Bronsted-Lowry Acids and Bases

An Arrhenius acid is a substance that produces a hydrogen ion when dissolved in water, and an Arrhenius base is a substance that produces an OH−, or hydroxide ion.

Hydrochloric acid is an Arrhenius acid as it dissociates into a hydrogen ion and a chloride ion when dissolved in water. Sodium hydroxide is an Arrhenius base as it dissociates into a sodium ion and a hydroxide ion when dissolved in water.

However, this definition cannot be used to describe acids and bases that are not in an aqueous solution or bases that do not contain hydroxide ions.

A broader definition by Brønsted and Lowry defines an acid as a hydrogen ion or proton donor, whereas a base is a proton acceptor.

When hydrochloric acid is dissolved in water, it acts as an acid by donating a proton to water, producing a hydronium ion and a chloride ion. When ammonia is dissolved in water, it acts as a base and accepts a proton from water, producing an ammonium ion and a hydroxide ion.

A Brønsted-Lowry acid will always react with a Brønsted-Lowry base and vice versa. When an acid, for example, acetic acid, donates its proton, water acts as a base and accepts the proton. Acetic acid is converted into a conjugate base, acet