Can someone help me out with this problem?
Aspirin has an acid dissociation constant Ka ~ 1 x 10^-4.
Diagram: C9H8O4 <--> C9H7O4- + H+
a) What is the pKa?
b) In what pH range is aspirin a good buffer?
c) When dissolved in the human stomach, a therapeutic dose of aspirin yields a 0.03 M solution. If the stomach contained only water
and the aspirin, what would be the concentration at equilibrium of aspirin (HA) and its conjugate base (A–), and the resulting
pH?
d) The stomach actually contains about .02M HCl. Under these conditions, how much of the conjugate base would be formed? What is the
pH?
This is what I have so far:
I assume that the "Diagram: C9H8O4 <--> C9H7O4- + H+" is equivalent to this: H2O + C9H8O4 <--> C9H7O4- + H3O+
a) pKa = -log(Ka) = 4
b) Henderson-Hasselbalch: pH = pKa + log([A-]/[HA]). Assuming [A-]/[HA] = 1, pH = 4.
And then I don't know how to do the others, since I don't know how to relate molarity to anything else.
Cheers,
axva1663