Brønsted–Lowry acid–base theory
The Brønsted–Lowry acid–base theory (also called proton theory of acids and bases)[1] is one of the two main definitions of acids and bases in modern chemistry, alongside the Lewis acid-base theory.[2] Johannes Nicolaus Brønsted and Thomas Martin Lowry developed the theory in 1923.[3][4]
A chemical is a Brønsted–Lowry acid if it can give a hydrogen ion to another chemical,[5] and a chemical is a Brønsted–Lowry base[6] if it can take a hydrogen ion from another chemical. When an acid loses a hydrogen, it becomes its conjugate base, and when a base gains a hydrogen ion, it becomes its conjugate acid.[7]
According to these definitions, an acid-base reaction always takes the form
- AH + B → A−
+ BH+
where AH is a Brønsted-Lowry acid, B is a Brønsted-Lowry base, A−
is the acid's conjugate base, and BH+
is the base's conjugate acid.
Comparison to Arrhenius theory
The Brønsted-Lowry theory (adds to or) expands the Arrhenius theory to understand amphoteric compounds, compounds like ammonia that act like a base without containing hydroxide, and solvents other than water.
In the Arrhenius theory, sodium hydroxide is a base, and hydrochloric acid is an acid, which has the Arrhenius neutralization reaction
- NaOH + HCl → NaCl + H
2O
that produces a salt (sodium chloride) and water.
In the Brønsted-Lowry theory, sodium hydroxide is no longer considered a base, but rather an equivalent of the actual base, the hydroxide ion OH−
. When sodium hydroxide dissolves, it splits into OH−
and Na+
. The sodium is considered a spectator ion that does not participate in the actual reaction. The acid-base reaction is
- HCl + OH−
→ Cl−
+ H
2O
Here, the chloride ion is the conjugate base of HCl, while water is the conjugate acid of OH−
. The dissolved ions making sodium chloride is not part of the acid-base reaction.
Brønsted–Lowry Acid–base Theory Media
The amphoteric nature of water
Adduct of ammonia and boron trifluoride
References
- ↑ Brønsted–Lowry theory | chemistry. Encyclopedia Britannica. Retrieved 2025-06-06.
- ↑ International Union of Pure and Applied Chemistry. "Acid". Compendium of Chemical Terminology Internet edition.
- ↑ Brönsted, J. N.. Einige Bemerkungen über den Begriff der Säuren und Basen. Recueil des Travaux Chimiques des Pays-Bas 42 (8) (1923). p. 718–728. doi:10.1002/recl.19230420815.
- ↑ Lowry, T. M.. The uniqueness of hydrogen. Journal of the Society of Chemical Industry 42 (3) (1923). p. 43–47. doi:10.1002/jctb.5000420302.
- ↑ International Union of Pure and Applied Chemistry. "Brønsted acid". Compendium of Chemical Terminology Internet edition.
- ↑ International Union of Pure and Applied Chemistry. "Brønsted base". Compendium of Chemical Terminology Internet edition.
- ↑ International Union of Pure and Applied Chemistry. "Conjugate acid-base pair". Compendium of Chemical Terminology Internet edition.