Textbook Question
(b) Calculate the pH of a buffer formed by mixing 85 mL of 0.13 M lactic acid with 95 mL of 0.15 M sodium lactate.
18. Aqueous Equilibrium
Henderson-Hasselbalch Equation
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A buffer consists of 0.120 M HNO2 and 0.150 M NaNO2 at 25 °C. The pKa of HNO2 is 3.40. What is the pH of the buffer?
A
3.52
B
3.28
C
3.60
D
3.40
Verified step by step guidance1
Identify the components of the buffer: HNO2 (weak acid) and NaNO2 (its conjugate base, NO2^-).
Use the Henderson-Hasselbalch equation to find the pH of the buffer: \( \text{pH} = \text{pKa} + \log \left( \frac{[\text{A}^-]}{[\text{HA}]} \right) \), where [A^-] is the concentration of the conjugate base and [HA] is the concentration of the weak acid.
Substitute the given concentrations into the equation: \( [\text{A}^-] = 0.150 \text{ M} \) and \( [\text{HA}] = 0.120 \text{ M} \).
Substitute the given pKa value into the equation: \( \text{pKa} = 3.40 \).
Calculate the pH using the equation: \( \text{pH} = 3.40 + \log \left( \frac{0.150}{0.120} \right) \).
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