Arrhenius Concept of Acids and Bases

The most commonly used concept of acids and bases was developed by Svante Arrhenius (1884).

Acid

According to this concept an acid is a substance that is capable of producing hydrogen ion (H⁺) by dissociating in aqueous solution.

HA (aq) → H⁺ (aq) + A^- (aq)

Hydrochloric acid (HCl) is an example of an Arrhenius acid.

The proton or hydrogen ion binds itself to a water molecule and form H3O⁺ ion which is called hydronium ion. The hydronium ion is also known as oxonium ion or the hydroxonium ion.

H⁺ + H²O → H3O⁺

Base

A base is defined as a substance capable of providing a hydroxyl ion (HO^-) on dissociation in aqueous solutions.

MOH (aq) → M⁺ (aq) + OH^- (aq)

Sodium hydroxide (NaOH) is an example of a Arrhenius base.

Drawbacks of Arrhenius Concept

It is limited to only aqueous solutions and require dissociation of the substance.

It does not explain the acidic behavior of some substances which do not contain hydrogen. For example, AlCl₃. Similarly, it does not explain the basic character of substances like NH₃ and Na₂CO₃ which do not have a hydroxide groups.