Chapter 2, Problem 5P

Interpretation Introduction

(a) Interpretation:

The pH of a 1 M NH₄Cl solution should be calculated.

Concept Introduction:

For a weak acid or a weak base, the dissociation reaction is in equilibrium and the equilibrium constant is known as acid or base dissociation constant. For such a solution, concentration of each species is calculated using ICE table.

The pH of solution is calculated as follows:

$\text{pH}=-\log \left[{\text{H}}^{+}\right]$

Here, $\left[{\text{H}}^{+}\right]$ is concentration of hydrogen ions in the solution.

Interpretation Introduction

(b) Interpretation:

The pH of solution resulting from addition of 10 mL of a 1 M NaOH to 40 mL of 1 M NH₄Cl.

Concept Introduction:

For a buffer solution, pH is calculated using Henderson-Hasselbalch equation as follows:

$\text{pH}={\text{pK}}_{\text{a}}+\log \frac{\left[\text{Conjugate base}\right]}{\left[\text{acid}\right]}$

Here, pH is $-\log \left[{\text{H}}^{+}\right]$ of solution and ${\text{pK}}_{\text{a}}$ is $\text{-log}\left({\text{K}}_{\text{a}}\right)$ of weak acid.

Interpretation Introduction

(c) Interpretation:

The pH of the solution that results from the addition of 30 mL of 1 M NaOH to 40 mL of 1 M NH₄Cl.

Concept Introduction:

For a buffer solution, pH is calculated using Henderson-Hasselbalch equation as follows:

$\text{pH}={\text{pK}}_{\text{a}}+\log \frac{\left[\text{Conjugate base}\right]}{\left[\text{acid}\right]}$

Here, pH is $-\log \left[{\text{H}}^{+}\right]$ of solution and ${\text{pK}}_{\text{a}}$ is $\text{-log}\left({\text{K}}_{\text{a}}\right)$ of weak acid.