Ionic Equilibrium
3.0 Arrehenius Theory of Electrolyte Ionization (Dissociation)
3.0 Arrehenius Theory of Electrolyte Ionization (Dissociation)
An acid is a substance which when dissolved in water provides ${H^ + }$ e.g. $HNO_3$, $HCl$.
A base is a substance which when dissolved in water provides $O{H^ - }$ ions e.g. $NaOH$, $KOH$.
A chemical equilibrium exists between the un-dissociated electrolyte molecules and the ions that resuts from dissociation. Consider ionization of a weak electrolyte say a monoprotic acid, $HA$
$$HA {\text{ }} \rightleftharpoons {\text{ }} {H^{ + {\text{ }}}} + {\text{ }}{A^ - }$$
Concentration before dissociation $C$ $0$ $0$
Concentration after dissociation $C\left( {1 - \alpha } \right)$ $C\alpha $ $C\alpha $
where $\alpha $ is degree of ionization of weak acid $HA$, $C$ is the initial concentration of acid $HA$ in $mole{\text{ }}litr{e^{ - 1}}$
According to equilibrium constant expression
$${K_a} = \frac{{\left[ {{H^ + }} \right]\left[ {{A^ - }} \right]}}{{\left[ {HA} \right]}} = \frac{{\left( {C\alpha .C\alpha } \right)}}{{C\left( {1 - \alpha } \right)}} = \frac{{C{\alpha ^2}}}{{\left( {1 - \alpha } \right)}}$$ where ${K_a}$ is ionization constant of an acid.
