Mass Spectrometry | Cambridge (CIE) AS Chemistry Exam Questions & Answers 2023 [PDF]

1a

2 marks

A sample of boron contains two isotopes, ¹⁰B and ¹¹B, with relative abundances of 20% and 80% respectively.

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

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1b

2 marks

Fig. 2.1 shows the mass spectrum of potassium.

Mass spectrum of potassium showing two peaks: m/e = 39 with relative abundance 130.6 and m/e = 41 with relative abundance 9.4

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

2 marks

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

Construct an equation for the formation of the molecular ion of octane. State the m / e value of this molecular ion.

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1d

1 mark

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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1e

2 marks

State whether butane or octane has a greater relative abundance of the [M+1] peak compared to the M peak. Explain your answer.

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1f

2 marks

State the ratio of the relative abundances of the M peak and the [M+2] peak in the mass spectra of 1-bromobutane and 1-chlorobutane.

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1a

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.

Mass spectrum of compound X showing a molecular ion peak at m/e 102 with 100% relative abundance and an M+1 peak at m/e 103 with 6.5% relative abundance

Fig. 1.1

Calculate the number of carbon atoms in compound X using information from Fig. 1.1. Show your working.

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1b

1 mark

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

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1c

1 mark

Deduce the formula of the fragment ion at m / e = 31.

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1d

2 marks

Fig. 1.2 shows the infrared spectrum of X.

Infrared spectrum of compound X showing a broad O-H absorption at approximately 3300 cm^-1^ in the hydroxyl region and an absorption in the C-H region at approximately 2900 cm^-1^

Fig. 1.2

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

State 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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2a

1 mark

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

Mass spectrum of magnesium showing three peaks at m/e values of 24, 25, and 26 with relative abundances of approximately 79%, 10%, and 11% respectively

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

2 marks

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

A_r (Mg) = ...........................

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2c

1 mark

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

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2d

2 marks

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

Use this information to calculate the relative abundance of each isotope. Show your working.

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3a

2 marks

Compound X was analysed by infrared spectroscopy and mass spectrometry. Fig. 3.1 shows the infrared spectrum of compound X and Fig. 3.2 shows the mass spectrum of compound X.

Infrared spectrum of compound X showing a strong absorption at approximately 2950 cm^-1^ in the C-H region with no other significant absorptions present

Fig. 3.1

Mass spectrum of compound X showing a molecular ion peak at m/e 58 and fragment ion peaks at m/e 43, 29 and 15

Fig. 3.2

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

Use Fig. 3.1, Fig. 3.2 and Table 3.1 to explain the evidence that compound X is a hydrocarbon.

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3b

1 mark

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

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3c

2 marks

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

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3d

5 marks

i) Deduce the formulae of the fragment ions of X at m/e = 15, m/e = 29 and m/e = 43.

[3]

ii) State the systematic name of compound X. Explain your answer.

[2]

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1a

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 infrared spectroscopy data are collected.

Mass spectrum

Molecular ion peak (M) at m / e = 86
M+1 peak at m / e = 87.0
Fragment ion peak at m / e = 28

Infrared spectrum

Sharp absorption at 1705 cm^-1
No broad absorption around 3200 cm^-1

Calculate the molecular formula of compound B. Show your working.

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1b

3 marks

Using Table 1.1 and the mass spectrometry and infrared spectroscopy data:

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

i) State the functional group present in compound B.

[1]

ii) Draw the skeletal formulae of two possible structures for compound B.

[2]

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1c

3 marks

A mass spectrum peak at m / e = 29 can be used to distinguish between the two isomers identified in (b)(ii).

Deduce the formula of the fragment ion responsible for this peak. Explain how this peak can be used to distinguish between the two isomers.

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3a

3 marks

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

i) Calculate the empirical formula of compound F. Show your working.

[2]

ii) Explain why this empirical formula cannot be the molecular formula of compound F.

[1]

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3b

1 mark

Fig. 3.1 shows the mass spectrum of compound F.

Mass spectrum of compound F showing a molecular ion peak at m/e 86 and fragment ion peaks at lower m/e values

Fig. 3.1

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

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3c

2 marks

Fig. 3.2 shows the infrared spectrum of compound F.

Infrared spectrum of compound F showing principal absorptions at 2500–3000 cm^-1^ (broad O-H carboxyl), 1710 cm^-1^ (C=O carboxyl) and 1620 cm^-1^ (C=C alkene)

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 infrared spectrum of compound F.

Table 3.2

Principal absorption in infrared spectrum	Bond responsible
2500 – 3000 cm^-1
1710 cm^-1
1620 cm^-1

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3d

3 marks

Compound F is an unbranched molecule.

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

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3e

2 marks

Compound F is the stereoisomer with the lowest boiling point.

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

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Mass Spectrometry (Cambridge (CIE) AS Chemistry): Exam Questions