Chapter 18, Problem 18.183P

(a)

Interpretation Introduction

Interpretation:

$pH$ of the saturated solution of quinine in water has to be calculated.

Concept Introduction:

The self-dissociation constant for water can be written as follows,

${\text{K}}_{\text{w}}{\text{ = K}}_{\text{a}}{\text{ × K}}_{\text{b}}$

Where,

  $\begin{array}{l}{\text{K}}_{\text{w}}\text{ = water dissociation constant}\\ {\text{K}}_{\text{a}}\text{ = acid dissociation constant}\\ {\text{ K}}_{\text{b}}\text{ = base dissociation constant}\end{array}$

  ${\text{K}}_{\text{w}}={10}^{-14}$

Also, $K_w=\left[H_3{O}^{+}\right]\left[O{H}^{-}\right]$

$pH$ can be calculated from the following equation if $[H_3{O}^{+}]$ is known.

$pH=-{\log }_{10}[H_3{O}^{+}]$

(b)

Interpretation Introduction

Interpretation:

Less contribution of aromatic N to the $pH$ has to be shown.

Concept Introduction:

The self-dissociation constant for water can be written as follows,

${\text{K}}_{\text{w}}{\text{ = K}}_{\text{a}}{\text{ × K}}_{\text{b}}$

Where,

  $\begin{array}{l}{\text{K}}_{\text{w}}\text{ = water dissociation constant}\\ {\text{K}}_{\text{a}}\text{ = acid dissociation constant}\\ {\text{ K}}_{\text{b}}\text{ = base dissociation constant}\end{array}$

  ${\text{K}}_{\text{w}}={10}^{-14}$

$pH$ can be calculated from the following equation if $[H_3{O}^{+}]$ is known.

$pH=-{\log }_{10}[H_3{O}^{+}]$

Also, $K_w=\left[H_3{O}^{+}\right]\left[O{H}^{-}\right]$

(c)

Interpretation Introduction

Interpretation:

$pH$ of quinine hydrochloride at given concentration has to be calculated.

Concept Introduction:

The self-dissociation constant for water can be written as follows,

${\text{K}}_{\text{w}}{\text{ = K}}_{\text{a}}{\text{ × K}}_{\text{b}}$

Where,

  $\begin{array}{l}{\text{K}}_{\text{w}}\text{ = water dissociation constant}\\ {\text{K}}_{\text{a}}\text{ = acid dissociation constant}\\ {\text{ K}}_{\text{b}}\text{ = base dissociation constant}\end{array}$

  ${\text{K}}_{\text{w}}={10}^{-14}$

$pH$ can be calculated from the following equation if $[H_3{O}^{+}]$ is known.

$pH=-{\log }_{10}[H_3{O}^{+}]$

Also, $K_w=\left[H_3{O}^{+}\right]\left[O{H}^{-}\right]$

(d)

Interpretation Introduction

Interpretation:

$pH$ of 1.5% of quinine hydrochloride has to be calculated.

Concept Introduction:

Molarity of a solution can be calculated using the following equation.

$Molarity=\frac{numberofmolesofsolute}{Volumeofsolutioninlitre}$

And number of moles of solute can be calculated using the following equation.

$\text{Number of moles = }\frac{\text{Given mass of solute}}{\text{Molecular mass of the solute}}$

Therefore molarity can be calculated as follows,

$Molarity=\frac{numberofmolesofsolute}{Volumeofsolutioninlitre}=\frac{W_2\times 1000}{M_2\times V\left(ml\right)}$

Where,

  $\begin{array}{l}{\text{W}}_{\text{2}}\text{ = given mass of solute}\\ {\text{M}}_{\text{2}}\text{= molecular mass of solute}\\ \text{V}\left(\text{ml}\right)\text{ = volume of solution in ml}\end{array}$