In: Chemistry
A 25.0 mL sample of 0.150 M hydrofluoric acid is titrated with a 0.150 M NaOH solution. What is the pH at the equivalence point? The Ka of hydrofluoric acid is 6.8 × 10-4.
volume of base at equivalence point needed = 25.0 mL
total volume of the solution = 25 + 25 = 50 .0 mL
at equivalence point only salt remains its concentration = 25 x0.150 / 50
= 0.075 M
pKa = -log Ka
pKa = -log (6.8 x 10^-4)
pKa = 3.17
pH = 7 + 1/2 [pKa + log C]
pH = 7 + 1/2 [3.17 + log 0.075]
pH = 8.02