How many moles of hydrochloric acid (pKa of HF=3.14) must be added to 500.0 mL of 0.30M sodium fluoride (NaF) to give a buffer of pH 3.50? Ignore the volume change due to the addition of hdrofluoric acid

Answer 1

500 mL x 0.30M NaF = 150 millimols NaF.
3.50 = 3.14 + log (base)/(acid)
3.50 = 3.14 + log (150/x)
Solve for x = millimoles HCl, then change to mols.

Answer 2

0.662moles