The pK_a of a weak acid was determined by measuring the pH of a solution containing the weak acid at 0.40 M and its conjugate base at 0.60 M. The measured pH was 7.8. What is the pK_a of the weak acid?

Question

Quizplus · Accepted Answer

The Henderson-Hasselbalch equation for a weak acid (HA) and its conjugate base (A⁻) is:

pH = pKa + log([A⁻]/[HA])

We are given the concentrations of HA and A⁻, and the pH of the solution. We can rearrange the equation and solve for pKa:

pKa = pH - log([A⁻]/[HA])

pKa = 7.8 - log(0.60/0.40)

pKa = 7.6

Therefore, the answer is choice C: 7.6.

The PKa of a Weak Acid Was Determined by Measuring

The PK_a of a Weak Acid Was Determined by Measuring