Cambridge IGCSE Science - Combined 0653 — 2019 May/June Paper 6 · Variant 1

1 A student investigates the nutrient content of an apple. (a) Fig. 1.1 shows a photograph of the cut surface of an apple. Fig. 1.1 (i) In the box, make an enlarged detailed drawing of the cut surface of the apple. [2] (ii) Use a ruler to measure your drawing, in millimetres, at its widest point and record this value. width of apple in drawing = ........................................................ mm Measure the same distance on the photograph in Fig. 1.1 and record this value. width of apple from photograph = ........................................................ mm [1] (iii) Calculate the magnification of your drawing. Show your working. magnification of drawing = ......................................................... [1] (b) Describe how you would test this fruit to show the presence of reducing sugar. Include the observation that shows a positive result. test ............................................................................................................................................ ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... observation for a positive result ................................................................................................ ............................................................................................................................................. [3] [Total: 7]

Mark scheme: 1(a)(i) fills more than 50% of space ; Continuous, smooth line around outside of apple shape and two pips in the core ; 2 1(a)(ii) photograph 54–58 (mm) ; 1 1(a)(iii) correct calculation for magnification (drawing over photograph) ; 1 1(b) Benedicts ; heat (with Benedicts) ; (independent) orange / (brick) red / yellow / green ; 3

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2 Fig. 2.1 shows a cut stem of the water plant Elodea placed in a beaker of water. When light shines on the Elodea it photosynthesises, and bubbles of gas are produced. water Elodea Fig. 2.1 Plan an investigation to find out how the rate of photosynthesis of Elodea is affected by the brightness of the light. In your answer, include: • the apparatus needed, including a labelled diagram if you wish • a brief description of the method, including how you will treat variables and any safety precautions • the measurements you will make • how you will process your results • how you will use your results to draw a conclusion. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [7]

Mark scheme: 2 1 apparatus lamp / sunlight / light source ; apparatus for collecting gas ; stop-clock / timer ; 2 method and variables change brightness of light / change distance (from lamp) ; same amount of time (at each brightness) ; repeat experiment at each brightness ; control length elodea / control volume of water ; control temperature / carbon dioxide / pH ; stated safety precaution linked to apparatus ; 3 measurements measure distance / intensity of light ; measure volume of gas / count bubbles ; 4 processing results and make conclusion calculate rate as volume / number of bubbles per unit time ; idea of looking for relationship between rate / volume / number of bubbles and intensity / brightness / distance ; graph of rate / volume / number of bubbles against intensity / brightness / distance ; 7

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3 A student investigates the temperature change which occurs when aqueous copper(II) sulfate reacts separately with excess magnesium and with excess zinc. (a) Method 1. Using a measuring cylinder the student places 25 cm3 aqueous copper(II) sulfate into a small glass beaker. 2. She measures the temperature of the aqueous copper(II) sulfate and records it in Table 3.1 to the nearest 0.5 °C for time = 0. 3. She starts the stop-clock and immediately adds 2 g magnesium powder, an excess, to the beaker and stirs. 4. She measures the temperature every 30 seconds for 4 minutes. She records the temperatures, to the nearest 0.5 °C, in Table 3.1. Table 3.1 reaction with magnesium time / min temperature / °C 0 20.0 0.5 1.0 47.0 1.5 60.0 2.0 60.0 2.5 58.0 3.0 56.5 3.5 4.0 53.0 Fig. 3.1 shows the thermometer scales for the temperatures at 0.5 and 3.5 minutes. °C °C 40 60 30 50 0.5 3.5 minutes minutes Fig. 3.1 Read the temperatures to the nearest 0.5 °C and record them in Table 3.1. [2] (b) (i) On the grid provided plot a graph of temperature (vertical axis) against time. temperature / °C 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 time / min [2] (ii) Draw a best-fit straight line for the increasing temperatures. Extend the line further than the highest point. Label the line magnesium. Draw a best-fit line through the decreasing temperatures. Extend the line back past the highest point. [1] (iii) The maximum temperature reached by the reaction is where the two lines cross. State the maximum temperature reached by the reaction. maximum temperature = ..................................................... °C [1] (c) Suggest a value for the maximum temperature reached if 5 g magnesium powder is reacted with 25 cm3 of the same copper(II) sulfate solution. maximum temperature = ..................................................... °C [1] (d) She then repeats the experiment using 2 g zinc powder, an excess, instead of magnesium powder. She records the temperatures in Table 3.2. Table 3.2 reaction with zinc time / mins temperature / °C 0 20.0 0.5 29.5 1.0 38.0 1.5 45.0 2.0 45.0 2.5 3.0 41.5 3.5 40.0 4.0 38.0 (i) Fig. 3.2 shows the thermometer scale for the temperature at 2.5 minutes. °C 50 40 2.5 minutes Fig. 3.2 Read the temperature to the nearest 0.5 °C and record it in Table 3.2. [1] (ii) Repeat (b) for the results for zinc. Draw the graph on the same grid as that used for magnesium. Label this graph zinc. State the maximum temperature reached by this reaction. maximum temperature = ..................................................... °C [2] (e) Suggest why the maximum temperature for magnesium is different from the maximum temperature for zinc. ................................................................................................................................................... ............................................................................................................................................. [1] (f) (i) State the name of a piece of apparatus which could be used to measure the volume of copper(II) sulfate more accurately. ..................................................................................................................................... [1] (ii) Suggest and explain one other improvement to the apparatus that would increase the accuracy of the maximum temperature for the reactions. improvement ..................................................................................................................... explanation ........................................................................................................................ ..................................................................................................................................... [1] [Total: 13]

Mark scheme: 3(a) 33.5 ; 55.0 ; 2 3(b)(i) linear scale more than half grid ; at least 6 points correctly plotted ± ½ a small square ; 2 3(b)(ii) 2 straight lines drawn with ruler, through all points and meet in a cross ; 1 3(b)(iii) maximum T from their graph ; 1 3(c) same as (b)(iii) ; 1 3(d)(i) 43.5 ; 1 3(d)(ii) lines labelled magnesium and zinc ; 2 straight lines drawn with ruler, through all points and meet in a cross and temperature ; 2 3(e) magnesium is more reactive (than zinc) ; 1 3(f)(i) burette / pipette ; 1 3(f)(ii) any 1 from lid AND reduces heat loss ; insulate cup AND reduce heat loss ; max 1

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4 A student calculates the density of a liquid using two different methods. Method 1 (a) He measures the mass mc of an empty measuring cylinder. mc = 102.31 g He adds approximately 75 cm3 of the liquid to the measuring cylinder. (i) Fig. 4.1 shows part of the measuring cylinder scale. cm3 100 90 80 70 Fig. 4.1 Read and record the volume VL of the liquid to the nearest 0.5 cm3. VL = .................................................. cm3 [1] (ii) State how parallax (line of sight) errors are avoided when using a measuring cylinder. ........................................................................................................................................... ..................................................................................................................................... [1] (iii) He measures and records the total mass of the measuring cylinder and liquid. total mass = 189.00 g Determine the mass mL of the liquid. Use the equation shown. mL = total mass − mc mL = ...................................................... g [1] (iv) Calculate the density ρL of the liquid. Use your answers in (a)(i) and (a)(iii) and the equation shown. Record your answer to a suitable number of significant figures. mL ρL = VL ρL = .............................................. g / cm3 [2] Method 2 (b) (i) The student measures the mass mt of a test-tube. Fig. 4.2 shows the balance reading. 15.827 g Fig. 4.2 Read and record the mass of the test-tube to the nearest 0.01 g. mt = ...................................................... g [1] (ii) He also measures the length lt and the diameter dt of the test-tube. His results are shown in Fig. 4.3. lt = 11.7 cm dt = 1.6 cm Fig. 4.3 Use the student’s values of lt and dt to calculate the volume Vt of the test-tube. Use the equation shown: Vt = 0.79 × dt2 × lt Vt = .................................................. cm3 [1] (iii) Calculate the density ρt of the test-tube. Use your answers to (b)(i) and (b)(ii) and the equation shown: mt ρt = Vt ρt = .............................................. g / cm3 [1] (iv) The student lowers the test-tube into a measuring cylinder containing the liquid until it floats, as shown in Fig. 4.4. Fig. 4.4 Use a ruler to measure the length lb of the test-tube, to the nearest 0.1 cm, that is below the surface of the liquid.

Mark scheme: 4(a)(i) 78.0 (cm3) ; 1 4(a)(ii) read perpendicular to the scale ; 1 4(a)(iii) 86.69 (g) ; 1 4(a)(iv) 1.11(1) g / cm3 ; 2 or 3 sig. figs and must be correctly rounded ; 2 4(b)(i) 15.83 (g) ; 1 4(b)(ii) 24 / 23.7 / 23.66 ; 1 4(b)(iii) 0.67 g / cm3 ; 1 4(b)(iv) 5.6 cm ; 1 4(b)(v) 1.4 g / cm3 ; 1 4(c) (expect no) answer values too far apart OWTTE 1 4(d)(i) test-tube is curved at the bottom 1 4(d)(ii) mark as a pair volume too high and density too low ; 1

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