pKb
The negative logarithm of the base dissociation constant.
Formula / equation
pKb = −log Kb
Unit
Dimensionless
In depth
A lower pKb indicates a stronger base. Because pKa and pKb of a conjugate pair always sum to 14 in water at 25 °C, modern practice increasingly quotes only the pKa of the conjugate acid, which conveys exactly the same information on a single scale.
Examples in the real world
Ammonia has pKb 4.75, corresponding to a pKa of 9.25 for the ammonium ion.