how much 0.1F HC2H3O2 is required to make 500 ml of solution with a Ph of 4.0?

Answer 1

HC2H3O2 = HAc
Let Y = (HAc) needed to make pH = 4.0 or (H^+) of 1E-4 M.
.......HAc ==> H^+ + Ac^-
I......Y.......0.....0
C.....-x.......x.....x
E.....Y-x......x.....x

Ka = (H^+)(Ac^-)/(HAc)
Ka = (x)(x)/(Y-x)
You know Ka (or you can look it up), you know x, solve for Y. I will use Y as the answer but you substitute that into the following.
mL1 x M1 = mL2 x M2
500 x Y = mL2 x 0.1
Solve for mL2. That will be the volume in mL of the 0.1M HAc needed.