Question

Absorption of aspirin (acetylsalicylic acid, C₉H₈O₄) into the bloodstream occurs only when the molecule is in its conjugate base form. If a patient takes two tablets of aspirin (325 mg each), how many grams of aspirin are available for immediate absorption in the stomach? The pH of the stomach is 1.6 and the pK_a of aspirin is 3.5.

Answer 1

pH = pKa + log(Aspirin ion / Aspinrin acid)

1.6 = 3.5 + log((Aspirin ion / Aspinrin acid))

(Aspirin ion / Aspinrin acid) = 10^(1.60-3.5) = 0.012589

(Aspirin ion / Aspinrin acid) =0.012589

therefore... if total C = 325 mg, then only

ASpirin ion = 0.012589*Aspinrin acid

ASpirin ion + Aspinrin acid = 325

0.012589*Aspinrin acid+ Aspinrin acid = 325

Aspirin acid = 325/(0.012589+1) = 320.959 mg are as acid

Aspirin base =  0.012589*Aspinrin acid = 0.012589*325 = 4.091mg will be present in bloodstream