Question
Define and explain dissociation constant of a weak acid.

Answer

Dissociation constant of a weak acid: It is defined as the equilibrium constant for dissociation equilibrium of a weak acid and denoted by $K _{ a }$.
Explanation : Consider an aqueous solution of a weak acid HA.
$HA _{( aq )} \rightleftharpoons H _{( aq )}^{+}+ A _{( aq )}^{-}$

The equilibrium constant called dissociation constant $Ka$ is represented as,
$K _{ a }=\frac{\left[ H ^{+}\right] \times\left[ A ^{-}\right]}{[ HA ]}$

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