Question

How to calculate the dissociation constant?

Answer 1

Dissociation constant:

• The dissociation constant is defined as the ratio of dissociated ions (products) to the original acid or bases in the solution(reactants).
• For acids, the acid dissociation constant ( ${\mathrm{K}}_{\mathrm{a}}$ ) is defined as the ratio of concentration of dissociated ions to the concentration of original acid.
• Whereas for the basic solutions, the base dissociation constant ( ${\mathrm{K}}_b$ ) is defined as the ratio of concentration of dissociated ions to the concentration of original base.

Calculation of the dissociation constant:

• The dissociation constant is generally calculated by dividing the individual concentration of the dissociated ion by the concentration of the solution.
• For a general acid-base reaction of the type: $\mathrm{HA}+{\mathrm{H}}_2\mathrm{O}\rightleftharpoons {\mathrm{H}}_3{\mathrm{O}}^{+}+{\mathrm{A}}^{⁻}$
• The dissociation constant can be written as;

${\mathrm{K}}_{\mathrm{a}}=\frac{\left[{\mathrm{H}}_3{\mathrm{O}}^{+}\right]\left[{\mathrm{A}}^{-}\right]}{\left[\mathrm{HA}\right]}$

Hence, by applying the above process we can calculate the value for the dissociation constant.