The `pK_(a)` of acteylsalicylic acid (aspirin) is `3.5`. The pH of gastric juice in human stomach is about `2-3` and the pH in the small intestine is about 8. Aspirin will be:

Options

A. Unionised in the small intestine and in the stomach.
B. Completely ionised in the small intestine and in the stomach.
C. Ionised in the stomach and alomost unionised in the small intestine.
D. Ionised in small intestine and almost unionised in the stomach.

Answer

D

Explanation

Aspirin is a weak acid and its ionisation is supressed due to common ion effect in acidic medium, i.e., in stomach. Therefore, aspirin is unionised is stomach whereas in small intestine its `pH` is basic. So the ionisation of aspirin increases, that is why it is completely ionised in small intenstine.

Base in intenstine `(NaOH)rarr Na^(o+) +overset(Theta)OH`
`H^(o+)` and `overset(Theta)OH` combines and aspirin forms sodium salt. Therefore, ionisation of aspirin increases.