Assume you have prepared 100.0 mL of a buffer solution using 0.400 mol of acetic acid (pKa = 4.74) and 0.400 mol of sodium acetate. The pH of this buffer solution is initially 4.74.

Question

After preparing this buffer solution, you added 55.0 mL of a 1.10 M NaOH solution to your buffer to see what would happen. What will the pH of this new solution be?

Answer 1

Try doing this to get you started.
HAc + NaOH ==> NaAc + H2O
mols HAc initially = 0.05 x 0.4 = 0.02
mols NaOH added = 0.055 x 1.10 = 0.065

Appears to me that the NaOH will neutralize all of the acetic acid and you no longer have a buffer solution.