Chapter 18, Problem 121A

Interpretation Introduction

Interpretation:

The differences between Arrhenius and the Bronsted concept are to be discussed.

Concept introduction:

According to Arrhenius,

Acid is a substance that gives hydrogen ion and base is a substance that gives hydroxyl ions in aqueous solution.

According to Bronsted-Lowry,

Acid is a substance that donates hydrogen ion and base is a substance that accepts hydrogen ion.

Answer to Problem 121A

Bronsted theory includes all the acids and bases which are described by Arrhenius's theory.

Bronsted theory also explains why some substances like ammonia are basic in nature although it doesn’t contain hydroxyl ion. It also explains the role of water in acid and basic solution.

Explanation of Solution

According to Arrhenius and Bronsted, the definition of an acid is the same. So all Arrhenius acids are Bronsted acids and all Bronsted acids are Arrhenius acids.

Example:

$\text{H}\text{C}\text{l}$ is Arrhenius as well as Bronsted Acid

$\text{H}\text{C}\text{l}\to {\text{H}}^{+}+\text{C}{\text{l}}^{-}$

But all Bronsted bases are not Arrhenius bases.

$\text{N}{\text{H}}_3$ is Bronsted base because it can donate electron as:

$\text{N}{\text{H}}_3+{\text{H}}^{+}\to \text{N}{\text{H}}_4{}^{+}$

but it cannot give hydroxyl ion in water. So, it is not an Arrhenius base.

Conclusion

Thus, the Bronsted theory is a better concept than the Arrhenius concept of acids and bases.