Question

Aspirin (acetylsalicylic acid) can cause stomach bleeding. Only the acid form can cross the stomach lining. Determine the ratio of base to its conjugate acid when the stomach pH=2.00. Ka aspirin = 2.75x10-5

Answer 1

Use the Henderson-Hasslebalch equation:
pH = pKa + log (base/acid).
You will need pKa. That is -log Ka.
You know pH and you can calculate pKa. Solve for (acid/base) and that is the ratio you want.