Cambridge IGCSE Sciences - Co-ordinated (Double) 0654 — 2023 Oct/Nov Paper 5 · Variant 3

1 You are going to investigate an enzyme controlled reaction. An enzyme found inside living cells of some plants catalyses (speeds up) the breakdown of hydrogen peroxide releasing oxygen gas. The oxygen gas released forms a foam with liquidised samples of beans and apples. (a) Procedure • Stir the liquidised beans. • Place approximately 1 cm depth of liquidised beans in a test-tube. • Add 1 cm3 of hydrogen peroxide solution to the test-tube. • Immediately start the stop-watch. • Measure the time it takes for the foam produced to reach the top of the test-tube. • This is trial 1. • If the foam does not reach the top of the test-tube in 2 minutes, record this as ‘120+’. (i) Record in Table 1.1 the time for trial 1 to the nearest second. [1] Table 1.1 time taken to fill test-tube / s sample trial 1 trial 2 average liquidised beans liquidised apples (ii) • Empty the test-tube into the beaker labelled waste and rinse with distilled water. • Repeat the procedure. This is trial 2. • Record in Table 1.1 the time for trial 2. • Repeat the procedure two more times using the liquidised apples instead of liquidised beans (remember to empty the liquidised beans into the waste beaker and rinse before starting and between the 2 trials). • Record in Table 1.1 the times for trials 1 and 2 for the liquidised apples. [3] (iii) Complete Table 1.1 by calculating and recording the average times. [1] (b) Use Table 1.1 to state a conclusion about the amount of enzyme present in the samples of beans and apples. ................................................................................................................................................... ............................................................................................................................................. [1] (c) Liquidising the beans and apples breaks open the cells. Suggest why the cells need to be broken open. ................................................................................................................................................... ............................................................................................................................................. [1] (d) Suggest why it is important to stir to mix the liquidised beans before using them. ................................................................................................................................................... ............................................................................................................................................. [1] (e) Explain why the test-tube must be rinsed to clean it before repeating with the liquidised apple. ................................................................................................................................................... ............................................................................................................................................. [1] (f) (i) Fig. 1.1 shows a test-tube containing liquidised beans and hydrogen peroxide solution. The oxygen gas produced can be collected and its volume measured. Complete Fig. 1.1 to show the assembled apparatus used to collect and measure the volume of oxygen gas produced. Label the apparatus. liquidised beans and hydrogen peroxide Fig. 1.1 [3] (ii) Suggest why measuring the volume of gas produced is a more accurate method than measuring the time taken for the foam to reach the top of the test-tube. ........................................................................................................................................... ..................................................................................................................................... [1] [Total: 13]

Mark scheme: Question Answer Marks 1(a)(i) time recorded for trial 1 ; 1 1(a)(ii) time recorded for beans trial 2 and similar to trial 1 ; 3 time recorded for apple trials 1 and 2 and both similar ; apple trials are 120+ / both higher than beans ; 1(a)(iii) correct calculation of means ; 1 1(b) beans contain (more) enzyme / apple contains (less) none / very little catalase ; 1 1(c) to release the enzyme ; 1 1(d) make sure even distribution of cells / enzyme ; 1 1(e) prevent contamination with beans / enzyme ; 1 1(f)(i) bung / stopper airtight and delivery tube ; 3 upturned measuring cylinder over water ; or bung / stopper airtight and delivery tube ; gas syringe; two correct labels on assembled apparatus ; 1(f)(ii) oxygen lost as it makes the foam / top of foam not easy to judge ; 1

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2 Amylase is a digestive enzyme that breaks down starch into sugars. The presence of starch in a solution is confirmed by adding iodine solution. When starch is present, the iodine solution turns from brown to blue-black. Plan an investigation to determine the relationship between temperature and the time taken for the starch to be completely broken down by the enzyme. You are provided with: • starch solution • amylase solution • iodine solution. You may also use any common laboratory apparatus. You are not required to do this investigation. Include in your plan: • the apparatus needed • a brief description of the method, explaining any safety precautions • the measurements you will take • the variables you will control • how you will process your results to reach a conclusion. You may include a results table if you wish, you are not required to enter any readings in the table. You may include a labelled diagram in your answer. .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .................................................................................................................................................... [7]

Mark scheme: 2 one mark from each section and any other two marks 7 apparatus timer to time reaction ; thermometer and water bath / electric heater ; spotting tile to sample mixture ; method mix starch and enzyme and some observation with iodine solution / mix starch and amylase and sample with iodine (spotting tile) ; goggles to protect eyes from enzyme / hot water or gloves to protect hands / skin from enzymes / burns / hot water ; measurements time for appearance of brown / no blue-black ; repeats at the same temperature ; minimum 5 different temperatures ; variables controlled same volume / concentration of starch solution ; same volume / concentration / batch enzyme ; same pH ; processing and conclusion repeats are to exclude anomalies (before averaging) / average to exclude anomalies (only if repeat of the same temperature) ; plot graph of time against temperature ; does time increase decrease or stay the same as temperature increases / decreases / describe shape of graph e.g. if straight line through the origin they are proportional ;

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3 You are going to determine the percentage purity of a sample of compound F and identify the ions it contains. When compound F is heated it decreases in mass because it gives off a gas. (a) Procedure • Measure the mass of a hard-glass test-tube and record the value in Table 3.1. • Add three spatula loads of compound F into the hard-glass test-tube. • Measure the total mass of the hard-glass test-tube and compound F and record the value in Table 3.1. • Heat compound F gently at first and then more strongly until there is no further change, approximately two minutes. • Allow the test-tube to cool. Continue with (b), (c) and (d) while you wait for the test-tube to cool. You will complete the data processing for this experiment in section (e). Table 3.1 mass of empty hard-glass test-tube / g mass of hard-glass test-tube and compound F / g mass of hard-glass test-tube and mixture after heating / g [3] (b) (i) Describe the appearance of compound F. ........................................................................................................................................... ..................................................................................................................................... [1] (ii) Describe the appearance of the mixture in the test-tube after heating ........................................................................................................................................... ..................................................................................................................................... [1] (iii) Explain one safety precaution you must take when heating compound F. ........................................................................................................................................... ..................................................................................................................................... [1] (c) Procedure You need to test the gas made in this procedure. • Add one spatula load of compound F into a boiling tube. • Add 4 cm depth of dilute hydrochloric acid. • Test the gas given off. • Keep the solution formed for use in (d). The procedure may need to be done more than once if you are not certain of the result. (i) Identify the gas given off in the reaction. Describe the test used to identify the gas. Include the observation for a positive result. identity of gas .................................................................................................................... test .................................................................................................................................... observation ........................................................................................................................ [2] (ii) Use the results of the gas test in (c)(i) to identify the anion (negative ion) in compound F. ..................................................................................................................................... [1] (d) (i) Procedure • Dip the end of a wooden splint into the solution formed in (c). • Place the wooden splint into the blue part of the Bunsen burner flame. • Record the initial colour of the flame observed. • If no colour is seen, repeat the test. colour of flame .............................................................................................................. [1] (ii) Procedure • Place 1 cm depth of the solution from (c) into a clean test-tube. • Add aqueous ammonia to the solution slowly until it is in excess. • Put a stopper on the test-tube and shake it gently to check if soluble or not in excess. • Record your observations. ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [2] (iii) Use your results from (d)(i) and (d)(ii) to identify the metal ion in compound F. ..................................................................................................................................... [1] (e) Go back to (a) and measure the mass of the hard-glass test-tube and mixture after heating. Record this mass in Table 3.1. (i) Calculate the mass of compound F added to the hard-glass test-tube. Use the equation shown. mass of mass of hard-glass mass of empty hard-glass = – compound F test-tube and compound F test-tube mass of compound F = ...................................................... g [1] (ii) Calculate the decrease in mass of compound F. Use the equation shown. decrease in mass of hard-glass mass of hard-glass = – mass test-tube and compound F test-tube and mixture after heating decrease in mass = ...................................................... g [1] (iii) Calculate the percentage purity of compound F. Use the equation shown. decrease in mass percentage purity = × 280 mass of compound F Give your answer to three significant figures. percentage purity = .......................................................... [2] (iv) Suggest two improvements to the experiment which will allow you to have more confidence in your value for the percentage purity of compound F. 1 ........................................................................................................................................ ........................................................................................................................................... 2 ........................................................................................................................................ ........................................................................................................................................... [2] (f) An unknown acid is added to compound F and a solution is formed. When nitric acid and barium nitrate are added to this solution a white precipitate is formed. Identify the acid added to compound F. ............................................................................................................................................. [1] [Total: 20]

Mark scheme: 3(a)(i) mass of hard glass test-tube ; 3 all three masses ; total mass after heating < mass of test-tube and compound F ; 3(b)(i) green solid ; 1 3(b)(ii) black solid ; 1 3(b)(iii) any one from: 1 use goggles to protect eyes from powder / (hot)gas ; use tongs to protect hands / skin from burns / hot apparatus ; don’t point at anyone to protect people from spitting powder ; 3(c)(i) carbon dioxide / CO2 ; 2 limewater and white precipitate ; 3(c)(ii) carbonate / CO32– ; 1 3(d)(i) green-blue ; 1 3(d)(ii) (pale) blue precipitate. ; 2 (dissolves to form) dark blue solution ; 3(d)(iii) copper(II) ion ; 1 3(e)(i) subtraction correct ; 1 3(e)(ii) subtraction correct ; 1 3(e)(iii) correct calculation ; 2 3 s.f. ; 3(e)(iv) any two from: 2 heat for longer / heat to constant mass / heat again ; repeat and average ; use a larger mass of compound F ; 3(f) sulfuric acid / H2SO4 ; 1

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4 You are going to investigate the oscillations of a simple pendulum. The period of a pendulum is the time for one complete oscillation (swing) of the pendulum. This is shown in Fig. 4.1, where the period is the time taken for the bob to swing from X to Y and back to X again. point of support X Y pendulum bob Fig. 4.1 The pendulum has been set up for you as shown in Fig. 4.2. clamp stand l bench Fig. 4.2 The length l of the pendulum is the distance from the point of support to the centre of the pendulum bob. (a) (i) Measure the length l of the pendulum to the nearest 0.1 cm. Record your result in the first row of Table 4.1. [1] Table 4.1 time for 20 l / cm period T / s oscillations / s 60.0 50.0 40.0 30.0 20.0 (ii) Describe one practical technique you use to measure l as accurately as possible. ........................................................................................................................................... ..................................................................................................................................... [1] (b) Procedure (i) • Give the bob a small sideways displacement (between 5 cm and 10 cm). • Release the bob so that it oscillates. Measure and record in Table 4.1 the time taken for 20 oscillations. [1] (ii) • Adjust the length l of the pendulum until it is 60.0 cm. Repeat the procedure described in (b)(i). [1] (iii) Repeat this procedure for lengths l of 50.0 cm, 40.0 cm, 30.0 cm and 20.0 cm. [1] (c) Use your results in Table 4.1 to calculate the period T of the pendulum for each set of readings. Remember that the period is the time for one oscillation. Record in Table 4.1 your values for T to one decimal place. [1] (d) (i) On the grid, plot a graph of T (vertical axis) against l. Start both axes of your graph from the origin (0, 0). 0 0 [3] (ii) Draw the best-fit curve. [1] (e) Use your graph to: (i) determine the length l of a pendulum that has a period of 1.0 s l = ................................................... cm [1] (ii) describe what happens to the period T of a pendulum as its length l increases. ..................................................................................................................................... [1] (f) State whether your graph shows that the period T of a pendulum is proportional to its length l. Explain your answer. ................................................................................................................................................... ............................................................................................................................................. [1] [Total: 13]

Mark scheme: 4(a)(i) l present and measured to the nearest millimetre ; 1 4(a)(ii) take reading / perpendicular to scale / rule close to pendulum / use of fiducial aid / use of set-square to ensure that rule is 1 vertical ; 4(b)(i) t value recorded and sensible ; 1 4(b)(ii) t recorded and < value in (b)(i) ; 1 4(b)(iii) all t values recorded and decreasing ; 1 4(c) all T values correct ; 1 4(d)(i) axes labelled, quantity and unit ; 3 linear scales and plotted points ⩾ ½ the grid used ; points plotted correctly to ± ½ small square ; 4(d)(ii) good best-fit line ; 1 4(e)(i) l read from graph correctly from results ; 1 4(e)(ii) as l increases T increases ; 1 4(f) NO and graph not a straight line through origin / doubling l doesn’t double T (or equivalent) / ratio T / l is not constant ; 1

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5 You are going to investigate the cooling of hot water in two beakers, P and Q. Both insulation and a lid each reduce the loss of thermal energy. Beaker P has a layer of insulation around it, but has no lid. Beaker Q has a lid, but has no insulation around it. These beakers are shown in Fig. 5.1. lid hot layer of insulation water beaker P beaker Q Fig. 5.1 (a) Procedure • Pour 200 cm3 of hot water into beaker P. • Place the thermometer into the water and when the reading stops rising measure the temperature θ0 of the hot water and start the stop-watch. (i) Record in Table 5.1 this temperature at time t = 0 to the nearest 0.5 °C. [1] Table 5.1 beaker P time t / s temperature θ/ °C 0 180 (ii) Measure the temperature of the hot water after 180 s. Record in Table 5.1 your result to the nearest 0.5 °C. [1] (b) Procedure • Pour 200 cm3 of hot water into beaker Q and replace the lid. Repeat the measurements in (a) using beaker Q instead of beaker P. Record your results in Table 5.2. Table 5.2 beaker Q time t / s temperature θ/ °C 0 180 [1] (c) State which of the two methods of reducing thermal energy loss from a beaker of hot water is the more effective. Use data from Table 5.1 and Table 5.2 to explain how you reach this conclusion. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [2] (d) State how the loss of thermal energy from beaker P can be reduced even further without adding a lid. ............................................................................................................................................. [1] (e) State one condition which must be controlled to ensure that the comparison between beaker P and beaker Q is fair. ............................................................................................................................................. [1] [Total: 7] NOTES FOR USE IN QUALITATIVE ANALYSIS Tests for anions anion test test result carbonate (CO32–) add dilute acid effervescence, carbon dioxide produced chloride (Cl –) acidify with dilute nitric acid, then white ppt. [in solution] add aqueous silver nitrate bromide (Br–) acidify with dilute nitric acid, then cream ppt. [in solution] add aqueous silver nitrate nitrate (NO3–) add aqueous sodium hydroxide, then ammonia produced [in solution] aluminium foil; warm carefully sulfate (SO42–) acidify, then add aqueous barium white ppt. [in solution] nitrate Tests for aqueous cations cation effect of aqueous sodium hydroxide effect of aqueous ammonia ammonium (NH4+) ammonia produced on warming – calcium (Ca2+) white ppt., insoluble in excess no ppt., or very slight white ppt. copper(II) (Cu2+) light blue ppt., insoluble in excess light blue ppt., soluble in excess, giving a dark blue solution iron(II) (Fe2+) green ppt., insoluble in excess green ppt., insoluble in excess iron(III) (Fe3+) red-brown ppt., insoluble in excess red-brown ppt., insoluble in excess zinc (Zn2+) white ppt., soluble in excess, giving a white ppt., soluble in excess, giving a colourless solution colourless solution Tests for gases Flame tests for metal ions gas test and test result metal ion flame colour ammonia (NH3) turns damp, red litmus paper blue lithium (Li+) red carbon dioxide (CO2) turns limewater milky sodium (Na+) yellow chlorine (Cl 2) bleaches damp litmus paper potassium (K+) lilac hydrogen (H2) ‘pops’ with a lighted splint copper(II) (Cu2+) blue-green oxygen (O2) relights a glowing splint

Mark scheme: 5(a)(i) temperature at t = 0 present ; 1 5(a)(ii) temperature at t = 180 present and < (a)(i) ; 1 5(b) the temperature drop in beaker P should be greater than the temperature drop in beaker Q ; 1 5(c) answer to match results, expect ‘using a lid’ ; 2 values from the table quoted and used to show that there is a smaller temperature decrease with the lid (over the same time period) ; 5(d) use thicker insulation / better insulation / insulate the bottom of the beaker ; 1 5(e) same volume of water / same initial temperature of water / same room temperature / same size (thickness) beakers ; 1

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