🧪 pH & Buffer Solutions

Acid-base buffering. A weak acid HA partly dissociates: HA ⇌ H⁺ + A⁻ with acidity constant Ka (pKa = −log Ka). In the buffer region the Henderson-Hasselbalch equation holds: pH = pKa + log([A⁻]/[HA]). Adding strong base converts HA into A⁻; at the half-equivalence point [HA] = [A⁻] so pH = pKa — the point of maximum buffer capacity β. At the equivalence point all HA has reacted and the pH jumps sharply (above 7 for a weak acid, since the conjugate base A⁻ is itself weakly basic). Beyond it, excess strong base dominates. Buffer capacity β = 2.303·C·x·(1−x) peaks at the half-equivalence point.