17 Spectroscopy
OCR Chemistry A Exam-style questions
1 Ultraviolet radiation from the sun causes the Earth to warm up and emit infrared
radiation. Greenhouse gases in the Earth’s atmosphere absorb this infrared radiation.
a Describe how infrared radiation interacts with a greenhouse gas molecule.
(1 mark)
b With reference to the relevant bonds, explain why the use of hydrofluorocarbons,
HFCs, rather than chlorofluorocarbons, CFCs, is advantageous for the levels of
ozone in the atmosphere, but disadvantageous in terms of global warming.
(2 marks)
c Give two factors that determine a gas's Global Warming Potential (GWP) – a
measure of how much heat a greenhouse gas traps.
(2 marks)
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17 Spectroscopy
OCR Chemistry A Exam-style questions
2 An alkane with an empirical formula of C2H5, produced the following spectrum
when analysed in a mass spectrometer:
a Use the mass spectrum to find the relative molecular mass of this alkane and
determine the molecular formula.
(2 marks)
b Draw the possible structural isomers of this molecule and name them.
(2 marks)
c Suggest the identity of the fragments producing the peaks at:
i m/z 15 (1 mark)
ii m/z 29 (1 mark)
d Identify the alkane under analysis. Give reasons for your choice.
(1 mark)
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17 Spectroscopy
OCR Chemistry A Exam-style questions
3 Breathalysers are used by the police to measure the level of the alcohol, ethanol,
in a driver's breath.
a One type of breathalyser changes colour when alcohol is detected. The
colour change is from orange to green. Suggest the name of the chemical
that reacts with alcohol to produce this colour change.
(1 mark)
b State the type of reaction occurring during this colour change.
(1 mark)
c Another type of breathalyser uses infrared spectroscopy. State how a
spectrum would provide evidence that ethanol is present in the breath.
(1 mark)
d The level of ethanol in the breath measured using a breathalyser is then
converted into a level of ethanol in the blood. The legal limit for drivers in England
in 2015 is 80 mg of ethanol per 100 cm3 of blood. Express this legal limit in
mol dm–3. Give your answer to three significant figures. (1 milligram 1 10–3 g)
(3 marks)
e Give an environmental application of infrared spectroscopy currently used by
scientists.
(1 mark)
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17 Spectroscopy
OCR Chemistry A Exam-style questions
4 Compound R is a straight chain alkene with a molecular formula of C4H8. When
compound R reacts with steam in the presence of an acid catalyst, compound S
is produced with the molecular formula C4H9O. When compound S was refluxed
with an acidified potassium dichromate(VI) the organic compound, T, was
produced. The infrared spectrum of compound T is shown below:
a Identify the structure of each compound R, S and T. Explain fully how the
information correlates to each structure.
(7 marks)
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17 Spectroscopy
OCR Chemistry A Exam-style questions
b Explain how the region below 1500 cm–1 is used to identify an organic compound.
(2 marks)
5 Compound B is a branched chain alcohol, which has the following percentage
composition by mass:
C, 70.6%; H, 13.7%; O, 15.7%
The mass spectrum of compound B is shown below:
a Calculate the empirical formula and deduce the molecular formula of
compound B.
(3 marks)
b Explain why there is a small peak at m/z 103.
(1 mark)
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17 Spectroscopy
OCR Chemistry A Exam-style questions
c When refluxed with acidified sodium dichromate(VI), compound B undergoes
a complete reaction and is converted into organic compound C. This organic
product was analysed using infrared spectroscopy and the spectrum is
shown below:
Use all of the information given to identify the functional group in compound C.
(3 marks)
d Classify compound B as a primary, secondary or tertiary alcohol with your
reasoning.
(1 mark)
e Explain how the infrared spectrum also provides evidence that the
conversion of B into C was a complete reaction.
(1 mark)
f Write the formulae for the particles causing the peaks labelled:
i X
ii Y (2 marks)
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17 Spectroscopy
OCR Chemistry A Exam-style questions
g It is known that the longest carbon chain within compound B is a chain of 4
carbons. Deduce the structure of compound B.
(1 mark)
h Write an equation using structural formulae for the conversion of compound B
into compound C. Use [O] to represent the acidified sodium dichromate(VI).
(2 marks)
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