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CAIE A-Level Chemistry AS 22 Analytical Techniques Questions

Practise interpreting spectra and abundance data to identify bonds, formulae, isotopes, fragments and relative atomic masses.

Syllabus
2028–2030
Course
Chemistry 9701
Level
AS

Covered syllabus points

22.1 Infrared spectroscopy22.2 Mass spectrometry

Question 1

[Maximum number: 1]

A sample of but-2-enoic acid, CH3CH=CHCOOH\mathrm{CH}_{3} \mathrm{CH}=\mathrm{CHCOOH}, is analysed using infrared spectroscopy.
The infrared spectrum shows a broad peak in the range 2500−3000 cm−12500-3000 \mathrm{~cm}^{-1}.

Table for Question 1 — CAIE A-Level Chemistry AS

Which bond is responsible for this peak?

A

C=C

B

C=O

C

C-O

D

O-H

Question 2

[Maximum number: 1]

Oxygen has three stable isotopes, 16O,17O{ }^{16} \mathrm{O},{ }^{17} \mathrm{O} and 18O{ }^{18} \mathrm{O}. All three isotopes are present in a sample of oxygen gas, O2\mathrm{O}_{2}, which was analysed using a mass spectrometer.

How many peaks associated with the O2+\mathrm{O}_{2}{ }^{+}ion would be expected?

A

3

B

5

C

6

D

9

Question 3

[Maximum number: 1]

The relative atomic mass of antimony is 121.76 .
Antimony has two isotopes. The mass numbers of the two isotopes differ by two. The isotope with the lower mass number is the more abundant.

What is the percentage abundance of the isotope with the higher mass number?

A

12 %

B

38\%

C

62 %

D

88\%

Question 4

[Maximum number: 4]

Organic compounds can be distinguished using chemical tests and analytical techniques.

Question (a)

(a)

Organic compound E contains three carbon atoms. E reacts with cold dilute acidified KMnO4(aq)\mathrm{KMnO}_{4}(\mathrm{aq}) to form a single compound F with Mr=154.9M_{\mathrm{r}}=154.9.
Fig. 3.1 shows the infrared spectrum of E.
Fig. 3.2 shows the infrared spectrum of F.

Fig. 3.1

Fig. 3.1

Fig. 3.2

Fig. 3.2

Table 3.2

Table 3.2

Both spectra show absorptions between 2850 and 2950 cm−12950 \mathrm{~cm}^{-1} owing to C-H bonds in each molecule.

[ 4 ]

Question (i)

(i)

Use the two infrared spectra and Table 3.2 to identify the functional group present only in E.
Explain your answer, referring only to absorptions at frequencies greater than 1500 cm−11500 \mathrm{~cm}^{-1}.
functional group explanation

[ 1 ]

Question (ii)

(ii)

Use the infrared spectrum of F to identify the functional group formed when E reacts with cold dilute acidified KMnO4(aq)\mathrm{KMnO}_{4}(\mathrm{aq}).
Explain your answer, referring only to absorptions at frequencies greater than 1500 cm−11500 \mathrm{~cm}^{-1}.
functional group explanation

[ 1 ]

Question (iii)

(iii)

The mass spectrum of E shows a molecular ion peak and an M+2 peak of approximately equal abundance at m / e=120 and 122 .

Deduce the relative molecular mass, MrM_{\mathrm{r}}, of E.

Mr=M_{r}=
[ 1 ]

Question (iv)

(iv)

Use the information in 3(c) to suggest a structure for E.

[ 1 ]
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