Chapter 16.13, Problem 1PPB

Interpretation Introduction

Interpretation:

From the given percent dissociation, the concentration of the weak acid is to be determined.

Concept introduction:

pH is the measure of the acidity of a solution and it depends on the concentration of hydronium ions and the temperature of the solution.

The formula to calculate the pH of the solution from the concentration of hydronium ions is: $\text{pH}=-\log \left[{\text{H}}_3{\text{O}}^{+}\right]$

The ionization of the weak acid takes place as:

${\text{HA}}_{\left(\text{aq}\right)}+{\text{H}}_2{\text{O}}_{\left(\text{l}\right)}\rightleftharpoons {\text{H}}_{\text{3}}{\text{O}}^{\text{+}}{}_{\left(\text{aq}\right)}+{\text{A}}^{-}{}_{\left(\text{aq}\right)}$

$K_{\text{a}}$ is the measure of dissociation of an acid and is known as acid-ionization constant and has a specific value at a particular temperature.

$K_{\text{a}}=\frac{\left[{\text{H}}_3{\text{O}}^{+}\right]\left[{\text{A}}^{-}\right]}{\left[\text{HA}\right]}$ …… (1)

Percent ionization is the percentage of acid that gets dissociated upon addition to water. It depends on the hydronium ion concentration.

$\%\text{ dissociation}=\frac{{\left[{\text{H}}_3{\text{O}}^{+}\right]}_{\text{eq}}}{{\left[\text{HA}\right]}_{\text{o}}}\times 100\%$ …… (2)

Here, ${\left[{\text{H}}_3{\text{O}}^{+}\right]}_{\text{eq}}$ is hydronium ions concentration at equilibrium and ${\left[\text{HA}\right]}_{\text{o}}$ is original acid concentration.