Analytical Techniques (A Level Only) | CIE A Level Chemistry Structured Questions 2022

1a3 marks

This question is about gas chromatography.

Name the three types of chemical that gas chromatography is used for.

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1b2 marks

Silica and alumina are commonly used as the stationary phase in thin layer chromatography.

State the type of chemical that is commonly used as the stationary phase in gas chromatography.

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1c2 marks

State the type of chemical that is used for the mobile phase in gas chromatography. You should include at least one specific example in your answer.

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1d4 marks

Results in gas chromatography are based on retention time.

i)

Define the term retention time.

[1]

ii)

State three factors that retention time depends upon.

[3]

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1e1 mark

State what information the relative size or area under the peak on a gas chromatogram provides.

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1f3 marks

Gas chromatography is carried out using a polar stationary phase and argon as the carrier gas.

Use the chromatogram in Fig. 1.1 to answer the following questions.

Fig. 1.1

i)

State which compound has the lowest retention time.

[1]

ii)

State which compound is the least polar.

[1]

iii)

State which compound has the greatest interaction with the stationary phase.

[1]

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1a

3 marks

Compound P is a naturally occurring chemical found in strawberries, apples and Parmesan cheese.

The percentage by mass is carbon 58.82%, hydrogen 9.80% and oxygen 31.38%.

The mass spectrum of compound P is recorded in Fig. 1.1.

Fig. 1.1

Determine the molecular formula of compound P. Show your working.

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1b4 marks

Table 1.1 shows the results of qualitative tests performed on compound P.

Table 1.1

Test	Observation
Addition of H₂O	Forms separate layers
Na₂CO₃(aq)	No visible change
2,4-DNPH	No visible change
Tollens' reagent	No visible change

Analyse the potential functional groups in compound P. Explain your answers.

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1c3 marks

The carbon-13 (¹³C) NMR spectrum of compound P is shown in Fig. 1.2.

6-9-q1c-ocr-a-as--a-level-hard-sq

Fig. 1.2

Table 1.2

Hybridisation of the carbon atom	Environment of carbon atom	Example	Chemical shift range δ / ppm
sp³	alkyl	CH₃–, CH₂–, –CH<, >C<	0 – 50
sp³	next to alkene / arene	–C–C=C, –C–Ar	25 – 50
sp³	next to carbonyl / carboxyl	C–COR, C–O₂R	30 – 65
sp³	next to halogen	C–X	30 – 60
sp³	next to oxygen	C–O	50 – 70
sp²	alkene or arene	>C=C<,	110 – 160
sp²	carboxyl	R−COOH, R−COOR	160 – 185
sp²	carbonyl	R−CHO, R−CO−R	190 – 220
sp	nitrile	R−C≡N	100 – 125

Identify the functional group(s) present in compound P using your answer in (b) and information from Fig. 1.2 and Table 1.2. Explain your answer.

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1d3 marks

The high-resolution proton NMR spectrum of compound P was recorded as shown in Fig. 1.3.

6-9_q1d-ocr-a-as--a-level-hard-sq

Fig. 1.3

Table 1.3

Environment of proton	Example	chemical shift range, δ / ppm
alkane	–CH₃, –CH₂–, >CH–	0.9 – 1.7
alkyl next to C=O	CH₃–C=O,–CH₂–C=O, >CH–C=O	2.2 – 3.0
alkyl next to aromatic ring	CH₃–Ar, –CH₂–Ar, >CH–Ar	2.3 – 3.0
alkyl next to electronegative atom	CH₃–O,–CH₂–O, –CH₂–Cl	3.2 – 4.0
attached to alkene	=CHR	4.5 – 6.0
attached to aromatic ring	H–Ar	6.0 – 9.0
aldehyde	HCOR	9.3 – 10.5
alcohol	ROH	0.5 – 6.0
phenol	Ar–OH	4.5 – 7.0
carboxylic acid	RCOOH	9.0 – 13.0
alkyl amine	R–NH–	1.0 – 5.0
aryl amine	Ar–NH₂	3.0 – 6.0
amide	RCONHR	5.0 – 12.0

Suggest the structure of compound P using your answers to (a), (b) and (c) and information from Fig. 1.3 and Table 1.3. Explain your answer.

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3a3 marks

Gas chromatography is often connected to mass spectroscopy in order to analyse each compound as it exits the gas chromatography column. This combined technique is called GC-MS.

The gas chromatogram of an organic mixture is shown in Fig. 3.1. The stationary phase is a polar, high-boiling point liquid on a solid support.

8-1-3a-h-gas-chromatogram

Fig. 3.1

i)

Name an appropriate mobile phase that could be used to form this gas chromatogram.

[1]

ii)

Identify the number of compounds present in this mixture and explain how to identify the most polar compound present.

[2]

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3b

6 marks

Two of the compounds in the organic mixture are hydrocarbons with similar retention times.

The mass spectra of the two compounds revealed that they have the same molecular formula but with subtle differences indicating structural isomerism is present.

The mass spectrum of one of the isomers is shown in Fig. 3.2.

Both isomers are tested with bromine water, which remains orange.

Fig. 3.2

i)

Identify the molar mass and hence the molecular formula of the isomers.

molar mass ................................................................................

molecular formula ................................................................................

[2]

ii)

Identify the fragments responsible for the following signals.

m / e = 29 ................................................................................

m / e = 43 ................................................................................

m / e = 57 ................................................................................

[3]

iii)

Suggest the most likely structure of the isomer responsible for this spectrum.

[1]

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3c3 marks

There is a small, additional peak on the far right of the mass spectrum.

i)

Explain the presence of the small peak at m / e = 87.

[1]

ii)

Suggest the type of molecules for which this would become more pronounced. Explain your answer.

[2]

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3d4 marks

One other isomer present in the original mixture was 2,3-dimethylbutane.

i)

Suggest one way in which the mass spectrum of 2,3-dimethylbutane will differ from Fig. 3.2 in part (b).

[1]

ii)

Suggest an alternative spectroscopic technique for distinguishing between 2,3-dimethylbutane and your answer to (b).

[1]

iii)

Predict which of the two isomers would have the longest retention time. Explain your answer.

[2]

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1a

10 marks

Verdigris is a green pigment that contains both copper(II) carbonate, CuCO₃, and copper(II) hydroxide, Cu(OH)₂, in varying amounts.

Both copper compounds react with dilute hydrochloric acid.

CuCO₃(s) + 2HCl (aq) → CuCl₂(aq) + CO₂(g) + H₂O (l)

Cu(OH)₂(s) + 2HCl (aq) → CuCl₂(aq) + 2H₂O (l)

You are to plan an experiment to determine the percentage of copper(II) carbonate in a sample of verdigris. Your method should involve the reaction of verdigris with excess dilute hydrochloric acid.

You are provided with the following:

• 0.494 g of verdigris
• 10.0 mol dm^–3 hydrochloric acid, HCl (aq)
• commonly available laboratory reagents and equipment.

You may assume that any other material present in verdigris is unaffected by heating and is not acidic or basic.

i)

A student suggests that finding the volume of dilute hydrochloric acid required to react with a known mass of verdigris would be a suitable method to determine the percentage of copper(II) carbonate in a sample of verdigris.

Suggest why this method would not work.

[1]

ii)

The 10.0 mol dm^–3 HCl is too concentrated for use in the experiment. Instead, a more dilute solution should be prepared.

Describe how you would accurately prepare 250.0 cm³ of 0.500 mol dm^–3 hydrochloric acid from the 10.0 mol dm^–3HCl provided.

Your answer should state the name and capacity in cm³ of any apparatus you would use.

[3]

iii)

The percentage of copper(II) carbonate in a sample of verdigris can be determined by measuring the volume of gas produced when excess hydrochloric acid is added to the sample of verdigris.

Draw a diagram to show how you would set up the apparatus and chemicals to measure the total volume of gas produced in this reaction.

Label your diagram.

[2]

iv)

Sketch a graph on the axes to show how the volume of gas produced would change during your experiment. The independent variable should be on the x-axis.
• Label both axes.
• Extend the graph beyond the point at which the reaction is complete.

[2]

v)

A student thinks that their 0.494 g sample of verdigris only contains CuCO₃.

Calculate the minimum volume, in cm³, of 0.500 mol dm^–3 HCl that is needed to completely react with this sample if the student is correct.
Show your working.
[M_r: CuCO₃ = 123.5]

volume of 0.500 mol dm^–3 HCl = .................................................... cm³ [2]

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1b

9 marks

Azurite is a blue copper-containing mineral. The copper compound in azurite has the formula Cu₃(CO₃)₂(OH)₂. This copper compound reacts with sulfuric acid according to the equation.

Cu₃(CO₃)₂(OH)₂(s) + 3H₂SO₄(aq) → 3CuSO₄(aq) + 2CO₂(g) + 4H₂O (l)

A student carries out a series of titrations on 1.50 g samples of solid azurite using 0.400 mol dm^–3 sulfuric acid.

Assume that any other material present in azurite does not react with sulfuric acid. Some titration data is given in Table 1.1.

Table 1.1

titration	rough	1	2	3
final reading / cm³	25.55	23.90	48.30	28.10
initial reading / cm³	0.00	0.00	23.90	3.95
titre / cm³

The indictor for the titration is bromophenol blue. Bromophenol blue is blue at pH 4.6 and yellow at pH 3.0.

i)

Complete Table 1.1.

[1]

ii)

Calculate the percentage uncertainty in titre 1.

[1]

iii)

The student concludes that 24.15 cm³ of 0.400 mol dm^–3 sulfuric acid completely reacts with 1.50 g of azurite.
Calculate the percentage by mass of Cu₃(CO₃)₂(OH)₂ in the sample of azurite using the student’s value of 24.15 cm³ of 0.400 mol dm^–3 sulfuric acid.

Write your answer to three significant figures.
Show your working.
[M_r: Cu₃(CO₃)₂(OH)₂ = 344.5]

percentage by mass of Cu₃(CO₃)₂(OH)₂ in the sample of azurite = ..........................% [3]

iv)

Identify two possible problems with the student’s titration experiment and suggest improvements to it.

problem 1 .............................................................

improvement 1 ....................................................

problem 2 ...............................................................

improvement 2 ........................................................

[4]

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2a

5 marks

Activated charcoal is a form of carbon with a very high surface area. It can be used to remove impurities from mixtures. It does this by a process called adsorption, where particles of the impurity bond (adsorb) to the activated charcoal surface.

A student wants to determine the ability of activated charcoal to adsorb a blue dye (the impurity) from aqueous solution.

The equation that links the mass of activated charcoal with the amount of blue dye adsorbed is shown.

log $(\frac{D}{m})$ = A + b log [X]

D = difference in concentration of dye (in g dm^–3) before and after adsorption
m = mass of activated charcoal (in g)
[X] = final concentration of dye (in g dm^–3) after adsorption
A and b are constants

The student uses the following procedure to investigate the ability of activated charcoal to adsorb a blue dye from an aqueous solution.

Place a 50.0 cm³ sample of a 25.00 g dm^–3 solution of blue dye in a conical flask.
Add a weighed mass of activated charcoal to the flask.
Stir the contents of the flask for three minutes and then leave for one hour.
Filter the mixture.
Determine the final concentration of the blue dye, [X].
Repeat the procedure using different masses of activated charcoal.

The procedure is carried out. The final concentrations of blue dye, [X], are shown in Table 2.1.

i)

Process the results to complete Table 2.1.

Record your data to two decimal places.

Table 2.1

mass of activated charcoal, m / g	initial concentration of blue dye / g dm^–3	final concentration of blue dye, [X] / g dm^–3	difference in concentration of blue dye, D / g dm^–3	$\frac{D}{m}$	log $\frac{D}{m}$	log [X]
0.20	25.00	0.96		120.20	2.08
0.25	25.00	0.69		97.24	1.99
0.30	25.00	0.60		81.33	1.91
0.35	25.00	0.41		70.26	1.85
0.40	25.00	0.33		61.68	1.79
0.45	25.00	0.27		54.96	1.74
0.50	25.00	0.23		49.54	1.69
0.55	25.00	0.20		45.09	1.65
0.60	25.00	0.17		41.38	1.62

[2]

ii)

Identify the dependent variable in this experiment.

[1]

iii)

State and explain the effect, if any, of increasing the mass of activated charcoal, m, on the amount of adsorption that occurs.

[2]

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2b2 marks

Plot a graph on the grid to show the relationship between log $(\frac{D}{m})$ and log [X].

Use a cross (×) to plot each data point. Draw the straight line of best fit.

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2c1 mark

Circle the most anomalous point on the graph.

Suggest why this anomaly may have happened during the experimental procedure.

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2d3 marks

i)

Use the graph to determine the gradient of the line of best fit. State the coordinates of both points you used in your calculation. These must be selected from your line of best fit.

Write your answer to three significant figures

coordinates 1 .................... coordinates 2 ..........................

gradient = ..........................................

[2]

ii)

Use the graph to determine a value for A.

A = ........................................................... [1]

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5a3 marks

During the production of an NMR spectrum, tetramethylsilane (TMS) is mixed with the sample.

i)

Give the structural formula of the standard reference chemical used for ¹H NMR spectroscopy.

[1]

ii)

Explain why tetramethylsilane is used as the standard reference chemical.

[2]

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5b1 mark

State the number of peaks in the C-13 NMR spectrum of 1,3-dichlorobenzene.

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5c2 marks

i)

Predict the number of peaks in the ¹³C NMR spectrum of ethylbenzene, shown in Fig. 5.1.

Fig. 5.1

[1]

ii)

The data in Table 5.1 should be used in answering this question.

One of the carbon atoms in the structure of ethylbenzene shown in Fig. 5.1 is labelled with an asterisk (*). Suggest a C-13 chemical shift range for this carbon environment.

Table 5.1

Hybridisation of the carbon atom	Environment of carbon atom	Example	Chemical shift range δ/ppm
sp³	alkyl	CH₃–, CH₂–, –CH<, >C<	0 – 50
sp³	next to alkene / arene	–C–C=C, –C–Ar	25 – 50
sp³	next to carbonyl / carboxyl	C–COR, C–O₂R	30 – 65
sp³	next to halogen	C–X	30 – 60
sp³	next to oxygen	C–O	50 – 70
sp²	alkene or arene	>C=C<,	110 – 160
sp²	carboxyl	R−COOH, R−COOR	160 – 185
sp²	carbonyl	R−CHO, R−CO−R	190 – 220
sp	nitrile	R−C≡N	100 – 125

[1]

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5d7 marks

Compound A contains the elements carbon, hydrogen, oxygen and nitrogen only. Compound A contains a benzene ring.

Part of the mass spectrum of A is shown in Fig. 5.2.

Fig. 5.2

i)

Give the identity of the molecular ion that gives rise to the peak at m / e = 76 in the Fig. 5.2.

[1]

ii)

Suggest the structures of the three possible dinitrobenzene isomers of A that contain a benzene ring.

[3]

iii)

The C-13 NMR spectrum of compound A has four peaks. Identify the structure of A. Explain your reasoning by labelling the different carbon environments in all the structures drawn in part (ii).

[3]

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6a2 marks

Methyl cinnamate, C₁₀H₁₀O₂, is a white crystalline solid used in the perfume industry.

The proton NMR spectrum of methyl cinnamate in the solvent CDCl₃ is shown in Fig. 6.1.

methyl-cinnamate-high-res-proton-nmr

Fig. 6.1

i)

Explain why CDCl₃ is used as a solvent instead of CHCl₃.

[1]

ii)

Explain why TMS is added to give the small peak at chemical shift δ = 0.

[1]

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6b3 marks

The structure of methyl cinnamate is shown in Fig. 6.2.

methyl-cinnamate-skeletal

Fig. 6.2

The data in Table 6.1 should be used in answering this question.

Identify the proton environment that gives rise to the peak at a chemical shift of 3.8 ppm in Fig. 6.1. Explain your answer.

Table 6.1

Environment of proton	Example	chemcial shift range, δ / ppm
alkane	–CH₃, –CH₂–, >CH–	0.9 – 1.7
alkyl next to C=O	CH₃–C=O,–CH₂–C=O, >CH–C=O	2.2 – 3.0
alkyl next to aromatic ring	CH₃–Ar, –CH₂–Ar, >CH–Ar	2.3 – 3.0
alkyl next to electronegative atom	CH₃–O,–CH₂–O, –CH₂–Cl	3.2 – 4.0
attached to alkene	=CHR	4.5 – 6.0
attached to aromatic ring	H–Ar	6.0 – 9.0
aldehyde	HCOR	9.3 – 10.5
alcohol	ROH	0.5 – 6.0
phenol	Ar–OH	4.5 – 7.0
carboxylic acid	RCOOH	9.0 – 13.0
alkyl amine	R–NH–	1.0 – 5.0
aryl amine	Ar–NH₂	3.0 – 6.0
amide	RCONHR	5.0 – 12.0

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6c2 marks

Proton NMR spectroscopy can be used to distinguish between isomers of C₆H₁₂O₂.

Draw the two esters with formula C₆H₁₂O₂ that each have only two peaks, both singlets, in their ¹H NMR spectra. The relative peak areas are 3:1 for both esters.

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6d5 marks

The proton NMR spectrum of another isomer of C₆H₁₂O₂ is shown in Fig. 6.3.

Fig. 6.3

The integration values for the peaks in the proton NMR spectrum of this isomer are given in Table 6.2.

Table 6.2

Chemical shift, δ/ppm	3.8	3.5	2.6	2.2	1.2
Integration value	0.6	0.6	0.6	0.9	0.9
Splitting pattern	triplet	quartet	triplet	singlet	triplet

i)

Deduce the simplest ratio of the relative numbers of protons in each environment in the isomer.

[1]

ii)

The data in Table 6.1 should be used in answering this question.

Describe and explain the splitting patterns of the peaks at δ = 3.5 and δ = 1.2.

splitting pattern at δ = 3.5 ...................................................................................................

reason for splitting pattern at δ = 3.5 ..................................................................................

splitting pattern at δ = 1.2 ...................................................................................................

reason for splitting pattern at δ = 1.2 ..................................................................................

[4]

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6e1 mark

Four isomers of C₆H₁₂O₂, A, B, C and D, are shown in Fig. 6.4.

c6h12o2-abcd

Fig. 6.4

The C-13 NMR spectrum of one of the four isomers of C₆H₁₂O₂ is shown in Fig. 6.5.

c6h12o2-abcd-13c-nmr

Fig. 6.5

The data in Table 6.3 should be used in answering this question.

Identify which of the four isomers, A, B, C or D of C₆H₁₂O₂ produced the C-13 NMR spectrum shown in Fig 6.5.

Table 6.3

Hybridisation of the carbon atom	Environment of carbon atom	Example	Chemical shift range δ/ppm
sp³	alkyl	CH₃–, CH₂–, –CH<, >C<	0 – 50
sp³	next to alkene / arene	–C–C=C, –C–Ar	25 – 50
sp³	next to carbonyl / carboxyl	C–COR, C–O₂R	30 – 65
sp³	next to halogen	C–X	30 – 60
sp³	next to oxygen	C–O	50 – 70
sp²	alkene or arene	>C=C<,	110 – 160
sp²	carboxyl	R−COOH, R−COOR	160 – 185
sp²	carbonyl	R−CHO, R−CO−R	190 – 220
sp	nitrile	R−C≡N	100 – 125

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Hard

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

CIE A Level Chemistry

Topic Questions

8.1 Analytical Techniques (A Level Only)

	Number of peaks
L	3
M	5
N	4

	Number of peaks	Relative Peak area
L
M
N

Spectrum	Organic compound	Explanation
A
B

Spectrum	Organic compound	Explanation
C
D