Multiple Choice
A 1.00 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 100.0 mL of 1.00 M HCl. The Ka for HF is 3.5 × 10⁻⁴.
18. Aqueous Equilibrium
Intro to Buffers
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A buffer solution is made by dissolving 0.780 moles of NaClO in 1.00 L of 0.560 M HClO. What is the pH of the solution after 0.140 moles of NaOH is added? The Ka of HClO is 2.9 × 10^-8.
A
7.54
B
6.80
C
7.00
D
8.20
Verified step by step guidance1
Identify the components of the buffer solution: NaClO (sodium hypochlorite) is the salt of the weak acid HClO (hypochlorous acid). The buffer solution consists of the weak acid HClO and its conjugate base ClO⁻.
Calculate the initial concentrations of HClO and ClO⁻ in the buffer solution. Since the volume of the solution is 1.00 L, the concentration of HClO is 0.560 M, and the concentration of ClO⁻ is 0.780 M.
Determine the effect of adding NaOH to the buffer. NaOH is a strong base and will react with the weak acid HClO: \( \text{HClO} + \text{OH}^- \rightarrow \text{ClO}^- + \text{H}_2\text{O} \). Calculate the moles of HClO and ClO⁻ after the reaction with 0.140 moles of NaOH.
Use the Henderson-Hasselbalch equation to find the pH of the buffer solution: \( \text{pH} = \text{pK}_a + \log \left( \frac{[\text{ClO}^-]}{[\text{HClO}]} \right) \). Calculate \( \text{pK}_a \) from \( \text{K}_a \) using \( \text{pK}_a = -\log(\text{K}_a) \).
Substitute the concentrations of ClO⁻ and HClO after the reaction into the Henderson-Hasselbalch equation to calculate the pH of the solution.
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