4. Acid-Base Reactions

Brønsted Acids and Bases

A Brønsted acid is any species capable of donating a proton; a Brønsted base is any capable of accepting a proton.

In chemistry, the Brønsted-Lowry theory is an acid-base theory, independently proposed by Johannes Nicolaus Brønsted and Thomas Martin Lowry in 1923. In this system, acids and bases are defined as follows: an acid is any species that is able to donate a hydrogen cation (H+, a proton); a base is any species with the ability to accept a hydrogen cation (H+). To that end, if a compound is to behave as an acid by donating a proton, there must be a base to accept that proton; the Brønsted-Lowry concept is therefore defined by the reaction:

acid + base ⇌ conjugate base + conjugate acid

The conjugate base is the ion or molecule that remains after the acid has donated its proton, and the conjugate acid is the species created after the base accepts the proton. The reaction can proceed either forward backward; in each case, the acid donates a proton to the base.

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