Lesson 3.3.6.3

3.3.6.3 Infrared spectroscopy Quiz: AQA Chemistry, Unit 3

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 3.3.6.3, Infrared spectroscopy: 20 multiple choice questions for the AQA Chemistry (7405), Unit 3: Organic chemistry, written with Revision Ninja.

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The 20 questions

  1. In an infrared spectrum, what unit is used for the absorption position?

    • mol dm-3, the unit of concentration used for solutions in titration
    • m/z, the mass-to-charge ratio recorded in mass spectrometry for ions
    • ppm, the unit of chemical shift on the delta scale used in NMR
    • cm-1 (wavenumber)

  2. Which bond gives a strong absorption around 1680-1750 cm-1?

    • C-H
    • O-H in alcohols
    • N-H in amines
    • C=O

  3. Which absorption indicates an alcohol O-H group?

    • A sharp absorption at about 1650 cm-1
    • A broad absorption at about 3200-3550 cm-1
    • A sharp absorption at about 1720 cm-1
    • A strong absorption at about 1000 cm-1 only

  4. What is the main use of the fingerprint region of an infrared spectrum?

    • Measuring the molar mass of the sample from the height of its tallest peak
    • Finding the number of carbon atoms directly from the position of each band
    • Measuring the concentration of a solution by comparing absorbance with a standard
    • Comparing the spectrum with a reference to identify the molecule

  5. Which gas in the atmosphere absorbs infrared radiation and contributes to global warming?

    • Nitrogen, which is diatomic and absorbs only in the ultraviolet region strongly
    • Carbon dioxide
    • Argon, which is a noble gas and does not vibrate, so it cannot absorb infrared
    • Oxygen, which is diatomic and forms a weak greenhouse effect in the stratosphere

  6. A spectrum shows a very broad absorption between 2500 and 3300 cm-1 and a sharp absorption near 1710 cm-1. Which group is most likely present?

    • Carboxylic acid
    • Alcohol, which shows a broad O-H band but no C=O band in the spectrum
    • Alkene, which shows a C=C band near 1650 but no O-H or C=O band
    • Amine, which shows N-H bands near 3300-3500 but no C=O band in the spectrum

  7. Which feature distinguishes ethanol from ethanal in an infrared spectrum?

    • Ethanal shows a broad O-H absorption at 3200-3550 cm-1 that ethanol lacks
    • Ethanol shows a C=O absorption at 1720 cm-1 that ethanal lacks
    • Ethanol shows a broad O-H absorption at 3200-3550 cm-1 that ethanal lacks
    • Ethanal shows a C=C absorption at 1650 cm-1 that ethanol lacks

  8. Which wavenumber range is characteristic of a C=O stretch?

    • 3200-3550 cm-1
    • 1620-1680 cm-1
    • 2850-3300 cm-1
    • 1680-1750 cm-1

  9. Which bond gives absorptions in the range 2850-3300 cm-1 in almost every organic compound?

    • C-H
    • N-H in primary amines only
    • C=O
    • C=C

  10. A sample of propanone is suspected of containing water. Which infrared feature would reveal this?

    • A sharp absorption around 1650 cm-1
    • A broad absorption around 3200-3550 cm-1
    • A sharp absorption around 1715 cm-1
    • A strong absorption around 1000 cm-1

  11. A spectrum shows an absorption at about 1650 cm-1 but none at 1700-1750 cm-1. Which bond is most likely present?

    • O-H
    • C=O
    • C-O
    • C=C

  12. Which statement distinguishes an amine N-H absorption from an alcohol O-H absorption?

    • N-H absorbs more sharply, around 3300-3500 cm-1, than the broad alcohol O-H band
    • N-H and O-H absorb at exactly the same wavenumber and cannot be separated
    • N-H absorbs at 1000 cm-1 while O-H absorbs at 3300 cm-1
    • N-H absorbs at 1700 cm-1 while O-H absorbs at 1650 cm-1

  13. Two isomers both show a C=O absorption near 1720 cm-1. Which isomer shows a very broad absorption between 2500 and 3300 cm-1?

    • The carboxylic acid
    • The aldehyde, which shows a sharp C=O band near 1725 and a C-H band near 2720
    • The ester, which shows a sharp C=O band near 1735 but no broad O-H band
    • The ketone, which shows a sharp C=O band near 1715 but no broad O-H band

  14. Why does carbon dioxide in the atmosphere contribute to global warming, in infrared terms?

    • Its bonds absorb infrared radiation emitted from Earth and re-emit it, trapping heat
    • Its bonds reflect all visible light back into space, so less heat reaches the surface
    • Its bonds convert infrared radiation into ultraviolet radiation that heats the atmosphere
    • Its bonds block all sunlight from reaching the surface, cooling the lower atmosphere

  15. Why are nitrogen and oxygen not significant greenhouse gases?

    • They are diatomic and do not change dipole moment on vibration, so they absorb little infrared
    • They absorb strongly only in the ultraviolet region, so they do not trap infrared
    • They react with carbon dioxide to remove its infrared absorption from the air
    • They are too heavy to rise into the upper atmosphere where infrared is absorbed

  16. A compound shows a strong absorption at 1715 cm-1 and no broad O-H absorption, with formula C3H6O. Which compound is most likely?

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

  17. Which compound shows a C=O absorption near 1735 cm-1 and no broad O-H absorption?

    • Ethanoic acid
    • Ethyl ethanoate
    • Ethanol
    • Ethanamine

  18. What must a student use alongside an infrared spectrum to identify functional groups?

    • A solubility table for ionic compounds, which does not list infrared absorptions
    • The Periodic Table of relative atomic masses only, which gives no bond information
    • The Chemistry Data Sheet or Booklet table of characteristic absorptions
    • A table of standard electrode potentials, which relates to redox reactions only

  19. Which wavenumber range is characteristic of a C-O single bond stretch?

    • 1620-1680 cm-1
    • 2850-3300 cm-1
    • 3200-3550 cm-1
    • 1000-1300 cm-1

  20. An infrared spectrum shows a strong absorption at 1700-1750 cm-1 and a band at 1000-1300 cm-1, with no broad O-H band. Which functional group is most likely?

    • Alkene
    • Ester
    • Amine
    • Alcohol

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