Multiple Choice
A 270.0 mL buffer solution initially contains 3.0×10⁻² M of HCHO₂ and 3.0×10⁻² M of NaCHO₂. To adjust the buffer pH to 4.10, should you add NaOH or HCl to the buffer mixture?
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18. Aqueous Equilibrium
Henderson-Hasselbalch Equation
Multiple Choice
A buffer solution has 0.625 M HCN and 0.575 M CN⁻. If 0.030 mol of HCl is added to 400. mL of the buffer solution, what is the pH after the addition? The pKa of hydrocyanic acid is 9.23.
A
9.23
B
9.15
C
9.30
D
9.05
Verified step by step guidance1
Identify the initial concentrations of the buffer components: 0.625 M HCN and 0.575 M CN⁻ in 400 mL of solution.
Calculate the moles of HCN and CN⁻ initially present using the formula: \( \text{moles} = \text{concentration} \times \text{volume} \).
Determine the moles of HCl added: 0.030 mol, and recognize that HCl will react with CN⁻ to form HCN.
Calculate the change in moles of CN⁻ and HCN after the reaction with HCl, considering the stoichiometry of the reaction: \( \text{CN}^- + \text{HCl} \rightarrow \text{HCN} + \text{Cl}^- \).
Use the Henderson-Hasselbalch equation to find the new pH: \( \text{pH} = \text{pKa} + \log \left( \frac{[\text{base}]}{[\text{acid}]} \right) \), substituting the adjusted concentrations of CN⁻ and HCN.
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