Multiple Choice
What is the pH of a 0.1 M solution of HF, given that the acid dissociation constant (Ka) for hydrofluoric acid is 7.1 x 10^-4?
17. Acid and Base Equilibrium
pH of Weak Acids
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What is the pH of a buffer solution that is 0.185 M in lactic acid and 0.132 M in sodium lactate? The Ka of lactic acid is 1.4 × 10^-4.
A
3.85
B
5.10
C
2.95
D
4.25
Verified step by step guidance1
Identify the components of the buffer solution: lactic acid (CH₃CH(OH)COOH) and its conjugate base, sodium lactate (CH₃CH(OH)COONa).
Use the Henderson-Hasselbalch equation to calculate the pH of the buffer solution: \( \text{pH} = \text{pKa} + \log \left( \frac{[\text{A}^-]}{[\text{HA}]} \right) \), where [A⁻] is the concentration of the conjugate base and [HA] is the concentration of the acid.
Calculate the pKa from the given Ka of lactic acid: \( \text{pKa} = -\log(\text{Ka}) \). Substitute \( \text{Ka} = 1.4 \times 10^{-4} \) into the equation to find pKa.
Substitute the concentrations of sodium lactate (0.132 M) and lactic acid (0.185 M) into the Henderson-Hasselbalch equation: \( \text{pH} = \text{pKa} + \log \left( \frac{0.132}{0.185} \right) \).
Solve the equation to find the pH of the buffer solution.
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