AP Chemistry · Unit 8: Acids and Bases
8.5 Acid-Base Titrations
In short
You must understand titration curves (pH vs. volume of titrant) for mono- and polyprotic acids and bases. You need to identify equivalence points (where moles of titrant equal moles of analyte) and half-equivalence points (where pH = pKa and [HA] = [A-]).
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What else do you need to know about Acid-Base Titrations?
You must be able to determine if the equivalence point pH is neutral, acidic, or basic based on the hydrolysis of the conjugate species. For polyprotic acids, you must be able to identify the number of acidic protons, the pKa for each, and qualitatively reason about species concentrations at any point. EXCLUSION: Computation of the concentration of each species present in the titration curve for polyprotic acids will not be assessed on the AP Exam (though qualitative reasoning regarding large vs. small concentrations is expected).
Can you do these?
- I can use a titration curve plotting pH against the volume of titrant added to summarize results from a titration.
- I can use the relationship at the equivalence point (moles of titrant added equals moles of analyte originally present) to obtain the concentration of the analyte for monoprotic acids or bases.
- I can determine the pKa of a weak acid or base from the pH at the half-equivalence point in a titration, where the conjugate acid and base have equal concentrations.
- I can determine the pH at the equivalence point based on the major species in solution, recognizing that strong acid-strong base titrations are neutral, while weak acid or weak base titrations produce basic or acidic solutions respectively.
- I can use titration curves for polyprotic acids to determine the number of acidic protons, identify the major species present at any point, and find the pKa associated with each proton.
How is Acid-Base Titrations tested on the exam?
Exam questions frequently require you to identify information presented graphically (Skill 5.D). Many students struggle to use titration curves to identify equivalence and half-equivalence points, or to estimate concentration/pH at specific points. Common pitfalls include confusing half-equivalence, equivalence, and endpoint, struggling with unit conversions, and failing to understand what different types of titration curves represent. The half-equivalence point is a helpful reference to visualize acid/conjugate base ratios.
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Acid-Base Titrations: common questions
What do you need to know about Acid-Base Titrations for AP Chemistry?
You must understand titration curves (pH vs. volume of titrant) for mono- and polyprotic acids and bases. You need to identify equivalence points (where moles of titrant equal moles of analyte) and half-equivalence points (where pH = pKa and [HA] = [A-]).
How is Acid-Base Titrations tested on the AP Chemistry exam?
Exam questions frequently require you to identify information presented graphically (Skill 5.D). Many students struggle to use titration curves to identify equivalence and half-equivalence points, or to estimate concentration/pH at specific points.
How do I know I have mastered Acid-Base Titrations?
Check you can do each of these: use a titration curve plotting pH against the volume of titrant added to summarize results from a titration; use the relationship at the equivalence point (moles of titrant added equals moles of analyte originally present) to obtain the concentration of the analyte for monoprotic acids or bases; determine the pKa of a weak acid or base from the pH at the half-equivalence point in a titration, where the conjugate acid and base have equal concentrations; determine the pH at the equivalence point based on the major species in solution, recognizing that strong acid-strong base titrations are neutral, while weak acid or weak base titrations produce basic or acidic solutions respectively; use titration curves for polyprotic acids to determine the number of acidic protons, identify the major species present at any point, and find the pKa associated with each proton.
Where does Acid-Base Titrations fit in AP Chemistry?
Acid-Base Titrations is topic 8.5 in Unit 8: Acids and Bases of AP Chemistry.
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