Multiple Choice
What is the ratio of of [CH 3COO-] / [CH3COOH] in an acetate buffer at pH = 7? pK a = 4.76.
2. Water
Henderson Hasselbalch Equation
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What is the pH of a mixture of 0.02 M sodium formate & 0.0025 M formic acid (pK a = 3.75)
A
pH = 4.21
B
pH = 1.27
C
pH = 4.65
D
pH = 9.34
Verified step by step guidance1
Identify the components of the buffer system: sodium formate (the salt, providing the conjugate base) and formic acid (the weak acid).
Use the Henderson-Hasselbalch equation to calculate the pH of the buffer solution: \( \text{pH} = \text{pK}_a + \log \left( \frac{[\text{A}^-]}{[\text{HA}]} \right) \), where \([\text{A}^-]\) is the concentration of the conjugate base (sodium formate) and \([\text{HA}]\) is the concentration of the weak acid (formic acid).
Substitute the given values into the equation: \( \text{pH} = 3.75 + \log \left( \frac{0.02}{0.0025} \right) \).
Calculate the ratio \( \frac{0.02}{0.0025} \) to find the concentration ratio of the conjugate base to the weak acid.
Use the calculated ratio in the Henderson-Hasselbalch equation to determine the pH of the buffer solution.
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