Q. The pH value of gastric juice in human stomach is about 1.8 and in the small intestine it is about 7.8. The ${pK}_{a}$ value of aspirin is 3.5. Aspirin will be
A) Completely ionized in the small intestine and in the stomach.
B) Unionized in the small intestine and in the stomach.
C) Ionized in the small intestine and almost unionized in the stomach.
D) Ionized in the stomach and almost unionized in the small intestine.
Explanation
(c)
Aspirin is a moderate acid$\left( pK_{a} = 3.5 \right),$ hence is almost unionized in stomach due to strong acidic medium of it (because of HCl). It is due to common ion effect.
While in small intestine, the medium is alkaline, hence aspirin will be sufficiently ionized in small intestine.
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.