Brønsted-Lowry

In chemistry, the Brønsted-Lowry system defines acids and bases. This acid-base theory was independently proposed by Johannes_Nicolaus_Br%C3%B8nsted and Thomas Lowry in 1923. In this system, an Brønsted-Lowry acid is defined as any substance which donates a proton (a Hydrogen Ion, H+) in a reaction; and a base as a substance which receives a proton in a reaction.

Related Topics:
Chemistry - Acid - Base - Acid-base theory - Johannes_Nicolaus_Br%C3%B8nsted - Thomas Lowry - Brønsted-Lowry acid - Hydrogen

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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:

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CH3COOH + H2O → H3O+ + CH3COO-

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Water can also act as an acid, for instance when it reacts with ammonia:

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NH3 + H2O → NH4+ + OH-

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in which H2O donates a proton to NH3.

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Thus water is amphoteric: able to act as either an acid or a base.

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These reactions can act in reverse as well as in the forward direction. The reverse of the reaction between acetic acid and water is:

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H3O+ + CH3COO- → CH3COOH + H2O

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In the reverse reactions H3O+ acts as an acid to donate a proton to CH3COO-, which is acting as a base.

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In the forward reaction, CH3COOH acts as an acid to donate a proton, and water as a base to receive it. H2O and H3O+ are therefore considered one acid-base conjugate pair, and CH3COOH and CH3COO- as another conjugate pair.

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