Question

A buffer solution is prepared by mixing 99.0 mL of 0.450 M HF and 55.0 mL of 1.15 M NaF. Determine the pH of the solution after the addition of 0.01 moles NaOH (assume there is no change in volume when the NaOH is added).

Answer 1

millimols HF = mL x M = approx 44.55
mmols NaF = approx 63.25
0.01 mols = 10 mmols NaOH added

..........HF + OH^- ==> F^- + H2O
I........44.55..0.......63.25......
add............10............
C........-10...-10......10
E.......34.55...0......73.25

Plug the E line into the Henderson-Hasselbalch equation and solve for pH.