Purity and separating mixtures: OCR GCSE Chemistry A questions

Every OCR GCSE Chemistry A exam question on C2.1 Purity and separating mixtures, 2018–2025, with its mark scheme and examiner’s report.

All 108 questions on Purity and separating mixtures, as a list

June 2025, Paper 1 Foundation, Q18 (6 marks): 18* A student has a mixture of iron filings, sand and salt. Iron filings Sand and salt The student wants to collect pure samples of: • iron filings • sand • sal
June 2025, Paper 1 Foundation, Q23(a) (1 mark): What is meant by a pure substance? [1]
June 2025, Paper 1 Foundation, Q23(b)(i) (2 marks): A student does a chromatography experiment to separate some dyes. The diagram shows how they set up their equipment. Chromatography paper Start line drawn in in
June 2025, Paper 1 Foundation, Q23(b)(ii) (2 marks): The student calculates that a dye has an Rf value of 0.67. The table shows the Rf value of different dyes. Colour of dye Rf value Blue 0.15–0.20 Red 0.35–0.40 P
June 2025, Paper 1 Foundation, Q23(c) (2 marks): The diagram shows a chromatogram for another dye. 3.4 cm 2.7 cm Calculate the Rf value of the dye. Use the equation: Rf = distance travelled by the substance di
June 2025, Paper 1 Foundation, Q23(d) (2 marks): A student separates substance S from a mixture of substances S and T. The starting mass of the mixture is 9.7 g and they obtain 5.1 g of pure substance S. Calcu
June 2025, Paper 3 Higher, Q17(a) (1 mark): What is meant by a pure substance? [1]
June 2025, Paper 3 Higher, Q17(b)(i) (2 marks): A student does a chromatography experiment to separate some dyes. The diagram shows how they set up their equipment. Chromatography paper Start line drawn in in
June 2025, Paper 3 Higher, Q17(b)(ii) (2 marks): The student calculates that a dye has an Rf value of 0.67. The table shows the Rf value of different dyes. Colour of dye Rf value Blue 0.15–0.20 Red 0.35–0.40 P
June 2025, Paper 3 Higher, Q17(c) (2 marks): The diagram shows a chromatogram for another dye. 3.4 cm 2.7 cm Calculate the Rf value of the dye. Use the equation: Rf = distance travelled by the substance di
June 2025, Paper 3 Higher, Q17(d) (2 marks): A student separates substance S from a mixture of substances S and T. The starting mass of the mixture is 9.7 g and they obtain 5.1 g of pure substance S. Calcu
June 2024, Paper 1 Foundation, Q5 (1 mark): Which equipment is used for filtration? A B C D Your answer [1]
June 2024, Paper 1 Foundation, Q22(b)(i) (1 mark): The spots on the chromatogram are colourless. State what the scientist could use to see the spots. [1]
June 2024, Paper 1 Foundation, Q22(b)(ii) (3 marks): After the scientist uses a method to see the spots, the chromatogram for Tablet A is shown. 7 Solvent front 6 5 4 3 2 1 Pencil line 0cm Tablet A Calculate the R
June 2024, Paper 1 Foundation, Q23(a) (2 marks): Draw lines to connect each separation method to the correct mixture. Separation method Mixture Insoluble solid Crystallisation and liquid Solution containing a
June 2024, Paper 1 Foundation, Q23(b)(i) (1 mark): A liquid in the mixture is flammable. Suggest a change the student could make to the apparatus to make the distillation safer. [1]
June 2024, Paper 1 Foundation, Q23(b)(ii) (1 mark): The student wants to record the boiling point of the pure liquid that is collected in the collection flask. Suggest an improvement the student could make to the
June 2024, Paper 1 Foundation, Q23(c) (2 marks): The pure liquid collected has the molecular formula (C2H5)2O and a boiling point of 35 °C. Which statements about the pure liquid are correct? Tick (3) two boxe
June 2024, Paper 3 Higher, Q16(b)(i) (1 mark): The spots on the chromatogram are colourless. State what the scientist could use to see the spots. [1]
June 2024, Paper 3 Higher, Q16(b)(ii) (3 marks): After the scientist uses a method to see the spots, the chromatogram for Tablet A is shown. 7 Solvent front 6 5 4 3 2 1 Pencil line 0cm Tablet A Calculate the R
June 2024, Paper 3 Higher, Q17(a) (2 marks): Draw lines to connect each separation method to the correct mixture. Separation method Mixture Insoluble solid Crystallisation and liquid Solution containing a
June 2024, Paper 3 Higher, Q17(b)(i) (1 mark): A liquid in the mixture is flammable. Suggest a change the student could make to the apparatus to make the distillation safer. [1]
June 2024, Paper 3 Higher, Q17(b)(ii) (1 mark): The student wants to record the boiling point of the pure liquid that is collected in the collection flask. Suggest an improvement the student could make to the
June 2024, Paper 3 Higher, Q17(c) (2 marks): The pure liquid collected has the molecular formula (C2H5)2O and a boiling point of 35 °C. Which statements about the pure liquid are correct? Tick (3) two boxe
June 2023, Paper 1 Foundation, Q17(a)(i) (1 mark): Explain what is meant by a pure substance. [1]
June 2023, Paper 1 Foundation, Q17(a)(ii) (1 mark): How can you tell that the three painkillers are pure from their melting points? [1]
June 2023, Paper 1 Foundation, Q17(b) (1 mark): The scientist uses gas chromatography to investigate a mixture of painkiller A and painkiller B. How many peaks will the scientist see in the gas chromatogram?
June 2023, Paper 1 Foundation, Q17(c)(i) (3 marks): Calculate the Rf value of painkiller D. distance travelled by substance Use the formula: Rf = distance travelled by solvent Give your answer to 2 decimal places
June 2023, Paper 1 Foundation, Q17(c)(ii) (2 marks): Which components are needed for thin layer chromatography? Put a ring around the two correct components. balance Bunsen burner mobile phase paper stationary pha
June 2023, Paper 1 Foundation, Q17(d) (2 marks): The scientist thinks that an impure painkiller will only have two spots on the thin layer chromatogram. Give two reasons why the scientist is incorrect. 1 2 [2]
June 2023, Paper 3 Higher, Q2 (1 mark): Which equipment is needed for distillation? A Condenser, funnel, thermometer B Condenser, round-bottomed flask, thermometer C Thermometer, beaker, pH probe D Th
June 2023, Paper 3 Higher, Q6 (1 mark): Which fraction is collected at the top of the fractional distillation column? Melting point range Boiling point range (°C) (°C) A –70 – –60 20 – 25 B –50 – –40
June 2023, Paper 3 Higher, Q15 (1 mark): A student investigates some samples using gas chromatography. The student also measures the melting point of each sample. Which results should the student expec
June 2023, Paper 3 Higher, Q20(a) (4 marks): A scientist has a sample of seawater. The sample contains sand, water and salt. The scientist wants to collect pure samples of: • sand • water • salt. Describe
June 2023, Paper 3 Higher, Q20(c)(iii) (1 mark): A scientist wants to separate magnesium sulfate from other compounds using thin layer chromatography. The spot does not move from the start line on the chromato
June 2022, Paper 1 Foundation, Q6 (1 mark): Which pieces of apparatus are used for filtration? A Beaker, filter paper and condenser B Beaker, filter paper and funnel C Beaker, funnel and mass balance D Fi
June 2022, Paper 1 Foundation, Q19(b) (3 marks): The student uses paper chromatography to separate the dyes. The diagram shows the apparatus at the start of the experiment. Label the apparatus. Use phrases fro
June 2022, Paper 1 Foundation, Q19(c)(i) (2 marks): Calculate the Rf value of this dye. Give your answer to 2 significant figures. Rf value of dye = [2]
June 2022, Paper 1 Foundation, Q19(c)(ii) (2 marks): Another dye, X, has an Rf value of 0.22. The student knows that the food colouring tartrazine has an Rf value of 0.11. The student thinks dye X is tartrazine. E
June 2022, Paper 1 Foundation, Q22(a)(i) (1 mark): State a method the student uses to find out if the sample is pure. [1]
June 2022, Paper 1 Foundation, Q22(a)(iii) (4 marks): The boiling point of hexane is lower than the boiling point of cyclohexane. Describe a method the student could use to obtain a sample of pure hexane from the m
June 2022, Paper 1 Foundation, Q22(b)(i) (2 marks): The student obtains 12.0 g of hexane from 15.2 g of the mixture of hexane and cyclohexane. Calculate the percentage of hexane obtained. Give your answer to 2 si
June 2022, Paper 3 Higher, Q7 (1 mark): A student wants to separate substances by filtration. They write a method for the experiment but not in the correct order as shown. 1. Pour the mixture through
June 2022, Paper 3 Higher, Q12 (1 mark): A scientist investigates the melting point of some substances that may contain paracetamol as shown in the table. The melting point of pure paracetamol is 169 °
June 2022, Paper 3 Higher, Q17(a)(i) (1 mark): State a method the student uses to find out if the sample is pure. [1]
June 2022, Paper 3 Higher, Q17(a)(iii) (4 marks): The boiling point of hexane is lower than the boiling point of cyclohexane. Describe a method the student could use to obtain a sample of pure hexane from the m
June 2022, Paper 3 Higher, Q17(b)(i) (2 marks): The student obtains 12.0 g of hexane from 15.2 g of the mixture of hexane and cyclohexane. Calculate the percentage of hexane obtained. Give your answer to 2 si
June 2022, Paper 3 Higher, Q20(a)(i) (3 marks): Calculate the Rf value of the blue spot in the dye in cake 3. Give your answer to 2 significant figures. Rf value of blue spot in the dye in cake 3 = [3]
June 2022, Paper 3 Higher, Q20(a)(ii) (2 marks): Which of the cakes would you expect to taste the same? Explain your answer using data from Fig. 20.1. [2]
June 2022, Paper 3 Higher, Q20(c) (1 mark): The student tests another dye. The chromatogram is shown in Fig. 20.2. Fig. 20.2 Solvent front Blue spot Yellow spot What should the student change in their exp
November 2021, Paper 1 Foundation, Q8 (1 mark): Fractional distillation is used to separate mixtures, such as crude oil. Which statement about fractional distillation is correct? A Fractional distillation cau
November 2021, Paper 1 Foundation, Q9 (1 mark): Which statement about the melting point of a substance is correct? A A pure substance has a sharp melting point. B A pure substance melts over a range of temper
November 2021, Paper 1 Foundation, Q18(a)(i) (1 mark): What could be used as the mobile phase in the experiment? [1]
November 2021, Paper 1 Foundation, Q18(a)(ii) (1 mark): Why does the scientist put a lid on top of the beaker? [1]
November 2021, Paper 1 Foundation, Q18(b)(i) (2 marks): Is the scientist correct? Explain your answer. [2]
November 2021, Paper 1 Foundation, Q18(b)(ii) (1 mark): Explain what is meant by a pure substance. [1]
November 2021, Paper 1 Foundation, Q18(b)(iii) (1 mark): Which two samples contain the same mixture of chemicals? Tick (✓) two boxes. Sample 1 Sample 2 Sample 3 Sample 4 [1]
November 2021, Paper 1 Foundation, Q18(c)(iii) (1 mark): Why does the scientist use gas chromatography, instead of thin layer chromatography, in this investigation? [1]
November 2021, Paper 1 Foundation, Q23(a) (1 mark): Which diagram shows the apparatus that should be used to separate a mixture of substance M and substance N? Tick (✓) one box. [1]
November 2021, Paper 1 Foundation, Q23(b)(i) (3 marks): Describe a method that could be used to separate a mixture of substance O and substance P to obtain pure samples. [3]
November 2021, Paper 1 Foundation, Q23(b)(ii) (3 marks): A student separates substance O from a mixture. They start with 6.2 g of the mixture and obtain 2.6 g of pure substance O. Calculate the mass of pure substance
November 2021, Paper 3 Higher, Q13 (1 mark): A student investigates if an unknown liquid sample is pure. Which method should the student use? A Filter the sample to see if any solid can be separated. B Gas
November 2021, Paper 3 Higher, Q17(a) (1 mark): Which diagram shows the apparatus that should be used to separate a mixture of substance M and substance N? Tick (✓) one box. [1]
November 2021, Paper 3 Higher, Q17(b)(i) (3 marks): Describe a method that could be used to separate a mixture of substance O and substance P to obtain pure samples. [3]
November 2021, Paper 3 Higher, Q17(b)(ii) (3 marks): A student separates substance O from a mixture. They start with 6.2 g of the mixture and obtain 2.6 g of pure substance O. Calculate the mass of pure substance
November 2021, Paper 3 Higher, Q21(a) (6 marks): A scientist uses chromatography and melting points to investigate the purity of three samples of a painkiller, A, B and C. • The scientist compares the three sa
November 2020, Paper 1 Foundation, Q1 (1 mark): Which separation technique is this equipment used for? A Crystallisation B Distillation C Evaporation D Filtration Your answer [1]
November 2020, Paper 1 Foundation, Q16(c)(i) (3 marks): Describe how you could separate substance B from the mixture. [3]
November 2020, Paper 1 Foundation, Q16(c)(ii) (2 marks): Describe how you would then obtain substance C after separating substance B. [2]
November 2020, Paper 1 Foundation, Q20(a) (1 mark): The start line is not drawn in ink. Explain why. [1]
November 2020, Paper 1 Foundation, Q20(b) (1 mark): Food additive D is insoluble in the solvent used. Draw on the diagram the spot for food additive D at the end of the experiment. [1]
November 2020, Paper 1 Foundation, Q20(c) (1 mark): Which additive is in the tomato sauce? Tick (3) one box. A B C [1]
November 2020, Paper 1 Foundation, Q20(d) (3 marks): Calculate the Rf value for additive C. distance travelled by the substance Use the equation: Rf = distance travelled by the solvent Give your answer to 2 signif
November 2020, Paper 1 Foundation, Q21(a)(i) (1 mark): What is the name of the piece of apparatus labelled X? [1]
November 2020, Paper 1 Foundation, Q21(a)(ii) (1 mark): Name the process shown in Fig. 21.1. [1]
November 2020, Paper 1 Foundation, Q21(a)(iii) (2 marks): Suggest two changes that the student should make to set-up the apparatus correctly. 1 2 [2]
November 2020, Paper 3 Higher, Q2 (1 mark): Which purification technique is used to separate ethanol and water from a mixture? A Chromatography B Distillation C Evaporation D Filtration Your answer [1]
November 2020, Paper 3 Higher, Q20(a)(i) (3 marks): Calculate the Rf value for C. Give your answer to 2 significant figures. Rf value = [3]
November 2020, Paper 3 Higher, Q20(a)(ii) (1 mark): Which additives are shown to be in the tomato sauce? Tick (3) all the correct boxes. A B C D [1]
November 2020, Paper 3 Higher, Q20(a)(iii) (1 mark): Suggest why D has not travelled as far up the plate as C. [1]
November 2020, Paper 3 Higher, Q20(b)(i) (2 marks): State one similarity and one difference between gas chromatography and thin-layer chromatography. Similarity Difference [2]
November 2020, Paper 3 Higher, Q20(b)(ii) (1 mark): Explain why thin-layer chromatography is used instead of gas chromatography to analyse the tomato sauce. [1]
June 2019, Paper 1 Foundation, Q16(a) (3 marks): Draw a line from each separation process to the apparatus used. Use only one line for each process. Separation process Apparatus used Crystallisation Filtration
June 2019, Paper 1 Foundation, Q16(b) (1 mark): A student is given a mixture of iron filings and sulfur powder. Suggest a method that he could use to separate the iron and sulfur. [1]
June 2019, Paper 1 Foundation, Q17(a)(ii) (1 mark): A scientist describes compound X as a pure substance. Explain what scientists mean when they describe compounds as pure. [1]
June 2019, Paper 1 Foundation, Q17(a)(iii) (1 mark): Explain how the scientists tell from the graph that compound X is a pure substance. [1]
June 2019, Paper 1 Foundation, Q18(a)(i) (1 mark): Look at the chromatogram for the sample of the paints from the painting. Which paint colour(s) is/are pure? [1]
June 2019, Paper 1 Foundation, Q18(a)(ii) (2 marks): The red, blue and yellow paint from the painting are dissolved in different solvents, X, Y and Z. The results are shown below. Solvent used X Y Z Red Red solid
June 2019, Paper 1 Foundation, Q18(a)(iii) (3 marks): Scientists use Rf values to compare the different spots on the chromatogram. Calculate the Rf value for the red paint in the sample of paints from the painting.
June 2019, Paper 1 Foundation, Q18(b) (1 mark): The laboratory think that the painting was completed in 1849. Is the laboratory correct? Explain your answer. [1]
June 2019, Paper 3 Higher, Q4 (1 mark): Rf values are used to compare the different spots on a chromatogram. What is the formula used to calculate an Rf value? Rf = distance travelled by solvent A dis
June 2019, Paper 3 Higher, Q12 (1 mark): Paper chromatography can be used to separate the colours in ink. Water is the solvent used to separate the colours in water soluble ink. What name is given to t
June 2019, Paper 3 Higher, Q18(a)(i) (2 marks): Which alcohol will be distilled first? Tick (✓) one box. Methanol Ethanol Propanol Explain your answer. [2]
June 2019, Paper 3 Higher, Q18(a)(iv) (2 marks): The scientist wants to improve the separation of the mixture of alcohols. Suggest a piece of equipment he could use. Explain how this will improve the separatio
June 2018, Paper 1 Foundation, Q18(a) (2 marks): Explain why her method does not work and describe the method she should use. [2]
June 2018, Paper 1 Foundation, Q18(b) (2 marks): The student wants to separate a mixture of two liquids. The liquids are: Boiling point Liquid (°C) Water 100 Ethanol 78 Which separation technique should she us
June 2018, Paper 1 Foundation, Q18(c)(i) (1 mark): What is meant by a pure solid? [1]
June 2018, Paper 1 Foundation, Q18(c)(ii) (3 marks): The student measures the melting points of four samples of solid A. Look at her results. Melting point Sample (°C) 1 115 2 119 3 114–118 4 120–122 She knows tha
June 2018, Paper 1 Foundation, Q23(a) (1 mark): What is the mobile phase in this experiment? [1]
June 2018, Paper 1 Foundation, Q23(b) (1 mark): Explain how paper chromatography separates the colours in ink. [1]
June 2018, Paper 1 Foundation, Q23(c)(i) (2 marks): Look at the green spot for ink A. Calculate the Rf value for the green spot. Answer = [2]
June 2018, Paper 1 Foundation, Q23(c)(ii) (2 marks): Which ink was used to forge the signature on the cheque? Explain how you can tell. [2]
June 2018, Paper 3 Higher, Q7 (1 mark): Which statement correctly describes a pure substance? A Consists of just one element or compound B Has a low melting point C Is a mixture of two or more substan
June 2018, Paper 3 Higher, Q8 (1 mark): A student separates a dye using thin layer chromatography. She puts a thin layer of solid alumina onto a glass plate. She puts the dye on the pencil line. She p
June 2018, Paper 3 Higher, Q18(a) (2 marks): The student’s method is not safe. Explain why it is not safe and explain how she could improve her method to make it safer. [2]
June 2018, Paper 3 Higher, Q20(a) (4 marks): Describe how the student can separate the mixture to get pure samples of all three substances. Explain why each method of separation works. [4]
June 2018, Paper 3 Higher, Q20(b) (3 marks): The student separates two solid substances A and B. She wants to check that they are pure. She measures the melting points of four samples of solid B. Look at h
June 2018, Paper 4 Higher, Q15 (1 mark): A student wants to test the purity of a liquid by testing its boiling point. The actual boiling point of the pure liquid is 85 °C. Which equation represents the

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