Using the Henderson-Hasselbalch equation, what is the pH of a buffer solution containing 0.6 M HF and 0.2 M NaF? The acid dissociation constant, Ka, for HF is 6.8 × 10^{-4}.

• A. 2.87
• B. 4.17
• C. 5.87
• D. 3.87

Answer: (D)

Verified step by step guidance

1. Identify the components of the buffer solution: HF is the weak acid and NaF provides the conjugate base F⁻. The concentrations are [HF] = 0.6 M and [F⁻] = 0.2 M.
2. Calculate the pKa from the given Ka using the formula: \(\mathrm{p}K_a = -\log_{10}(K_a)\). Substitute \(K_a = 6.8 \times 10^{-4}\) to find pKa.
3. Write down the Henderson-Hasselbalch equation: \(\mathrm{pH} = \mathrm{p}K_a + \log_{10}\left( \frac{[\text{base}]}{[\text{acid}]} \right)\), where the base is F⁻ and the acid is HF.
4. Substitute the values into the Henderson-Hasselbalch equation: \(\mathrm{pH} = \mathrm{p}K_a + \log_{10}\left( \frac{0.2}{0.6} \right)\).
5. Calculate the logarithmic term and add it to the pKa to find the pH of the buffer solution.