CAIE A-Level Chemistry 22. Analytical techniques Question Bank

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

[Maximum number: 4]

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

(a)

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

Fig. 3.1

Fig. 3.2

Table 3.2

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

[ 4 ]

(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 $1500 \mathrm{~cm}^{-1}$ .
functional group explanation

[ 1 ]

C=C (bond) / alkene

AND (absorption within) $\mathbf{1 5 0 0} \boldsymbol{-} \mathbf{1 6 8 0 ~} \mathbf{c m}^{-1}$ (present in E's IR spectrum only)

(ii)

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

[ 1 ]

hydroxyl / alcohol

AND (broad absorption within) $3200-3650 \mathrm{~cm}^{-1}$ (present in F's IR spectrum only)

(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, $M_{\mathrm{r}}$ , of E.

M_{r}=

[ 1 ]

(iv)

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

[ 1 ]

[Maximum number: 2]

Copper is used in electrical equipment. It has a melting point of $1085^{\circ} \mathrm{C}$ .

(a)

The relative isotopic masses and natural abundances of the two isotopes in a sample of copper are shown in Table 1.1.

Table 1.1

[ 1 ]

(i)

Calculate the relative atomic mass, $A_{\mathrm{r}}$ , of copper in this sample using the data in Table 1.1.

Show your working.

A_{r}=

[ 1 ]

$(62.93 \times 69.15) \div 100+(64.928 \times 30.85) \div 100=63.55 / 63.546$

(b)

The mass spectrum of a sample of pure copper is shown in Fig. 1.1.

Fig. 1.1

Identify the ion with an abundance of 23 % in the sample.

[ 1 ]

${ }^{63} \mathrm{Cu}^{2+}$

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Covered syllabus points

22. Analytical techniques question 1

Question (a)

Question (i)

Question (ii)

Question (iii)

Question (iv)

22. Analytical techniques question 2

Question (a)

Question (i)

Question (b)