Cambridge IGCSE Sciences - Co-ordinated (Double) 0654 — 2024 May/June Paper 6 · Variant 3

1 A student investigates the effect of temperature on the movement of molecules through a cell membrane. (a) Dialysis (Visking) tubing behaves like a cell membrane. Procedure The student: • adds 4 cm3 of iodine solution to each of two pieces of dialysis tubing which are tied at one end • ties the open end of each piece of tubing with a knot to enclose the iodine solution and make a bag • thoroughly rinses the outside of each bag with water • assembles the apparatus as shown in Fig. 1.1 bag of bag of iodine iodine solution solution warm starch cold starch solution solution Fig. 1.1 • lifts the bags out of the beakers every minute for 5 minutes and records in Table 1.1 the colour of the solution in each bag and the colour of the solution in each beaker. Table 1.1 colour observed time warm cold / minutes solution in bag solution in beaker solution in bag solution in beaker 0 brown colourless brown colourless 1 brown colourless brown colourless 2 brown blue-black brown colourless 3 brown blue-black brown colourless 4 brown blue-black brown colourless 5 brown blue-black brown blue-black (i) Iodine solution is a test for starch. Dialysis tubing allows small molecules to pass through it but not large molecules. Explain the student’s observations at 5 minutes for the solution in the warm beaker and the solution in the bag in the warm beaker. Use the results in Table 1.1. Include ideas about the size of molecules in your answer. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [3] (ii) Suggest the effect of increasing temperature on the rate of movement of molecules. Use the student’s observations for the warm and cold solutions in the beakers during the 5 minutes. ........................................................................................................................................... ..................................................................................................................................... [1] (iii) Name a piece of apparatus suitable for measuring 4 cm3 of iodine solution. ..................................................................................................................................... [1] (iv) Suggest why it is important that the dialysis tubing bags are rinsed in the procedure. ........................................................................................................................................... ..................................................................................................................................... [1] (v) Suggest why the student lifts the bags out of the solutions to record the colours. ........................................................................................................................................... ..................................................................................................................................... [1] (vi) Suggest one improvement to the procedure to increase confidence in the results. Explain your answer. improvement ..................................................................................................................... explanation ........................................................................................................................ ........................................................................................................................................... [1] (b) (i) Starch is broken down into reducing sugar by the enzyme amylase. Describe a test used to confirm the presence of reducing sugar. Include the colour observed for a positive result. test .................................................................................................................................... ........................................................................................................................................... observation ........................................................................................................................ [3] (ii) The enzyme amylase is a protein. Describe a test to confirm the presence of protein. Include the colour observed for a positive result. test .................................................................................................................................... ........................................................................................................................................... observation ........................................................................................................................ [2] [Total: 13]

Mark scheme: 1(a)(i) Any 3 from: bag doesn’t contain starch (as molecules too large to move) ; iodine (molecules move into) in beaker (as they are small) ; iodine (molecules are) small / can move through tubing/bag ; starch (molecules) are large / starch (molecules) cannot move through the tubing / bag ; starch and iodine produce blue-black / black / darker colour in beaker ; 1(a)(ii) (at the higher temperature) the molecules move faster ORA ; 1 1(a)(iii) syringe / burette ; 1 1(a)(iv) to rinse off any iodine solution from outside bag ; 1 1(a)(v) can’t see through the blue-black / dark solution ; 1 1(a)(vi) more temperatures used and cannot be certain of trend with only 2 temperatures ; 1 1(b)(i) Benedict’s ; heat ; yellow / green / orange / red ; 3 1(b)(ii) biuret ; purple ; 2

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2 Plant seedlings need light to grow. Plan an investigation to determine if the colour of the light affects the rate of growth of plant seedlings. You are provided with plant seedlings. You may use any common laboratory apparatus. Include in your plan: • the apparatus needed • a brief description of the method • what you will measure • the variables you will control • how you will process your results to draw a conclusion. You may include a labelled diagram if you wish. You may include a results table if you wish. You are not required to include any results. .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .................................................................................................................................................... [7]

Mark scheme: 2 One marking point from each section and any two others Apparatus ruler / balance and use ; method of illumination i.e. coloured light bulbs or filters with lamp / bulb and use ; Method block / turn off lights and use at least 2 colours of light separately and measure seedlings ; Measurement measure height / mass at start ; measure height / mass after stated time / measure height / mass at regular time intervals ; repeat each colour more than once / several seedlings and exclude / identify anomalies ; Control variables plant in white light ; amount of water ; amount of nutrients / amount of carbon dioxide / humidity ; temperature ; light intensity / light same distance from plant ; Process results and draw a conclusion calculate rate as change in height / mass ÷ time ; bar chart / histogram colour against rate ; if the colours give different rates of growth / heights in the same time / different sized bars then the colour does affect the rate ;

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3 A student investigates the thermal energy released during a neutralisation reaction. When aqueous sodium hydroxide neutralises dilute hydrochloric acid, the temperature of the mixture increases. (a) Procedure The student: step 1 places a polystyrene cup into a beaker step 2 uses a 25 cm3 measuring cylinder to add 25 cm3 of dilute hydrochloric acid to the polystyrene cup step 3 places a thermometer into the polystyrene cup as shown in Fig. 3.1 thermometer polystyrene cup beaker 25 cm3 dilute hydrochloric acid Fig. 3.1 step 4 records the initial temperature of the dilute hydrochloric acid 21.5 initial temperature = .......................................................... °C step 5 adds 5 cm3 of aqueous sodium hydroxide to the polystyrene cup step 6 stirs the mixture and records the temperature in Table 3.1. The student repeats steps 5 and 6 until a total volume of 40 cm3 of aqueous sodium hydroxide is added. Table 3.1 total volume of temperature temperature sodium hydroxide of mixture increase ΔT added / °C / °C / cm3 5 24.5 3.0 10 15 32.5 11.0 20 36.0 14.5 25 39.5 18.0 30 38.0 16.5 35 40 34.0 12.5 Fig. 3.2 shows the thermometer readings for 10 cm3 and 35 cm3 of aqueous sodium hydroxide added. °C °C 30 40 20 30 10 cm3 35 cm3 Fig. 3.2 Record in Table 3.1 these temperatures to the nearest 0.5 °C. [2] (b) (i) Suggest a piece of apparatus suitable for measuring the 25 cm3 of dilute hydrochloric acid more accurately. ..................................................................................................................................... [1] (ii) Suggest why the polystyrene cup is placed in a beaker. ........................................................................................................................................... ..................................................................................................................................... [1] (iii) Suggest a change to the apparatus which gives more confidence in the temperature measured. ........................................................................................................................................... ..................................................................................................................................... [1] (iv) Suggest why the mixture is stirred in step 6. ........................................................................................................................................... ..................................................................................................................................... [1] (c) (i) Calculate the temperature increase ΔT for 10 cm3 and 35 cm3 of aqueous sodium hydroxide added. Use step 4, Table 3.1 and the equation shown. ΔT = temperature of mixture – initial temperature of dilute hydrochloric acid Record your values in Table 3.1. [1] (ii) Calculate the thermal energy released when 20 cm3 of aqueous sodium hydroxide is added. Use Table 3.1 and the equation shown. thermal energy released = 189 × ΔT Record your answer to three significant figures. thermal energy released = ....................................................... J [2] (d) Estimate the volume of aqueous sodium hydroxide which exactly neutralises the dilute hydrochloric acid. Explain your answer using the results in Table 3.1. volume ...................................................................................................................................... explanation ............................................................................................................................... ................................................................................................................................................... [1] (e) State the name of an indicator the student adds to the reaction mixture to find out if the mixture is an acid, an alkali or neutral. State the colour of the indicator in acidic solution, in alkaline solution and in neutral solution. indicator .................................................................................................................................... colour in acidic solution ............................................................................................................ colour in alkaline solution ......................................................................................................... colour in neutral solution ........................................................................................................... [2] [Total: 12]

Mark scheme: 3(a) 28.5 ; 36.0 ; 2 3(b)(i) volumetric / graduated pipette / burette ; 1 3(b)(ii) for stability ; 1 3(b)(iii) add a lid ; 1 3(b)(iv) to ensure even T through solution ; 1 3(c)(i) 7.0 and 14.5 ; 1 3(c)(ii) 2740.5 ; 2740 to 3 sf ; 2 3(d) 25 cm3 AND highest temperature / temperature change ; 1 3(e) universal indicator / full range indicator ; red / orange / yellow AND blue / purple AND green ; 2

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4 A student investigates the identity of a solution H. The student does five different tests on solution H. The student identifies solution H as aqueous copper(II) chloride. (a) Complete Table 4.1 with the observations the student makes during the tests. Table 4.1 test observation add a few drops of aqueous sodium hydroxide add excess aqueous sodium hydroxide add a few drops of aqueous ammonia add excess aqueous ammonia add dilute nitric acid followed by a few drops of aqueous silver nitrate add dilute nitric acid followed by aqueous barium nitrate flame test [6] (b) Solution Y contains sodium chloride. State how the results for one of the tests for sodium chloride differs from those for copper(II) chloride in Table 4.1. ................................................................................................................................................... ............................................................................................................................................. [1] (c) Explain why a flame test uses a blue Bunsen burner flame rather than a yellow one. ................................................................................................................................................... ............................................................................................................................................. [1] [Total: 8]

Mark scheme: 4(a) blue ppt and blue ppt ; blue ppt ; dark blue solution ; white ppt ; colourless solution ; blue-green ; 4(b) the flame colour would be yellow ; 1 4(c) yellow masks the colour of the flame test ; 1

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5 A student investigates the stretching of a spring. The student assembles the apparatus as shown in Fig. 5.1. metre rule clamp clamp spring stand stand bench Fig. 5.1 (a) Fig. 5.2 shows a diagram of the unstretched spring and part of the rule. cm 31 32 33 34 35 Fig. 5.2 (i) Take readings from the rule to the nearest 0.1 cm for the top and the bottom of the spring in Fig. 5.2. Do not include the loops at the top and the bottom of the spring in your measurements. reading on rule at top of spring = .......................................................... cm reading on rule at bottom of spring = .......................................................... cm [1] (ii) Use your readings from (a)(i) to determine the length l 0 of the unstretched spring to the nearest 0.1 cm. l 0 = .................................................... cm [1] (iii) Describe how the student avoids a line-of-sight (parallax) error when measuring the length of the spring. ........................................................................................................................................... ..................................................................................................................................... [1] (b) The student suspends a load L of 1.0 N on the spring. (i) The stretched spring is shown full size in Fig. 5.3. l Fig. 5.3 Measure the length l of the spring to the nearest 0.1 cm. l = .................................................... cm [1] (ii) Calculate the extension e of the spring. Use the equation shown. e = l – l 0 Record your answer in Table 5.1. Table 5.1 load L extension e / N / cm 0.0 0.0 1.0 2.0 8.2 3.0 12.0 4.0 16.4 5.0 20.5 [1] (c) The student repeats (b) for loads of 2.0 N, 3.0 N, 4.0 N and 5.0 N. The student’s values are shown in Table 5.1. (i) On the grid, plot a graph of L (vertical axis) against e. Start both axes from the origin (0,0). [3] (ii) Draw the best-fit straight line. [1] (d) (i) Calculate the gradient G of your line. Show all working and indicate on your graph the values you choose to enable the gradient to be calculated. G = ......................................................... [2] (ii) The gradient of the graph measures the elastic stiffness of the spring. The greater the elastic stiffness, the harder it is to stretch the spring. On your graph, draw a line to show how the extension of another spring with a greater elastic stiffness changes as loads are added to it. Label this line E. [1]

Mark scheme: 5(a)(i) 32.1 and 34.2 ; 1 5(a)(ii) l0 = 2.1 ; 1 5(a)(iii) view scale at right angles (to the reading) / view scale perpendicular (to the reading) ; 1 5(b)(i) l = 6.3 ; 1 5(b)(ii) e = 4.2 ; 1 5(c)(i) axes labelled with quantity and units ; suitable linear scales where the plotted points cover ⩾ ½ the grid and all points can be plotted ; points plotted correctly ; 3 5(c)(ii) best-fit straight line through the origin ; 1 Question Answer Marks 5(d)(i) indication on graph of how data obtained and ⩾ ½ the line used ; calculation correct ; 2 5(d)(ii) line labelled E, starting from the origin and with a greater gradient ; 1

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6 A student investigates the resistance of lamps. The student assembles the circuit shown in Fig. 6.1. This is circuit 1. A X Y Fig. 6.1 (a) Procedure The student: • connects a voltmeter to measure the potential difference between X and Y • closes the switch • records in Table 6.1 the potential difference V and the current I for circuit 1 • opens the switch • disconnects the voltmeter. (i) On Fig. 6.1, draw the symbol for a voltmeter connected to measure the potential difference between X and Y. [1] (ii) The readings on the voltmeter and ammeter are shown in Fig. 6.2. 1 2 V 0 3 0.5 A 0 1 Fig. 6.2 Record in Table 6.1 the voltmeter and the ammeter readings. Table 6.1 potential difference V current I circuit / V / A 1 2 2.9 0.21 [2] (b) Procedure The student: • connects another identical lamp in series with the first lamp, as shown in Fig. 6.3 This is circuit 2. A X Y Fig. 6.3 • connects the voltmeter into circuit 2 to measure the potential difference between X and Y • closes the switch • records in Table 6.1 the potential difference V and the current I • opens the switch. The student’s results are shown in Table 6.1. Describe a difference in the observations of the lamp in circuit 1 compared to the lamps in circuit 2. ................................................................................................................................................... ............................................................................................................................................. [1] (c) Calculate the total resistance R1 measured between points X and Y for circuit 1. Use the equation shown. V R = I R1 = ............................................................ Ω Calculate the total resistance R2 measured between points X and Y for circuit 2. R2 = ............................................................ Ω [1] R2(d) Calculate the ratio . R1 R2 = ......................................................... [1] R1 (e) A teacher makes the following statement. R2 ‘If each lamp has the same resistance, the ratio equals 2.0.’ R1 Two values are considered to be equal within the limits of experimental accuracy if they are within 10% of each other. State if your answer to (d) agrees with the teacher’s statement, within the limits of experimental accuracy. Justify your statement with a calculation. statement .................................................................................................................................. justification ................................................................................................................................ ................................................................................................................................................... [2] [Total: 8]

Mark scheme: 6(a)(i) correct symbol and parallel connection ; 1 6(a)(ii) V = 2.8 ; I = 0.29 ; 2 6(b) lamp in circuit 1 is brighter than lamps in circuit 2 ; 1 6(c) R1 = 9.66 / 9.7 and R2 = 13.8 / 14 ; 1 6(d) 1.4 ; 1 6(e) 10% of 6(d) or 2 ; 10% used and relevant statement ; 2

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