Rate of reaction — Paper 4 · IGCSE Science - Combined 0653

2 A student investigates the rate of reaction between calcium carbonate and dilute hydrochloric acid. The reaction produces carbon dioxide. Fig. 2.1 shows some of the apparatus that the student uses. calcium carbonate dilute hydrochloric acid Fig. 2.1 The student measures the volume of carbon dioxide produced every minute for 10 minutes. (a) Complete Fig. 2.1 to show the labelled apparatus that he uses to measure the volume of carbon dioxide produced. [2] (b) Fig. 2.2 shows the volume of carbon dioxide produced during the investigation. volume of carbon dioxide 0 1 2 3 4 5 6 7 8 9 10 time / minutes Fig. 2.2 Describe and explain the change in the rate of the reaction during the first three minutes. Use ideas about concentration and particle collisions in your answer. change … explanation … … … [3] (c) Complete the balanced symbol equation for the reaction between dilute hydrochloric acid and calcium carbonate, CaCO3. … + … CaCl2 + … + … [2] (d) Describe the test for carbon dioxide and the positive result. test … result … [2] (e) Suggest the names of an acid and of a base that react together to produce magnesium sulfate. … and … [2]

11 marks

Mark scheme: 2(a) draws a gas syringe or an inverted measuring cylinder over water ; syringe or measuring cylinder labelled ; 2 2(b) decreases ; concentration (of acid) decreases ; particles collide less often ; 3 2(c) 2HCl + (CaCO3 ) → (CaCl 2) + CO2 + H2O ;; 2 2(d) limewater ; (turns) milky / cloudy / white solid / ppt ; 2 2(e) (acid) sulfuric (acid) / H2SO4 ; (base) magnesium oxide / MgO / magnesium hydroxide / Mg(OH)2 / magnesium carbonate / MgCO3 ; 2

This question in 0653/42 Feb/March 2017

5 A student investigates the reaction between dilute sulfuric acid and excess copper(II) carbonate powder. The apparatus she uses is shown in Fig. 5.1. gas syringe excess copper(II) carbonate powder dilute sulfuric acid Fig. 5.1 The reaction produces a gas which is collected in the gas syringe. A salt and another compound are also produced. (a) (i) Describe the pH change, if any, of the reaction mixture. Name this type of reaction. pH change … reaction type … [2] (ii) Complete the balanced symbol equation for the reaction between dilute sulfuric acid and copper(II) carbonate. H2SO4 + CuCO3 … + … + … [2] (b) Copper(II) carbonate is insoluble in water. The salt which is produced in this reaction is soluble in water. Suggest a method of making pure, dry crystals of this salt from the mixture that is left after the reaction is complete. … … … … [2] (c) The student records the volume of gas in the syringe for 10 minutes. Her results are shown in Fig. 5.2. volume of gas 0 1 2 3 4 5 6 7 8 9 10 time / minutes Fig. 5.2 Describe how the shape of the graph shows the change in the rate of the reaction. … … … … [2] (d) She repeats the experiment using the same volume of less concentrated sulfuric acid. (i) Draw a line on Fig. 5.2 to show her results. [2] (ii) Explain, in terms of particle collisions, the effect of using less concentrated sulfuric acid on the rate of the reaction. … … [1]

11 marks

Mark scheme: 5(a)(i) neutralisation / salt-making; 2 5(a)(ii) CuSO4 ; CO2 and H2O ; 2 5(b) filter (to remove excess solid / copper carbonate) ; heat the solution / filtrate / mixture ; reference to evaporation ; cool / leave (to allow crystals to form) ; 2 5(c) the idea that the gradient decreases ; the idea that the rate decreases ; the idea that the rate becomes zero ; 2 5(d)(i) less steep initial line ; levels off at a lower volume; 2 5(d)(ii) (decreases rate of reaction) because particles collide less frequently / owtte ; 1

This question in 0653/41 May/June 2017

5 (a) The atomic number of magnesium is 12. Complete Fig. 5.1 to show the electronic structure of a magnesium atom. X X Fig. 5.1 [2] (b) A student investigates the reaction between magnesium and dilute hydrochloric acid. The student uses the apparatus shown in Fig. 5.2 for the investigation. cotton wool conical flask dilute magnesium hydrochloric powder acid balance Fig. 5.2 Fig. 5.3 shows the mass of the conical flask and its contents during the reaction. mass time Fig. 5.3 (i) Explain why at first the mass decreases, … … later on the mass does not change. … … [2] (ii) Complete and balance the symbolic equation for this reaction. Mg + … … + MgCl2 [2] (c) (i) State the effect, if any, of using a higher temperature on the rate of a reaction. Explain your answer in terms of particle collisions. effect … explanation … … … [2] (ii) State the effect of using a catalyst on the rate of a reaction. Describe the change, if any, to the catalyst at the end of the reaction. effect … change to catalyst … [2]

10 marks

Mark scheme: 5(a) 2 electrons 3rd shell ; 2 5(b)(i) gas / H2 produced / lost ; reaction ends / over ; 2 5(b)(ii) (Mg) + 2HCl Î H2 + (MgCl2) 2HCl ; H2 ; 2 5(c)(i) increases ; particles collide more often / forcefully / energetically / successfully ; 2 5(c)(ii) increases / changes ; no change ; 2

This question in 0653/43 May/June 2017

2 (a) The arrangements of particles in four substances are shown in Fig. 2.1. A B C D Fig. 2.1 Use letters A, B, C and D to identify a pure substance, … a mixture, … an alloy, … a compound. … [2] (b) A student adds pieces of calcium to dilute hydrochloric acid. A vigorous reaction is observed. (i) Complete the balanced equation to show this reaction. Include state symbols in the equation. Ca(s) + 2 HCl ( … ) … ( … ) + … ( … ) [2] (ii) The student repeats the reaction using a solution of hydrochloric acid that has a lower concentration. State the effect of this change on the rate of the reaction. Explain this effect using ideas about colliding particles in your answer. effect on rate … explanation … … … [2] (iii) State a simple chemical test that shows the presence of chloride ions in dilute hydrochloric acid. test … result … [2] (c) A salt contains iron(III) ions, Fe3+, and sulfide ions, S2−. Determine the formula of this salt. formula … [1]

9 marks

Mark scheme: 2(a) (a pure substance) A or D ; (a mixture) B or C ; (an alloy) C ; (a compound) D ; (1) for any two or three correct (2) for all four correct 2 2(b)(i) (Ca(s)) + 2HCl )(aq) Î «CaCl 2«(aq) + «H2«(g) ;; species RHS (1) state symbols (1) for species given 2 2(b)(ii) (effect on rate) decreases ; (explanation) particles collide less often / less frequently / less chance of collisions ; 2 2(b)(iii) silver nitrate solution ; white solid / precipitate ; 2 2(c) Fe2S3 ; 1

This question in 0653/43 Oct/Nov 2017

8 Petroleum is separated into useful fractions by fractional distillation. Process Y produces short alkene molecules from longer alkane molecules. These processes are shown in Fig. 8.1. fractional process Y powdered distillation fraction P solid catalyst column strong heat petroleum fraction Q Fig. 8.1 (a) Fraction P and fraction Q contain different compounds. Describe two of the differences between the compounds in fraction P and those in fraction Q. 1. … … 2. … … [2] (b) Name process Y. … [1] (c) The rate of reaction in process Y is increased by using a powdered solid catalyst and a high temperature. (i) State why the catalyst is used in the form of a powder. … … [1] (ii) Explain how a high temperature increases the rate of reaction in process Y. Use ideas about particles in your answer. … … [2] (d) Bromine is added to two different samples of hydrocarbons A and B. Hydrocarbon A decolourises the bromine. Hydrocarbon B has no effect on the bromine. State these two types of hydrocarbon. A … B … [1] (e) The combustion of hydrocarbons produces a gas that turns limewater milky. (i) State the formula of this gas. … [1] (ii) Suggest one concern that people have as the proportion of this gas is increasing in the air. … … [1]

9 marks

Mark scheme: 8(a) (fraction P) lower boiling point ; smaller molecules ; weaker intermolecular (attractive) forces ; greater flammability ; lower viscosity ; max2 8(b) (catalytic or thermal) cracking ; 1 8(c)(i) increases surface area ; 1 8(c)(ii) particles move faster / have greater kinetic energy ; particles collide (with the catalyst) more often ; 2 8(d) (A) alkene / unsaturated and (B) alkane / saturated ; 1 8(e)(i) CO2 ; 1 8(e)(ii) reference to global warming / excessive (runaway / enhanced) greenhouse effect / negative effects such as climate change / polar melting / rising sea levels / ocean acidification ; 1

This question in 0653/42 Feb/March 2018

5 (a) A student adds magnesium powder to dilute hydrochloric acid. She then uses a balance to investigate the rate of this reaction, as shown in Fig. 5.1. cotton wool conical flask dilute hydrochloric acid magnesium powder 124.57g balance Fig. 5.1 (i) Describe the change in the mass, if any, of the conical flask and its contents. Explain your answer. change … explanation … … [2] (ii) State the effect of increasing the temperature on the rate of this reaction. Explain your answer. effect … explanation … … [2] (iii) Predict the effect of using calcium, rather than magnesium, on the rate of reaction. Explain your answer using ideas about reactivity. effect … explanation … … [2] (b) Magnesium is produced by the electrolysis of molten magnesium chloride. Magnesium chloride consists of magnesium ions, Mg2+, and chloride ions, Cl –. (i) Name the electrode at which magnesium forms. … [1] (ii) Describe, in terms of electrons, how chloride ions turn into chlorine atoms in this process. … … [1] (iii) Predict the formula of magnesium chloride. … [1] (iv) Magnesium is also produced by heating magnesium oxide with silicon. In this process, oxygen is removed from magnesium oxide. State the type of reaction that leads to the loss of oxygen from a substance. … [1]

10 marks

Mark scheme: 5(a)(i) (decrease) gas produced / released (by the reaction) ; to the surroundings / substance leaves the flask / apparatus ; 2 5(a)(ii) (increase) particles move faster / gain (kinetic) energy ; particles collide more often ; the idea that more of the collisions are successful ; max 2 5(a)(iii) increase ; calcium is more reactive (than magnesium) ; 2 5(b)(i) cathode ; 1 5(b)(ii) (each ion) loses (one) electron ; 1 5(b)(iii) MgCl2 ; 1 5(b)(iv) reduction ; 1 Que estion Answer Ma arks

This question in 0653/42 May/June 2018

2 Magnesium chloride is a soluble salt. It is made when dilute hydrochloric acid reacts with magnesium carbonate. Magnesium carbonate is insoluble in water. (a) (i) Excess magnesium carbonate powder is mixed with dilute hydrochloric acid. Suggest methods for 1. removing unreacted magnesium carbonate from the reaction mixture, … 2. obtaining solid magnesium chloride from the solution. … [2] (ii) The reaction is repeated using the same mass of larger pieces of magnesium carbonate instead of powder. Describe the effect of this change on the rate of the reaction. … … [1] (iii) Describe the effect of using the same volume of more concentrated hydrochloric acid on the rate of this reaction. Explain your answer. effect … explanation … … [2] (b) When the magnesium carbonate reacts with dilute hydrochloric acid, the temperature rises. State the name given to chemical reactions that cause the temperature to rise, and explain this observation. Use ideas about energy changes in your answer. reaction … explanation … … [2] (c) When magnesium carbonate reacts with dilute hydrochloric acid, a colourless gas and a colourless salt solution are formed. (i) Complete the balanced equation for this reaction. MgCO3 + … HCl … + … + … [2] (ii) Describe a test for aqueous chloride ions. State the result that shows chloride ions are present. test … result … … [2]

11 marks

Mark scheme: 2(a)(i) (remove MgCO3) filtration / filtering / filter ; (obtain solid salt) evaporation / crystallisation ; 2 2(a)(ii) decreases ; 1 2(a)(iii) (effect) increases ; (explanation) particles collide more frequently / more chance of collisions ; 2 2(b) exothermic ; chemical (energy changes) to heat / thermal (energy) ; 2 Question Answer Marks 2(c)(i) (MgCO3) + 2(HCl) → MgCl2 + CO2 + H2O ; formula of magnesium chloride ; all else correct ; 2 2(c)(ii) (test) (dil. nitric acid and) aqueous silver nitrate / AgNO3 ; (result) white precipitate / solid; 2

This question in 0653/42 Oct/Nov 2018

8 (a) Fig. 8.1 shows the apparatus a student uses to investigate the reaction between magnesium powder and excess dilute hydrochloric acid. The reaction produces a salt and hydrogen gas. gas syringe magnesium excess dilute powder hydrochloric acid Fig. 8.1 The student measures the volume of gas in the gas syringe at regular intervals. Fig. 8.2 shows a graph of her results. volume of hydrogen 0 0 time Fig. 8.2 (i) On Fig. 8.2 mark with an X a time at which the reaction has already finished. [1] (ii) The student repeats the investigation at a higher temperature. On Fig. 8.2 sketch a line to suggest the results of this experiment. [1] (iii) Explain the line you sketched in (a)(ii). … … … … [2] (b) Table 8.1 shows the composition of an alloy. Table 8.1 element % by mass aluminium 8.0 magnesium 91.2 manganese 0.2 zinc 0.6 Calculate the mass of magnesium in 500 g of the alloy. mass of magnesium = … g [1] (c) Magnesium is produced by the electrolysis of molten magnesium chloride. Name the substance produced at the anode. … [1] [Total: 6]

6 marks

Mark scheme: 8(a)(i) X anywhere on horizontal part of graph ; 1 8(a)(ii) curved portion steeper and horizontal line at same volume ; 1 8(a)(iii) rate of reaction faster (so steeper curve) ; same final volume of gas (so horizontal line at same height (volume)) ; 2 8(b) 456 (g) ; 1 8(c) chlorine ; 1

This question in 0653/42 Feb/March 2019

8 (a) Use the Periodic Table on page 24 to deduce the electronic structure of a calcium atom. … [2] (b) A student investigates the rate of reaction between excess dilute hydrochloric acid and powdered calcium carbonate. Carbon dioxide gas is produced in this reaction. Fig. 8.1 shows some of the apparatus the student uses. cotton wool conical flask excess dilute hydrochloric acid powdered calcium carbonate bubbles of carbon dioxide digital balance Fig. 8.1 The student measures the mass of the conical flask and its contents during the reaction. Fig. 8.2 is a graph of the student’s results. mass time Fig. 8.2 (i) Explain why the mass of the conical flask and its contents decreases. … … [1] (ii) Explain, in terms of particle collisions, the effect of a higher temperature on the rate of a chemical reaction. … … … … [2] (iii) The student repeats the experiment at a higher temperature. On Fig. 8.2, sketch a line to show the results. [2] (c) Calcium chloride is produced during the reaction between calcium carbonate and dilute hydrochloric acid. Name one other substance that reacts with dilute hydrochloric acid to produce calcium chloride. … [1] [Total: 8]

8 marks

Mark scheme: 8(a) 20 electrons ; 2,8,8,2 ; 2 8(b)(i) (carbon dioxide) gas released from the apparatus ; 1 8(b)(ii) particles have more energy/kinetic energy / move faster ; more successful collisions / collisions with enough energy ; greater frequency of collisions ; max 2 8(b)(iii) curved portion steeper ; horizontal line at same mass ; 2 8(c) calcium oxide / calcium hydroxide / calcium hydrogencarbonate / calcium ; 1

This question in 0653/41 May/June 2019

8 (a) Magnesium reacts with dilute hydrochloric acid. (i) Explain in detail why the rate of this reaction increases when the concentration of the acid increases. … … … … … [3] (ii) State one other change that increases the rate of this reaction. … [1] (iii) The reaction between magnesium and hydrochloric acid is exothermic. Explain why an exothermic reaction releases heat. Use ideas about energy, bond breaking and bond forming in your answer. … … … … [2] (b) Iron is extracted from iron oxide in a blast furnace. Explain why magnesium cannot be extracted from magnesium oxide in a blast furnace. … … [1] [Total: 7]

7 marks

Mark scheme: 8(a)(i) (at higher concentrations) more hydrogen ions / acid particles / reactant particles present ; increased rate of collisions ; so higher frequency of successful collisions ; 3 8(a)(ii) increase temperature / use a catalyst / increase surface area of magnesium ; 1 8(a)(iii) (thermal) energy is absorbed for bond breaking and released during bond formation ; more thermal energy is released than taken in ; 2 8(b) magnesium is too reactive / magnesium is above carbon in reactivity series ; 1

This question in 0653/43 Oct/Nov 2019

8 (a) When dilute sulfuric acid is electrolysed, hydrogen forms at the cathode. (i) Describe, in terms of electrons, what happens to one hydrogen ion at the cathode. … … [2] (ii) State the test for hydrogen gas and give the positive result. test … result … [2] (iii) Name the product at the anode. … [1] (b) Magnesium reacts with dilute sulfuric acid to produce magnesium sulfate. Explain why the rate of this reaction increases when the temperature of the acid is higher. Use ideas about particles in your answer. … … … … [2] (c) Name one other substance that reacts with dilute sulfuric acid to produce magnesium sulfate. … [1] [Total: 8]

8 marks

Mark scheme: 8(a)(i) (hydrogen ion) gains ; one electron ; 2 8(a)(ii) (test) lighted splint ; (result) goes pop ; 2 8(a)(iii) oxygen ; 1 8(b) any two from: particles, move faster / have more kinetic energy / move more ; particles, collide more frequently / more energetically ; more of the collisions provide the activation energy ; max 2 8(c) magnesium oxide / magnesium carbonate / magnesium hydroxide ; 1

This question in 0653/41 May/June 2020

5 The equation for the reaction between magnesium carbonate and dilute hydrochloric acid is shown. MgCO3 + 2HCl → MgCl2 + CO2 + H2O (a) The reaction between magnesium carbonate and dilute hydrochloric acid is exothermic. The energy level diagram for this reaction is shown in Fig. 5.1. energy reaction progress Fig. 5.1 (i) On Fig. 5.1, write the words reactants and products in suitable places. [1] (ii) On Fig. 5.1, draw a double headed arrow (↕) to show the activation energy for this reaction. [1] (b) A student investigates the effect of temperature on the rate of reaction between magnesium carbonate and dilute hydrochloric acid. She uses acid with a temperature of 20 °C. She measures the volume of carbon dioxide produced. (i) Fig. 5.2 is a graph of her results. volume of gas 20 °C 0 0 time Fig. 5.2 On Fig. 5.2, sketch a graph of the results she obtains when she repeats the experiment at a temperature of 30 °C. All other variables are kept constant. [2] (ii) Explain your answer to (b)(i) using ideas about particle collisions. … … … [2] (c) Carbon dioxide is one product of the reaction between magnesium carbonate and dilute hydrochloric acid. Explain why scientists are concerned about an increase in the concentration of carbon dioxide in the atmosphere. … … … … [2] (d) Magnesium chloride is another product of the reaction between magnesium carbonate and dilute hydrochloric acid. State one substance, other than magnesium carbonate, that reacts with dilute hydrochloric acid to produce magnesium chloride. … [1] [Total: 9]

9 marks

Mark scheme: 5(a)(i) reactants on left and products on right ; 1 5(a)(ii) activation energy correctly identified ; 1 5(b)(i) steeper ; finish at same volume ; 2 5(b)(ii) particles move faster / have more kinetic energy / move more ; particles collide more frequently / more energetically ; 2 5(c) carbon dioxide is a greenhouse gas ; (which contributes to) enhanced greenhouse effect / global warming / climate change ; 2 5(d) magnesium / magnesium oxide / magnesium hydroxide ; 1

This question in 0653/42 May/June 2020

8 When 1 g of copper carbonate powder is added to excess dilute hydrochloric acid, aqueous copper chloride and carbon dioxide gas are produced. Fig. 8.1 shows a graph of the mass of the reaction mixture against time. mass time Fig. 8.1 (a) The experiment is repeated using a 1 g lump of copper carbonate instead of powder. On Fig. 8.1, sketch a line to show the graph of the mass of the reaction mixture against time for this experiment. [2] (b) The carbon dioxide produced is released into the atmosphere. State why scientists are concerned about an increase in the concentration of carbon dioxide in the atmosphere. … … [1] (c) Copper(II) ions, Cu2+, in the aqueous copper chloride can be identified by chromatography. The Rf value for copper(II) ions is 0.4. Describe how a chromatogram can be used to show that a solution contains copper(II) ions. … … … … … [3] (d) During the electrolysis of aqueous copper(II) chloride, copper forms at the cathode. Describe how copper forms at the cathode. Use ideas about ions and electrons in your answer. … … … [2] [Total: 8]

8 marks

Mark scheme: 8(a) line with shallower gradient showing slower rate of reaction ; line starting and finishing at same mass ; 2 8(b) enhanced greenhouse effect / global warming / example of a consequence of climate change ; 1 8(c) measure distance to spot (from base line) ; measure distance to solvent front (from base line) ; show that Rf = distance to spot ÷ distance to solvent front = 0.4 ; 3 8(d) idea of electrons gained by copper ions ; two electrons gained (per ion) / ions discharged ; 2

This question in 0653/42 Oct/Nov 2020

8 (a) Copper chloride is made when copper oxide reacts with dilute hydrochloric acid. The equation for the reaction is shown. CuO + 2HCl CuCl2 + H2O → Explain why warm hydrochloric acid reacts faster than cold hydrochloric acid. Use ideas about particles and collisions in your answer. … … … … [2] (b) Copper is a transition element. Describe one property of copper that is not a property of Group I metals. … … [1] (c) Chlorine gas is made by the electrolysis of aqueous copper chloride. (i) Damp litmus paper is used to test for chlorine. State the positive result. … [1] (ii) Explain why chlorine is used in the treatment of water supplies. … … [1] (d) Copper ions, Cu2+, can be detected using chromatography. Fig. 8.1 shows a chromatogram of a solution containing copper ions. 10 9 8 7 solvent front copper ions 6 5 4 3 2 starting spot spotting line 1 0 measuring scale / cm Fig. 8.1 Use the measuring scale in Fig. 8.1 to calculate the Rf value for the copper ions. Rf value = … [2] [Total: 7]

7 marks

Mark scheme: 8(a) warm hydrochloric acid particles have more kinetic energy ; more successful collisions / more frequent collisions ; 2 8(b) hard / dense / high melting point / acts as a catalyst / forms coloured compounds ; 1 8(c)(i) bleaches (damp litmus paper) ; 1 8(c)(ii) sterilises water / kills microbes / kills bacteria ; 1 8(d) copper ions = 4.5 (cm) AND solvent front = 8 (cm) (from diagram) ; (4.5 ÷ 8.0 =) 0.56 ; 2

This question in 0653/43 Oct/Nov 2020

5 A student investigates the rate of reaction between solid calcium carbonate and dilute hydrochloric acid. (a) The student: • uses Universal Indicator paper to measure the pH of the acid before the reaction • then adds excess calcium carbonate to the acid • measures the pH of the mixture after the reaction is complete. (i) Describe how to use Universal Indicator paper to measure pH. … … … [2] (ii) Suggest a value for the pH of the dilute hydrochloric acid before the reaction and a value for the pH of the mixture after the reaction is complete. acid … mixture … [2] (b) The student repeats the experiment. The student uses the same mass of calcium carbonate and the same temperature of acid each time. The student uses different concentrations of acid and different sized pieces of calcium carbonate, as shown in Table 5.1. Table 5.1 concentration of experiment hydrochloric acid calcium carbonate pieces mol / dm3 1 0.5 large 2 0.5 small 3 1.0 large 4 1.0 small State which experiment has the highest rate of reaction and which has the lowest rate of reaction. Use ideas about colliding particles to explain your answer. highest … lowest … explanation … … … … … [4] [Total: 8]

8 marks

Mark scheme: 5(a)(i) place some acid on the paper OWTTE ; compare colours to a chart / colour indicates pH ; 2 5(a)(ii) acid: in the range 4 to 1 ; mixture: 7 ; 2 5(b) (highest) 4 AND (lowest) 1 ; faster reactions have more frequent collisions ; more concentrated acids have more particles (in the same volume) ; smaller pieces (of CaCO3) have a larger surface area (exposed to acid) ; 4

This question in 0653/42 May/June 2021

5 The pH values of four aqueous salt solutions are listed in Table 5.1. Table 5.1 aqueous salt solution pH copper sulfate 4 iron chloride 2 magnesium sulfate 6 sodium chloride 7 (a) Describe how an aqueous salt solution can be tested to find its pH value. … … … [2] (b) (i) Identify the most acidic aqueous salt solution listed in Table 5.1. Explain your choice. solution … explanation … … [1] (ii) State the names of the two aqueous salt solutions listed in Table 5.1 that react with zinc. … and … [1] (c) A student reacts solid copper carbonate with dilute sulfuric acid in four different experiments. The same mass of copper carbonate is used in each experiment. Table 5.2 shows the conditions used. Table 5.2 size of pieces temperature of acid experiment of copper carbonate / °C 1 large 20 2 large 40 3 small 20 4 small 40 State which experiment has the highest rate of reaction. Explain your answer using ideas about colliding particles and activation energy. experiment … explanation … … … … [4] [Total: 8]

8 marks

Mark scheme: 5(a) use universal indicator ; observe the colour ; 2 5(b)(i) iron(III) chloride AND has the lowest pH ; 1 5(b)(ii) copper(II) sulfate AND iron(III) chloride ; 1 5(c) experiment 4 ; more particles, have / collide with, the (minimum) activation energy ; plus any two from: higher temperature means higher, kinetic energy / speed ; small pieces have larger surface area ; reference to more frequent collisions ; 4

This question in 0653/42 Oct/Nov 2021

8 Energy level diagrams for two reactions are shown in Fig. 8.1. The diagrams are drawn to the same scale. reaction 1 reaction 2 products energy energy reactants reactants products progress of reaction progress of reaction Fig. 8.1 (a) (i) Compare the activation energies for reaction 1 and reaction 2. Explain your answer. comparison … explanation … … [1] (ii) The temperature of reaction 2 is increased. Use ideas about activation energy to explain why this increases the rate of reaction 2. … … [1] (b) One of the reactions represents the combustion of propane. Identify which reaction, 1 or 2, represents the combustion of propane. Give a reason for your answer. reaction … reason … … [1] (c) Arrows A and B on Fig. 8.2 represent changes occurring during reaction 1. energy A reactants B products progress of reaction Fig. 8.2 Put ticks (✓) in the boxes to show what these changes represent. energy is energy is bonds are bonds are being taken being given being broken being formed in out arrow A arrow B [2] (d) Equations for the combustion of propane are shown in Fig. 8.3. H H H H C C C H + 7 O O 3 O C O + 4 O H H H H H propane + oxygen carbon dioxide + water Fig. 8.3 (i) State the number of electrons that are shared between one oxygen atom and one carbon atom in a molecule of carbon dioxide. … [1] (ii) State two ways in which the structure of propane shows that it is an alkane. 1 … 2 … [2] [Total: 8]

8 marks

Mark scheme: 8(a)(i) (activation energy of ) reaction 2 is higher because the difference in energy of reactants and energy of the peak is greater / ORA ; 1 8(a)(ii) more collisions have the activation energy / frequency of successful collisions increases ; 1 8(b) reaction 1 AND because it is exothermic / energy is given out ; 1 8(c) bonds are being broken bonds are being formed energy is being taken in energy is being given out arrow A   ; arrow B   ; 2 8(d)(i) 4 ; 1 8(d)(ii) Any two from: contains (only) carbon and hydrogen ; all single bonds / saturated ; has the same general formula ; 2

This question in 0653/42 May/June 2022

8 Calcium carbonate reacts with dilute hydrochloric acid to produce a gas. (a) Name the gas produced in this reaction. … [1] (b) The reaction also produces calcium chloride. Calcium chloride contains calcium ions, Ca2+, and chloride ions, Cl –. Deduce the formula for calcium chloride. … [1] (c) In an investigation, 5 g of calcium carbonate reacts with 20 cm3 of dilute hydrochloric acid, as shown in Fig. 8.1. The volume of gas collected during the first 10 s is measured. gas syringe 20 cm3 dilute hydrochloric acid bubbles of gas 5 g calcium carbonate Fig. 8.1 The experiment is repeated using the same mass of calcium carbonate and the same volume of dilute acid. Different concentrations of dilute acid and different temperatures are used. The results are shown in Table 8.1. Table 8.1 volume of gas concentration of dilute temperature collected during the experiment hydrochloric acid / °C first 10 s mol / dm3 / cm3 1 1.0 20 25 2 2.0 20 43 3 0.5 10 9 4 0.5 20 14 5 1.0 30 37 (i) State the effect of increasing the temperature on the rate of a reaction. … … [1] (ii) Identify two experiments from Table 8.1 that can be used to show the effect of increasing the temperature on the rate of the reaction. Explain the reason for your choices. experiment … and experiment … explanation … … [2] (iii) Explain why the results for experiment 1 and experiment 4 are different. Use ideas about collisions between reacting particles in your answer. … … … … [3] (d) The energy level diagram for the reaction between calcium carbonate and dilute hydrochloric acid is shown in Fig. 8.2. energy reactants products progress of reaction Fig. 8.2 (i) Draw an arrow on Fig. 8.2 to show the activation energy for the reaction. Label this arrow A. [1] (ii) Draw an arrow on Fig. 8.2 to show the energy change of this reaction. Label this arrow B. [1] [Total: 10]

10 marks

Mark scheme: 8(a) carbon dioxide ; 1 8(b) CaCl2 ; 1 8(c)(i) increases rate / higher rate / faster ; 1 8(c)(ii) 3 and 4 OR 1 and 5 ; need to keep concentration same / 3 and 4 both have concentration of 0.5 / 1 and 5 both have concentration of 1.0 ; 2 Question Answer Marks 8(c)(iii) 4 has a lower concentration than 1 / lower concentration has a lower rate ORA ; particles are further apart in 4 / fewer particles per unit volume ORA ; collisions less frequent in 4 / fewer successful collisions in 4 ORA ; 3 8(d)(i) arrow A starts and ends in the correct place ; e.g. 1 8(d)(ii) arrow B starts and ends in the correct place ; 1

This question in 0653/43 May/June 2022

5 A student does five experiments to investigate the reaction between magnesium and dilute hydrochloric acid. In each experiment, the student measures the volume of gas given off during the first 10 seconds of the reaction, as shown in Fig. 5.1. gas syringe bubbles of gas dilute hydrochloric acid magnesium Fig. 5.1 The student: • uses the same mass of magnesium and the same volume of dilute hydrochloric acid in each experiment • uses different temperatures and different concentrations of dilute hydrochloric acid. Table 5.1 shows some of the results. Table 5.1 temperature concentration of acid volume of gas experiment / °C g / dm3 / cm3 1 20 1.0 25 2 30 1.0 42 3 20 1.5 36 4 1.0 9 5 20 14 (a) Complete Table 5.1 by suggesting the two missing values. [2] (b) Explain why the rate of reaction is higher for experiment 2 than for experiment 1. Use ideas about particles and energy in your answer. … … … … … [3] (c) Deduce which of the five experiments listed in Table 5.1 has the most closely packed acid particles. Give a reason for your answer. experiment … reason … … [2] (d) Experiment 1 is repeated using different metals. Table 5.2 shows the results. Table 5.2 volume of gas in 10 seconds metal / cm3 magnesium 25 calcium 90 copper 0 (i) Suggest a reason for the result for copper. … … [1] (ii) Suggest the name of a metal not listed in Table 5.2 that could produce a greater volume of gas in 10 seconds. Give a reason for your answer. metal … reason … … [1] [Total: 9]

9 marks

Mark scheme: 5(a) concentration of acid:  1.0 ; 2 5(b) experiment 2 is faster because it is at a higher temperature ; particles, have more energy / move faster / have more frequent collisions ; more particles have energy greater than the activation energy / more successful collisions ; 3 5(c) experiment 3 ; it is the highest concentration ; 2 5(d)(i) (no gas given off because) copper, is unreactive / does not react with acids ; 1 5(d)(ii) named metal, more reactive than calcium / any of the metals in the table ; 1

This question in 0653/42 May/June 2023

5 A student does five experiments to investigate the reaction between zinc granules and dilute hydrochloric acid. In each experiment, the student measures the volume of gas produced during the first 10 s of the reaction, using the apparatus shown in Fig. 5.1. gas dilute hydrochloric acid zinc granules Fig. 5.1 The student uses the same mass of zinc granules and the same volume of dilute hydrochloric acid in each experiment. The student uses different temperatures and different concentrations of dilute hydrochloric acid. Table 5.1 shows the results. Table 5.1 temperature of acid concentration of acid volume of gas produced experiment / °C mol / dm3 / cm3 1 20 1.0 25 2 20 1.5 38 3 30 1.0 45 4 1.0 15 5 20 9 (a) Suggest a value for: • the temperature of acid used in experiment 4 … °C • the concentration of acid used in experiment 5. … mol / dm3 [2] (b) Explain why the results for experiments 1 and 2 are different. Use ideas about reacting particles in your answer. … … … [2] (c) State which experiment listed in Table 5.1 contains the most colliding particles that have the minimum energy (activation energy) to react. Give a reason for your answer. experiment … reason … … [2] (d) The student repeats experiment 1 using different metals. Table 5.2 shows the results. Table 5.2 metal volume of gas produced / cm3 zinc 25 iron 14 magnesium 34 (i) Explain the differences in the results. … … … [2] (ii) Suggest what is observed when copper is used instead of zinc. Give a reason for your answer. observation … reason … [1] [Total: 9]

9 marks

Mark scheme: 5(a) > 0 to < 20 (°C) ; 2 > 0 to < 1.0 (mol / dm3) ; 5(b) more (acid) particles (per unit volume) in experiment 2 / concentration (of acid) in experiment 2 is higher, ORA ; 2 so more frequent collisions (between particles) ; 5(c) experiment 3 ; 2 it is the highest temperature / the most gas is produced (in 10 s) ; 5(d)(i) idea that the metals have different reactivities / correct order of reactivity implied, Mg > Zn > Fe ; 2 higher reactivity causes higher rate of gas production / reaction ; 5(d)(ii) no gas collected / no reaction AND 1 copper, is unreactive / does not react with acids ;

This question in 0653/41 Oct/Nov 2023

5 A student investigates the reaction of dilute hydrochloric acid with different metals. The student measures the volume of gas produced during the first 20 s of each reaction using the apparatus shown in Fig. 5.1. gas metal dilute hydrochloric acid Fig. 5.1 (a) The results for three metals are shown in Table 5.1. Table 5.1 metal volume of gas produced / cm3 magnesium 38 zinc 30 copper 0 (i) State which metal listed in Table 5.1 has the greatest tendency to form positive ions. Give a reason for your answer. metal … reason … … [1] (ii) State which metal listed in Table 5.1 is less reactive than hydrogen. Give a reason for your answer. metal … reason … … [1] (iii) The student repeats the experiment using iron. Predict the volume of gas produced after 20 s. Give a reason for your answer. volume … cm3 reason … … [2] (b) The student repeats the experiment for magnesium using dilute hydrochloric acid at a higher temperature. All other conditions are kept the same. (i) State the effect of using a higher temperature on the volume of gas produced after 20 s. Explain your answer using ideas about energy and particles. effect … explanation … … … [3] (ii) At the end of this reaction, some magnesium remains. The reaction mixture is tested with universal indicator at the start and at the end of the reaction. Suggest the pH of the reaction mixture at the start and at the end of the reaction. Explain your answer. pH at start … pH at end … explanation … … [2] [Total: 9]

9 marks

Mark scheme: 5(a)(i) magnesium AND 1 it is the most reactive or atoms lose electrons most readily ; 5(a)(ii) copper AND 1 copper does not displace hydrogen (from the acid) ; 5(a)(iii) any value greater than 0 AND less than 30 ; 2 reactivity of iron is between copper and zinc ; 5(b)(i) (volume of gas produced) increases ; 3 more frequent collisions more successful collisions OR particles move faster / particles have more kinetic energy ; more particles (have more than minimum) with activation energy ; 5(b)(ii) pH at start: 1–3 AND pH at end: 7 ; 2 (acid is fully neutralised) because magnesium is in excess OR the acid is used up;

This question in 0653/42 Oct/Nov 2023

4 A student investigates the rate of reaction between large pieces of magnesium carbonate, MgCO3, and dilute hydrochloric acid, HCl , using the apparatus shown in Fig. 4.1. The student records the time taken to produce 10 cm3 of gas. gas dilute hydrochloric acid dilute large pieces of water hydrochloric magnesium carbonate acid Fig. 4.1 (a) Three products are formed in the reaction: magnesium chloride MgCl 2, a gas and one other product. Give the balanced symbol equation for this reaction. … [2] (b) The student repeats the experiment using: • small pieces of magnesium carbonate • magnesium carbonate powder. All other conditions are kept constant. Table 4.1 shows the time taken to produce 10 cm3 of gas and the rate of reaction. Table 4.1 time taken to produce magnesium rate of reaction 10 cm3 of gas carbonate in cm3 per s in s large pieces 15.2 0.66 small pieces 8.3 1.2 powder 5.1 (i) Calculate the rate of reaction in cm3 per s for magnesium carbonate powder. Write your answer in Table 4.1. [1] (ii) State and explain how the size of the magnesium carbonate pieces affects the rate of this reaction. … … … … … … [3] (c) Fig. 4.2 shows an atom of magnesium and an atom of chlorine. Mg Cl magnesium atom chlorine atom Fig. 4.2 Complete the dot-and-cross diagram in Fig. 4.3 to show the ionic bonding in magnesium chloride, MgCl 2. Show only the outer-shell electrons and include the charges on the ions. … Cl … Mg … Cl Fig. 4.3 [3] [Total: 9]

9 marks

Mark scheme: 4(a) MgCO3 + 2HCl → MgCl2 + H2O + CO2 2 correct formulae ; correct balancing ; 4(b)(i) 2.0 ; 1 4(b)(ii) smaller the pieces the faster the reaction / ora ; 3 (smaller pieces) surface area higher / greater exposure to acid with smaller pieces/powder ; (so) more collisions per second / more frequent collision / more (chance of) successful collisions ; 4(c) 8 dot electrons on outer shell of magnesium ion ; 3 7 X electrons on outer shell of both chloride ions and 1 dot electron ; correct charges on all ions ;

This question in 0653/43 Oct/Nov 2025