Lesson 7B.1

7B.1 Identifying functional groups from IR spectra Quiz: Pearson Edexcel Chemistry, Unit 7

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 7B.1, Identifying functional groups from IR spectra: 20 multiple choice questions for the Pearson Edexcel Chemistry (9CH0), Unit 7: Modern Analytical Techniques I, written with Revision Ninja.

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The 20 questions

  1. Which absorption is characteristic of the O-H group in an alcohol?

    • An absorption around 700 cm-1 only
    • A broad absorption around 3200 to 3550 cm-1
    • A sharp absorption around 1700 cm-1
    • A sharp absorption around 1650 cm-1 only

  2. Which absorption is most characteristic of the C=O group in a ketone?

    • A strong absorption around 1700 to 1750 cm-1
    • A broad absorption around 2500 to 3300 cm-1
    • A medium absorption around 1620 to 1680 cm-1
    • A sharp absorption around 3300 to 3500 cm-1

  3. Which feature distinguishes a carboxylic acid from an aldehyde in an IR spectrum?

    • An absorption below 1000 cm-1 only, which identifies the acid by its fingerprint region alone
    • A C=C absorption at 1650 cm-1 that shows the presence of a double bond in the molecule
    • A sharp absorption at 3300 cm-1 from N-H bonds that is present in every carboxylic acid spectrum
    • A very broad O-H absorption from about 2500 to 3300 cm-1, overlapping the C-H stretches

  4. Which absorption is characteristic of a C=C stretch in an alkene?

    • A broad absorption around 3200 to 3550 cm-1
    • A sharp absorption at 3300 to 3500 cm-1 only
    • A strong absorption around 1700 to 1750 cm-1
    • A medium absorption around 1620 to 1680 cm-1

  5. Which IR absorption indicates an N-H bond in a primary amine?

    • A broad absorption around 2500 to 3300 cm-1 only
    • A strong absorption around 1000 cm-1 only
    • A strong absorption around 1700 cm-1
    • A medium absorption around 3300 to 3500 cm-1

  6. Which wavenumber range is characteristic of C-H stretching in alkanes?

    • About 2850 to 3000 cm-1
    • About 1700 to 1750 cm-1
    • About 3200 to 3550 cm-1
    • About 1620 to 1680 cm-1

  7. Which absorption in an aldehyde spectrum helps distinguish it from a ketone?

    • A sharp C=C stretch at 1650 cm-1 that shows the presence of an alkene in the molecule
    • Two weak C-H stretches near 2700 and 2800 cm-1 from the CHO group
    • A broad O-H stretch at 3300 cm-1 that shows the presence of an alcohol in the sample
    • A strong C-Cl stretch near 750 cm-1 that shows a halogen is bonded to the carbon chain

  8. A compound shows a strong sharp absorption at 1715 cm-1 and a very broad band from 2500 to 3300 cm-1. What is it most likely to be?

    • An alcohol
    • An alkene
    • A carboxylic acid
    • A primary amine

  9. Which absorption shows the presence of a C=O group in an ester?

    • A strong absorption around 1735 to 1750 cm-1
    • An absorption at 1650 cm-1 only, which shows the presence of a carbon-carbon double bond
    • A weak absorption at 2750 cm-1 that shows the presence of a C-H bond bonded to oxygen
    • A broad absorption at 3300 cm-1 that shows the presence of an O-H group in the molecule

  10. Which compound would show a broad absorption at 3200 to 3550 cm-1 and a C-O absorption near 1050 cm-1?

    • Ethanal
    • Ethene
    • Ethanol
    • Ethane

  11. Which statement about infrared spectroscopy is correct?

    • IR absorptions arise from bonds vibrating at characteristic frequencies, which identify functional groups
    • IR radiation is used to separate ions by mass in the instrument before detection
    • IR spectra give the relative molecular mass directly from the highest peak in the spectrum
    • IR spectra show the number of protons in each chemical environment in the molecule

  12. In an IR spectrum, which region is most useful for identifying functional groups rather than the whole molecule?

    • The region at exactly 1000 cm-1 only
    • Above about 1500 cm-1
    • The baseline between peaks
    • Below about 500 cm-1 only

  13. Which wavenumber range is characteristic of a C-H stretch in an alkene or aromatic structure, slightly above 3000 cm-1?

    • About 3300 to 3500 cm-1 only
    • About 1700 to 1750 cm-1
    • About 2500 to 3300 cm-1 only
    • About 3000 to 3100 cm-1

  14. Which compound shows a C=O stretch around 1715 cm-1 but no broad O-H band?

    • Propanoic acid
    • Propene
    • Propanone
    • Propan-1-ol

  15. A compound has IR absorptions at 3350 cm-1 (broad) and 1050 cm-1 but no peak at 1700 cm-1. Which compound best fits?

    • Propene
    • Propan-2-ol
    • Propanone
    • Propanal

  16. What bond vibration gives rise to the IR absorption near 1650 cm-1 in an alkene?

    • C=C stretching
    • C-H bending in an alkane
    • C-Cl stretching
    • O-H stretching in an alcohol

  17. Which IR feature best supports the identity of an amine rather than an alcohol?

    • N-H stretching absorptions around 3300 to 3500 cm-1, which are sharper than O-H bands
    • A broad band from 2500 to 3300 cm-1 that shows the presence of a carboxylic acid group
    • An absorption only below 800 cm-1, which identifies the compound from its fingerprint region
    • A strong band at 1700 cm-1 that shows the presence of a carbonyl group in the molecule

  18. Which combination of IR features is expected for propanoic acid, CH3CH2COOH?

    • A sharp O-H band near 3600 cm-1 and no C=O band, which is typical of a free alcohol
    • A N-H band near 3350 cm-1 and a strong C-Cl band, which is typical of a chloro amine
    • A broad O-H band from 2500 to 3300 cm-1 and a strong C=O band near 1710 cm-1
    • A C=C band near 1650 cm-1 and no O-H band, which is typical of an unsaturated hydrocarbon

  19. A student records an IR spectrum with no absorption between 3200 and 3550 cm-1 and no absorption at 1700 cm-1. Which compound is most likely?

    • Hexane
    • Butan-1-amine
    • Ethanoic acid
    • Ethanol

  20. Which region of the IR spectrum contains the C-O single bond stretch used to support an alcohol identification?

    • Around 3300 to 3500 cm-1
    • Around 1000 to 1300 cm-1
    • Around 2850 to 3000 cm-1
    • Around 1620 to 1680 cm-1

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