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In 1923, chemists Johannes Nicolaus Brønsted and Thomas Martin Lowry independently described acids and bases based on whether they donate or accept hydrogen ions (H+). The groups of acids and bases defined in this manner came to be known as either Bronsted, Lowry-Bronsted, or Bronsted-Lowry acids and bases.
A Bronsted-Lowry acid is defined as a substance that gives up or donates hydrogen ions during a chemical reaction. In contrast, a Bronsted-Lowry base accepts hydrogen ions. Another way of looking at it is that a Bronsted-Lowry acid donates protons, while the base accepts protons. Species that can either donate or accept protons, depending on the situation, are considered to be amphoteric.
The Bronsted-Lowry theory differs from the Arrhenius theory in allowing acids and bases that don't necessarily contain hydrogen cations and hydroxide anions.
Key Takeaways: Bronsted-Lowry Acid
- The Bronsted-Lowry theory of acids and bases was proposed independently in 1923 by Johannes Nicolaus Brønsted and Thomas Martin Lowry.
- A Bronsted-Lowry acid is a chemical species that donates one or more hydrogen ions in a reaction. In contrast, a Bronsted-Lowry base accepts hydrogen ions. When it donates its proton, the acid becomes its conjugate base.
- A more general look at the theory is as an acid as a proton donor and a base as a proton acceptor.
Conjugate Acids and Bases in Bronsted-Lowry Theory
Every Bronsted-Lowry acid donates its proton to a species which is its conjugate base. Every Bronsted-Lowry base similarly accepts a proton from its conjugate acid.
For example, in the reaction:
HCl (aq) + NH3 (aq)→ NH4+ (aq) + Cl- (aq)
Hydrochloric acid (HCl) donates a proton to ammonia (NH3) to form the ammonium cation (NH4+) and the chloride anion (Cl-). Hydrochloric acid is a Bronsted-Lowry acid; the chloride ion is its conjugate base. Ammonia is a Bronsted-Lowry base; its conjugate acid is the ammonium ion.
- Brönsted, J. N. (1923). "Einige Bemerkungen über den Begriff der Säuren und Basen" Some observations about the concept of acids and bases. Recueil des Travaux Chimiques des Pays-Bas. 42 (8): 718-728. doi:10.1002/recl.19230420815
- Lowry, T. M. (1923). "The uniqueness of hydrogen". Journal of the Society of Chemical Industry. 42 (3): 43-47. doi:10.1002/jctb.5000420302