DP Chemistry (last assessment 2024)

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Question 19N.2.hl.TZ0.a(iv)

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Date November 2019 Marks available [Maximum mark: 1] Reference code 19N.2.hl.TZ0.a(iv)
Level hl Paper 2 Time zone TZ0
Command term Calculate Question number a(iv) Adapted from N/A
a(iv).
[Maximum mark: 1]
19N.2.hl.TZ0.a(iv)

A molecule of citric acid, C6H8O7, is shown.

The equation for the first dissociation of citric acid in water is

C6H8O7 (aq) + H2O (l) ⇌ C6H7O7− (aq) + H3O+ (aq)

Calculate the standard Gibbs free energy change, ΔGθ, in kJ mol−1, for the first dissociation of citric acid at 298 K, using section 1 of the data booklet.

[1]

Markscheme

«ΔGθ = −RT ln K = −8.31 J K–1 mol–1 × 298 K × ln(5.01 × 10–4) ÷ 1000 =» 18.8 «kJ mol–1» ✔

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