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Henderson-Hasselbalch Equation quiz #1

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  • What is the pH of a buffer solution containing 0.6 M HF and 0.2 M NaF, given that the Ka of HF is 6.8 × 10⁻⁴?
    First, calculate pKa: pKa = -log(6.8 × 10⁻⁴) ≈ 3.17. Use the Henderson-Hasselbalch equation: pH = pKa + log([F⁻]/[HF]) = 3.17 + log(0.2/0.6) = 3.17 + log(0.333) ≈ 3.17 - 0.48 = 2.69. So, the pH is approximately 2.69.
  • Write the Henderson-Hasselbalch equation for a propanoic acid (C₂H₅COOH) buffer solution.
    The Henderson-Hasselbalch equation for a propanoic acid buffer is: pH = pKa + log([C₂H₅COO⁻]/[C₂H₅COOH]), where [C₂H₅COO⁻] is the concentration of the conjugate base (propanoate ion) and [C₂H₅COOH] is the concentration of the weak acid (propanoic acid).
  • When should you use the pH = pKa + log([conjugate base]/[weak acid]) form of the Henderson-Hasselbalch equation?
    You should use this form when the acid dissociation constant (Ka) is provided for the buffer solution.
  • What do the brackets in the Henderson-Hasselbalch equation represent?
    The brackets can represent either the molarity (concentration) or the number of moles of the buffer components.
  • How does the Henderson-Hasselbalch equation simplify when the concentrations of conjugate base and weak acid are equal?
    The equation simplifies to pH = pKa because log(1) equals 0.
  • What is the most effective pH range for a buffer according to the Henderson-Hasselbalch equation?
    A buffer is most effective within the pH range of pKa ± 1.
  • What happens to the buffer’s ability to resist pH changes outside the effective pH range?
    Outside the pKa ± 1 range, the buffer becomes less effective at resisting sharp changes in pH.
  • How can you use moles instead of molarity in the Henderson-Hasselbalch equation?
    You can substitute moles for molarity in the equation because the ratio remains the same for the calculation.
  • What is the relationship between moles, molarity, and volume in buffer calculations?
    Moles are calculated by multiplying molarity by volume (moles = molarity × liters).
  • Which form of the Henderson-Hasselbalch equation should you use if given the base dissociation constant (Kb)?
    Use pH = pKb + log([conjugate acid]/[weak base]) when Kb is provided.