What is the Henderson-Hasselbalch equation?

The Henderson-Hasselbalch equation is a mathematical expression that relates the pH of a solution to the pKa (acid dissociation constant) and the ratio of the concentrations of the conjugate base and the weak acid. It is given by: pH = pKa + log₁₀([A⁻]/[HA]), where [A⁻] is the concentration of the conjugate base, and [HA] is the concentration of the weak acid. This equation is derived from the rearrangement of the acid dissociation constant expression and provides a means to calculate the pH of buffer solutions.