Chapter 19.3, Problem 28LC

Interpretation Introduction

Interpretation: The acid dissociation constants vary between strong acids and weak acids is to be explained.

Concept introduction: The ratio of the concentration of the ionized form of an acid to the concentration of the unionized form of the acid is known as the dissociation constant or ionization constant.

Answer to Problem 28LC

The value of the acid dissociation constant ${\text{K}}_{\text{a}}$ is larger for strong acids and smaller for weak acids.

Explanation of Solution

The strength of an acid in solution is measured by the acid dissociation constant. It is denoted as ${\text{K}}_{\text{a}}$. In general, the dissociation of acid HA is written as follows:

  $HA\rightleftharpoons H^{+}+A^{-}$

The dissociation constant ${\text{K}}_{\text{a}}$ of the acid HA is written as,

  ${\text{K}}_{\text{a}}=\frac{\left[H^{+}\right]\left[A^{-}\right]}{\left[HA\right]}$

Strong acids completely dissociate or ionize in water or aqueous solution and have a larger value of ${\text{K}}_{\text{a}}$ . Weak acids slightly ionize or dissociate in an aqueous solution and have a smaller value of ${\text{K}}_{\text{a}}$ .