We want to find why aspirin will move from the stomach into the blood. (i) A neu

Question

We want to find why aspirin will move from the stomach into the blood. (i) A neutral molecule (drug) will reach same concentration anywhere in the body (i.e. [HA]_1 = [HA]_2) (ii) A neutral molecule (drug) will ionize to different degrees depending on the pH of the medium (i.e. [A^-]_1 notequalto [A^-]_2) (iii) The concentration of the drug is [HA] + [A^-] Find the ratio of concentrations of drug in blood and stomach. Comment on why the aspirin will move into blood. (pH_blood = 7.4, pH_stomach = 3.0, pKa_aspirin = 3.5) We want to find why aspirin will move from the stomach into the blood. (i) A neutral molecule (drug) will reach same concentration anywhere in the body (i.e. [HA]_1 = [HA]_2) (ii) A neutral molecule (drug) will ionize to different degrees depending on the pH of the medium (i.e. [A^-]_1 notequalto [A^-]_2) (iii) The concentration of the drug is [HA] + [A^-] Find the ratio of concentrations of drug in blood and stomach. Comment on why the aspirin will move into blood. (pH_blood = 7.4, pH_stomach = 3.0, pKa_aspirin = 3.5)

Explanation / Answer

Q6.

Find ratio of HA vs A-

pH = pKa + log(A-/HA)

pKa of aspirin = 3.5

then

in blood

pH = pKa + log(A-/HA)

7.4 = 3.5 + log(A-/HA)

A-/HA = 10^(7.4-3.5) = 7943.28

in the stomach

pH = pKa + log(A-/HA)

3= 3.5 + log(A-/HA)

A-/HA = 10^(3-3.5) = 0.31622

therefore, expect much more A- in stomach than HA

expect much more HA in blood than A-

thereofre, the aspirin goes from stomach to blood due to acidity

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