Chapter 16, Problem 71QP

Interpretation Introduction

Interpretation:

The pH of the solution prepared by the dissolution of a weak base with given concentration is to be determined.

Concept introduction:

The ionization of the weak base takes place as

${\text{B}}_{\left(\text{aq}\right)}+{\text{H}}_2{\text{O}}_{\left(\text{l}\right)}\rightleftharpoons {\text{OH}}^{-}{}_{\left(\text{aq}\right)}+{\text{HB}}^{+}{}_{\left(\text{aq}\right)}$

The formula to calculate the pOH of the solution from the concentration of hydroxide ions is

$\text{pOH}=-\log \left[{\text{OH}}^{-}\right]$ …… (1)

K_b is the measure of dissociation of a base and is known as the base-ionization constant, which is specific at a particular temperature.

$K_{\text{b}}=\frac{\left[{\text{OH}}^{-}\right]\left[{\text{BH}}^{+}\right]}{\left[\text{B}\right]}$ …… (2)

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

$\%\text{ dissociation}=\frac{{\left[{\text{OH}}^{-}\right]}_{\text{eq}}}{{\left[\text{B}\right]}_{\text{o}}}\times 100\%$ …… (3)

Here, ${\left[{\text{OH}}^{-}\right]}_{\text{eq}}$ is the hydroxide ion concentration at equilibrium and ${\left[\text{B}\right]}_{\text{o}}$ is the original base concentration.

pH is the measure of acidity of a solution, which depends on the concentration of hydronium ions and the temperature of the solution. The relationship between pH and pOH is

$\text{pH}+\text{pOH}=14$ …… (4)