Section 15.1: Brønsted-Lowry Acids and Bases

According to Brønsted-Lowry, an acid is a proton donor and a base is a proton acceptor. Therefore, in an acid-base reaction, a proton (H⁺) is transferred from an acid to a base.

Example: HCl _(aq) + H₂O _(l) D H₃O⁺_(aq) + Cl^-_(aq)

In this reaction: HCl is an acid

H₂O is a base

H₃O⁺ is the conjugate acid

Cl^- is the conjugate base

Conjugate acid: The species formed when a proton is added to a base is called the conjugate acid.

Conjugate base: The species formed when a proton is removed from an acid is called the conjugate base.

The conjugate acid-base pair consists of the two substances related to each other by the donation and acceptance of a single proton.

Example: In the following aqueous reaction, identify the acid, the base, the conjugate acid and the conjugate base.

H₂O _(l) + HONH₃⁺ _(aq) D HONH_{2 (aq)} + H₃O⁺_(aq)

Looking at the equation, one can conclude that H₂O has accepted a proton from HONH₃⁺ to form H₃O⁺.

Thus, HONH₃⁺ is a proton donor (the acid).

H₂O is the proton acceptor (the base).

H₃O⁺ is the species formed when the proton is added to the base (the conjugate acid).

HONH₂ is the species formed when a proton is removed from the acid (the conjugate base).