
Water can also act as an acid, for instance when it reacts with ammonia. The equation given for this reaction is:
:<math>\mbox{NH}_3 + \mbox{H}_2\mbox{O} \longrightarrow{} \mbox{NH}_4^{\, \mbox{+}} + \mbox{OH}^-</math>
in which H<sub>2</sub>O donates a proton to NH<sub>3</sub>. Thus water is [[amphoteric]]: able to act as either an acid or a base. These reactions can act in reverse as well as in the forward direction. The reverse of the reaction between acetic acid and water is:
:<math>\mbox{H}_3\mbox{O}^{+} + \mbox{CH}_3\mbox{COO}^- \longrightarrow{} \mbox{CH}_3\mbox{COOH} + \mbox{H}_2\mbox{O}</math>
In the reverse reactions H<sub>3</sub>O<sup>+</sup> acts as an acid to donate a proton to CH<sub>3</sub>COO<sup>-</sup>, which is acting as a base.
In the forward reaction, CH<sub>3</sub>COOH acts as an acid to donate a proton, and water as a base to receive it. H<sub>2</sub>O and H<sub>3</sub>O<sup>+</sup> are therefore considered one acid-base conjugate pair, and CH<sub>3</sub>COOH and CH<sub>3</sub>COO<sup>-</sup> as another conjugate pair.
==See also==
*[[Acid]]
*[[Acid-base reaction theories]]
*[[Base (chemistry)]]
*[[Lewis acid]]
*[[Lewis base]]
[[Category:Acid-base chemistry]]
[[bg:Теория на Брьонстед и Лаури]]
[[fr:Théorie de Bronsted-Lowry]]
[[it:Teoria acido-base di Brønsted-Lowry]]
[[pt:Teoria ácido-base de Bronsted-Lowry]]
[[zh:酸碱质子理论]]