What is the pH of a solution that consists of 0.50 M H₂C₆H₆O₆ (ascorbic acid) and 0.75 M NaHC₆H₆O₆ (sodium ascorbate)? [K_a(H₂C₆H₆O₆) = 6.8 × 10^-5]

Question

Quizplus · Accepted Answer

Ascorbic acid (H2A) is a weak acid that will dissociate in water as follows:
H2A ⇌ H+ + HA-
The Ka expression for the dissociation of ascorbic acid (H2A) is as follows:
Ka = [H+][A-]/[HA-]
We know that the H2A and the related anion A- (ascorbate) are present in the solution as a buffer, and thus we can use the Henderson-Hasselbalch equation to calculate the pH:
pH = pKa + log([A-]/[HA-])
From the given information, we know that the concentration of ascorbic acid (HA-) is 0.50 M and the concentration of ascorbate (A-) is 0.75 M. We also know the pKa value of ascorbic acid, which is given to be 6.8 × 10-5. Plugging these values into the Henderson-Hasselbalch equation yields:
pH = 4.34

What Is the PH of a Solution That Consists of 0.50