Cambridge IGCSE Sciences - Co-ordinated (Double) 0654 — 2023 May/June Paper 5 · Variant 2

1 You are going to investigate the effect of plants and animals on their aqueous environment. (a) Organisms that photosynthesise or respire affect the concentration of carbon dioxide dissolved in their aqueous environment. A sample of water W is provided. (i) Procedure • Add a few drops of hydrogencarbonate indicator to the sample of water in test-tube W. • Record the colour observed. colour observed ........................................................................................................... [1] (ii) Fig. 1.1 shows the aqueous environments set up in three beakers A, B and C. A B C water W and fish only water W and plants only water W and no animals or plants Fig. 1.1 The three beakers A, B and C are at the same temperature and are placed in the light for 1 hour. Hydrogencarbonate indicator changes colour depending on the concentration of carbon dioxide dissolved in the water. Fig. 1.2 shows the colour changes for the hydrogencarbonate indicator. concentration of colour of carbon dioxide hydrogencarbonate indicator high yellow medium red low purple Fig. 1.2 Use Fig. 1.2 and your answer in (a)(i) to deduce the concentration of carbon dioxide dissolved in water W at the start of the investigation. ..................................................................................................................................... [1] (iii) You are provided with three test-tubes A, B and C. These contain water samples taken at the end of the investigation from the three beakers A, B and C. • Add a few drops of hydrogencarbonate indicator to each test-tube and swirl to mix. Complete Table 1.1 by: • recording the final colour observed in each test-tube • transferring your answer from (a)(i) for the colour of hydrogencarbonate indicator with water W • using Fig. 1.2 to state the change in carbon dioxide concentration in each aqueous environment A, B and C. Table 1.1 change in carbon dioxide colour with water Wwater sample final colour observed concentration from (a)(i) (increase / decrease / no change) A B C [4] (b) Respiration releases carbon dioxide and photosynthesis uses carbon dioxide. (i) Explain your observation for aqueous environment B. ........................................................................................................................................... ..................................................................................................................................... [1] (ii) Aqueous environment C is a control. Explain why a control is used in this investigation. ........................................................................................................................................... ..................................................................................................................................... [1] (c) A student repeats the experiment using a beaker of water containing equal amounts of fish and plants. Suggest the colour of the hydrogencarbonate indicator. Explain your answer. colour of hydrogencarbonate indicator ..................................................................................... explanation ............................................................................................................................... ................................................................................................................................................... [1] [Total: 9]

Mark scheme: 1(a)(i) red ; 1 1(a)(ii) medium ; 1 1(a)(iii) yellow ; purple ; red ; increase decrease no change ; 4 1(b)(i) ref more carbon dioxide used in photosynthesis than released in respiration ; 1 1(b)(ii) check that changes in levels due to organisms / not due to water ; 1 1(c) red and rate of photosynthesis same as rate of respiration ; 1

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2 You are going to investigate three nutrient solutions D, E and F. Procedure • Add approximately 1 cm depth of Benedict’s solution to each test-tube D, E and F. • Place the test-tubes in a hot water-bath for at least 3 minutes. You may continue with Question 3 while you are waiting. Complete Table 2.1 with the final colour observed in each test-tube. State a conclusion for each nutrient solution. Table 2.1 nutrient final colour observed conclusion solution D E F [4]

Mark scheme: 2 D yellow / green ; E red / orange ; F is blue ; D and E contain reducing sugar and F does not contain reducing sugar ; 4

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3 The seeds of a sycamore tree are shown in Fig. 3.1. They have “wings” to help carry them in the wind. sycamore seeds Fig. 3.1 Fig. 3.2 shows sycamore seeds fallen from the parent tree. wind distance d sycamore parent tree seeds Fig. 3.2 Plan an investigation to determine the relationship between the vertical height the seeds fall from and the horizontal distance d the seeds travel from the height they were dropped. You are provided with several sycamore seeds. You may 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 • what you will measure • the variables you will control • how you will process your results to draw a conclusion. You may include a labelled diagram if you wish. You may include a results table if you wish. You are not required to include any results. .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .................................................................................................................................................... [7] Remember to go back and complete Question 2.

Mark scheme: 3 apparatus ruler / tape measure ; fan ; method drop seeds from set height and see where drop ; repeats at same height ; minimum 5 different heights ; measurements height of seed on tree / drop ; distance along ground to where seed lands ; control variables wing length / width ; mass / surface area of seed ; fan setting / wind speed ; processing and conclusion plot graph of height v distance ; straight line through origin proportional / straight line linear or as one increases other increases etc ; look to see if increasing height increases / decreases / doesn’t change distance ; 7

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4 You are going to investigate the rate of reaction between solutions H and K. When solutions of H, K and starch are mixed together, a blue-black colour is seen after a period of time. When the volume of solution H is changed, the time taken for the blue-black colour to appear changes. (a) (i) Procedure • Using the syringe labelled H, add 4 cm3 of solution H into a conical flask. • Add 5 drops of starch solution into the conical flask. • Using the syringe labelled K, add 10 cm3 of solution K into the conical flask, swirl the flask and immediately start the stop-watch. • Stop the stop-watch when the solution turns blue-black. • Record in Table 4.1 the time taken t in seconds to the nearest 0.1 second. Table 4.1 volume of volume of drops of volume of time taken t rate of reaction solution H distilled water starch solution K / s per 100 s / cm3 / cm3 solution / cm3 4.0 0 5 10.0 7.0 0 5 10.0 10.0 0 5 10.0 [1] (ii) Repeat the procedure in (a)(i) using the other volumes shown in Table 4.1. [3] (iii) Explain why a different syringe is used to measure solution H and solution K. ........................................................................................................................................... ..................................................................................................................................... [1] (iv) The substance made when solution H and solution K react together turns the starch solution blue-black. Identify the substance made. ..................................................................................................................................... [1] (v) Explain why the results are more reliable if the experiment is repeated and averages calculated. ........................................................................................................................................... ..................................................................................................................................... [1] (b) (i) Calculate the rate of reaction per 100 s for each of the three experiments. Use the equation shown. 100 rate of reaction per 100 s = t Record in Table 4.1 the values of rate to three significant figures. [3] (ii) State the relationship between volume of solution H added and rate of reaction. ........................................................................................................................................... ..................................................................................................................................... [1] (iii) Look at Table 4.1 at the volumes of solutions added to each conical flask. To be able to compare the rates of reaction fairly, distilled water needs to be added to some of the experiments. Complete Table 4.2 to show the volumes of distilled water that need to be added so that a fair comparison can be made. Table 4.2 volume of volume of distilled water solution H that needs to be added / cm3 / cm3 4.0 7.0 10.0 [1] [Total: 12]

Mark scheme: 4(a)(i) time recorded ; 1 4(a)(ii) all times recorded ; order of times matches supervisors results ; all to nearest 0.1 second ; 3 4(a)(iii) avoid contamination ; 1 4(a)(iv) iodine ; 1 4(a)(v) recognise / exclude anomalies ; 1 4(b)(i) 1 value calculated correctly ; 3 values calculated correctly and correctly rounded ; 3sf for all 3 values ; 3 4(b)(ii) relationship between volume and rate matches results in (a)(ii) ; 1 4(b)(iii) 6 and 3 and 0 / any number so that the total is the same in each flask ; 1

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5 You are going to identify solution L and solution M. (a) Procedure • Add approximately 2 cm depth of solution L into four test-tubes. • Place a wooden splint to one of the test-tubes of solution L. • Do the tests described in Table 5.1 with solution L. Use a different test-tube of solution L for each test. • Add approximately 2 cm depth of solution M into the other four test-tubes. • Place a wooden splint to one of the test-tubes of solution M. • Do the tests described in Table 5.1 with solution M. Use a different test-tube of solution M for each test. Table 5.1 observation test solution L solution M add a few drops of aqueous sodium hydroxide add excess aqueous sodium hydroxide add approximately 1 cm depth each of dilute nitric acid and aqueous silver nitrate add approximately 1 cm depth each of dilute nitric acid and aqueous barium nitrate place the wooden splint into the top of a blue Bunsen burner flame and record the first colour seen (if no colour seen, dip the splint in the solution and repeat) [6] (b) State the identities of solution L and solution M. solution L is .............................................................................................................................. solution M is .............................................................................................................................. [2] [Total: 8]

Mark scheme: 5(a) no reaction no reaction no reaction no reaction ; white ppt ; no reaction and no reaction ; white ppt ; red ; lilac ; 5(b) lithium chloride ; potassium sulfate ; 2

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6 You are going to measure the mass M of an object using a balancing method. The object has been secured to the metre rule. Its position is fixed with its centre over the 15.0 cm mark. Do not attempt to move the object during the experiment. (a) Procedure • Place the pivot directly under the 50.0 cm mark. • Place a mass m = 80 g on the rule. • Adjust the position of the mass until the rule is as close as possible to balance, as shown in Fig. 6.1. fixed object metre rule mass M 80 g mass m d 0 100 pivot 15.0 cm 50.0 cm mark mark Fig. 6.1 Calculate, to the nearest 0.1 cm, the distance d from the centre of the 80 g mass to the 50.0 cm mark on the rule. Record this distance in Table 6.1. Table 6.1 mass m distance d (m × d) / g / cm / g cm 80 60 40 [1] (b) Repeat the procedure in (a) using masses of 60 g and 40 g. Record your values in Table 6.1. [2] (c) Describe how you locate the position of the centres of the 40 g, 60 g and 80 g masses. ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [1] (d) (i) Calculate the product (m × d) for each mass m. Record your answers in Table 6.1. [1] (ii) The teacher says that the product (m × d) for each mass is constant. Quantities can be considered to be equal, within the limits of experimental error, if their values are within 10% of each other. Compare your values of (m × d) for each mass in Table 6.1. State, giving a reason, if you agree with the teacher. statement .......................................................................................................................... reason ............................................................................................................................... ........................................................................................................................................... [1] (e) The mass M of the fixed object is calculated using the equation shown. (m × d) M = 35 Calculate M using your results for the 80 g mass. M = ...................................................... g [2] (f) State one practical problem that makes it difficult to get accurate measurements when doing this experiment. ................................................................................................................................................... ............................................................................................................................................. [1] [Total: 9]

Mark scheme: 6(a) d present and less than 50 and to 0.1 cm ; 1 6(b) d recorded for 60 g and 40 g ; d values increasing ; 2 6(c) note reading at either side of mass and find the mean ; 1 6(d)(i) all products correctly evaluated ; 1 6(d)(ii) correct matching statement (yes / no – expect yes) AND suitable one 10% calculation (and compare all 3 values) ; 1 6(e) calculation correct ; M = 40  5 ; 2 6(f) difficult to achieve an exact balance / difficult to locate the centre of the mass ; 1

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7 You are going to investigate the image formed by a convex lens. The apparatus is assembled as shown in Fig. 7.1. convex lens in holder lamp illuminated object screen u v Fig. 7.1 (a) Procedure • Switch on the lamp. • Place the lens a distance u = 20.0 cm from the illuminated object (the triangular hole in the card). • Adjust the position of the screen by moving it backwards and forwards along the bench, until a sharp image of the illuminated object is formed on the screen. Measure, to the nearest 0.1 cm, the image distance v from the screen to the lens. Record the image distance v in Table 7.1. Table 7.1 object distance u image distance v / cm / cm 20.0 25.0 35.0 40.0 50.0 60.0 [1] (b) (i) The diagram in Fig. 7.2 shows the illuminated object. object Fig. 7.2 In the space next to the object, draw a diagram to show the image that you observe on the screen. [1] (ii) The magnification m of the image is calculated using the equation shown. v m = u Calculate the magnification of the image. m = ......................................................... [1] (c) Repeat the procedure in (a) for values of u = 25.0 cm, 35.0 cm, 40.0 cm, 50.0 cm, and 60.0 cm. Record your values of v in Table 7.1. [2] (d) (i) On the grid, plot a graph of v (vertical axis) against u. 60 50 40 30 20 10 00 10 20 30 40 50 60 [2] (ii) Draw the best-fit curve. [1] (e) Use your graph to find the value of v when u = 30.0 cm. v = ................................................... cm [2] (f) State one precaution you take when doing the experiment to ensure that the readings you obtain are as accurate as possible. ................................................................................................................................................... ............................................................................................................................................. [1] [Total: 11]

Mark scheme: 7(a) v recorded to the nearest 0.1 cm ; 1 7(b)(i) image drawn inverted and magnified ; 1 7(b)(ii) candidate’s value of v/u for u = 20.0 cm ; 1 7(c) remaining values of v present ; values decreasing ; 2 7(d)(i) axes labelled with units ; plots correct to  ½ small square ; 2 7(d)(ii) good best-fit curve judgement ; 1 7(e) candidate’s value of v for u = 30.0 cm correctly read from graph ; v = 30  6 ; 2 7(f) move screen slowly / to and from (until the sharpest image is formed) / read metre rule at right angles to scale / carry out experiment in a darkened part of the laboratory ; 1

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