Controlling reactions: OCR GCSE Combined Science A questions

Every OCR GCSE Combined Science A exam question on C5.1 Controlling reactions, 2018–2025, with its mark scheme and examiner’s report.

All 100 questions on Controlling reactions, as a list

June 2025, Chemistry Paper 4 Foundation, Q6 (1 mark): When marble chips react with an acid, they produce a colourless solution and a gas. Which method is used to determine the rate of reaction? A A disappearing cro
June 2025, Chemistry Paper 4 Foundation, Q10 (1 mark): The graph shows the volume of gas produced during a reaction. A tangent has been drawn at 50 seconds. The gradient of the tangent gives the rate of reaction. 10
June 2025, Chemistry Paper 4 Foundation, Q16(c)(i) (1 mark): What name is given to biological catalysts? [1]
June 2025, Chemistry Paper 4 Foundation, Q16(c)(ii) (2 marks): Describe and explain the effect of adding the piece of potato to the hydrogen peroxide solution. Include ideas about rate of reaction and activation energy. [2]
June 2025, Chemistry Paper 4 Foundation, Q16(c)(iii) (1 mark): The student measures the total volume of oxygen produced in the reaction with and without the piece of potato. With the potato, the total volume is: increased,
June 2025, Chemistry Paper 4 Foundation, Q16(d)(i) (2 marks): Surface area of the piece of potato = cm2 [2]
June 2025, Chemistry Paper 4 Foundation, Q16(d)(ii) (1 mark): A student thinks that cutting the potato into smaller pieces will make the catalyst more effective. Explain why the student is correct. Tick (✓) one box. The sm
June 2025, Chemistry Paper 4 Foundation, Q16(e) (1 mark): The student measures the rate of reaction when the piece of potato is added to the hydrogen peroxide. The rate of reaction is 1.5 cm3 / s. They then measure the
June 2025, Chemistry Paper 10 Higher, Q2 (1 mark): The graph shows the volume of gas produced during a reaction. A tangent has been drawn at 50 seconds. The gradient of the tangent gives the rate of reaction. 10
June 2025, Chemistry Paper 10 Higher, Q4 (1 mark): Why do reactions happen faster at higher temperatures? A The activation energy increases. B The particles are closer together. C The particles collide with more
June 2025, Chemistry Paper 10 Higher, Q11(c)(i) (1 mark): What name is given to biological catalysts? [1]
June 2025, Chemistry Paper 10 Higher, Q11(c)(ii) (2 marks): Describe and explain the effect of adding the piece of potato to the hydrogen peroxide solution. Include ideas about rate of reaction and activation energy. [2]
June 2025, Chemistry Paper 10 Higher, Q11(c)(iii) (1 mark): The student measures the total volume of oxygen produced in the reaction with and without the piece of potato. With the potato, the total volume is: increased,
June 2025, Chemistry Paper 10 Higher, Q11(d)(i) (2 marks): Surface area of the piece of potato = cm2 [2]
June 2025, Chemistry Paper 10 Higher, Q11(d)(ii) (1 mark): A student thinks that cutting the potato into smaller pieces will make the catalyst more effective. Explain why the student is correct. Tick (✓) one box. The sm
June 2025, Chemistry Paper 10 Higher, Q11(e) (1 mark): The student measures the rate of reaction when the piece of potato is added to the hydrogen peroxide. The rate of reaction is 1.5 cm3 / s. They then measure the
June 2024, Chemistry Paper 4 Foundation, Q2 (1 mark): What are catalysts found in biological systems called? A Bacteria B Enzymes C Isotopes D Vitamins Your answer [1]
June 2024, Chemistry Paper 4 Foundation, Q15 (6 marks): 15* A student investigates the rate of reaction between pieces of marble chips and an excess of dilute hydrochloric acid. The diagram shows the equipment they u
June 2024, Chemistry Paper 10 Higher, Q4 (1 mark): Which of the catalysts is an example of an enzyme? A Alumina – used in the cracking of hydrocarbons B Copper – used in the reaction between zinc and dilute sulf
June 2024, Chemistry Paper 10 Higher, Q7 (1 mark): A student investigates the rate of reaction between marble chips and dilute hydrochloric acid. The graph shows how the mass of the reactants changes during the
June 2024, Chemistry Paper 10 Higher, Q16 (6 marks): 16* A student investigates the rate of reaction between magnesium and an excess of dilute hydrochloric acid. Dilute hydrochloric acid Strip of magnesium Dilute
June 2023, Chemistry Paper 4 Foundation, Q7 (1 mark): The diagram shows the reaction profile for an uncatalysed reaction. X Reactants Energy Y Products Progress of reaction How does adding a catalyst to the reactio
June 2023, Chemistry Paper 4 Foundation, Q9 (1 mark): Which reactions can be catalysed by an enzyme? A Combustion reactions B Electrolysis of metal ores C Reactions in biological systems D Reactions of metals with
June 2023, Chemistry Paper 4 Foundation, Q10 (1 mark): The rate of reaction between magnesium and dilute hydrochloric acid depends on the concentration of the dilute hydrochloric acid. Which concentration of dilute
June 2023, Chemistry Paper 4 Foundation, Q16(a) (3 marks): The student has difficulty filling the measuring cylinder with water. They change the measuring cylinder for a different piece of apparatus which allows them to
June 2023, Chemistry Paper 4 Foundation, Q16(c) (2 marks): The student records the results of the experiment every 30 seconds. The graph shows the student’s results. Write the correct label, including the units, for the
June 2023, Chemistry Paper 4 Foundation, Q16(d) (2 marks): The student repeats the experiment. The only difference is they use a higher concentration of acid. [2] Draw a line on the graph to show the results of this exp
June 2023, Chemistry Paper 4 Foundation, Q16(e) (3 marks): If the experiment is repeated at a higher temperature, the rate of reaction increases. Explain why. Use ideas about particles and collisions. [3]
June 2023, Chemistry Paper 10 Higher, Q1 (1 mark): Which reactions can be catalysed by an enzyme? A Combustion reactions B Electrolysis of metal ores C Reactions in biological systems D Reactions of metals with
June 2023, Chemistry Paper 10 Higher, Q10 (1 mark): When marble chips react with dilute hydrochloric acid, the mass of the reactants decreases. The graph shows the loss in mass of the reactants with time. 50 40 3
June 2023, Chemistry Paper 10 Higher, Q11(a) (3 marks): The student has difficulty filling the measuring cylinder with water. They change the measuring cylinder for a different piece of apparatus which allows them to
June 2023, Chemistry Paper 10 Higher, Q11(c) (2 marks): The student records the results of the experiment every 30 seconds. The graph shows the student’s results. Write the correct label, including the units, for the
June 2023, Chemistry Paper 10 Higher, Q11(d) (2 marks): The student repeats the experiment. The only difference is they use a higher concentration of acid. [2] Draw a line on the graph to show the results of this exp
June 2023, Chemistry Paper 10 Higher, Q11(e) (3 marks): If the experiment is repeated at a higher temperature, the rate of reaction increases. Explain why. Use ideas about particles and collisions. [3]
June 2022, Chemistry Paper 4 Foundation, Q3 (1 mark): A teacher investigates the rate of reaction between magnesium and dilute hydrochloric acid. The diagram shows the equipment they use. X Conical flask Dilute hyd
June 2022, Chemistry Paper 4 Foundation, Q7 (1 mark): A student has four different solids. • One of the solids is a catalyst. • The student tests 1 g of each solid in a chemical reaction. The table shows the studen
June 2022, Chemistry Paper 4 Foundation, Q9 (1 mark): A student investigates the rate of reaction between magnesium and an excess of dilute sulfuric acid. Which graph shows how the rate of reaction changes with tim
June 2022, Chemistry Paper 4 Foundation, Q14(b)(i) (1 mark): What effect does the porous pot have on the rate of the reaction? Put a ring around the correct answer. decreases it increases it no effect [1]
June 2022, Chemistry Paper 4 Foundation, Q14(b)(ii): What effect does the porous pot have on the activation energy of the reaction? Put a ring around the correct answer.
June 2022, Chemistry Paper 10 Higher, Q1 (1 mark): A student investigates the rate of reaction between magnesium and an excess of dilute sulfuric acid. Which graph shows how the rate of reaction changes with tim
June 2022, Chemistry Paper 10 Higher, Q3 (1 mark): A student investigates the rate of reaction between magnesium and dilute hydrochloric acid. Measuring cylinder Conical flask Dilute hydrochloric acid Magnesium
June 2022, Chemistry Paper 10 Higher, Q13(a) (2 marks): The equation shows the reaction between calcium carbonate and hydrochloric acid. CaCO3(s) + 2HCl (aq) CaCl 2(aq) + H2O(l) + CO2(g) Use this equation to explain
June 2022, Chemistry Paper 10 Higher, Q13(b) (2 marks): The student decides to use Experiment 2 because they think it will produce more accurate results than Experiment 1. Explain why the student is correct. [2]
June 2022, Chemistry Paper 10 Higher, Q13(c) (4 marks): Fig. 13.2 shows the graph of the student’s results. Fig. 13.2 4 3 Loss of 2 mass (g) 1 0 0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 Time (s) T
June 2022, Chemistry Paper 10 Higher, Q13(d)(i) (2 marks): Describe two variables the student must keep the same in this experiment. 1 2 [2]
June 2022, Chemistry Paper 10 Higher, Q13(d)(ii) (2 marks): Describe and explain the effect of using smaller pieces of calcium carbonate on the rate of the reaction. [2]
November 2021, Chemistry Paper 4 Foundation, Q17(a) (3 marks): The gradient of the tangent gives the rate of reaction. Use the tangent to calculate the rate of reaction at the start of the reaction. Give your answer to 1 de
November 2021, Chemistry Paper 4 Foundation, Q17(b) (3 marks): What happens to the rate of reaction as the reaction progresses? Explain your answer using ideas about particles and collisions. [3]
November 2021, Chemistry Paper 4 Foundation, Q17(c)(i) (1 mark): Does the gradient of the graph at the start of this student’s reaction decrease, increase or stay the same compared to the first student’s experiment? Tick (3)
November 2021, Chemistry Paper 4 Foundation, Q17(c)(ii) (1 mark): Write down the volume of hydrogen gas that is produced at the end of this reaction. Volume = cm3 [1]
November 2021, Chemistry Paper 4 Foundation, Q18 (4 marks): A student investigates the reaction between zinc and dilute sulfuric acid. Dilute sulfuric acid Zinc powder The student observes that bubbles are produced slowl
November 2021, Chemistry Paper 10 Higher, Q11(a) (3 marks): The gradient of the tangent gives the rate of reaction. Use the tangent to calculate the rate of reaction at the start of the reaction. Give your answer to 1 de
November 2021, Chemistry Paper 10 Higher, Q11(b) (3 marks): What happens to the rate of reaction as the reaction progresses? Explain your answer using ideas about particles and collisions. [3]
November 2021, Chemistry Paper 10 Higher, Q11(c)(i) (1 mark): Does the gradient of the graph at the start of this student’s reaction decrease, increase or stay the same compared to the first student’s experiment? Tick (3)
November 2021, Chemistry Paper 10 Higher, Q11(c)(ii) (1 mark): Write down the volume of hydrogen gas that is produced at the end of this reaction. Volume = cm3 [1]
November 2021, Chemistry Paper 10 Higher, Q12 (4 marks): A student investigates the reaction between zinc and dilute sulfuric acid. Dilute sulfuric acid Zinc powder The student observes that bubbles are produced slowl
November 2020, Chemistry Paper 4 Foundation, Q6 (1 mark): Look at the energy profile for a reaction. 6 Energy Products Progress of reaction Which letter shows the activation energy of the reaction with a catalyst? Your
November 2020, Chemistry Paper 4 Foundation, Q8 (1 mark): Marble chips react with dilute hydrochloric acid and release a gas. 8 The graph shows how the mass of the reactants changes as the reaction progresses. A Mass (
November 2020, Chemistry Paper 4 Foundation, Q9 (1 mark): What is an example of a biological catalyst? 9 A Alipid B An amino acid C An enzyme D A substrate Your answer [1]
November 2020, Chemistry Paper 4 Foundation, Q18(a) (1 mark): Look at the equation for the reaction. Na,S,O3(aq) + 2HCl(aq) → 2NaCl(aq) + H2O(l) + S(s) + SO2(g) Which product in the reaction makes the cross disappear? Tick
November 2020, Chemistry Paper 4 Foundation, Q18(b) (3 marks): The rate of reaction can be calculated using the equation: 1 Rate of reaction = reaction time Use the graph in Fig. 18.2 to calculate the rate of reaction when
November 2020, Chemistry Paper 4 Foundation, Q18(c)(i) (1 mark): Describe the trend shown by the graph in Fig. 18.2. ... [1]
November 2020, Chemistry Paper 4 Foundation, Q18(c)(ii) (1 mark): State how the rate of reaction changes as the sodium thiosulfate concentration changes. [1]
November 2020, Chemistry Paper 4 Foundation, Q18(d) (1 mark): Another student investigates the effect of temperature on the rate of reaction. She calculates the rate of reaction at different temperatures, as shown in the t
November 2020, Chemistry Paper 10 Higher, Q1 (1 mark): What is an example of a biological catalyst? A A lipid B An amino acid C An enzyme D A substrate Your answer [1]
November 2020, Chemistry Paper 10 Higher, Q7 (1 mark): Look at the reaction. PCl 3(g) + Cl 2(g) PCl 5(g) Which statement explains why the rate of reaction changes as the pressure increases? A The energy of the parti
November 2020, Chemistry Paper 10 Higher, Q8 (1 mark): The rate of reaction of marble chips with dilute hydrochloric acid depends on the surface area of the marble chips. Which surface area of the marble chips gives
November 2020, Chemistry Paper 10 Higher, Q12(a) (1 mark): Look at the equation for the reaction. Na2S2O3(aq) + 2HCl (aq) → 2NaCl (aq) + H2O(l) + S(s) + SO2(g) Which product in the reaction makes the cross disappear? Ti
November 2020, Chemistry Paper 10 Higher, Q12(b) (3 marks): The rate of reaction can be calculated using the equation: 1 Rate of reaction = reaction time Use the graph in Fig. 12.2 to calculate the rate of reaction when
November 2020, Chemistry Paper 10 Higher, Q12(c)(i) (1 mark): Describe the trend shown by the graph in Fig. 12.2. [1]
November 2020, Chemistry Paper 10 Higher, Q12(c)(ii) (1 mark): State how the rate of reaction changes as the sodium thiosulfate concentration changes. [1]
November 2020, Chemistry Paper 10 Higher, Q12(d) (1 mark): Another student investigates the effect of temperature on the rate of reaction. She calculates the rate of reaction at different temperatures, as shown in the t
November 2020, Chemistry Paper 10 Higher, Q13 (4 marks): Hydrogen peroxide solution decomposes slowly to form water and oxygen. Look at the equation for the reaction. 2H2O2(aq) → 2H2O(l) + O2(g) This reaction, shown i
June 2019, Chemistry Paper 4 Foundation, Q1 (1 mark): How does a catalyst speed up a reaction? A It decreases the activation energy. B It decreases the energy of the reactant particles. C It increases the activatio
June 2019, Chemistry Paper 4 Foundation, Q6 (1 mark): A teacher adds calcium carbonate to an acid in four separate flasks, A, B, C and D. He measures the time it takes for the same volume of carbon dioxide to be pr
June 2019, Chemistry Paper 4 Foundation, Q10 (1 mark): Two pieces of chalk, X and Y, both have the same volume. A student cuts Y into two pieces. The student reacts X and both pieces of Y with separate samples of an
June 2019, Chemistry Paper 4 Foundation, Q16(b)(i) (1 mark): Identify the independent variable in the investigation. [1]
June 2019, Chemistry Paper 4 Foundation, Q16(b)(ii) (2 marks): Identify two control variables in the investigation. 1 2 [2]
June 2019, Chemistry Paper 4 Foundation, Q16(c) (1 mark): The student measures the time it takes from adding the magnesium to the hydrochloric acid until the reaction mixture stops bubbling. The table shows the student
June 2019, Chemistry Paper 4 Foundation, Q16(d) (3 marks): The results at 0.75 mol / dm3 are repeated. This is a graph of the student’s results. 300 250 200 150 Time (s) 100 50 0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 Concentratio
June 2019, Chemistry Paper 10 Higher, Q1 (1 mark): What is an enzyme? A A biological catalyst B A biological reactant C A natural monomer D A starch molecule Your answer [1]
June 2019, Chemistry Paper 10 Higher, Q5 (1 mark): Manganese dioxide, MnO2, can act as a catalyst. A student mixes 10 g of MnO2, a black solid, with 4 different solutions, A, B, C and D. With which solution does
June 2019, Chemistry Paper 10 Higher, Q12(b)(i) (1 mark): Identify the independent variable in the investigation. [1]
June 2019, Chemistry Paper 10 Higher, Q12(b)(ii) (2 marks): Identify two control variables in the investigation. 1 2 [2]
June 2019, Chemistry Paper 10 Higher, Q12(c) (1 mark): The student measures the time it takes from adding the magnesium to the hydrochloric acid until the reaction mixture stops bubbling. The table shows the student
June 2019, Chemistry Paper 10 Higher, Q12(d) (3 marks): The results at 0.75 mol / dm3 are repeated. This is a graph of the student’s results. 300 250 200 Time (s) 150 100 50 0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 Concentratio
June 2018, Chemistry Paper 4 Foundation, Q2 (1 mark): Which statement about catalysts is correct? A A catalyst decreases the rate of many different reactions. B A catalyst for one reaction will be the catalyst for
June 2018, Chemistry Paper 4 Foundation, Q11(a)(i) (2 marks): Plot the results for the small marble chips. [2]
June 2018, Chemistry Paper 4 Foundation, Q11(a)(ii) (1 mark): Draw a line of best fit. [1]
June 2018, Chemistry Paper 4 Foundation, Q11(b)(i) (1 mark): How long does it take for the reaction to finish? Answer = minutes [1]
June 2018, Chemistry Paper 4 Foundation, Q11(b)(ii) (1 mark): What mass of carbon dioxide is given off after 15 minutes? Answer = g [1]
June 2018, Chemistry Paper 4 Foundation, Q11(c) (2 marks): The reaction is faster with small marble chips. Write down two ways that the graph shows this is correct. 1 2 [2]
June 2018, Chemistry Paper 4 Foundation, Q11(d) (1 mark): Both small and large marble chips give off the same mass of carbon dioxide at the end of the experiments. Suggest why. [1]
June 2018, Chemistry Paper 4 Foundation, Q11(e) (1 mark): A balance was used to measure the amount of carbon dioxide given off. Write down the name of a different piece of equipment that could be used to measure the am
June 2018, Chemistry Paper 4 Foundation, Q18 (4 marks): A student investigates the rate of reaction between magnesium and hydrochloric acid. The reaction gives off hydrogen gas. Magnesium ribbon Hydrochloric acid The
June 2018, Chemistry Paper 10 Higher, Q9 (1 mark): Why does a catalyst speed up a chemical reaction? A It causes the reactants to collide less frequently. B It decreases the overall energy change of the reaction
June 2018, Chemistry Paper 10 Higher, Q12 (4 marks): A student investigates the rate of reaction between magnesium and hydrochloric acid. The reaction gives off hydrogen gas. Magnesium ribbon Hydrochloric acid The
June 2018, Chemistry Paper 10 Higher, Q14(a)(i) (3 marks): Calculate the rate of reaction during the first 8 minutes for the small marble chips and the large marble chips. Include the units. Give your answers to 2 decim
June 2018, Chemistry Paper 10 Higher, Q14(a)(ii) (2 marks): Which reaction is faster? Explain how you can tell using data from the graph. [2]
June 2018, Chemistry Paper 10 Higher, Q14(b) (3 marks): Explain why changing the size of the marble chips changes the rate of the reaction. [3]

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