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Chromatography and tests for functional groups

Past-paper questions pack

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Questions are numbered; the mark schemes (the answer key) follow on separate pages so the question pages can be handed out alone. www.chemistryaleveltutor.com

OCR AS and A-level Chemistry past-paper questions since 2016 · 31 parts · mark schemes follow the questions · www.chemistryaleveltutor.com · Questions and mark schemes © OCR

1. June 2025 · Paper 2 · Q21(b) · 2 marks ·
(b) A chemical test is carried out which gives a positive result for all three compounds. Suggest the reagent and observation of this chemical test. Reagent ............................................................................................................................................ Observation ...................................................................................................................................... [2]
2. June 2025 · Paper 2 · Q21(c) · 3 marks ·
(c) A student is provided with three unlabelled sample tubes, containing either pyruvic acid, methylglyoxal or acetol. The student carries out three chemical tests on each sample. Complete the table with the expected observations, including ‘no change’ where appropriate. Expected observations Chemical test Pyruvic acid Methylglyoxal Acetol Tollens’ reagent .................................... .................................... .................................... .................................... .................................... .................................... Na2CO3(aq) .................................... .................................... .................................... .................................... .................................... .................................... Cr2O7 2–(aq)/H+(aq) .................................... .................................... .................................... .................................... .................................... .................................... [3]
3. June 2025 · Paper 2 · Q22(a)(i) · 1 marks ·
22 This question is about organic acids. α-Amino acids have the general formula RCH(NH2)COOH. (a) Compound S is made of two α-amino acids bonded together. Compound S is hydrolysed into its component α-amino acids. The resulting mixture is analysed using TLC to produce a chromatogram: solvent front start line The R group and the Rf value is shown for some α-amino acids. R group Rf value –H 0.18 –CH3 0.25 –CH2CH(CH3)2 0.64 –CH(CH3)2 0.77 (i) Determine the Rf values of the two α-amino acids in the chromatogram. [1]
4. June 2025 · Paper 2 · Q22(a)(ii) · 2 marks ·
(ii) Compound S has two possible structures. Draw both of these structures. [2]
5. June 2025 · Paper 3 · Q2(b)(i) · 1 marks ·
(b) Nuromol tablets are used to relieve pain. Nuromol tablets contain a mixture of ibuprofen and paracetamol. The structures of ibuprofen and paracetamol are shown. H3C OH CH2 O O CH C C CH3 OH H3C N CH H CH3 Ibuprofen Paracetamol A student carries out an investigation to determine the mass of ibuprofen and the mass of paracetomol in one nuromol tablet. • Ibuprofen reacts with aqueous sodium carbonate, Na2CO3(aq), to produce a gas. 2RCOOH + Na2CO3 2RCOONa + CO2 + H2O • Paracetamol does not react with Na2CO3(aq). (i) Why does paracetamol not react with Na2CO3(aq)? .......................................................................................................................................................... .......................................................................................................................................................... ..................................................................................................................................................... [1]
6. June 2024 · Paper 2 · Q3 · 1 marks ·
3 A student investigates the rate of hydrolysis of different iodoalkanes using aqueous silver nitrate in ethanol. What colour of precipitate is seen? A Brown B Cream C White D Yellow Your answer [1]
7. June 2024 · Paper 2 · Q5 · 1 marks ·
5 Geraniol, shown below, is a component in many natural oils. OH Geraniol Which pair of reagents identifies both functional groups in geraniol? A Acidified dichromate(VI) and 2,4-dinitrophenylhydrazine. B Bromine water and 2,4-dinitrophenylhydrazine. C Bromine water and acidified dichromate(VI). D Tollens’ reagent and aqueous silver nitrate in ethanol. Your answer [1]
8. June 2024 · Paper 2 · Q13 · 1 marks ·
13 A sample containing a mixture of 3 components, X, Y and Z, is analysed using gas chromatography. The gas chromatogram below is obtained. The relative peak areas of X, Y and Z are included. Z Relative peak areas X = 1.0 1000 Y Y = 3.5 Z = 5.5 X Recorder response 500 0 0 5 10 15 Time / min Which statement(s) is/are true? 1 The peak for component X shows the mass of one mole. 2 Component Y stays in the column for longer than component X. 3 Component Z consists of more than half of the sample. A 1, 2 and 3 B Only 1 and 2 C Only 2 and 3 D Only 1 Your answer [1]
9. June 2024 · Paper 3 · Q5(a)(i) · 1 marks ·
5 This question is about the analysis of organic compounds. (a) A student investigates the alkaline hydrolysis of 1-bromopropane as outlined below. Step 1 The student adds 1-bromopropane to an excess of aqueous potassium hydroxide, KOH(aq), in a pear-shaped flask. Step 2 A TLC chromatogram is run using propan-1-ol and the reaction mixture. Step 3 The reaction mixture is refluxed. A TLC chromatogram of the reaction mixture is run every 10 minutes. The TLC chromatograms are shown below. Before reflux After 10 minutes After 20 minutes After 30 minutes solvent front origin propan-1-ol reaction mixture propan-1-ol reaction mixture propan-1-ol reaction mixture propan-1-ol reaction mixture (i) Determine the Rf value of propan-1-ol. Show your working. Rf = ................... [1]
10. June 2024 · Paper 3 · Q5(a)(iii) · 3 marks ·
(iii) A student investigates the alkaline hydrolysis of 1-chloropropane using the same method as for 1-bromopropane. Predict, with reasons, how the appearance of the reaction mixture in the chromatogram produced after 20 minutes would be different when 1-chloropropane is used instead of 1-bromopropane. Suggest why propan-1-ol is run alongside the reaction mixture. .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... ..................................................................................................................................................... [3]
11. June 2024 · Paper 3 · Q5(b)(ii) · 6 marks ·
(ii)* The student is provided with further information about compounds F–I. • They all have the molecular formula C5H10O. • One of the compounds is alicyclic. • The other compounds are unbranched. Use this further information and the student’s observations in Table 5.1 to answer the following. • How do the observations provide evidence for the possible functional groups in compounds F–I? • Suggest a possible structure for each of the compounds F–I. Show your reasoning. [6] .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... Extra answer space if required. .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... ..........................................................................................................................................................
12. June 2023 · Paper 2 · Q2 · 1 marks · AO1
2 Which compound reacts with 2,4-dinitrophenylhydrazine but does not react with Tollens’ reagent? A C6H5COCOOH B C6H5CH(OH)CHO C CH3COCHO D CH3CH2CH(OH)CH3 Your answer [1]
13. June 2022 · Paper 2 · Q18(a)(i) · 3 marks · AO1
18 This question is about carbonyl compounds. (a) (i) Describe a chemical test to confirm the presence of a carbonyl group. How could the product of this test be used to identify the carbonyl compound? Your answer should not include spectroscopy. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ...................................................................................................................................... [3]
14. June 2022 · Paper 2 · Q18(a)(ii) · 1 marks · AO1
(ii) Describe a chemical test that would identify whether a carbonyl compound is an aldehyde. Your answer should include the reagent and observations. ........................................................................................................................................... ........................................................................................................................................... ...................................................................................................................................... [1]
15. June 2022 · Paper 2 · Q20(a)(i) · 1 marks · AO1
20 This question is about the chemistry of aromatic compounds. (a) Compounds J, K and L, shown below, are structural isomers. CH3 CH2CH2OH OH H3C OH CH3 CH3 Compound J Compound K Compound L (i) What chemical test(s) could be used to confirm the presence of the phenol group in compounds K and L? ........................................................................................................................................... ........................................................................................................................................... ...................................................................................................................................... [1]
16. November 2021 · Paper 2 · Q10 · 1 marks ·
10 A TLC chromatogram for two compounds is shown below. solvent front origin What is the Rf value for the compound that is most strongly adsorbed onto the stationary phase? A 0.25 B 0.33 C 0.69 D 0.78 Your answer [1]
17. November 2021 · Paper 2 · Q21 · 6 marks · AO3
21* Compounds D, E and F are isomers with the molecular formula C5H10O. One of the compounds is alicyclic. A student carries out test-tube tests on the compounds. The observations are shown below. Compound 2,4-DNP H+/Cr2O7 2–, reflux Bromine water D No change Green solution No colour change Orange E No colour change No colour change precipitate Orange F No colour change No colour change precipitate 13C NMR spectrum of D Compound D has 3 peaks at δ / ppm: 24, 36, 73. 1H NMR spectra of E and F The integration data has been omitted. Compound E 3 2 1 0 chemical shift, δ / ppm Compound F Expansion of multiplet 3 2 1 0 chemical shift, δ / ppm Analyse the observations and results to identify the structures of D, E and F. Explain your reasoning. [6] ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... Additional answer space if required. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ...................................................................................................................................................
18. November 2020 · Paper 2 · Q13 · 1 marks · AO1
13 Which statement(s) is/are correct for gas chromatography? 1 The components in a mixture can be identified from their retention time. 2 The relative peak areas give the proportions of components in a mixture. 3 Calibration curves are used to confirm the concentrations of components in a mixture. A 1, 2 and 3 B Only 1 and 2 C Only 2 and 3 D Only 1 Your answer [1]
19. November 2020 · Paper 2 · Q19(b) · 4 marks · AO2, 3
(b) Describe suitable chemical tests, with observations, that would confirm the presence of the functional groups in F and G. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... .............................................................................................................................................. [4]
20. June 2019 · Paper 2 · Q16(b)(i) · 2 marks · AO1
(b) Geraniol and citronellal, shown below, are isomers present in ‘citronella oil’, used as an insect repellent. OH O Geraniol Citronellal • Geraniol and citronellal are structural isomers of each other. • They also show stereoisomerism. (i) Describe how the observations from a chemical test would distinguish between geraniol and citronellal. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ...................................................................................................................................... [2]
21. June 2019 · Paper 2 · Q17(b)(i) · 1 marks · AO1
(b) The student is provided with another amino acid. The student attempts to identify the unknown amino acid using chromatography. The student obtains two TLC chromatograms of the unknown amino acid and the four amino acids in Table 17.1, using two different solvents, W and X. solvent front origin unknown ala ser leu gly unknown ala ser leu gly amino amino acid acid Solvent W Solvent X (i) What is the Rf value of serine (ser) in solvent W? Rf = ......................................................... [1]
22. June 2019 · Paper 2 · Q17(b)(ii) · 2 marks · AO2
(ii) Analyse the chromatograms to identify the unknown amino acid. Explain your reasoning. Name of unknown amino acid ........................................................................................... Explanation ....................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ...................................................................................................................................... [2]
23. June 2019 · Paper 2 · Q18(c) · 1 marks · AO3
(c) Compound B is a structural isomer of ester A. • Compound B reacts with aqueous sodium carbonate. • The 13C NMR spectrum of B has 4 peaks. Draw a possible structure for compound B. [1]
24. June 2019 · Paper 3 · Q4(a)(iii) · 2 marks · AO1, 2
(iii) Name the functional group responsible for the acidity of chloroxylenol and describe a simple test which would confirm the presence of this group. Functional group ................................................................................................................ Test .................................................................................................................................... ........................................................................................................................................... ...................................................................................................................................... [2]
25. June 2018 · Paper 2 · Q19(c)(ii) · 3 marks ·
(ii) Analyse the information to identify E, F and G. Show your working. [3]
26. June 2018 · Paper 2 · Q20(b)(i) · 1 marks ·
(b) A student plans to carry out some chemical tests on both cinnamaldehyde and methylcinnamaldehyde. CHO CHO cinnamaldehyde methylcinnamaldehyde (i) Suggest a suitable chemical test to confirm that both compounds contain an unsaturated carbon chain. Your answer should include the reagent and observations. ........................................................................................................................................... ...................................................................................................................................... [1]
27. June 2018 · Paper 2 · Q20(b)(ii) · 1 marks ·
(ii) Describe a chemical test to confirm that both compounds contain an aldehyde functional group. Your answer should include the reagent and observations. ........................................................................................................................................... ...................................................................................................................................... [1]
28. June 2018 · Paper 2 · Q20(b)(iii) · 3 marks ·
(iii) Describe a chemical test to confirm that cinnamaldehyde and methylcinnamaldehyde contain a carbonyl group. How could the products of this test be used to distinguish between the two compounds? Your answer should not include spectroscopy. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ...................................................................................................................................... [3]
29. June 2018 · Paper 2 · Q21(c)(i) · 2 marks ·
(c) A cosmetic product containing four esters, J, K, L and M, is analysed by gas chromatography and mass spectrometry. The results are shown below. Gas chromatogram M 5.9 K J 4.3 4.2 L 1.0 0 1 2 3 4 5 retention time / minutes The numbers by the peaks are the relative molar proportions of the compounds in the mixture. Mass spectrometry ester m/z of molecular ion peak J 152 K 166 L 180 M 180 (i) The concentration of ester K in the cosmetic product is 9.13 × 10−2 g dm−3. Using the results, calculate the concentration, in mol dm−3, of ester M in the cosmetic product. Give your answer to two significant figures. concentration of ester M = .......................................... mol dm−3 [2]
30. June 2017 · Paper 2 · Q20(b) · 3 marks ·
(b) Qualitative tests are carried out on the aromatic compound. The results are shown below. Test Acidity Na2CO3(aq) 2,4-DNP Tollens’ reagent No observable No observable Observation pH = 5 Orange precipitate change change Determine the functional groups in the compound. Explain your reasoning. Functional groups ..................................................................................................................... Explanation ............................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [3]
31. June 2017 · Paper 3 · Q5(b) · 6 marks ·
(b)* The structures for six naturally occurring organic compounds with pleasant smells, B–G, are shown below. The common names in brackets relate to their source and smell. OH O B C (linalool) (citral) O OH D (geraniol) E (camphor) O OH F G (menthol) (ionone) Explain how chemical tests would allow each compound to be distinguished from the other compounds. In your answer, include essential details for all test procedures and observations. Details of apparatus and quantities are not required. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [6]

Mark schemes

1. June 2025 · Paper 2 · Q21(b)
Mark scheme June 2025 Paper 2 Q21(b)
2. June 2025 · Paper 2 · Q21(c)
Mark scheme June 2025 Paper 2 Q21(c)
3. June 2025 · Paper 2 · Q22(a)(i)
Mark scheme June 2025 Paper 2 Q22(a)(i)
4. June 2025 · Paper 2 · Q22(a)(ii)
Mark scheme June 2025 Paper 2 Q22(a)(ii)
5. June 2025 · Paper 3 · Q2(b)(i)
Mark scheme June 2025 Paper 3 Q2(b)(i)
6. June 2024 · Paper 2 · Q3
Mark scheme June 2024 Paper 2 Q3
7. June 2024 · Paper 2 · Q5
Mark scheme June 2024 Paper 2 Q5
8. June 2024 · Paper 2 · Q13
Mark scheme June 2024 Paper 2 Q13
9. June 2024 · Paper 3 · Q5(a)(i)
Mark scheme June 2024 Paper 3 Q5(a)(i)
10. June 2024 · Paper 3 · Q5(a)(iii)
Mark scheme June 2024 Paper 3 Q5(a)(iii)
11. June 2024 · Paper 3 · Q5(b)(ii)
Mark scheme June 2024 Paper 3 Q5(b)(ii)
12. June 2023 · Paper 2 · Q2
Mark scheme June 2023 Paper 2 Q2
13. June 2022 · Paper 2 · Q18(a)(i)
Mark scheme June 2022 Paper 2 Q18(a)(i)
14. June 2022 · Paper 2 · Q18(a)(ii)
Mark scheme June 2022 Paper 2 Q18(a)(ii)
15. June 2022 · Paper 2 · Q20(a)(i)
Mark scheme June 2022 Paper 2 Q20(a)(i)
16. November 2021 · Paper 2 · Q10
Mark scheme November 2021 Paper 2 Q10
17. November 2021 · Paper 2 · Q21
Mark scheme November 2021 Paper 2 Q21
18. November 2020 · Paper 2 · Q13
Mark scheme November 2020 Paper 2 Q13
19. November 2020 · Paper 2 · Q19(b)
Mark scheme November 2020 Paper 2 Q19(b)
20. June 2019 · Paper 2 · Q16(b)(i)
Mark scheme June 2019 Paper 2 Q16(b)(i)
21. June 2019 · Paper 2 · Q17(b)(i)
Mark scheme June 2019 Paper 2 Q17(b)(i)
22. June 2019 · Paper 2 · Q17(b)(ii)
Mark scheme June 2019 Paper 2 Q17(b)(ii)
23. June 2019 · Paper 2 · Q18(c)
Mark scheme June 2019 Paper 2 Q18(c)
24. June 2019 · Paper 3 · Q4(a)(iii)
Mark scheme June 2019 Paper 3 Q4(a)(iii)
25. June 2018 · Paper 2 · Q19(c)(ii)
Mark scheme June 2018 Paper 2 Q19(c)(ii)
26. June 2018 · Paper 2 · Q20(b)(i)
Mark scheme June 2018 Paper 2 Q20(b)(i)
27. June 2018 · Paper 2 · Q20(b)(ii)
Mark scheme June 2018 Paper 2 Q20(b)(ii)
28. June 2018 · Paper 2 · Q20(b)(iii)
Mark scheme June 2018 Paper 2 Q20(b)(iii)
29. June 2018 · Paper 2 · Q21(c)(i)
Mark scheme June 2018 Paper 2 Q21(c)(i)
30. June 2017 · Paper 2 · Q20(b)
Mark scheme June 2017 Paper 2 Q20(b)
31. June 2017 · Paper 3 · Q5(b)
Mark scheme June 2017 Paper 3 Q5(b)