Why are weak organic acids more likely to cross membranes in the stomach?

Weak organic acids are more likely to cross cell membranes in the stomach because of the organ's highly acidic environment, which typically maintains a pH between 1 and 2.1

Most chemicals diffuse across cell membranes most effectively in their nonionized (electrically neutral) form. Because organic acids dissociate into ionized forms based on the pH of their environment, the strongly acidic conditions of the stomach suppress this dissociation. In this acidic setting, weak organic acids remain primarily in their nonionized, lipid-soluble state.1

Because the cell membrane consists of a lipid bilayer, substances that are lipid-soluble can dissolve into and permeate the membrane much more easily than ionized, water-soluble substances. Consequently, the acidic environment of the stomach facilitates the absorption of these specific compounds by ensuring they remain in the form most capable of crossing the lipid barrier.21