Base Dissociation Constant
The equilibrium constant for the reaction of a base with water to produce hydroxide ions.
Formula / equation
Kb = [BH⁺][OH⁻] / [B]
Unit
mol/L
In depth
A larger Kb indicates a stronger base. Because water appears as a pure liquid it is omitted from the expression. Kb is related to the Ka of the conjugate acid through the ionic product of water, so tabulating either one suffices.
Examples in the real world
Ammonia has Kb = 1.8 × 10⁻⁵; methylamine is stronger at 4.4 × 10⁻⁴; aniline far weaker at 4.3 × 10⁻¹⁰.