Question

Explain giving example, Arrhenius acid-base theory. Mention the limitations of this theory.

Answer 1

Hint: Arrhenius theory as opposed to the Lewis theory, talks about acids and bases on the basis of ions released in aqueous solution. Take an example of an acid and a base and then explain the ions that are released in each case. Limitations of Arrhenius theory can be explained by taking an example of Lewis acid or base as they are acid/base and yet do not release any ions upon dissociation.

Complete Solution :
- The Arrhenius theory was first introduced in the year, 1887 by Swedish scientist Svante Arrhenius.
According to the Arrhenius theory, acid is defined as a substance that gives hydrogen ions on dissolving in an aqueous solution. It increases the concentration of hydrogen ions in the solution.
For example, hydrochloric acid in water. It undergoes dissociation reactions to produce hydrogen and chlorine ions as explained above.
On the other hand, a base is defined as a substance that releases hydroxide ions when dissolved in an aqueous solution. It increases the hydroxide concentration in solution.
For example, sodium hydroxide in water. It undergoes dissociation reactions to produce sodium and hydroxide ions as explained above.

Although the theory provided a detailed understanding of acids and bases, it had some limitations as well. Some are mentioned below:
- It is broadly applicable to aqueous solution only.
- It is incapable to explain the basic nature of ammonia in an aqueous solution.
- Hydroxide ions released according to the Arrhenius theory are highly unstable. They combine with water to form stable hydronium ions.

Note: It is important to know that although ammonia is not considered as a base according to Arrhenius theory, its basic nature is explained mainly by the Lewis theory. Lewis theory mainly talks about transfer of protons for an acid and base.