The answer is E. I'm confused doing the step by step procedure. I'm not sure why we use [H+]=10^-pH and Ka*Kb=Kw.
What mass of potassium fluoride must be added to 500.0 mL of water to give a solution with pH = 8.07? [Ka(HF) = 7.1 × 10-4]
A) 68 g B) 1.7 × 10-4 g C) 1.96 g D) 0.95 g E) 2.91 g