A 50mL of 0.50M hydrofluoric acid (Ka = 7.2 x 10^-4) is titrated with a 0.20M

sodium hydroxide solution. What is the pH of the solution when 35mL of base
has been added?
will the solution have a pH less that 7 or more than 7

2 answers

Didn't I show you how to do one like this just a day or so ago. That one had a final solution that was a buffer and used the Henderson-Hasselbalch equation to calculate the pH.
In fact, I think it was the same problem.