Limitations of the Arrhenius Concept of Acids & Bases
Despite
its successes, the Arrhenius concept/definition of acids and bases proved to be
inadequate for several reasons.
- It is and was recognized that acid-base reactions also take place in solvents other than water. But the Arrhenius concept is not applicable for non-aqueous solutions,i.e., it cannot explain the properties of acids and beses in abscence of water.
- Compounds which do not contain hydrogen can release H+ ion by reacting with water. For instance,
- Some bases do not contain OH- ions. For example, NH3, CaO etc.
- It is also believed that a H+ ion cannot exist in free state in any solvent because of its high charge density. A hydrogen ion would combine with one or more molecules of the solvent. In the case of water as solvent H+ ion would combine with water molecule to form what is known as a hydronium/hydroxonium/oxonium ion(H3O+).
These
facts together with the studies on the catalysis by acids and bases suggested
that the ideas of Arrhenius were inadequate and had to be modified.
