Answer:
To determine the pKa of acetic acid, we need to locate the equivalence point on the pH curve of the titration. The equivalence point is the point at which the number of moles of NaOH added is stoichiometrically equivalent to the number of moles of acetic acid in the solution.
In the titration curve for acetic acid and NaOH, the equivalence point occurs when the moles of NaOH added are equal to the moles of acetic acid initially present in the solution. At this point, all of the acetic acid has been converted to acetate ion and the pH is determined by the concentration of acetate ion in the solution.
Looking at the titration curve, the equivalence point appears to be at a pH of about 8.5. At this pH, the concentrations of acetic acid and acetate ion are equal, so we can use the Henderson-Hasselbalch equation to determine the pKa of acetic acid:
pKa = pH + log([A^-]/[HA])
At the equivalence point, [A^-] = [HA], so we can simplify the equation to:
pKa = pH + log(1) = pH
Therefore, the pKa of acetic acid is approximately 8.5, which is the pH at the equivalence point of the titration curve.