Chapter 16, Problem 124AP

Interpretation Introduction

Interpretation:

The percentage of ${\text{NH}}_3$, which is present in ${\text{NH}}_4{}^{+}$, is to be determined.

Concept introduction:

The ionization of a 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)

${\text{K}}_{\text{b}}$ is a measure of dissociation of a base and is known as base-ionization constant, which is specific at a particular temperature.

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

Percent ionization is the percentage of base that gets ionized upon addition of water. It depends on the hydroxide ion concentration or the conjugate acid concentration.

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

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