1. The problem statement, all variables and given/known data The pKa of acetylsalicylic acid (aspirin) is 3.5. The pH of gastric juice in the stomach is about 2-3 and the pH in the small intestine is about 8. Aspirin will be Answer is ionised in the small intestine and almost unionised in the stomach. 2. Relevant equations 3. The attempt at a solution I understand from the pH values given that the stomach is acidic and small intestine basic. So, I could already qualitatively figure out what the answer would be. However, is it quantitatively correct to say that aspirin is unionised in the stomach because the pH of stomach is less than the pKa of aspirin? What if the pKa of aspirin was 1.5? Would it then be ionised in the stomach? Basically, I just want someone to clarify what pKa tells us in this context.