Chapter 3, Problem 18PP

Interpretation Introduction

Interpretation:

Acid-base reactions are to be written, and the stronger base and weaker base, and the weaker acid using $\text{p}{K}_{\text{a}}$ values are to be labeled.

Concept Introduction:

The value of $\text{p}{K}_{\text{a}}$ of an acid gives the quantitative measurement of a molecule’s acidity. It can be used to predict the direction of acid-base equilibrium of organic molecules. Comparing the energies of weak/strong acids and bases, weak acids and bases are lower in energy than strong acids and bases.

For any reaction, equilibria are favored to that side of the reaction which has the lowest energy. This doubtlessly reflects the fact that acid-base reactions will go to the side of weak acids and bases.

The strength of an acid is generally described in terms of acidity constant $\left(K_{\text{a}}\right)$ and $\text{p}{K}_{\text{a}}$ values.

A large value of $K_{\text{a}}$ indicates that the acid is strong and a small value of $K_{\text{a}}$ indicates a weak acid.

The value of ${\text{pK}}_{\text{a}}$ of a reagent can be mathematical defined as:

${\text{pK}}_{\text{a}}{\text{= - log(K}}_{\text{a}}\text{) }$,

The higher is the dissolution constant, i.e., the reagent can produce more ions when dissolved in water, the stronger is the acid. Thus, by the above relation, strong acids have low ${\text{pK}}_{\text{a}}$.

The stronger the acid, the weaker is its conjugate base.

Larger the value of ${\text{pK}}_{\text{a}}$ of the conjugate base, the stronger is the acid.