Question

The $pK_a$ 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. A spirin 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)

ionised in the small intestine and almost unionised in the stomach

Answer 2

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.