Arrhenius concept of acids and bases

Based on certain characteristic observable properties, electrolytes were classified into acids and bases.

Arrhenius Concept of Acids and Bases

Arrhenius in 1887 put forward this concept. Accordingly, an acid is a hydrogen-containing compound, which gives free hydrogen ions when dissolved in water.

A base is a hydroxyl group containing compound which gives free hydroxyl ions (OH^-) when dissolved in water.

Thus, according to the Arrhenius concept, hydrogen chloride, acetic acid, and sulphuric acid, are acids because all these compounds give free H⁺ ions in aqueous solutions.

Compounds such as NaOH and NH₄OH are bases, because these compounds give free OH^- ions in aqueous solutions.

Thus, according to Arrhenius concept of acids and bases, the neutralization of an acid with a base involves the reaction between H⁺_(aq) and OH^-_(aq) i.e.,

However, the Arrhenius concept is applicable to the acid-base behaviour only in the aqueous medium. It does not provide any explanation to the acid-base behaviour in the absence of water.

This concept defines acids and bases as compounds-containing hydrogen and hydroxyl group respectively. There are however, many compounds, which act as acid even when there is no hydrogen in their molecule. Similarly, there are many bases, which do not contain hydroxyl group.

For example, CO₂ acts as an acid in its reaction with NaOH; and NH₃ acts as a base although it does not contain OH^- group.

In aqueous solutions, hydrogen ion exist as hydrated species (H₉O₄⁺) which is described by a simple formula H₃O⁺