Cambridge IGCSE Sciences - Co-ordinated (Double) 0654 — 2022 Oct/Nov Paper 6 · Variant 1

1 A student investigates the effect of temperature on the release of a red pigment from beetroot cells. When beetroot with damaged cells is placed in water, the red pigment leaves the beetroot and turns the water red. (a) Procedure The student: step 1 cuts three cylinders of beetroot of the same size step 2 rinses the beetroot cylinders in water step 3 half fills three test-tubes with water at room temperature, 40 °C and 60 °C. step 4 puts one beetroot cylinder into each test-tube step 5 places the test-tubes in beakers of water to maintain their temperatures at room temp, 40 °C and 60 °C as shown in Fig. 1.1 step 6 leaves the test-tubes for 5 minutes step 7 removes the cylinders of beetroot from the test-tubes step 8 observes the water in each test-tube and judges how much colour has transferred from the beetroot into the water. test-tube test-tube test-tube beaker beaker beaker water water water beetroot beetroot beetroot cylinder cylinder cylinder water at room water at 40 °C water at 60 °C temperature Fig. 1.1 Table 1.1 shows the order in which the student places the test-tubes. Table 1.1 colour of water temperature of water in test-tube / °C lightest red 40.0 room temperature = ............................. 60.0 darkest red Fig. 1.2 shows the thermometer reading for the test-tube with water at room temperature. °C 30 20 10 Fig. 1.2 Record in Table 1.1 the temperature of the water to the nearest 0.5 °C. [1] (b) Fig. 1.3 shows one of the pieces of beetroot, drawn full size. Fig. 1.3 (i) Record the length of the piece of beetroot in millimetres to the nearest millimetre. length = .................................................. mm [1] (ii) In step 1 all of the beetroot cylinders are cut to the same size to make sure the test is fair. Suggest why it is important that the beetroot cylinders are all cut to the same size. ........................................................................................................................................... ..................................................................................................................................... [1] (iii) In step 2 all of the beetroot cylinders are rinsed with water. Suggest why the beetroot cylinders are rinsed. ........................................................................................................................................... ..................................................................................................................................... [1] (iv) The teacher says that the water at room temperature should be the lightest red. Suggest what may have caused the student to obtain a different result. ........................................................................................................................................... ..................................................................................................................................... [1] (c) Another student repeats the investigation using six different temperatures. The student compares the colours of the solutions to a colour chart. The colour chart gives each shade of colour a number. The results are shown in Table 1.2. Table 1.2 colour number temperature of water / °C trial 1 trial 2 average 10 1.2 1.4 1.3 20 1.4 1.6 1.5 30 1.5 1.7 50 3.0 2.6 2.8 60 4.8 4.4 4.6 80 11.5 11.9 11.7 Complete Table 1.2 by calculating the average colour number for 30 °C. [1] (d) (i) On the grid plot a graph of average colour number (vertical axis) against temperature of water. [3] (ii) Draw the best-fit curve. [1] (iii) Use your graph to estimate the colour number for a temperature of water of 70 °C. Show on your graph how you arrived at your answer. colour number at 70 °C = ......................................................... [2] (e) (i) Describe the relationship between temperature and the colour number of the solution. ........................................................................................................................................... ..................................................................................................................................... [1] (ii) Suggest the relationship between temperature and the number of beetroot cells damaged. ........................................................................................................................................... ..................................................................................................................................... [1] [Total: 14]

Mark scheme: Question Answer Marks 1(a) 20.5 ; 1 1(b)(i) 33 ; 1 1(b)(ii) same surface (area in contact with water) ; 1 1(b)(iii) to remove any red/pigment/colour (on the surface) ; 1 1(b)(iv) not rinsed enough / still had red pigment on outside / different beetroots / different part of the beetroot ; 1 1(c) 1.6 ; 1 1(d)(i) axes correct way round and labelled with quantity and units ; 3 sensible linear scale with plots covering at least half the grid ; plots correct  ½ square ; 1(d)(ii) curve of best fit ; 1 1(d)(iii) correct reading from graph  1 small square ; 2 lines on graph ; 1(e)(i) higher the temperature higher the colour number ; 1 1(e)(ii) higher the temperature higher the number of damaged cells ; 1

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2 A student investigates the lungs and breathing. (a) The student uses a straw to blow exhaled air into a sample of limewater. The limewater turns milky. State what this shows about the content of exhaled air. ................................................................................................................................................... ............................................................................................................................................. [1] (b) The apparatus in Fig. 2.1 is used to measure the maximum volume of air exhaled (breathed out) in one breath. The student puts the mouthpiece into their mouth and breathes out through the tube. Exhaled air enters the large measuring bottle. clamp 1 dm3 rubber tubing 2 large measuring bottle 3 4 mouthpiece water stand Fig. 2.1 (i) Suggest what the student does to make sure they measure the maximum volume of air in their lungs. ........................................................................................................................................... ..................................................................................................................................... [1] (ii) The student does the experiment four times. The results are shown in Table 2.1. Table 2.1 trial 1 trial 2 trial 3 trial 4 average volume of air breathed out 3.8 2.2 4.2 4.3 4.1 / dm3 Suggest why trial 2 is not used to calculate the average. ........................................................................................................................................... ..................................................................................................................................... [1] (iii) State the maximum volume of air exhaled (breathed out) by the student. volume = .................................................. dm3 [1] (c) Suggest a safety precaution that must be taken to allow several students to use the same apparatus. Explain your answer. suggestion ................................................................................................................................ ................................................................................................................................................... explanation ............................................................................................................................... ................................................................................................................................................... [2] [Total: 6]

Mark scheme: 2(a) (contains) carbon dioxide ; 1 2(b)(i) (breathe in fully and) breathe out fully / breathe out for as long as possible / breathe out until no change (in volume / level of 1 water) / repeat AND take the largest ; 2(b)(ii) it is an anomaly ; 1 2(b)(iii) 4.3 only ; 1 2(c) sterilise / disinfect / change the mouthpiece ; 2 prevent spread of bacteria/virus/disease/infection ;

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3 A student investigates the pH of milk and vinegar. The student also investigates the mass of solid formed when different volumes of milk react with vinegar. The pH scale for universal indicator is a continuous colour spectrum as partly shown in Fig. 3.1. pH 1 7 14 pale dark colour red orange yellow blue purple green green strongly weakly weakly strongly description neutral acidic acidic alkaline alkaline Fig. 3.1 (a) Procedure The student: step 1 adds about 1 cm3 of vinegar to a test-tube step 2 adds 3 drops of universal indicator to the vinegar in the test-tube step 3 records in Table 3.1 the pH of the vinegar step 4 repeats steps 1 to 3 using milk instead of vinegar. Table 3.1 substance colour with universal indicator pH description vinegar 4 milk 7 (i) Record in Table 3.1 the colour of each solution with the universal indicator. Use the pH scale in Fig. 3.1. [2] (ii) Explain why it is difficult for the student to be sure of the pH of milk. ........................................................................................................................................... ..................................................................................................................................... [1] (iii) Complete Table 3.1 using information from Fig. 3.1. [1] (b) Sodium carbonate gives off carbon dioxide gas when it reacts with acids. The student adds some sodium carbonate powder to separate test-tubes of vinegar and milk. Complete Table 3.2 with the observations the student sees in each test-tube. Use information from Table 3.1. Table 3.2 substance observation when sodium carbonate is added vinegar milk [1] (c) The student reacts hot milk with vinegar to make a white solid. Procedure The student: step 1 places 30 cm3 of hot milk into a small beaker step 2 adds 1 cm3 of vinegar to the beaker step 3 stirs the mixture and filters off the white solid formed step 4 scrapes the white solid onto a paper towel and squeezes out as much liquid from the solid as possible step 5 uses a balance to find the mass of the white solid and records its mass in Table 3.3 step 6 repeats steps 1 to 5 using 2, 3, 4 and 5 cm3 of vinegar instead of 1 cm3. Table 3.3 volume of vinegar mass of white solid / cm3 / g 1 1.6 2 3 5.0 4 5 6.6 (i) Fig. 3.2 shows the readings on the balance for 2 and 4 cm3 of vinegar added. 3.32 g 6.58 g 2 cm3 of vinegar 4 cm3 of vinegar Fig. 3.2 Record these masses to two significant figures in Table 3.3. [2] (ii) Look at steps 4 and 5. The mass of each solid is a little more than expected. Suggest a reason why the mass of each solid is more than expected. ........................................................................................................................................... ..................................................................................................................................... [1] (iii) Suggest what the student can do to have more confidence in the mass of each solid formed. Do not repeat your answer to (c)(ii). ........................................................................................................................................... ..................................................................................................................................... [1] (iv) A student adds 10 cm3 of vinegar to the milk and finds the mass of the white solid is the same as that for 5 cm3 of vinegar. Suggest why the masses are the same. ........................................................................................................................................... ..................................................................................................................................... [1] (v) State the relationship between the volume of vinegar added and the mass of white solid made. ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [2] [Total: 12]

Mark scheme: 3(a)(i) orange / yellow ; 2 pale green ; 3(a)(ii) colour of milk masks colour of UI ; 1 3(a)(iii) (vinegar) (weakly) acidic AND 1 (milk) neutral ; 3(b) fizz/bubbles / effervesces AND 1 no fizz / no reaction / no change / stays the same ; 3(c)(i) 3.3 ; 2 6.6 ; 3(c)(ii) still wet / still has liquid / not all liquid squeezed out ; 1 3(c)(iii) repeat (and average) ; 1 3(c)(iv) all the milk used up ; 1 3(c)(v) as the volume of vinegar increases the mass of solid increases / proportional ; 2 until 4 cm3 added when it stays the same) ;

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4 Copper is an unreactive metal. It is a pink-orange colour. In an experiment a grey coloured iron key is attached to the negative terminal of a power supply. A piece of copper is attached to the positive terminal of the power supply. The iron key and the piece of copper are both dipped in aqueous copper sulfate. A diagram of the apparatus is shown in Fig. 4.1. + – piece of iron key copper aqueous copper sulfate Fig. 4.1 The power supply is turned on. The voltage on the power supply must not be higher than 20 V for safety reasons. The iron key becomes covered in copper metal. The piece of copper becomes smaller. Plan an experiment to find out the relationship between the voltage of the power supply and the amount of copper plated onto the iron key. You will not be doing this experiment. Include in your plan: • the apparatus needed, you do not need to include what is shown in Fig. 4.1 • a brief description of the method, explaining any safety precautions • the measurements you will make including how to make them as accurate as possible • the variables you will control • how you will process your results to draw a conclusion. You may include a table that can be used to record results if you wish. You are not required to include any results. .................................................................................................................................................................. .................................................................................................................................................................. .................................................................................................................................................................. .................................................................................................................................................................. .................................................................................................................................................................. .................................................................................................................................................................. .................................................................................................................................................................. .................................................................................................................................................................. .................................................................................................................................................................. .................................................................................................................................................................. .................................................................................................................................................................. .................................................................................................................................................................. .................................................................................................................................................................. .................................................................................................................................................................. .................................................................................................................................................................. .................................................................................................................................................................. .................................................................................................................................................................. .................................................................................................................................................................. .................................................................................................................................................................. .................................................................................................................................................................. .................................................................................................................................................................. .................................................................................................................................................................. .................................................................................................................................................................. .................................................................................................................................................................. .................................................................................................................................................................. .................................................................................................................................................................. .................................................................................................................................................................. ............................................................................................................................................................ [7]

Mark scheme: 4(a) note: to gain 7 marks at least 1 mark must come from each section 7 apparatus balance ; paper towel / tissue / cloth ; stop-watch / clock / timer ; method more than one voltage AND all voltages lower than or equal to 20 V ; minimum 5 voltages ; repeat each voltage ; dry key (before weighing) ; measurements and processing weigh key at start AND end ; subtract masses to find mass gain ; control amount of time ; temperature ; same mass of key ; concentration of copper sulfate ; processing and use of results draw graph mass increase against voltage ; straight line means proportional ; if mass increases as voltage increase then positive relationship / if decreases then negative relationship ;

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5 A student investigates different methods of thermally insulating two beakers, X and Y. Beaker X has a lid, but no insulation. Beaker Y has a layer of insulation wrapped around it but has no lid. lid thermometer hot layer of water insulation beaker X beaker Y Fig. 5.1 (a) Procedure The student: • pours 150 cm3 of hot water into beaker X and replaces the lid • places a thermometer into the water • measures the temperature of the hot water when the reading stops rising • immediately starts a stop-watch. Fig. 5.2 shows the maximum temperature of the hot water. °C 90 80 Fig. 5.2 (i) Record the temperature to the nearest 0.5 °C in Table 5.1. This is the temperature at time t = 0. Table 5.1 temperature of beaker X temperature of beaker Y time t / s / °C / °C 0 85.0 30 81.0 79.0 60 78.5 75.0 90 76.0 71.0 120 74.0 67.5 150 72.5 64.0 180 71.0 61.0 [1] (ii) The student measures the temperature of the hot water every 30 s for 180 s, stirring the water before reading each temperature. The student’s results are shown in Table 5.1. State why it is important to stir the water before reading its temperature. ..................................................................................................................................... [1] (iii) Describe two safety precautions that must be observed when working with hot water. Explain how each precaution reduces the risk. 1 ........................................................................................................................................ ........................................................................................................................................... 2 ........................................................................................................................................ ........................................................................................................................................... [2] (iv) Calculate the decrease in temperature θX of the hot water in beaker X during the 180 s. Use the equation shown. θX = temperature at 0 s – temperature at 180 s θX = .....................................................°C [1] (v) Calculate the average rate of temperature decrease RX of the hot water in beaker X during the 180 s. Use the equation shown. θX RX = 180 Give your answer to two significant figures. RX = ................................................ °C / s [2] (b) Procedure The student: • pours 150 cm3 of hot water into beaker Y. • places a thermometer into the water • measures the temperature of the hot water when the reading stops rising • immediately starts a stop-watch. The student’s results are shown in Table 5.1. (i) The temperature of the water in both beakers decreases as the time increases. State one other similarity in the way the water temperature decreases in beaker X and beaker Y. ........................................................................................................................................... ..................................................................................................................................... [1] (ii) Calculate the decrease in temperature θY of the hot water in beaker Y during the 180 s. θY = .....................................................°C [1] (iii) Calculate the average rate of temperature decrease RY of the hot water in beaker Y during the 180 s. Use the equation shown. θY RY = 180 RY = ................................................ °C / s [1] (c) State which is the more effective method of insulating a beaker to prevent thermal energy loss from hot water. Use your results from (a)(v) and (b)(iii) and explain how you reach this conclusion. more effective method .............................................................................................................. explanation ............................................................................................................................... ................................................................................................................................................... [1] (d) State one factor which is controlled to ensure that the comparison between beaker X and beaker Y is fair. ............................................................................................................................................. [1] (e) Suggest one way, apart from adding a lid, that the rate of cooling of the water in beaker Y can be further reduced. ............................................................................................................................................. [1] [Total: 13]

Mark scheme: 5(a)(i) 84.0 ; 1 5(a)(ii) to ensure that all the water is at the same temperature ; 1 5(a)(iii) wear goggles to avoid splashes/hot water in the eyes ; 2 use tongs/gloves to avoid burns/hot water to hands/fingers/skin/arms ; 5(a)(iv) 13 / 13.0 ; 1 5(a)(v) 0.07222 ; 2 0.072 ; 5(b)(i) both cool faster at the start / at higher temperature ; 1 5(b)(ii) 24(.0) ; 1 5(b)(iii) 0.1333 ; 1 5(c) using a lid because RX < RY ; 1 5(d) (same) size beakers / (same) volume of water / (same) initial temperature of the hot water / (same) room temperature ; 1 5(e) more/thicker insulation / lag the bottom of the beaker / 1 carry out the experiment in a warmer room ;

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6 A student measures the density of the material from which a metre rule is made. (a) Procedure The student: • places a load M on a metre rule and adjusts its position carefully until the centre of the load is directly above the 15.0 cm mark on the metre rule • places a pivot under the rule and adjusts the position of the pivot carefully until the rule is as close to balance as possible. Fig. 6.1 shows the metre rule at balance viewed from the side. load M metre rule 0 15 100 pivot Fig. 6.1 Fig. 6.2 shows the position of the pivot at balance viewed from above. 26 27 28 29 30 31 32 cm position of pivot Fig. 6.2 (i) Record the position r of the pivot in centimetres to the nearest 0.1 cm. r = ................................................... cm [1] (ii) Calculate the distance d from the centre of load M to the pivot. d = ................................................... cm [1] (b) Describe how the student makes sure that the centre of load M is directly above the 15.0 cm mark on the metre rule. You may draw a diagram if you wish. ................................................................................................................................................... ............................................................................................................................................. [1] (c) (i) Calculate the mass m of the metre rule. Use the equation shown. 150 × d m = (35 – d) m = ...................................................... g [1] (ii) State the name of a piece of apparatus that the student uses to check the result in (c)(i). ..................................................................................................................................... [1] (d) The student measures the thickness t and the width w of the metre rule. The student’s results are shown. t = 0.5 cm w = 2.5 cm Calculate the volume V of the metre rule. Use the equation shown. V = 100 × t × w V = .................................................. cm3 [1] (e) Use your answers to (c)(i) and (d) to calculate the density ρ of the material from which the metre rule is made. Use the equation shown. m ρ = V ρ = ................................. unit = ............. [2] [Total: 8]

Mark scheme: 6(a)(i) 29.2 ; 1 6(a)(ii) 14.2 ; 1 6(b) note reading on either side of load and find the mean value and place on 15 cm mark ; 1 6(c)(i) 102 (g) ; 1 6(c)(iii) (top pan) balance ; 1 6(d) 125 (cm3) ; 1 6(e) 0.816 / 0.82 ; 2 g / cm3 ;

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