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ASChemistryCIEExam Questions22. Analytical Techniques22.2 Mass Spectrometry

Mass Spectrometry (CIE AS Chemistry)

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22.2 Mass Spectrometry

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22.2 Mass Spectrometry

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1a
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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. 

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1b
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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.

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1c
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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.

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1d2 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.

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1e1 mark

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

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1f2 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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1a
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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.

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1b
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Suggest the molecular formula of X using information from Fig. 1.1.

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1c
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Suggest the molecular formula of the fragment of X at m / e = 31.

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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  
 

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2b
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Use your values in (a) to calculate the relative atomic mass, Ar, of magnesium to two decimal places.


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

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2c1 mark

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

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2d
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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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3a2 marks

Infrared spectroscopy and mass spectrometry are used in the search for extra-terrestrial organic compounds.

Compound X was analysed using both techniques. Fig. 3.1 shows the infrared spectrum of compound X and Fig. 3.2 shows the mass spectrum of compound X.

compound-x-ir-spec

Fig. 3.1 

q3a-mass-spectrum

Fig. 3.2 

Table 3.1

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
 

 

Use Fig. 3.1, Fig. 3.2 and Table 3.1 to suggest what evidence there is to support that compound X is a hydrocarbon.

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3b1 mark

Explain how the mass spectrum supports that compound X has a molecular formula of C4H10.

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3c1 mark

Draw the fully displayed formulae of two possible isomers for compound X.

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3d4 marks
i)
Suggest the molecular formulae of the fragments of X at m/e = 15, m/e = 29 and m/e = 43.
 
[3]
 
ii)
Name compound X. Give a reason for your answer.
 
[1]

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1a
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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.

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1b3 marks

Using Table 1.1 and the incomplete mass spectrometry and infra-red spectroscopy data, identify two possible isomers for compound B.

 
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
 

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

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1c3 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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2a
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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. 

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2b1 mark

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

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2c4 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 ..................................................
 

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2d1 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. 

 

 

 

 

 

  
 

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2e1 mark

Alcohol E has a branched chain.

 

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

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3a
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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 F 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]

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3b
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Fig. 3.1 shows the mass spectrum of compound F.

 
4-1-5b-h-crotonic-acid-mass-spec
 
Fig. 3.1
 

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

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3c1 mark

Fig. 3.2 shows the infra-red spectrum of compound F. 

 
4-1-5c-h-crotonic-acid-ir-spec
 
Fig. 3.2
 

Table 3.1 shows the characteristic infrared absorption frequencies for some selected bonds.

 
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
 

Complete Table 3.2 with the bond responsible for each of the principal absorptions seen in the infra-red spectrum of compound F.

 
Table 3.2
 
principal absorptions
in infra-red spectrum		 bond responsible
2500 - 3000 cm-1  
1710 cm-1  
1620 cm-1  
 

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3d3 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 ................................
 

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3e1 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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