Modern analytical techniques IEdexcel A-Level Chemistry: Topic test

20 questions, 54 marks

Edexcel A-Level Chemistry

Modern analytical techniques I topic test

Total 54 marks

Name

Class

Date

1
A straight-chain alkane, whose relative molecular mass is 58, is analysed by mass spectrometry. The mass spectrum shows a molecular ion peak at m/z 58 and major fragment peaks at m/z 43 and m/z 29. Relative atomic masses: H = 1, C = 12.
(a)
Which species causes the peak at m/z 58?
[1 mark]
A[C₄H₉]⁺
B[C₃H₈]⁺
C[C₄H₁₀]⁺
D[C₄H₁₀]²⁺
(b)
Which fragmentation of the molecular ion gives the peak at m/z 43?
[1 mark]
A[C₄H₁₀]⁺ → [C₃H₇]⁺ + •CH₃
B[C₄H₁₀]⁺ → [C₃H₇]• + CH₃⁺
C[C₄H₁₀]⁺ → [C₂H₅]⁺ + •C₂H₅
D[C₄H₁₀]⁺ → [C₃H₈]⁺ + CH₂
(c)
Write an equation, showing the radical, for the formation of the ion at m/z 29 from the molecular ion.
[2 marks]
Total for question 1: 4 marks
2
Compound X has the molecular formula C₅H₁₀. Its infrared spectrum shows absorptions at 3080 cm⁻¹, 2960 cm⁻¹ and 1648 cm⁻¹. Its mass spectrum has a molecular ion peak at m/z 70 and a strong peak at m/z 41. Infrared data (cm⁻¹): C–H in alkanes 2850–2960, C–H in alkenes 3010–3095, C–H in aldehydes 2700–2900, C=C 1620–1669, C=O 1680–1750, O–H in alcohols 3200–3550, O–H in carboxylic acids 2500–3300 (very broad), N–H 3300–3500.
(a)
Which bond is responsible for the absorption at 1648 cm⁻¹?
[1 mark]
AC=O
BO–H
CC–H in an alkane
DC=C
(b)
Which compound is consistent with both the formula and the infrared spectrum of X?
[1 mark]
ACyclopentane
BPent-1-ene, CH₂=CHCH₂CH₂CH₃
CPentane
DPentan-1-ol
(c)
Compound X is pent-1-ene, CH₂=CHCH₂CH₂CH₃. Write an equation, showing the radical, for the formation of the ion at m/z 41 from its molecular ion.
[2 marks]
Total for question 2: 4 marks
3
An organic compound W contains carbon, hydrogen and oxygen only. Its infrared spectrum shows a very broad absorption from about 2500 to 3300 cm⁻¹ and a strong absorption at 1710 cm⁻¹. Its mass spectrum shows a molecular ion peak at m/z 74 and fragment peaks at m/z 57, 45 and 29. Infrared data (cm⁻¹): C–H in alkanes 2850–2960, C–H in alkenes 3010–3095, C–H in aldehydes 2700–2900, C=C 1620–1669, C=O 1680–1750, O–H in alcohols 3200–3550, O–H in carboxylic acids 2500–3300 (very broad), N–H 3300–3500.
(a)
Use the infrared data to identify the functional group in W. Explain your answer.
[3 marks]
(b)
Use the mass spectrum to deduce the structure of W, identifying the ions at m/z 45 and m/z 29.
[4 marks]
Total for question 3: 7 marks
4
A liquid Q has the molecular formula C₄H₈O. Its infrared spectrum shows strong absorptions at 2960 cm⁻¹ and 1718 cm⁻¹. There are no absorptions between 3200 and 3550 cm⁻¹, between 1620 and 1670 cm⁻¹ or between 2700 and 2900 cm⁻¹. Its mass spectrum has a molecular ion peak at m/z 72 and fragment peaks at m/z 57, 43 and 29. Infrared data (cm⁻¹): C–H in alkanes 2850–2960, C–H in alkenes 3010–3095, C–H in aldehydes 2700–2900, C=C 1620–1669, C=O 1680–1750, O–H in alcohols 3200–3550, O–H in carboxylic acids 2500–3300 (very broad), N–H 3300–3500.
(a)
Use the infrared data to deduce the functional group in Q and suggest its structure.
[6 marks]
(b)
Explain how the molecular ion peak and the fragment peaks at m/z 57, 43 and 29 support the identification of Q as butanone, CH₃COCH₂CH₃. Include equations, showing the radicals.
[6 marks]
Total for question 4: 12 marks
5
Butan-1-ol, CH₃CH₂CH₂CH₂OH, has a relative molecular mass of 74. A chemist records its mass spectrum, which shows peaks at m/z 74, 56, 43 and 31 (the base peak), and also its infrared spectrum. Relative atomic masses: H = 1, C = 12, O = 16. Infrared data (cm⁻¹): C–H in alkanes 2850–2960, C–H in alkenes 3010–3095, C–H in aldehydes 2700–2900, C=C 1620–1669, C=O 1680–1750, O–H in alcohols 3200–3550, O–H in carboxylic acids 2500–3300 (very broad), N–H 3300–3500.
(a)
Which ion gives the base peak at m/z 31?
[1 mark]
A[CH₂OH]⁺
B[C₂H₅]⁺
C[CH₃CH₂CH₂]⁺
D[OH]⁺
(b)
Which absorptions would be seen in the infrared spectrum of butan-1-ol?
[1 mark]
AAn absorption at about 1715 cm⁻¹ and an absorption at about 2900 cm⁻¹
BA broad absorption at about 3300 cm⁻¹ and an absorption at about 1715 cm⁻¹
CA very broad absorption from 2500 to 3300 cm⁻¹ and an absorption at about 1710 cm⁻¹
DA broad absorption at about 3300 cm⁻¹ and an absorption at about 2900 cm⁻¹
(c)
Explain how the ion at m/z 56 forms from the molecular ion, and write an equation.
[2 marks]
Total for question 5: 4 marks
6
A chemist checks a bottle labelled propylamine, CH₃CH₂CH₂NH₂ (relative molecular mass 59). The infrared spectrum shows absorptions at 3350 cm⁻¹ and 2930 cm⁻¹, and the mass spectrum shows a molecular ion peak at m/z 59 and a base peak at m/z 30. Relative atomic masses: H = 1, C = 12, N = 14. Infrared data (cm⁻¹): C–H in alkanes 2850–2960, C–H in alkenes 3010–3095, C–H in aldehydes 2700–2900, C=C 1620–1669, C=O 1680–1750, O–H in alcohols 3200–3550, O–H in carboxylic acids 2500–3300 (very broad), N–H 3300–3500.
(a)
Which bond is responsible for the absorption at 3350 cm⁻¹?
[1 mark]
AO–H
BN–H
CC=O
DC–H
(b)
Which ion gives the base peak at m/z 30?
[1 mark]
A[CH₃CH₂CH₂]⁺
B[C₂H₅]⁺
C[CH₂NH₂]⁺
D[NH₂]⁺
(c)
The chemist suspects that the propylamine is contaminated with propanoic acid, CH₃CH₂COOH. State two features that would appear in the infrared spectrum of the contaminated sample.
[2 marks]
Total for question 6: 4 marks
7
Propan-2-ol is made by reacting propene with steam in the presence of an acid catalyst. A chemist tests the liquid product. Its infrared spectrum shows a strong broad absorption at 3340 cm⁻¹, a strong absorption at 2970 cm⁻¹ and a weak absorption at 1648 cm⁻¹, with none near 1700 cm⁻¹. After purification, the mass spectrum shows a molecular ion peak at m/z 60 and a base peak at m/z 45, with no significant peak at m/z 31. Infrared data (cm⁻¹): C–H in alkanes 2850–2960, C–H in alkenes 3010–3095, C–H in aldehydes 2700–2900, C=C 1620–1669, C=O 1680–1750, O–H in alcohols 3200–3550, O–H in carboxylic acids 2500–3300 (very broad), N–H 3300–3500.
(a)
Use the infrared data to explain what the chemist can conclude about the liquid product.
[3 marks]
(b)
Use the mass spectrum to show that the alcohol is propan-2-ol, CH₃CH(OH)CH₃, and not propan-1-ol, CH₃CH₂CH₂OH. Include an equation for the formation of the ion at m/z 45.
[4 marks]
Total for question 7: 7 marks
8
Two colourless liquids both have a relative molecular mass of 88.0. One is pentan-1-ol, CH₃(CH₂)₄OH, and the other is butanoic acid, CH₃CH₂CH₂COOH. A technician has one bottle of each with the labels missing, and has access to a mass spectrometer and an infrared spectrometer. Relative atomic masses: H = 1, C = 12, O = 16. Infrared data (cm⁻¹): C–H in alkanes 2850–2960, C–H in alkenes 3010–3095, C–H in aldehydes 2700–2900, C=C 1620–1669, C=O 1680–1750, O–H in alcohols 3200–3550, O–H in carboxylic acids 2500–3300 (very broad), N–H 3300–3500.
(a)
Explain how the infrared and mass spectra could be used to tell the two liquids apart. Give the key absorptions and the key fragment ions.
[6 marks]
(b)
A student claims that infrared spectroscopy alone is enough to confirm that a sample is pure pentan-1-ol. Pentan-2-ol is another alcohol with a relative molecular mass of 88.0. Evaluate the student's claim.
[6 marks]
Total for question 8: 12 marks

End of questions

Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).