OCR A-Level Chemistry Synthesis and analytical techniques (02), June 2022: Question 2
1 mark · Easy difficulty · Multiple Choice
Identify the correct statement regarding the absorption and effects of infrared and ultraviolet radiation.
Practise this questionQuestion
Question text
2 Which statement about absorption of radiation is correct?
A Infrared radiation can result in the breakdown of the ozone layer.
B Ultraviolet radiation can cause some polymers to photodegrade to benefit the environment.
C Ultraviolet radiation is linked to global warming.
D Ultraviolet radiation is used in modern breathalysers to measure ethanol in the breath.
Your answer
[1]
Mark scheme
Show the mark scheme
2 B 1 AO1.1
How to answer it
Absorption of Radiation: UV vs Infrared
What this question tests
This question tests recall and understanding of the distinct roles and consequences of ultraviolet (UV) and infrared (IR) radiation, including photodegradable polymers, the greenhouse effect, atmospheric ozone depletion, and analytical instrumentation (breathalysers).
Question 2 Breakdown
Multiple Choice • 1 Mark • AO1.1
✅ Correct Answer: B
Ultraviolet radiation can cause some polymers to photodegrade to benefit the environment.
💡 Key Knowledge
- Photodegradable polymers: Contain light-sensitive bonds (such as carbonyl C=O bonds) that absorb high-energy UV radiation. This breaks covalent bonds within the polymer backbone, causing it to break down into non-harmful or smaller fragments.
- Ozone breakdown: Initiated by high-energy UV radiation breaking C–Cl bonds in CFCs via homolytic fission, forming chlorine radicals (Cl•), NOT infrared radiation.
- Global warming: Driven by bonds in greenhouse gases (C=O in CO₂, C–H in CH₄, O–H in H₂O) absorbing infrared (IR) radiation and vibrating more vigorously.
- Breathalysers: Modern breathalysers use infrared spectroscopy to detect the absorption band of the C–H bond (around 2850–3000 cm⁻¹) or C–O bond in ethanol.
🧠 Exam Technique: Elimination Strategy
- Statement A: Mentions IR for ozone breakdown → False. IR radiation only excites molecular vibrations; it does not have enough energy to break bonds in the stratosphere.
- Statement B: Mentions UV for polymer photodegradation → True. Explicitly covered in polymer disposal topics.
- Statement C: Links UV to global warming → False. Global warming is caused by IR absorption.
- Statement D: Links UV to breathalysers → False. Breathalysers use IR spectroscopy.
Radiation Type Comparison Matrix
| Option | Topic | Stated Radiation | Correct Radiation | Status |
|---|---|---|---|---|
| A | Ozone depletion | Infrared | Ultraviolet (UV) | Incorrect |
| B | Polymer photodegradation | Ultraviolet | Ultraviolet (UV) | Correct |
| C | Global warming | Ultraviolet | Infrared (IR) | Incorrect |
| D | Breathalysers | Ultraviolet | Infrared (IR) | Incorrect |
❌ Common Errors & Misconceptions
- Confusing the Greenhouse Effect with Ozone Depletion: A very common confusion. Remember:
• Ozone layer absorbs harmful UV radiation.
• Greenhouse gases absorb re-emitted IR radiation. - Breathalyser Radiation Type: Students frequently forget that breathalysers are a practical application of IR spectroscopy, directly related to organic analysis in OCR Module 4.
- Energy Scales: Remember that UV photons have much higher frequency and energy ( E = hf ) than IR photons. UV can break chemical bonds (photolysis); IR only excites bond stretching and bending.
Topics
Module 4: Core organic chemistry · 4.1 Basic concepts and hydrocarbons · 4.2 Alcohols, haloalkanes and analysis
Question and mark scheme from the OCR A-Level Chemistry examination, Synthesis and analytical techniques (02), June 2022. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.