Textbook Question
Determine whether or not the mixing of each pair of solutions results in a buffer. b. 125.0 mL of 0.14 M HF; 195.0 mL of 0.070 M NaOH
18. Aqueous Equilibrium
Intro to Buffers
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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 0.150 moles of solid NaOH. Assume no volume change upon the addition of base. The Ka for HF is 3.5 × 10^-4.
A
3.74
B
3.46
C
4.06
D
2.85
Verified step by step guidance1
Identify the components of the buffer solution: HF (weak acid) and NaF (its conjugate base). The initial concentrations are both 0.250 M.
Calculate the moles of HF and F⁻ in the buffer. Since the volume is 1.00 L, the moles of HF and F⁻ are both 0.250 moles.
Determine the moles of NaOH added: 0.150 moles. NaOH will react with HF to form water and F⁻, increasing the concentration of F⁻ and decreasing the concentration of HF.
Calculate the new moles of HF and F⁻ after the reaction with NaOH. Subtract the moles of NaOH from the moles of HF and add the moles of NaOH to the moles of F⁻.
Use the Henderson-Hasselbalch equation to find the pH: \( \text{pH} = \text{pK}_a + \log \left( \frac{[\text{F}^-]}{[\text{HF}]} \right) \). Calculate \( \text{pK}_a \) from \( K_a \) and substitute the concentrations of F⁻ and HF into the equation to find the pH.
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