Question

To 10ml of a 0.10 acetic acid solution a 0.10M NaOH solution is added what is ph of the solution when 9.5ml of NaOH have been added

Answer 1

acetic acid = HAc
sodium acetate = NaAc

millimols HAc = mL x M = 10 x 0.1 -= 1
mmols NaOH = 0.95

............HAc + NaOH ==> NaAc + H2O
I...........1......0........0......0
add..............0.95...............
C........-0.95..-0.95......0.95....
E.........0.05.....0......0.95.....

So you have formed a buffered solution consisting of 0.05 mmols HAc and 0.95 mmols of sodium acetate (NaAc) in 20 mL of solution. Plug that into the Henderson-Hasselbalch equation and solve for pH.