Question

The $p{K}_a$ of acetyl salicylic 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

• 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 almost unionised in the small intestine
• D. ionised in the small intestine and almost unionised in the stomach

Answer 1

Answer: (D)

In stomach, pH is $2-3$, i.e. strongly acidic and aspirin will be almost unionised here due to common ion effect. However. pH in small intestine is $8$, basic, aspirin will be neutralised here.