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The Brønsted-Lowry Theory of Acids and Bases

In 1923, independently, both Johannes Nicolaus Br�nsted in Denmark and Thomas Martin Lowry in England published theories about how acids and bases behave. These were quite similar in nature so this theory of acids and bases has become known as the Brønsted-Lowry Theory of Acids and Bases. Many times the acid or base will simply be called a Brønsted Acid or Brønsted Base, respectively.

Johannes Nicolaus Br�nsted Some Remarks on the Concept of Acids and Bases Recueil des Travaux Chimiques des Pays-Bas: Vol. 42, pp. 718-728 1923

How is the proton represented?

A hydrogen atom ₁H contains one proton p⁺ and one electron e^-.

p⁺ + e^-₁H

If we were to remove the electron e^-, only the proton p⁺ would be left.

When a hydrogen H is removed from a compound leaving the electron e^- behind,
the compound is said to be "deprotonated".

A compound to which a hydrogen ion H⁺ has been added is said to have been "protonated".

A "proton" may be represented either as a p⁺ or as anH⁺


Note: The proton is immediately transfered from one compound to another compound,
either directly or via the solvent; there is no "bare" proton in the solution.

H⁺, a bare proton, can not exist in isolation for very long, especially in water. The proton affinity of H₂O is about 799 kJ/mol. This is sufficient to drive the almost instantaneous formation of Hydronium Ions (H₃O⁺). The concentration of free protons in water has been estimated to be 10^-130 M.

The Generalized Brønsted-Lowry Acid-Base Reaction

HA + B:BH⁺ + A:^-

Where:

HA is the Brønsted Acid.

B: is the Brønsted Base.

BH⁺ is the Conjugate Acid.

A:^- is the Conjugate Base.

Note that Brønsted-Lowry acid-base reactions require the presence of a protic solvent. Water is the protic solvent in most cases.

Table of Bronsted-Lowry Acids and Bases

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