Multiple Choice
Which of the following compounds would make for the best buffer at pH 8?
2. Water
Buffer Solution
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A. What volume of 0.1 M acetic acid (pK a = 4.8) is required to make 1 liter of 0.1 M buffer solution at pH = 5.8?
B. What volume of 0.1 M sodium acetate is required to make the same buffer solution?
a. 193 mL
b. 91 mL
c. 909 mL
d. 807 mL
A
193 mL
B
91 mL
C
909 mL
D
807 mL
Verified step by step guidance1
Understand that the problem involves preparing a buffer solution using acetic acid and sodium acetate. The Henderson-Hasselbalch equation will be used to find the required volumes.
The Henderson-Hasselbalch equation is: \( \text{pH} = \text{pK}_a + \log \left( \frac{[\text{A}^-]}{[\text{HA}]} \right) \), where [A^-] is the concentration of the acetate ion and [HA] is the concentration of acetic acid.
Rearrange the equation to solve for the ratio \( \frac{[\text{A}^-]}{[\text{HA}]} \): \( \frac{[\text{A}^-]}{[\text{HA}]} = 10^{(\text{pH} - \text{pK}_a)} \). Substitute the given values: pH = 5.8 and pK_a = 4.8.
Calculate the ratio \( \frac{[\text{A}^-]}{[\text{HA}]} \) using the values from the previous step. This will give you the ratio of sodium acetate to acetic acid needed in the buffer.
Use the ratio and the total volume of the buffer (1 liter) to set up equations for the volumes of acetic acid and sodium acetate. Solve these equations to find the required volumes of each component to achieve the desired buffer concentration and pH.
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