OCR A-Level Chemistry AS Breadth in chemistry (01), June 2019: Question 19

1 mark · Medium difficulty · Multiple Choice

Identify the incorrect statement about infrared radiation among four given statements involving molecular vibrations, greenhouse gases, air pollution monitoring, and CFC photolysis.

Practise this question

Question

Multiple choice question 19 asking which statement about infrared radiation is not correct, with options A to D covering IR vibrations, global warming, monitoring air pollution, and the action of IR radiation on CFCs in the upper atmosphere. A box for the answer and the mark allocation of [1] are shown at the bottom.
Question text

19 Which statement about infrared radiation is not correct?

A The energy from IR radiation causes some covalent bonds to vibrate more.

B Absorption of IR radiation by some atmospheric gases is linked by some scientists to global

warming.

C IR radiation is used to monitor gases causing air pollution.

D The action of IR radiation on CFCs in the upper atmosphere leads to the formation of chlorine

radicals.

Your answer [1]

Mark scheme

Show the mark scheme Mark scheme for question 19 indicating the correct answer is D, worth 1 mark under assessment objective AO1.1.

19 D 1 AO1.1

How to answer it

Infrared Radiation & Atmospheric Chemistry

What this question tests

This question assesses your knowledge of electromagnetic radiation interactions with matter, specifically how infrared (IR) radiation affects covalent bonds, its role in greenhouse gases and global warming, its analytical applications in monitoring air pollution, and how higher-energy ultraviolet (UV) radiation—not IR radiation—causes photodissociation of CFCs in the upper atmosphere.

Question 19: Evaluating Statements About Infrared Radiation

Exam Part Assessment (Multiple Choice - 1 Mark)

✅ Correct Answer: D

Statement D is the not correct statement. Therefore, D is the correct choice to select.

Why? Infrared radiation does not have enough photon energy to break covalent bonds (photodissociation). It is ultraviolet (UV) radiation in the upper atmosphere that provides the high energy required to break C-Cl bonds in CFCs, producing chlorine radicals.

💡 Key Knowledge

  • IR Vibrations (A): Absorption of IR radiation causes covalent bonds to bend and stretch more (vibrate).
  • Global Warming (B): Greenhouse gases like CO₂, CH₄, and H₂O absorb IR radiation emitted by the Earth's surface and trap heat.
  • Air Pollution (C): IR spectroscopy and remote sensing are actively used to monitor atmospheric pollutants (e.g., CO and NO).
  • CFC Breakdown (D): UV light (shorter wavelength, higher frequency and energy) breaks C-Cl bonds homolytically to form radicals. IR cannot do this.

🧠 Exam Technique

When facing a "not correct" multiple-choice question, scan all options systematically and mentally check them off against your core specification knowledge. Do not stop at the first plausible-sounding statement you read!

❌ Common Errors

Students frequently confuse the roles of UV radiation and IR radiation in the atmosphere. Remember: UV causes bond fission and radical formation; IR causes greenhouse warming and molecular bond vibration.

Mark Scheme Allocation: 1 mark awarded for selecting D (AO1.1: Demonstrate knowledge and understanding of scientific ideas).

Topics

Module 4: Core organic chemistry · Module 6: Organic chemistry and analysis · 4.2 Alcohols, haloalkanes and analysis · 6.3 Analysis

Question and mark scheme from the OCR A-Level Chemistry examination, AS Breadth in chemistry (01), June 2019. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.