Cambridge IGCSE Science - Combined 0653 — 2023 May/June Paper 6 · Variant 2

1 Fig. 1.1 is a section through okra, a fruit which contains five seeds. A B Fig. 1.1 (a) In the box provided, draw a large, clear pencil drawing of the section of okra. [3] (b) (i) The distance between point A and point B on Fig. 1.1 represents a diameter of the okra. Measure the distance between point A and point B on Fig. 1.1. distance on Fig. 1.1 = .................................................. mm [1] (ii) Suggest why the distance between point A and point B is only an estimate of the diameter of the okra in Fig. 1.1. ........................................................................................................................................... ..................................................................................................................................... [1] (iii) Measure the distance between the same two points on your drawing as in (b)(i). Mark A and B on your drawing to show where you have measured. distance on your drawing = .................................................. mm [1] (iv) Calculate the magnification of your drawing. Use the equation shown. distance on your drawing magnification = distance on Fig. 1.1 magnification = ......................................................... [1] [Total: 7]

Mark scheme: 1(a) size – greater than half available space ; quality – continuous smooth outer line with no shading ; detail – five seeds and pentagon shape ; 1(b)(i) diameter of okra 48–52 mm ; 1 1(b)(ii) irregular shape / not circular / AW ; 1 1(b)(iii) correct diameter for drawing in mm ; 1 1(b)(iv) correct calculation of magnification ; 1

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2 The enzyme amylase breaks down starch to form a reducing sugar. Iodine is a brown solution that turns blue/black in the presence of starch. Plan an investigation to determine the relationship between temperature and the time taken to completely break down starch by amylase. You are provided with: • 1% amylase solution • 1% starch solution • iodine solution. You may also use any other common laboratory apparatus. In your plan include: • the additional apparatus needed • a brief description of the method and an explanation of any safety precautions you will take • what you will measure • which variables you will keep constant • how you will process your results to draw a conclusion. You may include a labelled diagram if you wish. You may include a table that can be used to record the results if you wish. You do not need to include any results in your table. .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .................................................................................................................................................... [7]

Mark scheme: 2 One marking point from each section and any two others (if one section is missing max 6 etc). 1 Apparatus syringe / measuring cylinder and stop-watch / stop-clock ; thermometer ; water-bath ; 2 Brief description of method and safety precautions mix starch and amylase and start timer (immediately) ; remove samples from mixture at set time intervals and test with iodine ; use different temperatures ; use at least 5 different temperatures ; to stop reaction mixture / iodine / starch / amylase, from entering eye wear goggles / hot apparatus so, do not touch / use tongs / test-tube holder ; 3 Measurements measure time taken when sample, stays brown colour with iodine solution / not blue-black ; detail of measurement of temperature of water-bath, e.g. set thermostat / measure water temperature in beaker ; measure volume / cm3 of amylase or volume / cm3 of starch ; 4 Control variables use same volume / concentration, starch ; use same volume / concentration, amylase ; 5 Process results to draw a conclusion repeat at the same temperature and take averages ; plot graph of time (to break down starch) against temperature (of mixture) ; 7

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3 A student investigates a white solid H. (a) Procedure The student: • measures the mass of an empty test-tube and records this mass in Table 3.1 • places some solid H into the test-tube • measures the mass of the test-tube and solid H and records this mass in Table 3.1 • heats solid H for one minute using the blue flame of a Bunsen burner • lets the test-tube cool down • measures the mass of the test-tube and the solid after heating and records this mass in Table 3.1. Table 3.1 mass / g empty test-tube 16.23 test-tube and solid H before heating test-tube and the solid after heating (i) Suggest why the student lets the test-tube and the solid cool down before measuring its mass. ........................................................................................................................................... ..................................................................................................................................... [1] (ii) Fig. 3.1 shows two of the balance readings. 18.731 g 17.846 g test-tube and solid H before heating test-tube and the solid after heating Fig. 3.1 Record in Table 3.1 these readings to two decimal places. [2] (iii) Calculate the mass of solid H in the test-tube before heating. Use the equation shown. mass of solid H mass of test-tube and = – mass of empty test-tube before heating solid H before heating mass of solid H before heating = ...................................................... g [1] (iv) Calculate the mass of the solid in the test-tube after heating. Use the equation shown. mass of the solid mass of test-tube and = – mass of empty test-tube after heating the solid after heating mass of the solid after heating = ...................................................... g [1] (v) There is a loss in mass when solid H is heated. Suggest one reason for this loss in mass. ..................................................................................................................................... [1] (vi) Calculate the percentage loss in mass. Use the equation shown. mass of solid H before heating – mass of the solid after heatingpercentage loss in mass = × 100 mass of solid H before heating Give your answer to two significant figures. percentage loss in mass = ......................................................... [2] (vii) Explain why it is better to heat solid H for at least five minutes rather than one minute. ........................................................................................................................................... ..................................................................................................................................... [1] (viii) State one reason why the test-tube must be heated with a blue Bunsen burner flame rather than a yellow Bunsen burner flame. ........................................................................................................................................... ..................................................................................................................................... [1] (b) The student puts some solid H into dilute hydrochloric acid. The mixture forms a colourless solution and bubbles of carbon dioxide gas are seen. (i) Describe the test to confirm that the gas made is carbon dioxide. Include the observation for a positive result. test .................................................................................................................................... observation ........................................................................................................................ [1] (ii) Identify the anion (negative ion) present in solid H. ..................................................................................................................................... [1] (iii) The student adds aqueous sodium hydroxide to the colourless solution. A white precipitate forms which is soluble in excess aqueous sodium hydroxide. Tick (3) the name of the cation present in the colourless solution. ammonium calcium copper(II) iron(III) zinc [1] [Total: 13]

Mark scheme: 3(a)(i) touching hot test-tube may cause injury / AW ; 1 3(a)(ii) 18.73 ; 17.85 ; 2 3(a)(iii) 2.50 ; 1 3(a)(iv) 1.62 ; 1 3(a)(v) gas produced (which escapes) ; 1 3(a)(vi) 35.2 ; answer quoted to two sig. figs. = 35 (%) ; 2 3(a)(vii) to ensure complete, reaction / decomposition ; 1 3(a)(viii) blue flame is hotter / reaches a higher temperature ORA / yellow flame causes black (carbon / soot) to form on tube ; 1 3(b)(i) limewater and goes milky ; 1 3(b)(ii) carbonate / CO32– ; 1 3(b)(iii) zinc (ticked) ; 1

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4 A student does an experiment to determine the focal length F of a convex lens. D illuminated object screen u v lens bench 0 100 metre rule Fig. 4.1 (a) Procedure The student: • arranges the equipment as shown in Fig. 4.1 • switches on the lamp • places the illuminated object (a triangle) at the 0 cm mark on the metre rule • places the lens at a distance u = 10.0 cm from the illuminated object • places the screen at a distance D = 95.0 cm from the illuminated object. An out of focus fuzzy image appears on the screen. • moves the lens slowly towards the screen until the image formed is in focus, and as sharp as possible • measures u and v and records the values in Table 4.1. (i) The illuminated object is 1.5 cm high. Fig. 4.2 shows the actual size of the image on the screen. h Fig. 4.2 Measure and record the height h of the image. h = ................................................... cm [1] (ii) The student repeats the procedure for values of D = 85.0 cm, 75.0 cm, 70.0 cm and 65.0 cm. Fig. 4.3 shows the lens and part of the metre rule when the image is in focus for D = 75.0 cm. u lens 18 19 20 21 22 23 Fig. 4.3 Record the value of u shown on the metre rule in Table 4.1 in the row for D = 75.0 cm. Table 4.1 D u v uv / cm / cm / cm / ........... 95.0 19.2 75.8 1460 85.0 20.5 64.5 1320 75.0 70.0 22.2 47.8 1060 65.0 24.8 40.2 997 [1] (iii) Calculate the distance v for D = 75.0 cm and record the value in Table 4.1. [1] (iv) Calculate the product uv and record it for D = 75.0 cm in the final column of Table 4.1. Use the equation shown. uv = u × v [1] (v) Add the unit to the column heading for uv in Table 4.1. [1] (b) (i) On the grid, plot a graph of uv (vertical axis) against D. Do not start your graph from the origin (0, 0). [3] (ii) Draw the best-fit straight line. [1] (c) The focal length F of the lens is equal to the gradient of your line. Calculate the gradient of your line. Indicate on your graph the values you choose to calculate the gradient. F = ......................................................... [2]

Mark scheme: 4(a)(i) h = 5.9 (cm) ; 1 4(a)(ii) u = 21.3 (cm) ; 1 4(a)(iii) v = 53.7 (cm) ; 1 4(a)(iv) 1140 ; 1 Question Answer Marks 4(a)(v) cm2 ; 1 4(b)(i) axes labelled: y-axis: uv / cm2 and x-axis: D / cm ; suitable linear scale, plotted points fill more than 50% of available space ; points plotted correctly to  ½ a small square ; 3 4(b)(ii) straight line of best fit and reasonable spread of points above and below the line ; 1 4(c) F in range 14–16 cm ; gradient triangle drawn on graph to cover at least half the length of candidate’s line ; 2 4(d)(i) the straight line is a way of taking an average OR anomalous results can be, seen / identified ; 1 4(d)(ii) move lens back and forwards (to find sharpest image) ; 1

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