pOH
The negative logarithm of the hydroxide ion concentration.
Formula / equation
pOH = −log[OH⁻]; pH + pOH = 14
Unit
Dimensionless
In depth
Because Kw links the two ion concentrations, pH and pOH always sum to 14 at 25 °C. Working in pOH is often quicker for alkaline solutions, where the hydroxide concentration is known directly from the base concentration.
Examples in the real world
A 0.01 M NaOH solution has pOH = 2 and therefore pH = 12.