Chapter 18.2, Problem 18SSC

Interpretation Introduction

Interpretation:

The strength of weak acid is to be related to its conjugate base.

Concept introduction:

The concept of conjugate acid-base pair is given by Bronsted-Lowry.

According to it,

Acid is a substance which donate hydrogen ion and Base is a substance which accept hydrogen ion.

When acid donates $H^{+}$, the species form is conjugate base and when base accepts $H^{+}$, the species form is conjugate acid.

Answer to Problem 18SSC

Stronger the acid, weaker is its conjugate base and vice-versa.

Explanation of Solution

According to Bronsted-Lowry,

If an acid is strong, its conjugate base is weak and if acid is weak then conjugate base is strong. For example:

$HCl+H_{2}O\to C{l}^{-}+H_3{O}^{+}$

Here $HCl$ is strong acid. According to the concept, $C{l}^{-}$ its conjugate base is weak.

$C{H}_{3}COOH+H_{2}O\rightleftharpoons C{H}_{3}CO{O}^{-}+H_3{O}^{+}$

Here $C{H}_{3}COOH$ is weak acid. According to the concept, $C{H}_{3}CO{O}^{-}$ its conjugate base is strong.

Conclusion

Thus, if an acid is strong, its conjugate base is weak and if acid is weak then conjugate base is strong.