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CAIE A-Level Chemistry AS 22.1 Infrared Spectroscopy Questions

Practise matching infrared absorptions to bonds and functional groups and using missing peaks to reject structures.

Syllabus
2028–2030
Course
Chemistry 9701
Level
AS

Exam points

  • match a significant absorption range to both its bond and the functional group containing it
  • combine several diagnostic peaks such as C=O, C–O, O–H, C=C or C≡N before identifying a compound
  • use the absence of an expected diagnostic absorption as evidence against a proposed structure

Covered syllabus points

22.1.1—Analyse an infrared spectrum of a simple

Question 1

[Maximum number: 1]

A sample of but-2-enoic acid, CH3CH=CHCOOH\mathrm{CH}_{3} \mathrm{CH}=\mathrm{CHCOOH}, is analysed using infrared spectroscopy.
The infrared spectrum shows a broad peak in the range 2500−3000 cm−12500-3000 \mathrm{~cm}^{-1}.

Table for Question 1 — CAIE A-Level Chemistry AS

Which bond is responsible for this peak?

A

C=C

B

C=O

C

C-O

D

O-H

Question 2

[Maximum number: 1]

Compound X reacts with acidified K2Cr2O7\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7} to form compound Y .
The infrared spectrum of compound Y is shown.

Figure for Question 2 — CAIE A-Level Chemistry AS
Table for Question 2 — CAIE A-Level Chemistry AS

What is the identity of compound X ?

A

propan-1-ol

B

propan-2-ol

C

propanone

D

propanoic acid

Question 3

[Maximum number: 1]

The infrared spectrum of a compound is shown.

Figure for Question 3 — CAIE A-Level Chemistry AS
Table for Question 3 — CAIE A-Level Chemistry AS

Which functional group could the compound contain?

A

alcohol

B

carboxylic acid

C

ester

D

nitrile

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