What is the equilibrium reaction for stomach acid (can be with food or medicine)?

Question

I am doing an assessment and need to find a correlation between stomach acidity and medicine and then relate this to an equilibrium reaction / constant.

If anyone has any ideas would be extremely helpful!

Thank you!

Answer 1

If I understand the question, I think it would depend on the nature of the food or the medicine. For example, let us look at a drug. It would depend on if the active ingredient was acidic or basic. Most active ingredients are basic (because they generally contain an amine -NH₂). We can represent this drug as R-NH₂ and the stomach acid (HCl) simply as H⁺.

RNH₂ + H⁺ <==> RNH₃⁺

Ka = [RNH₃⁺]/[RNH₂][H⁺]

I'm not sure what else you are asked to do with this type of relationship. The correlation would be that the lower the pH of the stomach, i.e. the higher the [H+], the more RH₃⁺ will be formed. This could be important depending on whether this form or the other form (RNH₂) is better absorbed and/or the more active form of the drug.