Cambridge IGCSE Science - Combined 0653 — 2023 May/June Paper 5 · Variant 2

1 You are going to investigate okra, a fruit which contains many seeds. You are provided with a section of okra on a white tile. (a) In the box provided, draw a large, clear pencil drawing of the cut surface of the okra. [3] (b) (i) Measure the diameter of the section of okra on the white tile. diameter of okra on white tile = .................................................. mm [1] (ii) Suggest why it is difficult to measure the diameter of the okra accurately. ........................................................................................................................................... ..................................................................................................................................... [1] (iii) Measure the diameter of your drawing in (a). Draw a line on your drawing to show where you have measured. diameter of your drawing = .................................................. mm [1] (iv) Calculate the magnification of your drawing. Use the equation shown. diameter o f yo ur drawin g magnification = diameter of okra on white tile magnification = ......................................................... [1] [Total: 7]

Mark scheme: 1(a) quality – continuous smooth outer line with no shading ; detail – seeds and pentagon / hexagon shape ; 3 1(b)(i) diameter of okra 15–30 mm ; 1 1(b)(ii) (okra) not circular / irregular shape / AW ; 1 1(b)(iii) correct diameter for drawing in mm ; 1 1(b)(iv) correct calculation for magnification ; 1

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2 The enzyme amylase breaks down starch to form a reducing sugar. Plan an investigation to determine the relationship between temperature and the time taken to completely break down starch by amylase. Iodine is a brown solution that turns blue/black in the presence of starch. You are provided with: • 1% amylase solution • 1% starch solution • iodine solution You may also use any other common laboratory apparatus. You are not required to do this investigation. 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 results table. .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .................................................................................................................................................... [7]

Mark scheme: 2 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 You are going to investigate a white solid H. (a) (i) Procedure • Measure the mass of the clean dry test-tube labelled H. • Record this mass in Table 3.1. • Place two spatula loads of solid H into the test-tube. • Measure the mass of the test-tube and solid H. • Record this mass in Table 3.1. • Using the test-tube holder, heat solid H safely for one minute using a blue Bunsen burner flame. • Observe solid H during heating. • Lay the test-tube on the laboratory mat and allow the test-tube to cool down. Table 3.1 mass / g empty test-tube test-tube and solid H before heating test-tube and the solid after heating [2] (ii) Describe your observation of solid H during heating. ..................................................................................................................................... [1] While you are waiting for the test-tube to cool down do part (b). (iii) When the test-tube is cool, measure the mass of the test-tube and the solid after heating. Record this mass in Table 3.1. [1] (iv) Describe your observation of the solid after cooling. ..................................................................................................................................... [1] (v) 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] (vi) 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] (vii) There is a loss in mass when solid H is heated. Suggest one reason for this loss in mass. ..................................................................................................................................... [1] (viii) Calculate the percentage loss in mass. Use the equation shown. mass of solid H before heating – mass of the solid after heating percentage loss in mass = × 100 mass of solid H before heating Give your answer to two significant figures. percentage loss in mass = ......................................................... [2] (ix) Explain why it is a good idea to heat solid H for at least five minutes rather than one minute. ........................................................................................................................................... ..................................................................................................................................... [1] (x) 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) Put about 3 cm depth of dilute hydrochloric acid in a clean test-tube. Add one spatula load of solid H. Describe one observation. ............................................................................................................................................. [1] Go back to (a)(iii) to finish question (a). [Total: 13]

Mark scheme: 3(a)(i) both values to same and at least 1 decimal place ; mass of test tube and solid H being higher than mass of empty test-tube ; 2 3(a)(ii) (on heating) turns yellow ; 1 3(a)(iii) mass that is greater than empty test-tube but less than with solid H ; 1 3(a)(iv) (on cooling) goes white ; 1 3(a)(v) correct mass of solid H ; 1 3(a)(vi) correct mass of solid after heating ; 1 3(a)(vii) gas produced (which escapes) ; 1 3(a)(viii) correct percentage loss of mass ; correct rounding to two sig. figs.  working shown ; 2 3(a)(ix) to ensure complete, reaction / decomposition ; 1 3(a)(x) blue flame is hotter / reaches a higher temperature ORA / yellow flame causes black (carbon / soot) to form on tube ; 1 3(b) bubbles / fizzes / effervesces / solid disappears / colourless solution ; 1

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4 You are going to measure the focal length F of a convex lens. Arrange the equipment as shown in Fig. 4.1. D illuminated object screen u v lens bench 0 100 metre rule Fig. 4.1 (a) Procedure • Switch on the lamp. • Place the illuminated object (a triangle) at the 0 cm mark on the metre rule. • Place the lens at a distance u = 10.0 cm from the illuminated object. • Place the screen at a distance D = 95.0 cm from the illuminated object. An out of focus, fuzzy image appears on the screen. • Move the lens slowly towards the screen until the image formed is in focus, and as sharp as possible. (i) Measure the distances u and v to the nearest 0.1 cm. Record u and v in the first row of Table 4.1. Table 4.1 D u v uv / cm / cm / cm / ....................... 95.0 85.0 75.0 70.0 65.0 [1] (ii) Repeat the measurements for the four other values of D shown in Table 4.1. Record the distances u and v in Table 4.1 against the correct values of D. [2] (iii) Calculate the product uv and record it for each value of D in the final column of Table 4.1. Use the equation shown. uv = u × v [1] (iv) 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. You do not need to 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] (d) (i) F can also be calculated without plotting a graph, by using the results for one value of D. Suggest why plotting a graph and calculating a gradient to find the value of F gives a more accurate answer than calculating F for one value of D. ........................................................................................................................................... ..................................................................................................................................... [1] (ii) State one precaution that you take when doing the experiment to make your readings as accurate as possible. ........................................................................................................................................... ..................................................................................................................................... [1] [Total: 13]

Mark scheme: 4(a)(i) values shown for u and v in first row that add up to 95.0 cm ; 1 4(a)(ii) all u and v values present to the nearest mm ; u values ascending, v values descending ; 2 4(a)(iii) five values in final column correctly calculated ; 1 4(a)(iv) 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) evidence of gradient calculation read-offs seen (on graph) AND read-offs use at least half the candidate’s drawn line ; correct value from their graph (expect F in range 14–16 cm) ; 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 (slowly) back and forwards (through focus) to find sharpest image ; 1

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