pOH = −log₁₀[OH⁻] | pH + pOH = 14
pOH = −log₁₀[OH⁻] is the hydroxide counterpart of pH. At 25°C, pH + pOH = 14 (from Kw = [H⁺][OH⁻] = 10⁻¹⁴). For a 0.001 M NaOH solution: [OH⁻] = 0.001 M, pOH = 3, pH = 11. Lower pOH means more basic (higher [OH⁻]). Strong bases like NaOH and KOH fully dissociate: pOH = −log(concentration). Weak bases require the equilibrium expression: [OH⁻] = √(Kb × C). While pH is more commonly used, pOH is useful when working directly with bases and is essential for the Kb/pKb calculations. The relationship pKa + pKb = pKw = 14 at 25°C links acid and base dissociation constants. At temperatures other than 25°C, pKw changes (e.g., at 37°C, pKw = 13.6).