Chapter 16, Problem 87QP

Interpretation Introduction

Interpretation:

The diagram that represents a solution of a weak diprotic acid and the diagram that represents a chemically implausible situation is to be identified out of the given options.

Concept introduction:

An acid that donates two protons per molecule to an aqueous solution is called diprotic acid. Example, sulphuric acid.

The first ionization of the weak diprotic acid takes place as shown below,

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

$K_{\text{a1}}$ is the measure of the dissociation of the first proton of an acid and is known as first acid-ionization constant, it is specific at specific values of temperature.

$K_{\text{a1}}=\frac{\left[{\text{H}}_3{\text{O}}^{+}\right]\left[{\text{HA}}^{-}\right]}{\left[{\text{H}}_2\text{A}\right]}$ …… (1)

The second ionization of the weak diprotic acid takes place as follows,

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

$K_{\text{a2}}$ is the measure of the dissociation of the second proton of an acid and is known as second acid-ionization constant, it is specific at specific values oftemperature.

$K_{\text{a2}}=\frac{\left[{\text{H}}_3{\text{O}}^{+}\right]\left[{\text{A}}^{-}\right]}{\left[{\text{HA}}^{-}\right]}$ …… (2)