The dissociation constant Kₐ for an acid [HA] is written as,
Kₐ = [H⁺] [A⁻] / [HA]
It is the ratio of dissociated Ions to undissociated acid. Means, Kₐ represents the extent of Ionization of an Acid. Greater the value of Kₐ, greater will be the dissociation, greater will be the production of H⁺ and greater will be the strength of an acid.
Examples:
Kₐ of Strong Acid HI = 3.2 × 10⁹
Kₐ of Weak Acid CH₃COOH = 1.8 × 10⁻⁵
