To find the pH of the buffer solution, we can use the Henderson-Hasselbalch equation:
pH = pKa + log([A-]/[HA])
In this case, HF is the acid (HA) and F- is the conjugate base (A-).
Given:
Volume of the buffer = 311.0 mL = 0.311 L
Concentration of HF (acid) = 1.11 M
Concentration of F- (conjugate base) = 0.240 M
Ka for HF = 3.50 × 10^(-4)
First, let's calculate the ratio of [A-]/[HA]:
[A-]/[HA] = (concentration of F-) / (concentration of HF)
[A-]/[HA] = 0.240 M / 1.11 M
[A-]/[HA] = 0.2162
Now, let's calculate the pKa:
pKa = -log(Ka)
pKa = -log(3.50 × 10^(-4))
pKa ≈ 3.4559
Finally, we can use the Henderson-Hasselbalch equation to find the pH:
pH = pKa + log([A-]/[HA])
pH = 3.4559 + log(0.2162)
pH ≈ 3.4559 - 0.6650
pH ≈ 2.7909
Therefore, the pH of the buffer solution is approximately 2.7909.