Chemistry · May / June 2025 · Paper 11 · Question 20

The pH of dilute ethanoic acid is measured. The equation for the partial dissociation of ethanoic acid is shown. CH3COOH(aq) ⇌ CH3COO–(aq) + H+(aq) Aqueous sodium ethanoate, CH3COONa, is added to the dilute ethanoic acid and the pH is measured again. What is the initial pH of the dilute ethanoic acid and how does it change after the addition of the aqueous sodium ethanoate?

1. A3–4, increases
2. B3–4, decreases
3. C8–9, increases
4. D8–9, decreases

As printed in the paper