Multiple Choice
Which of the following statements about H3PO4 is FALSE?
17. Acid and Base Equilibrium
Acids Introduction
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A 370.0 mL buffer solution is 0.150 M in HF and 0.150 M in NaF. What mass of NaOH can this buffer neutralize before the pH rises above 4.00? (Ka(HF) = 3.5 × 10⁻⁴.)
A
0.75 g
B
0.42 g
C
0.68 g
D
0.56 g
Verified step by step guidance1
Identify the components of the buffer solution: HF (weak acid) and NaF (its conjugate base). The buffer capacity is determined by the concentrations of these components.
Use the Henderson-Hasselbalch equation to find the pH of the buffer solution: \( \text{pH} = \text{pKa} + \log \left( \frac{[\text{A}^-]}{[\text{HA}]} \right) \). Calculate \( \text{pKa} \) from \( \text{Ka} \) using \( \text{pKa} = -\log(\text{Ka}) \).
Determine the change in the buffer system when NaOH is added. NaOH will react with HF to form water and NaF, increasing the concentration of \([\text{A}^-]\) and decreasing \([\text{HA}]\).
Set up the equation for the buffer system after adding NaOH: \( \text{pH} = \text{pKa} + \log \left( \frac{[\text{A}^-] + x}{[\text{HA}] - x} \right) \), where \( x \) is the moles of NaOH added. Solve for \( x \) when \( \text{pH} = 4.00 \).
Convert the moles of NaOH (\( x \)) to mass using the molar mass of NaOH. This will give you the mass of NaOH that can be added before the pH exceeds 4.00.
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