Explain how the pH of the environment affects the absorption of weak bases, using the Henderson-Hasselbalch equation.

Weakly basic drugs are absorbed most effectively when they are in their unionized (non-polar, lipid-soluble) form, as this form can readily pass through cell membranes. The degree of ionization of a weak base depends on the pH of the environment and its pKa.

For a weak base (B), the equilibrium is $\text{B} + \text{H}^+ \rightleftharpoons \text{BH}^+$. The unionized form is B, and the ionized form is $\text{BH}^+$. The Henderson-Hasselbalch equation relating pH, pKa, and the ratio of unionized