A-Level AQA Chemistry Halogenoalkanes: This question is about the ozone

Question

This question is about the ozone layer in the upper atmosphere.

1. State why the ozone layer is beneficial for living organisms.

The ozone layer absorbs harmful ultraviolet (UV) radiation from the sun, which prevents skin cancer and protects ecosystems.

2. State how chlorofluorocarbons (CFCs) form chlorine atoms in the upper atmosphere.

Chlorofluorocarbons undergo photodissociation, wherein UV light breaks the carbon-chlorine bonds, resulting in the release of chlorine atoms.

3. Give equations to show how chlorine atoms catalyse the decomposition of ozone.

The reactions can be represented as follows:

$$Cl 	ext{ + } O_3 ightarrow ClO 	ext{ + } O_2$$  
$$ClO 	ext{ + } O ightarrow Cl 	ext{ + } O_2$$

This demonstrates that a single chlorine atom can catalyse the reaction multiple times, leading to ozone depletion.

4. Hydrochlorofluorocarbons (HCFCs) have been used in place of CFCs. In the mechanism to make an HCFC from a fluoroalkane, two incomplete steps are shown. Complete each step in the mechanism.

$$	ext{Cl}^* 	ext{ + } CHF_2 ightarrow 	ext{ } CHFC 	ext{ + } HCl$$

$$	ext{Cl}^* 	ext{ + } CCl_2 ightarrow 	ext{ } CHFCl 	ext{ + } Cl^*$$

Give the name of the type of step shown by both these equations.

- Type of step: Propagation

This question is about the ozone layer in the upper atmosphere - AQA - A-Level Chemistry - Question 9 - 2021 - Paper 2

Worked Solution & Example Answer:This question is about the ozone layer in the upper atmosphere - AQA - A-Level Chemistry - Question 9 - 2021 - Paper 2

State why the ozone layer is beneficial for living organisms.

State how chlorofluorocarbons (CFCs) form chlorine atoms in the upper atmosphere.

Give equations to show how chlorine atoms catalyse the decomposition of ozone.

Complete each step in the mechanism.

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