Chapter 16, Problem 81QP

Interpretation Introduction

Interpretation:

From the given monoprotic acid systems, the conjugate base with the smallest $K_{\text{b}}$ value and the strongest anion base are to be determined.

Concept introduction:

The ionization of a weak acid takes place as:

${\text{HA}}_{\left(\text{aq}\right)}+{\text{H}}_2{\text{O}}_{\left(\text{l}\right)}\rightleftharpoons {\text{H}}_{\text{3}}{\text{O}}^{\text{+}}{}_{\left(\text{aq}\right)}+{\text{A}}^{-}{}_{\left(\text{aq}\right)}$

$K_{\text{a}}$ is the measure of dissociation of an acid and is known as the acid-ionization constant, which is specific at a particular temperature.

$K_{\text{a}}=\frac{\left[{\text{H}}_3{\text{O}}^{+}\right]\left[{\text{A}}^{-}\right]}{\left[\text{HA}\right]}$ …… (1)

The ionization of its conjugate base takes place as:

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

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

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

The equation that relates the $K_{\text{a}}$ for a weak acid and the $K_{\text{b}}$ for its conjugate base is:

$K_{\text{w}}=K_{\text{a}}\times K_{\text{b}}$ …… (3)

Here, $K_{\text{w}}$ has the value $1.0\times {10}^{-14}$.