How do you derive the Henderson-Hasselbalch equation?

The derivation starts from the expression of the acid dissociation constant (Ka) for a weak acid (HA): Ka = [H⁺][A⁻]/[HA]. Taking the negative logarithm of both sides: -log Ka = -log([H⁺][A⁻]/[HA]). This simplifies to: pKa = pH – log([A⁻]/[HA]). Rearranging gives the Henderson-Hasselbalch equation: pH = pKa + log([A⁻]/[HA]).