Edexcel IAL Chemistry 14.15 Draw and interpret titration curves

Use starting pH, final pH, vertical sections and equivalence volumes to infer acid and base strength, sketch missing sections or read salt pH from a curve.

Exam points

Match curve shape, starting pH and final pH to the acid-base strength combination.
Sketch weak-acid or diprotic titration curves with correct equivalence volumes.
Use vertical sections and midpoint data to interpret salts, endpoints or pKa values.

[Maximum number: 3]

The number of moles of propanoic acid in a solution may be determined by titration with aqueous sodium hydroxide.

Sketch the titration curve showing the change in pH when $50 \mathrm{~cm}^{3}$ of $0.500 \mathrm{~mol} \mathrm{dm}^{-3}$ sodium hydroxide is added to $25.0 \mathrm{~cm}^{3}$ of propanoic acid of the same concentration, using your answers to (b)(iii) and (c)(i).

Figure for Question 14.15—Draw and interpret titration curves question 1 — Edexcel A-Level Chemistry A2

An answer that makes reference to three of the following points:

- start pH between 2 and 4 and finish at 12-14

- vertical section of at least 3 pH units starting at or above 6 and finishing at or below 11 .

- S-shaped curve with equivalence( vertical section) at $25 \mathrm{~cm}^{3}$

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Example of sketch

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14.15—Draw and interpret titration curves question 1