What is the pH of a solution that is 0.10 M formic acid and 0.0065 M formate (the conjugate base) ? Ka of formic acid = 1.77 x 10-4

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