If 50. 0 mL of a buffer contains 8. 5 x 10-3 mol HAc and 4. 2 x 10-3 mol Ac-, what is the pH of the solution after the addition of 12. 0 mL of 0. 25 M NaOH? (Give your answer to 2 s. f)
a) 7. 05
b) 7. 20
c) 7. 35
d) 7. 50