Calculate the pH of a solution created by adding 5.00g of LiF to 150.0mL of 1.25M HF. Ka = 7.2 x 10-4
(LiF) = grams/molar mass = 5/about 26 = about 0.2M but you should do it more accurately.
.......HF ==> H^+ F^-
I......1.25...0...0.2M
C......-x.....x....x
E.....1.25-x..x...0.2+x
Ka HF = (H^+)(F^-)/(HF)
Substitute the E line and solve for x, then convert to pH.