OCR A-Level Chemistry AS Breadth in chemistry (01), November 2021: Question 19

1 mark · Easy difficulty · Multiple Choice

Identify the correct statement regarding the absorption of radiation from four given options relating to infrared and ultraviolet radiation.

Practise this question

Question

Multiple choice question 19 asking which statement about absorption of radiation is correct, with four options A to D. Option A states absorption of IR radiation can break covalent bonds forming radicals, B states it causes covalent bonds to vibrate more, C states UV radiation causes global warming, and D states UV radiation is used in modern breathalysers.
Question text

19 Which statement about absorption of radiation is correct?

A Absorption of IR radiation can break covalent bonds, forming radicals.

B Absorption of IR radiation causes covalent bonds to vibrate more.

C Absorption of UV radiation is a major cause of global warming and climate change.

D Absorption of UV radiation is used in modern breathalysers to measure ethanol in the

breath.

Your answer [1]

Mark scheme

Show the mark scheme Mark scheme for question 19 indicating the correct answer is B, worth 1 mark.

19 B 1 AO1.1

How to answer it

Absorption of Radiation

What this question tests

This question assesses your core knowledge of electromagnetic radiation (specifically Infrared and Ultraviolet) and how its interaction with chemical bonds causes physical and environmental effects, including vibrational spectroscopy and greenhouse gas mechanisms.

Question 19 Analysis

Exam Breakdown

✅ Correct Answer: B

Absorption of IR radiation causes covalent bonds to bend and stretch more (vibrate).

💡 Key Knowledge

  • IR Radiation: Has lower energy than UV/Visible light. It does not break bonds; instead, it causes covalent bonds to increase their rate of vibration (stretching and bending).
  • Greenhouse Effect: IR absorption by atmospheric gases (like CO₂, H₂O, and CH₄) contributes to global warming.
  • UV Radiation: Has higher energy and can cause bond fission, generating radicals (photodissociation).
  • Breathalisers: Modern infrared breathalisers use IR radiation (not UV) to measure ethanol levels.

🧠 Exam Technique

Read through each statement carefully and eliminate distractors using core definitions. Link energy levels directly to molecular outcomes: High energy (UV) = bond breaking/electronic transitions; Medium/Low energy (IR) = molecular vibrations.

❌ Common Errors

  • Confusing the effects of UV and IR radiation (assuming IR breaks bonds like UV does in ozone depletion or radical substitution).
  • Mixing up which type of radiation is used in breathalisers (IR spectroscopy is used for functional group and breath alcohol analysis).
  • Attributing global warming to UV absorption instead of IR absorption (greenhouse gases absorb outgoing IR radiation emitted from the Earth's surface).
Mark Allocation: [1] mark available (AO1.1 - Demonstrating knowledge and understanding of scientific ideas).

Topics

Module 6: Organic chemistry and analysis · 6.3 Analysis

Question and mark scheme from the OCR A-Level Chemistry examination, AS Breadth in chemistry (01), November 2021. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.