Question

How many moles of HF must be present at equilibrium 0.200 L to form a solution with a pH of 3.25.
Ka= 6.8 x 10-4. (Solve for [HF]. There is no need to subtract [H+] because they want the concentration at equilibrium)

Answer 1

The formula for obtaining [H+] is pH= -log([H+])

Answer 2

after you get your concentration for H+, you should write out the molecular equation for HF. Do these two steps first then I'll come back