AP®︎ Chemistry: Topic 8.9 Flashcards

Master key terms and definitions for Topic 8.9 of AP Chemistry – Henderson-Hasselbalch Equation to help you prep for quizzes and the AP exam.

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Term

Henderson-Hasselbalch Equation

Definition

pH = pKa + log([A−]/[HA]) for a buffer made from a weak acid and conjugate base.

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Henderson-Hasselbalch Equation
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pH = pKa + log([A−]/[HA]) for a buffer made from a weak acid and conjugate base.

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pKa and Acid Strength
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pKa equals -log(Ka); lower values indicate stronger acids and higher values indicate weaker acids.

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Conjugate Acid-Base Pair in a Buffer
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A weak acid HA and its conjugate base A−, or a weak base and conjugate acid.

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Buffer Resistance to Small pH Changes
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Small added acid or base changes [A−]/[HA] only slightly, so pH changes very little.

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Using Henderson-Hasselbalch After Partial Neutralization
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Use stoichiometry first to find remaining weak acid and formed conjugate base, then apply the equation.

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Using Moles or Millimoles in Buffer Ratios
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If both species are in the same total volume, their mole ratio equals their concentration ratio.

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Buffer pH and Equal Concentrations
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Buffer pH depends on pKa and [A−]/[HA]; when equal, pH equals pKa.

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Strongest Buffer When Concentrations Are Equal
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A buffer is most effective when conjugate acid and base concentrations are equal.

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