We need to find the Ka value of HF. First, set up the balanced chemical equation:
HF ===> H+ + F-
The formula for the Ka value of an acid is
Ka = [concentration of products] / [concentration of reactants]
Ka = [H+] [F-} / [HF]
So if we are given the concentration of the products and reactants, we will be able to solve for the Ka value of HF.