AP®︎ Chemistry: Topic 8.7 Flashcards

Master key terms and definitions for Topic 8.7 of AP Chemistry – pH and pKa to help you prep for quizzes and the AP exam.

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Term

p Notation

Definition

A quantity written as the negative base-10 logarithm of a value, such as pH or pKa.

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p Notation
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A quantity written as the negative base-10 logarithm of a value, such as pH or pKa.

8.7.A
pKa and Acid Strength
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Lower values mean larger Ka and a stronger acid on a logarithmic scale.

8.7.A
pKa and pKb Relationship
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For a conjugate acid-base pair in water at 25°C, their values add to 14.

8.7.A
Henderson-Hasselbalch Equation
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pH = pKa + log([A−]/[HA]), relating solution pH to conjugate base-to-acid ratio.

8.7.A8.7.A.1
pH vs. pKa Rule
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If pH < pKa, HA predominates; if pH > pKa, A− predominates; if equal, concentrations match.

8.7.A8.7.A.1
Predominant Form of a Weak Base
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Compare solution pH to the pKa of its conjugate acid to predict protonated versus unprotonated form.

8.7.A8.7.A.1
Effective Buffer Range
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A buffer works best when solution pH is within about 1 unit of the pKa.

8.7.A
Acid-Base Indicators
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Weak acids or bases whose protonated and deprotonated forms have different colors or properties.

8.7.A8.7.A.2
Indicator Transition Range
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Color change occurs mainly over about pKa ± 1, where both indicator forms are present.

8.7.A8.7.A.2
Choosing an Indicator for a Titration
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Select one whose pKa or transition range is close to the equivalence-point pH.

8.7.A8.7.A.3
pH = pKa Condition
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When conjugate acid and base concentrations are equal, neither form predominates and buffering is strongest.

8.7.A8.7.A.1