Degree of Ionization or Degree of Dissociation

Weak acids and bases do not ionize completely and an equilibrium exists between the ionized and unionized species. The degree of ionization is defined as the fraction of total amount of a weak acid or a base that exists in the ionized form. It is denoted by α (alpha). The equilibrium constant can be used to calculate the degree of ionization of a weak acid or a base.

Consider a weak acid HA which partially dissociates in its aqueous solutions and the following equilibrium is established:

Since the acid HA is very weak, α << 1. You can neglect α in comparison to 1.

K_a = cα²

If you know the value of the dissociation constant of the acid and the concentration of the weak acids, you can find its degree of dissociation or ionization.