Syllabus Edition

First teaching 2020

Last exams 2024

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Analytical Techniques (CIE AS Chemistry)

Exam Questions

2 hours42 questions
1a
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2 marks

There are three possible isomers, AB and C, with the molecular formula C3H8O.

Isomers A and are positional isomers of each other.

Isomer is a functional group isomer of A and B.

A student uses the following equation to calculate that the percentage by mass of carbon in all three isomers is 60.0%.

 
Percentage space by space mass equals fraction numerator total space mass space of space element over denominator overall space mass space of space compound end fraction cross times 100
 

Calculate the percentage by mass of hydrogen and oxygen in all three isomers.

1b2 marks

The infrared spectrum of isomer C shown in Fig. 1.1 does not have a peak in the region of 3200 - 3600 cm-1

 
4-7_q4b-ocr-a-as--a-level-easy-sq


Fig. 1.1

 
i)
Using the infrared spectrum in Fig. 1.1 and Table 1.1, suggest a structure for isomer C.
 
Table 1.1
 
Bond  Functional groups containing
the bond
Characteristic infrared absorption range (in wavenumber) / cm–1
C−O   hydroxy, ester  1040 – 1300
C=C   aromatic compound, alkene  1500 – 1680
C=O   amide
 carbonyl, carboxyl
 ester
1640 – 1690
1670 – 1740
1710 – 1750
C≡N   nitrile  2200 – 2250
C−H   alkane  2850 – 2950
N−H    amine, amide 3300 – 3500
O−H   carboxyl
 hydroxy
2500 – 3000
3200 – 3600
 
[1]

ii)
Suggest which bonds the highlighted peak at around 1130 cm-1 could represent.
 
[1]
1c1 mark

Isomers A and B both have a peak at 3200 - 3600 cm-1 in their infrared spectra.

 

State two possible chemical names for isomers A and B.

1d
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2 marks

Isomer A has a major peak on its mass spectrum at m/e = 31.

 

Suggest, with a reason, which compound is isomer A.

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2a
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2 marks

Mass spectroscopy is an analytical technique that can be used to analyse elements and compounds.

Using mass spectroscopy, a sample of boron was found to contain two isotopes 10B and 11B with a relative abundance of 20% and 80% respectively.

 

Calculate the relative atomic mass of boron. Show your working. 

2b
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2 marks

Fig. 2.1 represents the mass spectrum of potassium.


2-1_q2c-ocr-a-as--a-level-easy-sq

Fig. 2.1
 

Use the information in Fig 2.1 to calculate the relative atomic mass of potassium. Show your working.

2c
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2 marks

The mass spectra of octane and butane were obtained and analysed.

Write the equation for the formation of the molecular ion of octane and predict its m / e value.

2d2 marks

The mass spectrum of butane shows a molecular ion peak at m / e = 58.0.

 

Explain why there is also a smaller peak at m / e = 59.0 on the mass spectrum of butane.

2e1 mark

State, with a reason, whether butane or octane will have a higher [M+1] peak.

2f2 marks

State what the difference would be in the ratio of the peak heights of the M+ peak to the [M+2] peak in 1-bromobutane and 1-chlorobutane.

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3a2 marks

This question is about some isomeric alcohols with the molecular formula C5H12O.

Some alcohols were heated with potassium dichromate(VI) and sulfuric acid. The organic compounds were separated from the reaction mixtures and purified.

 

The infrared spectra of two of these organic compounds are shown in Fig. 3.1.

 
compound-y-and-z
 
Fig. 3.1
 

Using the data in Table 3.1, deduce the type of compound responsible for each spectrum.

 
Table 3.1
 
Bond  Functional groups containing
the bond

Characteristic infrared absorption range (in wavenumber) / cm–1

C−O   hydroxy, ester  1040 – 1300
C=C   aromatic compound, alkene  1500 – 1680
C=O   amide
 carbonyl, carboxyl
 ester
1640 – 1690
1670 – 1740
1710 – 1750
C≡N   nitrile  2200 – 2250
C−H   alkane  2850 – 2950
N−H    amine, amide 3300 – 3500
O−H   carboxyl
 hydroxy
2500 – 3000
3200 – 3600
 

Your answer should include references to wavenumbers and their corresponding bonds.

3b1 mark

The infrared spectrum a student obtained of an organic molecule which contains carbon, hydrogen and oxygen atoms is shown in Fig. 3.2.

 
ir-spectrum-2
 
Fig. 3.2
 

Use Table 3.1 in part (a) and information from the infrared spectrum to explain how the student deduced that the spectrum shows the presence of a carbonyl group.

3c2 marks

In an experiment to prepare a sample of ethanal, CH3CHO, ethanol, C2H5OH, is reacted with acidified potassium dichromate(VI) and the reaction mixture is distilled. The infrared spectra for ethanol and ethanal are shown in Fig. 3.3.

ethanol-ir-spectrum

ethanal-ir-spectrum

Fig. 3.3

i)
State the bonds that give rise to the absorption in the ethanol spectrum at 3400 cm-1 and the absorption in the ethanal spectrum at 1720 cm-1.

[1]

 

ii)
Explain why the absorption at 3400 cm-1 in the ethanol spectrum does not appear in the spectrum for ethanal.

[1]

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1a
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2 marks

Compound X contains atoms of carbon, hydrogen and oxygen only.

The mass spectrum of X is recorded. Information about the two peaks with m / e greater than 100 is shown in Fig. 1.1.

fig-5-1-9701-y22-sp-2-cie-ial-chem

Fig. 1.1

A molecule of X contains 6 carbon atoms.

Demonstrate that this is correct using information from Fig 1.1. Show your working.

1b
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1 mark

Suggest the molecular formula of X using information from Fig. 1.1.

1c
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1 mark

Suggest the molecular formula of the fragment of X at m / e = 31.

1d1 mark

Fig 1.2 shows the infra-red spectrum of X.

 
fig-5-2-9701-y22-sp-2-cie-ial-chem
 
Fig. 1.2
 

The data in Fig 1.2, Table 1.1 and your answer to (b) should be used in answering this question.

 

Identify the functional group present in X. Explain your answer.

 
Table 1.1
 
Bond  Functional groups containing
the bond
Characteristic infrared absorption
range (in wavenumber) / cm–1
C−O  hydroxy, ester  1040 – 1300
C=C  aromatic compound, alkene  1500 – 1680
C=O  amide
carbonyl, carboxyl
ester
1640 – 1690
1670 – 1740
1710 – 1750
C≡N  nitrile  2200 – 2250
C−H  alkane  2850 – 2950
N−H   amine, amide 3300 – 3500
O−H  carboxyl
hydroxy
2500 – 3000
3200 – 3600
 

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2a1 mark

The mass spectrum of magnesium is shown in Fig. 2.1. 

 
4-1-2a-m-mass-spectrum-of-magnesium
 
Fig. 2.1
 

From the mass spectrum, complete Table 2.1 with the relative abundances of the three isotopes.

 
Table 2.1
 
isotope relative abundance
24Mg  
25Mg  
26Mg  
 
2b
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1 mark

Use your values in (a) to calculate the relative atomic mass, Ar, of magnesium to two decimal places.


Ar (Mg) = ...........................

2c1 mark

Give the full electronic configuration of the magnesium ion, 26Mg2+.

2d
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3 marks

Boron has two naturally occurring isotopes, 10B and 11B. The relative atomic mass of boron is 10.8

Use this information to deduce the relative abundance of each isotope.

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3a
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2 marks

A student wanted to distinguish between the following three compounds using mass spectrometry. 

xyz

Explain why determining the exact mass using mass spectrometry would not help in distinguishing between the samples of X, Y and Z.

3b2 marks

Compounds X, Y and Z were analysed using IR spectroscopy. The spectrum of one of the compounds is shown in Fig 3.1.

3c-ir-spec

Fig 3.1

Identify which of the three compounds X, Y or Z this spectrum belongs to. Explain your reasoning.

3c2 marks

Explain why infrared spectroscopy alone could not be used to distinguish between compounds X and Y.

3d
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3 marks

Explain how mass spectrometry can distinguish between compounds X and Y.

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4a1 mark

The isomers A and B, C5H10O, both form an orange precipitate when reacted with 2,4-DNPH.

A is unbranched and reacts with alkaline aqueous iodine to produce a yellow precipitate.

B does not react with alkaline aqueous iodine. It contains a chiral centre and produces a silver mirror when warmed with Tollens’ reagent.

Draw the structure of the yellow precipitate produced by the reaction between A and alkaline aqueous iodine.

4b3 marks
i)
Give the structural formula of A and of B.

A ..............................................................................................................

B ..............................................................................................................
[2]

ii)
Explain the meaning of the term chiral centre. 
[1]
4c2 marks

C and D are isomers with the molecular formula C3H6O. The infra-red spectra of isomers C and D are shown in Fig. 4.1 and Fig. 4.2.


4-1-4c-m-ir-propanoic-acid-ir-methyl-ethanoate-a

Fig. 4.1



4-1-4c-m-ir-propanoic-acid-ir-methyl-ethanoate-b

Fig. 4.2

Table 4.1

 
Bond  Functional groups containing
the bond
Characteristic infrared absorption
range (in wavenumbers)/cm–1
C−O  hydroxy, ester  1040 – 1300
C=C  aromatic compound, alkene  1500 – 1680
C=O  amide
carbonyl, carboxyl
ester
1640 – 1690
1670 – 1740
1710 – 1750
C≡N  nitrile  2200 – 2250
C−H  alkane  2850 – 2950
N−H   amine, amide 3300 – 3500
O−H  carboxyl
hydroxy
2500 – 3000
3200 – 3600
 

Using Table 4.1, identify the bonds responsible for the principal peaks above 1500 cm–1 in each spectrum.

spectrum of ............................................................................................


spectrum of D ............................................................................................

4d2 marks

Draw possible structures of isomers C and D

 








Isomer C Isomer D

4e3 marks

Identify the ions responsible for peaks at 73, 45 and 29 in the mass spectrum for compound C.

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1a2 marks

This question is about the analysis of alcohols.

Alcohol A can be prepared by hydrolysing the halogenoalkane C2H5CHBrCH3 with aqueous sodium hydroxide. The melting and boiling point information of alcohol A and C2H5CHBrCH3 are given in Table 1.1.

 
Table 1.1
 
  melting point / K boiling point / K
alcohol A 158 373
C2H5CHBrCH3  161 364
 

Write an equation for the hydrolysis of C2H5CHBrCH3 with aqueous sodium hydroxide. Include state symbols in your answer

1b3 marks

Using the information in Table 1.1, explain how alcohol A can be separated from the products identified in part (a)

1c2 marks

Describe two chemical tests and their expected observations to confirm the identity of the inorganic product.

1d3 marks

The infra-red spectrum of C2H5CHBrCH3 is shown in Fig. 1.1 with the C–Br bond absorption labelled.

 
2-bromobutane-ir-spec
 
Fig. 1.1
 

Using Fig. 1.1 and Table 1.2, predict three main differences that would be seen between the spectra of C2H5CHBrCH3 and alcohol A.

 
Table 1.2
 
Bond  Functional groups containing
the bond
Characteristic infrared absorption range (in wavenumber) / cm–1
C−O  hydroxy, ester  1040 – 1300
C=C  aromatic compound, alkene  1500 – 1680
C=O  amide
carbonyl, carboxyl
ester
1640 – 1690
1670 – 1740
1710 – 1750
C≡N  nitrile  2200 – 2250
C−H  alkane  2850 – 2950
N−H   amine, amide 3300 – 3500
O−H  carboxyl
hydroxy
2500 – 3000
3200 – 3600
 
1e1 mark

The mass spectrum of (CH3)2CHCH2OH is shown in Fig. 1.2.

 
SW-bcju4_2-methylpropan-2-ol-mass-spec
 
Fig. 1.2
 

Identify the ion that is responsible for the peak with the greatest relative intensity.

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2a
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3 marks

An unknown compound, B, is analysed and shown to have a composition of 69.7% carbon, 18.6% oxygen and the remainder is hydrogen.

The following incomplete mass spectrometry and IR spectroscopy data are collected.

Mass spectrum

  • M+1 peak at m / e = 87.0
  • Fragment ion peak at m / e = 28

Iinfra-red spectrum 

  • Sharp peak at 1705 cm-1 
  • No broad peak around 3200 cm-1 

Calculate the molecular formula of compound B.

2b3 marks

Using Table 2.1 and the incomplete mass spectrometry and infra-red spectroscopy data, identify two possible isomers for compound B.

 
Table 2.1
 
Bond  Functional groups containing
the bond
Characteristic infrared absorption range (in wavenumber) / cm–1
C−O  hydroxy, ester  1040 – 1300
C=C  aromatic compound, alkene  1500 – 1680
C=O  amide
carbonyl, carboxyl
ester
1640 – 1690
1670 – 1740
1710 – 1750
C≡N  nitrile  2200 – 2250
C−H  alkane  2850 – 2950
N−H   amine, amide 3300 – 3500
O−H  carboxyl
hydroxy
2500 – 3000
3200 – 3600
 

Your answer should include an explanation proving your two possible isomers and disproving one other isomer. 

2c3 marks

A mass spectrum peak at m / e = 29 could be used to distinguish between the two remaining isomers.

 

Identify the fragment responsible for this peak and explain how it can be used to distinguish between the two isomers.

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3a3 marks

Unknown organic compound C is analysed by mass spectrometry and infra-red spectroscopy. The mass spectrum is shown in Fig. 3.1 and the infra-red spectrum is shown in Fig. 3.2.

4-7_q3a-ocr-a-as--a-level-hard-sq

Fig 3.1

4-7_q3a2-ocr-a-as--a-level-hard-sq

Fig 3.2

Deduce one possible identity for compound C. Explain your answer.

 

In your answer, use the molecular ion peak at m / e = 55, relevant infra-red absorptions in the region above 1500 cm-1 and Table 3.1.

 
Table 3.1
 
Bond  Functional groups containing
the bond
Characteristic infrared absorption range (in wavenumber) / cm–1
C−O  hydroxy, ester  1040 – 1300
C=C  aromatic compound, alkene  1500 – 1680
C=O  amide
carbonyl, carboxyl
ester
1640 – 1690
1670 – 1740
1710 – 1750
C≡N  nitrile  2200 – 2250
C−H  alkane  2850 – 2950
N−H   amine, amide 3300 – 3500
O−H  carboxyl
hydroxy
2500 – 3000
3200 – 3600
 
3b1 mark

The mass spectrum of compound C shows an M+1 peak at m / e = 56.

 

Suggest two ways that this peak could be formed.

3c
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2 marks

Calculate the expected elemental percentage composition by mass of an 8.0 g sample of compound C. Give your answers to significant figures. 

3d2 marks

Compound C undergoes a reaction to form compound D. The IR spectrum of compound D is shown in Fig. 3.3.

 
4-7_q3d-ocr-a-as--a-level-hard-sq
 
Fig. 3.3
 

State the reagents required for this reaction. In your answer, use Table 3.1 and identify any relevant absorptions in the infra-red spectrum to justify your answer. 

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4a
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3 marks

Alcohol E is analysed using a combination of techniques. The analytical data is shown below.

Elemental analysis by mass

  • C = 68.2%, H = 13.6%, O = 18.2%

Mass spectrum

  • Molecular ion peak at m / e = 88.0
  • Major ion peak at m / e = 45.0

Determine the molecular formula of alcohol E. 

4b1 mark

Alcohol E oxidises to form a carboxylic acid. Suggest what information this gives about the structure of alcohol E.

4c4 marks
Using the information from part (b), draw the fully displayed formulae and give the systematic names of the four possible structural isomers that could be alcohol E.
 

 

 

 

 

Name ..................................................

 

 

 

 

Name ..................................................

 

 

 

 

Name ..................................................

 

 

 

 

Name ..................................................

 
4d1 mark

The mass spectrum of alcohol E has a major peak at m / e = 45.

 

Draw the structure of the species that could give this peak. 

 

 

 

 

 

  

 
4e1 mark

Alcohol E has a branched chain.

 

Identify the isomer from part (d) that is alcohol E. Explain your answer. 

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5a
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1 mark

The term carbohydrate is often associated with sugars or suggests a compound that contains carbon, hydrogen and oxygen. It was previously used in chemistry to define any compound of the general formula Cm(H2O)n.

Compound F contains 6.98 % hydrogen and 37.21 % oxygen by mass. The remainder of the mass is carbon.

 
i)
Determine whether compound is a carbohydrate according to the previous chemistry definition. Justify your answer.
 
[4]
 
ii)
Explain why this empirical formula cannot be the molecular formula of compound F. You should justify your answer in terms of hydrogen atoms and include a minimum of three displayed formulae.
 
[4]
5b
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2 marks

Fig. 5.1 shows the mass spectrum of compound F.

 
4-1-5b-h-crotonic-acid-mass-spec
 
Fig. 5.1
 

Using your answer to part (a)(i), deduce the molecular formula of compound F.

5c1 mark

Fig. 5.2 shows the infra-red spectrum of compound F

 
4-1-5c-h-crotonic-acid-ir-spec
 
Fig. 5.2
 

Table 5.1 shows the characteristic infrared absorption frequencies for some selected bonds.

 
Table 5.1
 
Bond  Functional groups containing
the bond
Characteristic infrared absorption range (in wavenumber) / cm–1
C−O  hydroxy, ester  1040 – 1300
C=C  aromatic compound, alkene  1500 – 1680
C=O  amide
carbonyl, carboxyl
ester
1640 – 1690
1670 – 1740
1710 – 1750
C≡N  nitrile  2200 – 2250
C−H  alkane  2850 – 2950
N−H   amine, amide 3300 – 3500
O−H  carboxyl
hydroxy
2500 – 3000
3200 – 3600
 

Complete Table 5.2 with the bond responsible for each of the principal absorptions seen in the infra-red spectrum of compound F.

 
Table 5.2
 
principal absorptions
in infra-red spectrum
bond responsible
2500 - 3000 cm-1  
1710 cm-1  
1620 cm-1  
 
5d3 marks

Compound F is a straight-chain molecule.

 

Using all of the available information including your answers from parts (b) and (c), draw the displayed formulae and give the systematic names of the three possible isomers that could be compound F.

 

 

 

 

 

Name ................................

 

 

 

 

Name ................................

 

 

 

 

Name ................................

 
5e1 mark

Compound F is the stereoisomer with the lowest boiling point.

 

Using the isomers identified in part (d), give the name of compound F. Explain your answer.

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