Multiple Choice
An 8.36 g sample of NH4Cl was added to 26.0 mL of 1.00 M NaOH and the resulting solution diluted to 0.100 L. What is the pH of this buffer solution?
17. Acid and Base Equilibrium
pH of Weak Acids
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What is the pH of a solution formed by mixing 140.0 mL of 0.25 M HF with 225.0 mL of 0.31 M NaF, given that the Ka of hydrofluoric acid (HF) is 6.8 x 10^-4?
A
3.46
B
4.75
C
5.20
D
3.14
Verified step by step guidance1
Calculate the moles of HF and NaF in the solution. Use the formula: \( \text{moles} = \text{concentration} \times \text{volume} \). For HF: \( 0.25 \text{ M} \times 0.140 \text{ L} \). For NaF: \( 0.31 \text{ M} \times 0.225 \text{ L} \).
Determine the total volume of the solution by adding the volumes of HF and NaF: \( 140.0 \text{ mL} + 225.0 \text{ mL} \). Convert this total volume to liters.
Calculate the concentrations of HF and NaF in the mixed solution using the moles calculated in step 1 and the total volume from step 2: \( \text{concentration} = \frac{\text{moles}}{\text{total volume}} \).
Use the Henderson-Hasselbalch equation to find the pH of the buffer solution: \( \text{pH} = \text{pKa} + \log \left( \frac{[\text{A}^-]}{[\text{HA}]} \right) \). Here, \( \text{pKa} = -\log(\text{Ka}) \) and \([\text{A}^-]\) is the concentration of NaF, \([\text{HA}]\) is the concentration of HF.
Substitute the values of \( \text{pKa} \), \([\text{A}^-]\), and \([\text{HA}]\) into the Henderson-Hasselbalch equation to calculate the pH.
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