The pH value of gastric juice in the human stomach is about 1.8 and in the small intestine it is about 7.8. The pKa value of aspirin is 3.5. Aspirin will be:

A. Completely ionised in the small intestine and in the stomach

B. Unionised in the small intestine and in the stomach

C. Ionised in the small intestine and almost unionised in the stomach

D. Ionised in the stomach and almost unionised in the small intestine

Solution: (C)

Aspirin will be almost unionised in stomach due to strong acidic medium (because of HCI). On the other hand, in small intestine, since the medium is alkaline aspirin will be sufficiently ionised.