pOH Definition (Chemistry)

pOH is a measure of hydroxide ion (OH-) concentration. It is used to express the alkalinity of a solution. Aqueous solutions at 25 degrees Celcius with pOH less than 7 are alkaline, pOH greater than 7 are acidic and pOH equal to 7 are neutral. How to Calculate pOH pOH is calculated based on pH or hydrogen ion concentration ([H]). Hydroxide ion concentration and hydrogen ion concentration are related: [OH-] Kw / [H] Kw is the self-ionization constant of water. Taking the logarithm of both sides of the equation: pOH pKw - pH An approximation is that: pOH 14 - pH While the approximation works well in many settings, there are exceptions for which the pKw value should be used instead.