Multiple Choice
Consider a buffer solution that is 0.50 M in NH3 and 0.20 M in NH4Cl. For ammonia, pKb = 4.75. Calculate the pH of 1.0 L of the solution upon the addition of 30.0 mL of 1.0 M HCl to the original buffer solution.
18. Aqueous Equilibrium
Henderson-Hasselbalch Equation
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What is the pH of a buffer system that has 0.25 M HCN and 0.38 M CN⁻, given that the pKa of hydrocyanic acid is 9.23?
A
9.03
B
8.83
C
9.43
D
9.23
Verified step by step guidance1
Identify the components of the buffer system: HCN (weak acid) and CN⁻ (conjugate base).
Use the Henderson-Hasselbalch equation to calculate the pH of the buffer: \( \text{pH} = \text{pKa} + \log \left( \frac{[\text{A}^-]}{[\text{HA}]} \right) \), where \([\text{A}^-]\) is the concentration of the conjugate base (CN⁻) and \([\text{HA}]\) is the concentration of the weak acid (HCN).
Substitute the given values into the equation: \( \text{pH} = 9.23 + \log \left( \frac{0.38}{0.25} \right) \).
Calculate the ratio \( \frac{0.38}{0.25} \) to find the value to be used in the logarithm.
Add the result of the logarithm to the pKa value (9.23) to find the pH of the buffer system.
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