Calculate the pH of a solution that is 0.25 M in HF and 0.10 M in NaF.

Verified step by step guidance

1. Identify that the solution is a buffer solution, consisting of a weak acid (HF) and its conjugate base (F^- from NaF).
2. Use the Henderson-Hasselbalch equation for buffer solutions: \( \text{pH} = \text{pK}_a + \log \left( \frac{[\text{A}^-]}{[\text{HA}]} \right) \), where \([\text{A}^-]\) is the concentration of the conjugate base and \([\text{HA}]\) is the concentration of the weak acid.
3. Look up or calculate the \(\text{pK}_a\) of HF. The \(\text{K}_a\) of HF is typically around \(6.8 \times 10^{-4}\), so \(\text{pK}_a = -\log(\text{K}_a)\).
4. Substitute the given concentrations into the Henderson-Hasselbalch equation: \( [\text{A}^-] = 0.10 \text{ M} \) and \( [\text{HA}] = 0.25 \text{ M} \).
5. Calculate the pH using the equation: \( \text{pH} = \text{pK}_a + \log \left( \frac{0.10}{0.25} \right) \).