Chapter 5, Problem 5.41P

(a)

Interpretation Introduction

Interpretation:

The pH of an aqueous solution of $\text{0}{\text{.10 M NH}}_{\text{4}}\text{Cl}$ has to be calculated.

Concept Introduction:

Acid ionization constant, $K_a$:

The ionization of a weak acid $\text{HA}$ can be given as follows,

${\text{HA}}_{(aq)}\rightleftarrows {\text{H}}^{+}{}_{(aq)}+{\text{A}}^{\text{-}}{}_{(aq)}$

The equilibrium expression for the above reaction is given below.

$K_a=\frac{[{\text{H}}^{\text{+}}{\text{][A}}^{\text{-}}\text{]}}{[\text{HA]}}$

Where $K_a$ is acid ionization constant,

  $[{\text{H}}^{\text{+}}\text{]}$  is concentration of hydrogen ion

  $[{\text{A}}^{\text{-}}\text{]}$  is concentration of acid anion

  $[\text{HA]}$ is concentration of the acid

pH definition:

The concentration of hydrogen ion is measured using pH scale.  The acidity of aqueous solution is expressed by pH scale.

The pH of a solution is defined as the negative base-10 logarithm of the hydrogen or hydronium ion concentration.

$\text{pH}\text{=}{\text{-log[H}}_{\text{3}}{\text{O}}^{\text{+}}\text{]}$

(b)

Interpretation Introduction

Interpretation:

The pH of an aqueous solution of $\text{0}{\text{.25 M NaCH}}_{\text{3}}{\text{CO}}_{\text{2}}$ has to be calculated.

Concept Introduction:

Base ionization constant, $K_b$:

The ionization of a weak base $\text{B}$ is given by the below equation.

${\text{B}}_{(aq)}+{\text{H}}_{\text{2}}{\text{O}}_{(l)}\rightleftarrows {\text{HB}}^{\text{+}}{}_{(aq)}+{\text{OH}}^{\text{-}}{}_{(aq)}$

The equilibrium expression for the ionization of weak base $\text{B}$ will be,

${\text{K}}_b=\frac{[{\text{HB}}^{\text{+}}][{\text{OH}}^{\text{-}}]}{[\text{B}]}$

Where $K_b$ is base ionization constant,

  $[{\text{OH}}^{-}\text{]}$ is concentration of hydroxide ion

  $[{\text{HB}}^{\text{+}}\text{]}$  is concentration of conjugate acid

$[\text{B]}$ is concentration of the base

pOH definition:

The pOH of a solution is defined as the negative base-10 logarithm of the hydroxide ion ${\text{[OH}}^{\text{-}}\text{]}$ concentration. pOH scale is analogous to pH scale.

$\text{pOH}\text{=}{\text{-log[OH}}^{\text{-}}]$

Relationship between pH and pOH:

$\text{pH}\text{+}\text{pOH}\text{=}\text{14,}\text{at}\text{25}{}^{\text{o}}\text{C}$

(c)

Interpretation Introduction

Interpretation:

The pH of an aqueous solution of $\text{0}{\text{.200 M CH}}_{\text{3}}\text{COOH}$ has to be calculated.

Concept Introduction:

Acid ionization constant, $K_a$:

The ionization of a weak acid $\text{HA}$ can be given as follows,

${\text{HA}}_{(aq)}\rightleftarrows {\text{H}}^{+}{}_{(aq)}+{\text{A}}^{\text{-}}{}_{(aq)}$

The equilibrium expression for the above reaction is given below.

$K_a=\frac{[{\text{H}}^{\text{+}}{\text{][A}}^{\text{-}}\text{]}}{[\text{HA]}}$

Where $K_a$ is acid ionization constant,

  $[{\text{H}}^{\text{+}}\text{]}$  is concentration of hydrogen ion

  $[{\text{A}}^{\text{-}}\text{]}$  is concentration of acid anion

  $[\text{HA]}$ is concentration of the acid