# Explain why the pH at the equivalence point of a titration of 25.0 cm³ of 0.100 mol dm⁻³ ethanoic acid with 0.100 mol dm⁻³ sodium hydroxide solution is greater than 7 at 25 °C.

> IB DP Chemistry Higher Level (2023 syllabus) — R3.1 Proton transfer reactions · Explain · 4 marks

## Mark scheme (4 marks)

1. At the equivalence point, all the ethanoic acid has been neutralised and the solution contains only sodium ethanoate (CH₃COONa).
2. The ethanoate ion is the conjugate base of a weak acid and acts as a Brønsted–Lowry base, accepting a proton from water.
3. The relevant equilibrium is: CH₃COO⁻(aq) + H₂O(l) ⇌ CH₃COOH(aq) + OH⁻(aq)
4. The production of OH⁻ ions makes the solution basic, so [OH⁻] > [H⁺] and pH > 7.

## Key terms

- [equivalence point](https://www.gradenine.co.uk/glossary/equivalence-point)

## Related

- [Revision notes for IB DP Chemistry Higher Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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