DP Chemistry (last assessment 2024)

Question 20N.2.hl.TZ0.1e(iii)

e(iii).

[Maximum mark: 2]

20N.2.hl.TZ0.1e(iii)

Chlorine undergoes many reactions.

${CCl}_{2} F_{2}$ is a common chlorofluorocarbon, $CFC$ .

(e(iii))

$CFC$ s produce chlorine radicals. Write two successive propagation steps to show how chlorine radicals catalyse the depletion of ozone.

[2]

Markscheme

$O_{3} + Cl \cdot \to O 2 + ClO \cdot$ ✔

$ClO \cdot + O \cdot \to O_{2} + Cl \cdot$
OR
$ClO \cdot + O_{3} \to Cl \cdot + 2 O_{2}$ ✔

Penalize missing/incorrect radical dot (∙) once only.

Examiners report

Few could construct the propagation equations showing how CFCs affect ozone, and many lost marks by failing to identify ClO· as a radical.

Syllabus sections