Question

The ${p{K}_a}^o$of acetylsalicyclic acid (aspirin) is 3.5. The pH of gastric juice in the human stomach is about 2 to 3 and the pH in small intestine is about 8. Aspirin will be

• A. unionized in the small intestine and in the stomach
• B. completely ionized in the small intenstine and in the stomach
• C. ionized in the stomach and almost unionized in the small intestine
• D. ionized in the small intenstine and almost unionized in the stomach

Answer 1

The correct option is D

ionized in the small intenstine and almost unionized in the stomach

In water, acids stronger than water are all completely ionized. So the strongest acid in water will be ${H_{3}O}^{+}$. Stronger acids than water will be fully ionized. Weaker acids will undergo very small ionization.

From the given data, the gastric juice (stomach) is much more acidic than aspirin and thus very less ionization. On the other hand, the intestine is somewhat basic. There aspirin will behave like a strong acid and dissociate very appreciably