Please explain and or show steps. Absorption of food in the stomach and intestin
ID: 863292 • Letter: P
Question
Please explain and or show steps.
Absorption of food in the stomach and intestine depends on the ability of molecules to perpetrate the cell membranes and pass into the bloodstream. Because hydrophobic molecules are more likely to be absorbed than hydrophilic or charged molecules, the ab-sorption of orally administered drugs may depend on their pKa values and the pH in the digestive organs. Aspirin (acetylsalicylic acid) has an ionizable carboxyl group (pKa = 3.5). Calculate the percentage of the protonated form of aspirin available for absorption in the stomach (pH = 2.0) and in the intestine (pH = 5.0).Explanation / Answer
The solution can be solved using Henderson-hassalbalch equation, i.e.,
pH= pKa + log (conjugate base)/(acid). The log (conjugate base)/(acid) ratio represents the ratio of deprotonated to the protonated aspirin molecules.
The pH in stomach is 2. So,
2 = 3.5 + log (conjugate base)/(acid)
log (conjugate base)/(acid) = -1.5
(conjugate base)/(acid) = 0.032.
Thus, for each single protonated molecule 0.032 conjugate bases will be there.
Percent protonated form of aspirin in the stomach = 1/0.032 *100 = 96.9%
Similarly, the pH in intestine is, 5. Substituting in Henderson-hassalbalch equation gives,
5 = 3.5- log (conjugate base)/(acid)
log (conjugate base)/(acid) = 1.5
(conjugate base)/(acid)= 31.6
Percent protonated form of aspirin in the stomach = 1/32.6 *100 = 3.1%