To find the pH of this solution....?

Question

that's only given:

0.10 M CH3COOH and 0.10 M NaCH3COO

..i know I would have to look up the Kb and turn that into Ka and calculate the pH...right...but Kb for what CH3COOH? or NaCH3COO?

would it be the same step for any other solutions

Answer 1

Since you have equal amounts of weak acid and conjugate base then the pH of the buffer is equal to the pKa. The Ka of acetic acid is 1.8 x 10^-5, so the pH is 4.74.

My quick analysis is based on the Henderson-Hasselbalch equation, which is often used to determine the pH of a buffer, like this one.

Other problems might be more involved than this one.  This one is somewhat a special case.

pH = pKa + log ( [base]/[acid] )

Since the concentrations of the conjugate base and weak acid are the same then [base]/[acid] = 1, and the log of 1 is zero.  So pH = pKa.