Cambridge IGCSE Science - Combined 0653 — 2020 Feb/March Paper 5 · Variant 2

1 (a) You are going to investigate different types of bean. You are provided with two different types of bean, A and B. You have been given three beans of each type. (i) Measure the longest length of each bean and record your measurements in Table 1.1. Table 1.1 bean number bean A length / ...................... bean B length / ...................... 1 2 3 [2] (ii) Complete the headings of Table 1.1 by adding the units. [1] (iii) Calculate the average length of each type of bean. Give your answers to an appropriate number of significant figures. average length of type A ........................................... average length of type B ........................................... [1] (iv) Plot a bar chart of the average length of the two types of bean. [2] (v) Identify one possible source of error when measuring the longest length of each bean. ........................................................................................................................................... ..................................................................................................................................... [1] (vi) Suggest a different measurement you could take for comparing the size of the beans. ..................................................................................................................................... [1] (vii) Apart from size, state one other visible difference between the types of beans provided. ..................................................................................................................................... [1] (b) Remove the outer layer of one of the type A beans and crush the bean carefully on a white tile. Add five drops of iodine solution to the crushed bean. (i) Record your observations: colour of iodine solution before adding to crushed bean .................................................. colour of iodine solution after adding to crushed bean ..................................................... [1] (ii) State a conclusion for this test. ........................................................................................................................................... ..................................................................................................................................... [1] (iii) Describe how you would test a bean for the presence of reducing sugars. ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [2] [Total: 13]

Mark scheme: 1(a)(i) six measurements recorded to nearest mm ; values for A higher than values for B ; 2 1(a)(ii) units included in headings (mm or cm) ; 1 1(a)(iii) correct average value for both ; 1 1(a)(iv) correct axis with units – average length / mm or cm, A and B identified and bars more than half the grid ; correct plotting of bars ± half small square ; 2 1(a)(v) bean shape prevents direct measurement ; 1 1(a)(vi) mass / volume ; 1 1(a)(vii) pattern on surface / shape / colour ; 1 1(b)(i) before: brown / yellow / orange and after: blue-black / black / dark blue ; 1 1(b)(ii) starch present if second colour is blue-black / black / dark blue OR starch is absent if second colour is brown/ yellow / orange ; 1 1(b)(iii) add Benedict’s solution ; heat / warm ; 2

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2 You are going to investigate the reactivity of four metals G, H, J and L. (a) Procedure Read the whole of procedure 2(a) before you begin the investigation. • Label one well on the spotting tile G, a second H, a third J and a fourth L. Put the label next to the well. • Half fill each of the four labelled wells with aqueous copper sulfate. • Record the colour of each of the metals in Table 2.1. • Put a small amount of metal G into well G. • Put a small amount of metal H into well H. • Put a small amount of metal J into well J. • Put a small amount of metal L into well L. Leave this experiment until after you have completed part 2(b). After you have completed 2(b) look at each well in the spotting tile. (i) Record these final observations in Table 2.1. Table 2.1 colour of aqueous copper colour of metal sulfate before final observation metal the metal is added G blue H blue J blue L blue [3] (ii) State which of the metals have reacted with aqueous copper sulfate. Explain your answer. metal ................................................................................................................................. explanation ........................................................................................................................ ........................................................................................................................................... [1] (b) (i) Procedure Read the whole of procedure 2(b)(i) before you begin. • Place about 2 cm depth of dilute sulfuric acid into a boiling tube. • Measure the initial temperature of the sulfuric acid in the boiling tube. • Record in Table 2.2 this initial temperature to the nearest 0.5 °C against metal G. • Add the rest of the sample of metal G to the boiling tube. • Stir and record in Table 2.2 your observations of the mixture in the boiling tube. • Measure the temperature in the boiling tube after 2 minutes. • Record in Table 2.2 this temperature to the nearest 0.5 °C. Repeat the procedure in 2(b)(i) for metals H, J and L. Use a clean boiling tube for each reaction. Table 2.2 initial temperature metal temperature of after observations acid / °C 2 minutes / °C G H J L [4] (ii) Use the results in Table 2.2 to suggest which one of the four metals G, H, J and L, is the most reactive. ..................................................................................................................................... [1] (iii) State two different reasons for your choice in 2(b)(ii). reason 1 ............................................................................................................................ ........................................................................................................................................... reason 2 ............................................................................................................................ ........................................................................................................................................... [2] (iv) Suggest how the experiment in 2(b)(i) could be changed to make the comparison of reactivity of the metals more reliable. Do not include repeating the experiment. ........................................................................................................................................... ..................................................................................................................................... [1] Go back and complete parts 2(a)(i) and 2(a)(ii). (c) Place the metals in order of reactivity, starting with the most reactive. Use the results and observations in Table 2.1 and Table 2.2 to help you. metal ................................... most reactive metal ................................... metal ................................... metal ................................... least reactive [1] [Total: 13]

Mark scheme: 2(a)(i) colour of metal: G, H, J grey and L pink / orange / brown ; final observation: G, H and J pink / not grey and (copper sulfate) solution pale blue / colourless ; final observation: L same colour as M1, (copper sulfate) solution blue ; 3 2(a)(ii) G, H and J and changed colour / blue solution decolourises ; 1 2(b)(i) initial and final temperatures for one metal ; all eight temperatures recorded, final temperature H highest and L lowest ; observations with H as most reactive and L as no reaction ; observation different for all four metals ; 4 2(b)(ii) H ; 1 2(b)(iii) fastest bubbles ; largest change in temperature ; 2 2(b)(iv) measure volume with measuring cylinder / same initial temperature / same mass or amount or size of metal / wait until temperature stops changing ; 1 2(c) H > G > J > L ; 1

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3 You are going to determine the period T of a pendulum. (a) The apparatus shown in Fig. 3.1 has been set up for you. clamp pendulum 40.0 cm bob Fig. 3.1 The period T is the time it takes for the pendulum to complete one full oscillation (from S to P, P to Q and then from Q back to S), as shown in Fig. 3.2. P Q S Fig. 3.2 (i) Pull the pendulum a few centimetres to one side and release it. Observe the oscillations. Explain why it will be difficult to time one oscillation accurately using the stop‑watch. ........................................................................................................................................... ..................................................................................................................................... [1] (ii) Timing a larger number of oscillations n, allows you to calculate the period T using the equation shown. time for n oscillations T = n Suggest a suitable number for n. Give a reason for the number you have chosen. n = ........... reason ............................................................................................................................... ........................................................................................................................................... [2] (iii) Complete the heading in Table 3.1 with the number of oscillations n chosen in 3(a)(ii). Measure the time for n oscillations. Record in Table 3.1 the time for n oscillations to the nearest 0.01 s. [1] Table 3.1 time for ..... oscillations / s period T / s (iv) Measure the time for n oscillations two more times. Record each time in Table 3.1 to the nearest 0.01 s. [1] (b) (i) Calculate and record in Table 3.1 the period T of the pendulum for each of your results. Use the equation in 3(a)(ii). Give your answers to the nearest 0.01 s. [1] (ii) Calculate the average value of T from your three experiments. average T = ............................................................ s [1] [Total: 7]

Mark scheme: 3(a)(i) one oscillation is too quick ; 1 3(a)(ii) number between 5–20 inclusive ; big enough to spread the effect of human reaction time error / small enough that oscillations can still be observed and counted ; 2 3(a)(iii) sensible value recorded in Table 3.1 based on their n ; 1 3(a)(iv) all answers with similar values ; 1 3(b)(i) three values of T correctly calculated ; 1 3(b)(ii) correct value of average T ; 1

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4 Fig. 4.1 shows a beam that is balanced by placing masses on opposite sides of a central pivot. A has a mass of 50 g and is placed a fixed distance from the pivot. The mass of B can be changed. B can also be moved to different positions on the beam. 50 g mass A B beam pivot Fig. 4.1 Mass B is heavier than mass A. It must be placed closer to the pivot than A for the beam to balance. Plan an investigation to find out how the distance of mass B from the pivot, when the beam is balanced, depends on its mass. You are provided with: • a metre rule which can act as the beam • a pivot • 50 g mass A • a selection of 10 g and 100 g masses which can be combined to make different values for mass B. You may use any other common laboratory apparatus in your plan. You are not required to do this investigation. In your plan, include: • a brief description of the method • how you will ensure that your results are as accurate as possible • the values of mass that you will use for mass B • the column headings (including any appropriate units) for the table you will use to record your results • how you will process your results to draw a conclusion. .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... [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 nitrate (NO3–) add aqueous sodium hydroxide, ammonia produced [in solution] then 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 (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 white ppt., soluble in excess, a colourless solution giving a colourless solution Tests for gases gas test and test result ammonia (NH3) turns damp, red litmus paper blue carbon dioxide (CO2) turns limewater milky chlorine (Cl 2) bleaches damp litmus paper hydrogen (H2) ‘pops’ with a lighted splint oxygen (O2) relights a glowing splint

Mark scheme: 4 one mark from each section and any two others (if one section is missing max 6 etc.) Method: set up beam with A (a fixed distance) and place B / fixing A to the beam and place B ; move mass B until beam is balanced ; measure distance of B from pivot (when beam is balanced) ; Accuracy: sensible description of how to find location of centre of mass B ; repeat all readings / repeat every mass ; description of how to avoid parallax error when taking readings ; Values: at least 3 values of mass B ; values of mass B all > 50 g ; Table: suitable column headings for method, e.g. value of mass B AND distance of B (from pivot) ; appropriate units for each column heading, e.g. (mass) g AND (distance) cm / mm / m ; Processing and Conclusion: calculate average of distances for each mass used / distance of B from pivot is (reading – 50) ; plot a graph of mass of B versus distance of B from pivot at balance ; draw best-fit line or curve ; as mass increases is distance more or less / as mass increases look for trend in distance ; 7

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