Cambridge IGCSE Science - Combined 0653 — 2024 Feb/March Paper 6 · Variant 2

1 Penguins stand close together in a huddle, as shown in Fig. 1.1. Fig. 1.1 A student investigates the effect on heat loss of standing together in a huddle. The student uses test-tubes to represent the penguins. Procedure The student: • assembles the apparatus as shown in Fig. 1.2 thermometer middle clamp test-tube elastic band beaker single huddle Fig. 1.2 • fills all of the test-tubes with hot water • records in Table 1.1 the temperature readings on the two thermometers every minute for a total of 5 minutes. (a) Fig. 1.3 shows the reading on the thermometer at 4 minutes in the middle test-tube of the huddle. °C 70 60 50 Fig. 1.3 (i) Record in Table 1.1 the temperature shown in Fig. 1.3 to the nearest 0.5 °C. Table 1.1 temperature / °C time / minutes single test-tube middle test-tube 0 78.0 76.5 1 72.5 72.0 2 67.5 69.5 3 62.0 67.0 4 58.0 5 56.0 64.5 [1] (ii) Calculate the overall change in temperature for each of the two test-tubes after 5 minutes. single test-tube = .......................................................... °C middle test-tube = .......................................................... °C [1] (iii) State a conclusion for your answer to (a)(ii). ........................................................................................................................................... ..................................................................................................................................... [1] (iv) Predict the change in temperature for one of the outer test-tubes of the huddle. Give a reason for your answer. temperature change ..................................................................................................... °C reason ................................................................................................................................ ........................................................................................................................................... [1] (b) Suggest why it is better to use the change in temperature to compare the heat loss rather than the final temperature. ................................................................................................................................................... ............................................................................................................................................. [1] (c) In this procedure the effect on heat loss of standing in a huddle is investigated. Suggest one other variable that affects heat loss in penguins. ................................................................................................................................................... ............................................................................................................................................. [1] (d) The test-tubes are left for a further 24 hours. Suggest why the two test-tubes have the same temperature as each other after 24 hours. ................................................................................................................................................... ............................................................................................................................................. [1] [Total: 7]

Mark scheme: Question Answer Marks 1(a)(i) 65.5 (°C) ; 1 1(a)(ii) 22(.0) and 12(.0) (°C) ; 1 1(a)(iii) heat loss is reduced / is less, in a huddle / slower heat loss in huddle / greater / faster heat loss, in single test tube ; 1 1(a)(iv) value between 12 and 22 (°C) 1 AND heat loss greater than middle and less heat loss than single AW ; 1(b) starting temperatures were not the same ; 1 1(c) surface area of penguins / surface area of huddle / external temperature / wind speed / volume of penguin / thickness of 1 feathers ; 1(d) they have cooled to room temperature ; 1

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2 When a person exercises, their pulse rate changes. Plan an investigation to determine the relationship between the intensity of exercise a person does and the change in their pulse rate. You may use any common laboratory apparatus. In your plan, include: • the 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 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.). 7 1 Apparatus stop-clock / pulse meter / heart rate monitor (to measure pulse / exercise duration) ; exercise apparatus, e.g. treadmill / measuring apparatus for distance / height, e.g. tape measure ; 2 Method and safety describes a method to vary intensity ; measure pulse rate before and after three intensities of exercise ; wait until pulse rate returns to initial / resting, pulse rate between repeats ; check for health concerns / specific safety linked to apparatus used ; 3 What you will measure counts number of pulses in a fixed time, e.g. 15 s / measures pulse in bpm ; gives units for measurement, e.g. distance m / time s or min / height cm / speed in km / h ; 4 Which variables you will keep constant the same person each time / same characteristics of more than one person, e.g. same age / sex ; controls intensity of exercise, e.g. same duration of exercise (different intensity / speed) / same distance (different speeds) / same speed (different duration) / same exercise (different number of repetitions) ; 5 Processing results subtract initial pulse rate from final pulse rate / find change from initial and final pulse rate ; plot distance / duration / height, of exercise against pulse rate (dependent on candidate’s method) ; repeat measurements of pulse rates for the same intensity AND identify anomalies / take average AW ;

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3 A student investigates some of the properties of solution H. (a) Procedure The student: Step 1 pours solution H into a boiling tube Step 2 records the temperature of solution H Step 3 adds pieces of aluminium foil to the boiling tube Step 4 stirs the mixture in the boiling tube Step 5 records the highest temperature reached Step 6 filters the mixture from the boiling tube into a test-tube. Fig. 3.1 shows the temperature readings in step 2 and step 5. °C °C 30 60 20 50 step 2 step 5 Fig. 3.1 (i) Record in Table 3.1 these temperature readings to the nearest 0.5 °C. Table 3.1 temperature of solution H in step 2 / °C highest temperature of mixture at end of step 5 / °C temperature increase / °C [2] (ii) Calculate the temperature increase between step 2 and step 5. Record your answer in Table 3.1. [1] (iii) Calculate the amount of thermal (heat) energy released q. Use the equation shown. q = 10.0 × 3.96 × temperature increase Give your answer to three significant figures. thermal (heat) energy released q = ...................................................... J [2] (iv) Explain why the reaction mixture is stirred in step 4. ........................................................................................................................................... ..................................................................................................................................... [1] (v) The temperature increase is not as large as expected because thermal (heat) energy is transferred to the surroundings. Suggest one improvement to the apparatus that will give a more accurate value for the thermal energy released. ........................................................................................................................................... ..................................................................................................................................... [1] (vi) Draw a diagram to show the assembled apparatus used to filter the mixture in step 6. Label the apparatus, the filtrate and the residue. [3] (b) Solution H contains copper(II) ions. (i) The student adds aqueous ammonia slowly to solution H until there is no further change. State the observations the student makes. ........................................................................................................................................... ..................................................................................................................................... [2] (ii) The student adds dilute nitric acid and then aqueous silver nitrate to solution H. The student observes a white precipitate. Identify the anion (negative ion) present in solution H. Tick (3) one box. carbonate chloride nitrate sulfate [1] [Total: 13]

Mark scheme: 3(a)(i) 24.0 (°C) ; 2 55.5 (°C) ; 3(a)(ii) 31.5 (°C) ; 1 3(a)(iii) (10.0  3.96  31.5 =) 1247.4 (J) ; 2 1250 (J) ; 3(a)(iv) to get even distribution of temperature / to ensure complete reaction ; 1 3(a)(v) insulate boiling tube / lid on boiling tube / use a, plastic beaker / plastic boiling tube ; 1 3(a)(vi) 3 correct apparatus shown assembled (filter) funnel, filter paper and collecting vessel ; filtrate (in collecting vessel) and residue (in filter paper) and labelled ; (filter) funnel and filter paper and collecting vessel (beaker / test-tube / boiling tube / flask) labelled ; 3(b)(i) (light) blue precipitate ; 2 (in excess) changes to a dark blue solution ; 3(b)(ii) chloride ; 1

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4 A student investigates how the resistance R of a resistance wire varies with its length l. The student uses the circuit shown in Fig. 4.1. A crocodile clip 0 cm metre rule resistance wire length l Fig. 4.1 (a) (i) The student connects a voltmeter to measure the potential difference across a length l of the resistance wire. On Fig. 4.1, draw the symbol for a voltmeter connected to measure the potential difference across the resistance wire. [1] (ii) The student: • closes the switch • places the crocodile clip on the resistance wire at a length l = 15.0 cm from the 0 cm end of the metre rule • records in Table 4.1 the current I in the circuit and the potential difference V across the resistance wire • opens the switch. The student then repeats this procedure for the values of length l shown in Table 4.1. Suggest why the switch is opened after each measurement. ........................................................................................................................................... ..................................................................................................................................... [1] (iii) Fig. 4.2 shows the readings on the voltmeter and ammeter when length l = 45.0 cm. 2 3 0.4 0.6 1 4 0.2 0.8 0 5 0 1 V A Fig. 4.2 Record in Table 4.1 the potential difference V and the current I shown in Fig. 4.2. Table 4.1 length l of potential current I resistance R resistance wire difference V / A / Ω / cm / V 15.0 0.45 0.27 1.7 30.0 0.80 0.25 3.2 45.0 60.0 1.40 0.21 6.7 75.0 1.60 0.20 8.0 [2] (b) Calculate the resistance R of the wire when length l = 45.0 cm. Use the equation shown. V R = I Record your value of R in Table 4.1. [1] (c) (i) On the grid, plot a graph of the resistance R on the vertical axis against length l. R / Ω 0 0 l / cm [2] (ii) Draw the straight line of best fit. [1] (iii) Calculate the gradient of the line. Show on your graph the triangle you use to calculate the gradient. gradient = ......................................................... [2] (iv) The gradient of the line is a measure of the resistance per unit length of the wire. State the unit for the resistance per unit length of the wire. unit = ......................................................... [1]

Mark scheme: 4(a)(i) correct symbol for voltmeter connected across the resistance wire ; 1 4(a)(ii) prevent battery running down / wire overheating ; 1 4(a)(iii) 1.10 (V) ; 2 0.23 (A) ; 4(b) 4.8 () ; 1 4(c)(i) appropriate scales (vertical axes shows values 0–8.0 and y axis 0–75.0 and plots occupying at least ½ grid) ; 2 plots all correct to ½ small square and precise plots ; 4(c)(ii) thin straight line of best fit drawn with even distribution of points ; 1 4(c)(iii) triangle method seen on graph and triangle at least half the length of line of best fit between first and last point ; 2 correct calculation of gradient ; 4(c)(iv)  / cm ; 1 4(d) can identify / exclude, anomalous values / check that values are similar / close together ; 1 (4)(e) difficult to position crocodile clip exactly / wire may not be uniform diameter / wire not perfectly straight / has kinks in it ; 1

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