Chapter 20, Problem 20.19P

Interpretation Introduction

Interpretation:

The acid dissociation constant for the unknown acid has to be calculated.

Concept introduction:

$K_a$: Acid dissociation constant ${\text{K}}_{\text{a}}$ represents how strong the acid is in a solution.

Equilibrium constant ${\text{K}}_{\text{eq}}$ represents extend of dissociation of acid in aqueous solution.

For a dissociation of acid $\left(HA\right)$ in aqueous solution,

  $HA+H_{2}O\underset{}{\overset{}{\rightleftharpoons }}{H}_3{O}^{+}+A^{-}$

  $k_{eq}=\frac{\left[H_3{O}^{+}\right]\left[A^{-}\right]}{\left[HA\right]\left[H_{2}O\right]}$

Where,

  ${\text{K}}_{\text{a}}$ is the Acid Ionization constant.

  $\left[{\text{H}}^{\text{+}}\right]$ is the Concentration of Hydrogen ion

  $\left[{\text{A}}^{-}\right]$ is the Concentration of acid anion

  $\left[\text{HA}\right]$ is the Concentration of the acid

Relationship between ${\text{K}}_{\text{eq}}$ and ${\text{K}}_{\text{a}}$ shown as follows,

  ${\text{K}}_{\text{a}}\text{=}{\text{K}}_{\text{eq}}\left[{\text{H}}_{\text{2}}\text{O}\right]$

  where, $\left[{\text{H}}_{\text{2}}\text{O}\right]$ is the molar concentration of water.

Generally, strong acids have ${\text{K}}_{\text{a}}>1$ and weak acids have ${\text{K}}_{\text{a}}<1$.