In: Chemistry
A 1.50 L buffer solution is 0.250 M in HF and 0.250 M in NaF. Calculate the pH of the solution after the addition of 0.0500 moles of solid NaOH. Assume no volume change upon the addition of base. The Ka for HF is 3.5 × 10-4.
no of moles of HF = molarity * volume in L
= 0.25*1.5 = 0.375 moles
no of moles of NaF = molarity * volume in L
= 0.25*1.5 = 0.375 moles
By the addition of NaOH
no of moles of HF = 0.375-0.05 = 0.325 moles
no of moles of NaF = 0.375 + 0.05 = 0.425 moles
Pka = -logKa
= -log3.5*10-4 = 3.4559
PH = PKa + log[NaF]/[HF]
= 3.4559 + log0.425/0.325
= 3.4559 + 0.1165 = 3.5724