Infrared spectroscopy
Cambridge A-Level Chemistry (9701) · Unit 22: Analytical techniques · 8 flashcards
Infrared spectroscopy is topic 22.1 in the Cambridge A-Level Chemistry (9701) syllabus , positioned in Unit 22 — Analytical techniques , alongside Mass spectrometry. In one line: Infrared spectroscopy uses the infrared (IR) region of the electromagnetic spectrum. This region lies between the microwave and visible regions.
Marked as A2 Level: examined at A Level in Paper 4 (A Level Structured Questions) and Paper 5 (Planning, Analysis and Evaluation). It is not tested on the AS-only papers (Papers 1, 2 and 3).
The deck below contains 8 flashcards — 5 definitions and 3 key concepts — covering the precise wording mark schemes reward. Use the 5 definition cards to lock down command-word answers (define, state), then move on to the concept and calculation cards to handle explain, describe, calculate and compare questions.
What region of the electromagnetic spectrum is used in infrared spectroscopy
Infrared spectroscopy uses the infrared (IR) region of the electromagnetic spectrum. This region lies between the microwave and visible regions.
What the Cambridge 9701 syllabus says
Official 2025-2027 spec · A2 LevelThese are the exact learning outcomes Cambridge sets for this topic. The candidate is expected to be able to do each of these on the relevant paper.
- analyse an infrared spectrum of a simple molecule to identify functional groups (see the Data section for the functional groups required)
Cambridge syllabus keywords to use in your answers
These are the official Cambridge 9701 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.
Tips to avoid common mistakes in Infrared spectroscopy
- › Read the question stem carefully to distinguish between the 'identity of compound X' and its derivative 'compound Y'.
What region of the electromagnetic spectrum is used in infrared spectroscopy?
Infrared spectroscopy uses the infrared (IR) region of the electromagnetic spectrum. This region lies between the microwave and visible regions.
What property of a molecule causes it to absorb IR radiation?
Molecules absorb IR radiation when the frequency of the radiation matches the vibrational frequency of a bond within the molecule. This causes a change in the amplitude of the vibration.
What is wavenumber, and what are its units?
Wavenumber is the reciprocal of wavelength (1/λ) and is proportional to the frequency of vibration. It is commonly expressed in units of cm⁻¹.
List the characteristic absorption range (wavenumber) for the O-H stretch in alcohols.
The O-H stretch in alcohols typically absorbs in the range of 3200-3600 cm⁻¹. This band is usually broad due to hydrogen bonding.
List the characteristic absorption range (wavenumber) for the C=O stretch in carbonyl compounds.
The C=O stretch in carbonyl compounds (aldehydes, ketones, carboxylic acids, esters) typically absorbs in the range of 1680-1750 cm⁻¹.
List the characteristic absorption range (wavenumber) for the C-H stretch in alkanes.
The C-H stretch in alkanes typically absorbs in the range of 2850-3000 cm⁻¹.
What information can be obtained from the fingerprint region of an IR spectrum?
The fingerprint region (below 1500 cm⁻¹) contains complex vibrational modes that are unique to each molecule. It can be used to identify a specific compound by comparing its IR spectrum to a reference spectrum.
How can IR spectroscopy distinguish between a carboxylic acid and an alcohol?
Both show a broad O-H stretch. However, carboxylic acids exhibit a very broad O-H stretch (2500-3300 cm⁻¹) due to strong hydrogen bonding and also a C=O stretch (1680-1750 cm⁻¹).
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All Chemistry FlashcardsMore topics in Unit 22 — Analytical techniques
Infrared spectroscopy sits alongside these A-Level Chemistry decks in the same syllabus unit. Each uses the same spaced-repetition system, so progress in one informs the next.
Key terms covered in this Infrared spectroscopy deck
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