OCR A-Level Chemistry Synthesis and analytical techniques (02), June 2024: Question 7

1 mark · Easy difficulty · Multiple Choice

Identify the valid scientific reason for global warming from the given statements about greenhouse gases and radiation.

Practise this question

Question

Multiple choice question 7 asking which statement gives a valid scientific reason for global warming. Option A: Infrared radiation causes bonds in CH4 molecules to vibrate more. Option B: Infrared radiation causes O2 molecules to vibrate more. Option C: Ultraviolet radiation causes bonds in CO2 to vibrate more. Option D: Ultraviolet radiation causes bonds in CFC molecules to break.
Question text

7 Which statement gives a valid scientific reason for global warming?

A Infrared radiation causes bonds in CH4 molecules to vibrate more.

B Infrared radiation causes O2 molecules to vibrate more.

C Ultraviolet radiation causes bonds in CO2 to vibrate more.

D Ultraviolet radiation causes bonds in CFC molecules to break.

Your answer

[1]

Mark scheme

Show the mark scheme Mark scheme indicating the correct answer is A for question 7, worth 1 mark.

7 A 1

How to answer it

Global Warming Mechanisms & Greenhouse Gases

What this question tests

This question assesses your understanding of atmospheric chemistry, specifically the interaction between electromagnetic radiation and greenhouse gas molecules (like CH₄ and CO₂ ). It tests your ability to link molecular vibrations to infrared absorption and distinguish between global warming processes and ozone depletion mechanisms.

Question 7 Breakdown

Multiple Choice Question (1 Mark)

✅ Correct Answer: A

Infrared radiation causes bonds in CH₄ molecules to vibrate more.

Methane ( CH₄ ) is a greenhouse gas. Its polar bonds absorb infrared radiation emitted from the Earth's surface, causing the covalent bonds to bend and stretch (vibrate more intensely), trapping thermal energy in the atmosphere.

💡 Key Knowledge

  • Greenhouse Gases: Molecules like H₂O , CO₂ , and CH₄ absorb IR radiation because their overall dipole moment changes when their bonds vibrate.
  • Radiation Type: Greenhouse gases interact with Infrared (IR) radiation, not Ultraviolet (UV) radiation.
  • Homonuclear Diatomics: Molecules like O₂ and N₂ do not absorb IR radiation because they lack a dipole change during vibration.

🧠 Exam Technique

Eliminate distractors systematically by checking two criteria for each statement:

  1. Does the stated radiation type match the physical process? (IR for greenhouse warming; UV for bond breaking/ozone).
  2. Is the molecule a greenhouse gas capable of absorbing IR?

❌ Common Errors

  • Confusing UV and IR: Students often mix up global warming (IR radiation trapped by greenhouse gases) with ozone depletion (UV radiation breaking bonds in CFCs or ozone).
  • Assuming Diatomics Absorb IR: Incorrectly selecting option B because students forget that O₂ is not a greenhouse gas.
Mark Scheme Allocation: 1 mark for selecting A. No other alternative is accepted.

Topics

Module 6: Organic chemistry and analysis · 6.3 Analysis

Question and mark scheme from the OCR A-Level Chemistry examination, Synthesis and analytical techniques (02), June 2024. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.