Answer:
pH = 2.56
Explanation:
The Henderson-Hasselbalch equation relates the pH to the Ka and ratio of the conjugate acid-base pair as follows:
pH = pKa + log([A⁻]/[HA]) = -log(Ka) + log([A⁻]/[HA])
Substituting in the value gives:
pH = -log(1.77 x 10⁻⁴) + log((0.0065M) / (0.10M))
pH = 2.56