1. The problem statement, all variables and given/known data The antimalarial drug quinine has pka = 8.4; is it likely to be absorbed by passive diffusion through lipid membranes in the stomach (ph = 0.9) or ileum (ph [tex]\approx[/tex] 8)? Why? 2. Relevant equations n/a 3. The attempt at a solution If the pH of the environment is equal to the pKa of the substance, then the substance will be ionized by 50%. Beyond that, I am unsure what the effect will be if the pH environment differs from that of the pKa. Strictly looking at the question from a chemistry viewpoint, I think that passive diffusion of quinine will more likely be absorbed in the ileum since the pKa and pH are close. On the other hand, I think that's a too large of an assumption to make since the differences between 8.4 and 8 are considerable. Biologically speaking, it would make more sense that passive diffusion of quinine should occur more readily at the ileum since the intestines are able to facilitate absorption better than in the stomach. While some absorption does takes place in the stomach, I don't think it compares to the intestines.