Cambridge IGCSE Sciences - Co-ordinated (Double) 0654 — 2023 May/June Paper 6 · Variant 1

1 A student investigates the use of an enzyme for the extraction of juice from apples. (a) Procedure The student: • assembles two beakers, A and B, with the same volumes of apple puree in each beaker • adds the same volume of enzyme solution to beaker A and water to beaker B as shown in Fig. 1.1 apple puree apple puree and enzyme solution and water beaker A beaker B Fig. 1.1 • stirs the contents of each beaker with a glass rod • leaves the beakers in a warm water-bath for 5 minutes • after the 5 minutes, assembles the apparatus as shown in Fig. 1.2 apple puree apple puree and enzyme solution and water filter paper 20 20 measuring 15 cylinder 15 10 10 5 5 cm3 cm3 measuring cylinder A measuring cylinder B Fig. 1.2 • measures and records in Table 1.1 the total volume of juice collected in each measuring cylinder every 2 minutes for 8 minutes. (i) Fig. 1.3 shows the thermometer reading for the water-bath. °C 30 20 Fig. 1.3 Record the temperature of the water-bath to the nearest 0.5 °C. temperature = .................................................... °C [1] (ii) Suggest why it is important to clean the glass rod between stirring beaker A and beaker B. ........................................................................................................................................... ..................................................................................................................................... [1] (iii) Explain why it is important to stir and mix the contents of the two beakers. ........................................................................................................................................... ..................................................................................................................................... [1] (b) Table 1.1 shows the student’s results. Table 1.1 total volume of juice collected time / cm3 / minutes measuring cylinder A measuring cylinder B 0 0.0 0.0 2 9.2 1.0 4 12.1 1.5 6 13.6 1.6 8 13.9 1.7 (i) Beaker B is set up as a control. Explain why a control is used in this investigation. ........................................................................................................................................... ..................................................................................................................................... [1] (ii) Use the results in Table 1.1 to suggest why an enzyme is used in the large-scale production of fruit juice. ........................................................................................................................................... ..................................................................................................................................... [1] (c) (i) On the grid, plot a graph of total volume of juice collected (vertical axis) against time for only measuring cylinder A. [3] (ii) Draw the best-fit curve. Label the curve A. [1] (iii) Use your graph to estimate the volume of juice produced at 5 minutes. Show your working on your graph. volume of juice produced at 5 minutes = ...................................................cm3 [2] (iv) Increasing the temperature to 40 °C increases the rate of apple juice production. The student repeats the procedure for beaker A at the higher temperature of 40 °C. On the grid, draw a curve to predict the results the student obtains. Label the curve T. [1] (v) The enzyme used in this investigation denatures (stops working) at temperatures above 50 °C. The student repeats the procedure for beaker A at 80 °C. On the grid, draw a curve to predict the results the student obtains. Label the curve N. [2] [Total: 14]

Mark scheme: 1(a)(i) 30.0 ; 1 1(a)(ii) (prevent contamination with) no enzyme (in B) ; 1 1(a)(iii) to make sure enzyme is in maximum contact with apple ; 1 1(b)(i) shows comparison without enzyme ; 1 1(b)(ii) more juice produced with enzyme / faster production of juice ; 1 1(c)(i) axes right way round and labelled with quantity and units ; sensible linear scale and plots cover at least half the grid ; plots correct  ½ small square ; 3 1(c)(ii) best-fit curve goes through origin and labelled A ; 1 1(c)(iii) graph marked at 5 mins ; correct reading off graph ; 2 1(c)(iv) higher across all points and labelled T ; 1 1(c)(v) start at 0 and lower than A across all points and labelled N ; close to values for measuring cylinder B ; 2

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2 The student tests some apple juice for its nutrient content. (a) The apple juice tests positive with Benedict’s solution and negative with biuret solution. (i) Record in Table 2.1 the final colours the student observes. Table 2.1 testing solution final colour observed conclusion Benedict’s biuret [2] (ii) Complete Table 2.1 by stating a conclusion for the result obtained with each testing solution. [2] (b) Name the reagents used to test for the presence of fat. State the observation for a positive result. reagents .............................................................. and .............................................................. observation ............................................................................................................................... [2] [Total: 6]

Mark scheme: 2(a)(i) yellow / green / orange / red ; blue ; 2 2(a)(ii) contains reducing sugar ; does not contain protein ; 2 2(b) water and ethanol ; white and emulsion ; 2

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3 A student investigates the rate of the reaction between solutions H and K. When solutions of H, K and starch are mixed together, a blue-black colour is observed after a period of time. (a) Procedure Experiment 1 The student: Step 1 adds 10 cm3 of solution H into a conical flask Step 2 adds 5 drops of starch solution into the conical flask Step 3 adds 2 cm3 of distilled water into the conical flask Step 4 adds 10 cm3 of solution K into the conical flask, swirls the flask and immediately starts a stop-watch Step 5 stops the stop-watch when the mixture in the conical flask turns blue-black Step 6 records in Table 3.1 the time taken in seconds to the nearest second for the mixture to turn blue-black. The student repeats the procedure for experiment 2. Table 3.1 volume of drops of volume of experiment extra solution time taken solution H starch solution K number added / s / cm3 solution / cm3 2 cm3 distilled 1 10 5 10 92 water 2 cm3 distilled 2 10 5 10 86 water 2 cm3 aqueous 3 10 5 10 iron(II) chloride 2 cm3 aqueous 4 10 5 10 90 sodium chloride 2 cm3 aqueous 5 10 5 10 11 iron(III) chloride 2 cm3 aqueous 6 10 5 10 copper chloride (i) Suggest a piece of apparatus suitable for measuring accurately solutions H and K. ..................................................................................................................................... [1] (ii) Experiment 2 is a repeat of experiment 1. This is done to check the reliability of the experiment. Two results are considered to be equal, within the limits of experimental error, if they are within 10% of each other. Suggest if experiments 1 and 2 give reliable results. Include data and a calculation in your answer. ........................................................................................................................................... ..................................................................................................................................... [2] (iii) The substance made when solutions H and K react together turns the starch solution blue-black. Identify the substance made in the reaction. ..................................................................................................................................... [1] (iv) All experiments use the same volume of extra solution added. Explain why experiments 1 and 2 use the same volume of solution H, the same volume of solution K and the same number of drops of starch. ........................................................................................................................................... ..................................................................................................................................... [1] (b) The student repeats the procedure in (a) for experiments 3, 4, 5 and 6, using the solutions in Table 3.1. (i) The readings on the stop-watch for experiments 3 and 6 are shown in Fig. 3.1. min s min s experiment 3 experiment 6 Fig. 3.1 Record in Table 3.1 these times in seconds to the nearest second. [2] (ii) A student suggests that another experiment is needed. “Each of the four additional solutions, aqueous iron(II) chloride, aqueous sodium chloride, aqueous iron(III) chloride and aqueous copper chloride, need to be tested with starch alone.” Suggest why this improves the investigation with solutions H and K. ........................................................................................................................................... ..................................................................................................................................... [1] (iii) The reading of a volume of solution K is shown in Fig. 3.2. cm3 10 9 Fig. 3.2 State if the volume of solution K is 10 cm3. Circle the correct answer. yes no Explain your answer. ........................................................................................................................................... ..................................................................................................................................... [1] (c) A catalyst is a substance that increases the rate of a chemical reaction. State which extra solutions added are catalysts for the reaction between solutions H and K. Explain your answer with reference to data in Table 3.1. solutions ................................................................................................................................... explanation ............................................................................................................................... ................................................................................................................................................... [2] (d) The pH of a solution can be measured using a pH meter. Describe one other way the student can find the pH of aqueous iron(III) chloride. ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [2] [Total: 13]

Mark scheme: 3(a)(i) syringe / burette / (volumetric / graduated) pipette ; 1 3(a)(ii) either 9.2 or 8.6 calculated ; yes as they are within the 10% and use of the 10% ; 2 3(a)(iii) iodine ; 1 3(a)(iv) so that the concentrations stay the same / so the volume isn’t responsible for the changes / so the times can be compared ; 1 3(b)(i) 15 ; 5 ; 2 3(b)(ii) as a control / to find out if the additional solution turns blue-black ; 1 3(b)(iii) no AND bottom of meniscus is at 9.9 / reading is at top of meniscus not bottom ; 1 3(c) iron(II) (chloride), iron(III) (chloride) and copper (chloride) ; reaction takes less time / shortest time and some time data quoted ; 2 3(d) add universal indicator / pH indicator / pH paper/solution / UI ; check the colour against the pH colour chart ; 2

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4 Aqueous hydrogen peroxide is a solution that breaks down slowly into water and oxygen gas. hydrogen peroxide water + oxygen A catalyst is a substance that increases the rate of a chemical reaction. Manganese(IV) oxide is a catalyst for this reaction. The reaction is too fast to count the bubbles of gas formed. Plan an investigation to find the relationship between the mass of manganese(IV) oxide added and the rate of this reaction. You are provided with: • aqueous hydrogen peroxide • manganese(IV) oxide solid. You may use any common laboratory apparatus. Include in your plan: • the apparatus needed • a brief description of the method, with an explanation of 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 use your results to draw a conclusion. You may include a diagram if it helps to explain your plan. You may include a results table. You are not required to include any results. .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .................................................................................................................................................... [7]

Mark scheme: 4 One mark from each section and any two others Collecting gas method apparatus (gas) syringe / (upturned) mc or burette (in water) for collecting oxygen gas ; timer / stop-watch / stop-clock ; balance ; method powder into hydrogen peroxide in container and collect gas (and airtight diagram) or described well ; do each mass more than once ; use minimum 5 different masses / amounts of manganese(IV) oxide ; goggles / gloves protect eyes / hands / skin against hydrogen peroxide / MnO2 ; measurements volume of gas ; time for fixed volume / time fixed for a volume ; mass of manganese(IV) oxide ; control variables volume / amount hydrogen peroxide / concentration hydrogen peroxide ; temperature ; surface area of manganese(IV) oxide ; processing and conclusion plot graph of mass of manganese(IV) oxide against volume of oxygen in fixed time/time for fixed volume of oxygen gas or against rate ; straight line through origin proportional / straight line linear or as one increases other increases etc ; look to see if increasing mass increases / decreases / doesn’t change amount gas in fixed time / time for fixed volume of gas ; Question Answer Marks 4 One mark from each section and any two others Timing reaction to stop method apparatus timer / stop-watch / stop-clock ; balance ; method powder into hydrogen peroxide in container until bubbles stop ; do each mass / amount of manganese dioxide more than once ; use minimum 5 different masses / amounts of manganese(IV) oxide ; goggles / gloves protect eyes / hands / skin against hydrogen peroxide / MnO2 ; measurements time for end of reaction / bubbles stop ; mass of manganese(IV) oxide ; control variables volume / amount hydrogen peroxide / concentration hydrogen peroxide ; temperature ; surface area of manganese(IV) oxide ; processing and conclusion plot graph of mass of manganese(IV) oxide against time ; straight line through origin proportional / straight line linear or as one increases other increases etc ; look to see if increasing mass increases / decreases / doesn’t change amount gas in fixed time / time for fixed volume of gas ; 7 Question Answer Marks 4 One mark from each section and any two others Mass decrease method apparatus timer / stop-watch / stop-clock ; balance ; method powder into hydrogen peroxide in container on balance ; do each mass more than once ; use minimum 5 different masses / amounts of manganese(IV) oxide ; goggles / gloves protect eyes / hands / skin against hydrogen peroxide / MnO2 ; measurements mass of reaction vessel and contents at start and end / at a fixed time ; time of reaction / time for fixed mass decrease ; mass of manganese(IV) oxide ; control variables volume / amount hydrogen peroxide / concentration hydrogen peroxide ; temperature ; surface area of manganese(IV) oxide ; processing and conclusion plot graph of mass of manganese(IV) oxide against loss in mass ; straight line through origin proportional / straight line linear or as one increases other increases etc ; look to see if increasing mass increases / decreases / doesn’t change time for mass to decrease ; 7

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5 A student investigates the stretching of a spring. The student assembles the spring and a metre rule as shown in Fig. 5.1. metre rule clamp clamp spring stand stand bench Fig. 5.1 (not to scale) Fig. 5.2 shows a full-size diagram of the unstretched spring and part of the metre rule. cm 32 spring 33 metre rule 34 35 36 Fig. 5.2 (a) (i) Take readings from the metre rule of the top and the bottom of the coiled part of the spring. Do not include the loops at the ends of the spring. Record your readings to the nearest 0.1 cm. reading of top of spring = ......................................................... cm reading of bottom of spring = ......................................................... cm [2] (ii) Calculate the length l 0 of the coiled part of the spring. Show your working. Record in Table 5.1 this value of l 0 for load L = 0.0 N. Table 5.1 load L 0.0 1.0 2.0 3.0 4.0 5.0 / N length l 6.3 1.9 11.9 14.7 17.5 / cm [1] (b) Procedure The student: • places a load L = 1.0 N on the spring • records in Table 5.1 the length l of the coiled part of the spring • repeats this procedure for load L = 2.0 N, 3.0 N, 4.0 N and 5.0 N. The student records the length l of the coiled part of the spring, produced by one of the loads, incorrectly. State for which load the incorrect length has been recorded. load = ........................................................... N Deduce the length that the student should have recorded. length ......................................................... cm [2] (c) Line of sight (parallax) errors can occur when readings are taken from the metre rule. State two practical precautions that the student takes to ensure that accurate readings are taken from the metre rule. precaution 1 .............................................................................................................................. ................................................................................................................................................... precaution 2 .............................................................................................................................. ................................................................................................................................................... [2] (d) Another student suggests that the stretched length l of the spring is proportional to load L. State if the readings support this suggestion. Use values from Table 5.1 to justify your answer. statement .................................................................................................................................. justification ................................................................................................................................ ................................................................................................................................................... [1] (e) A student wants to stretch the spring to four times the length l 0 of the unstretched spring. Use the results in Table 5.1 to predict the load L the student needs to add to the spring. predicted load L = ..................................................... N [1] (f) Stretched springs are potentially dangerous because of the elastic energy stored in them. State and explain one safety precaution that the student takes when doing the experiment. precaution ................................................................................................................................. explanation ............................................................................................................................... ................................................................................................................................................... [1] [Total: 10]

Mark scheme: 5(a)(i) 32.0 ; 35.5 ; 2 5(a)(ii) 3.5 ; 1 5(b) 2(.0) ; 9.1 ; 2 5(c) any two from: view reading at eye level / perpendicular to rule ; place rule close / parallel to the spring ; use of a fiducial aid e.g., set-square ; 2 5(d) NO and doubling L does not double l (or similar) / the ratio l / L / L / l is not constant ; 1 5(e) 3.5 – 3.9 inclusive ; 1 5(f) wear goggles to protect the eyes in case the spring breaks / comes loose / flies off / place a heavy load on the base of the stand to protect feet / hands / legs in case topples over / steel toe cap shoes protects feet from loads falling from spring / spring breaks ; 1

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6 A student investigates the cooling of hot water in a beaker. (a) Procedure The student: • measures the room temperature as 22.0 °C • pours 200 cm3 of hot water into a beaker • places a thermometer into the hot water • waits for 30 seconds • stirs the water and measures its initial temperature T • continues recording in Table 6.1 the temperature of the water every 60 seconds for 360 seconds. The reading on the thermometer at time t = 60 seconds is shown in Fig. 6.1. °C 80 70 Fig. 6.1 Record this value of T to the nearest 0.5 °C in Table 6.1 for time t = 60 s. Table 6.1 time t temperature T / s / °C 0 82.5 60 120 74.0 180 70.5 240 67.0 300 64.0 360 61.0 [1] (b) (i) State why it is good experimental technique for the student to wait for 30 seconds before measuring the initial temperature of the hot water. ........................................................................................................................................... ..................................................................................................................................... [1] (ii) State why the student stirs the water before taking the reading. ........................................................................................................................................... ..................................................................................................................................... [1] (c) (i) Use the temperature values in Table 6.1 to calculate the average rate of cooling of the water during the first 180 seconds of cooling. Use the equation shown. temperature decrease during the first 180 seconds average rate of cooling = 180 Give your answer to two significant figures. average rate of cooling during the first 180 seconds = ................................................ °C / s [2] (ii) Use the temperature values in Table 6.1 to calculate the average rate of cooling of the water during the last 180 seconds of cooling. average rate of cooling during the last 180 seconds = ................................................ °C / s [1] (d) Write a conclusion about the rate at which hot water cools in a beaker. ................................................................................................................................................... ............................................................................................................................................. [1] (e) The student completes the experiment and leaves the water in the beaker. Predict the temperature T of the water 1 hour later. T = .................................................... °C [1] (f) The experiment is repeated by another student. Suggest two changes the student makes to reduce the rate of cooling of the water during the experiment. change 1 ................................................................................................................................... change 2 ................................................................................................................................... [2]

Mark scheme: 6(a) 78.0 ; 1 6(b)(i) to allow the maximum temperature of the water to be reached / to allow liquid in thermometer to expand ; 1 6(b)(ii) to ensure temperature is the same throughout the water / all water same temperature / temperature even throughout ; 1 6(c)(i) 0.06667 ; 0.067 (answer given to 2 significant figures) ; 2 6(c)(ii) 0.052778 ; 1 6(d) the rate of cooling decreases as the temperature decreases / as the liquid cools ; 1 6(e) 22 / 22.0 / room temperature ; 1 6(f) Any two from: thicker beaker / plastic beaker / polystyrene beaker ; lagging around beaker/insulation ; lid on beaker / cover top of beaker ; lower initial (hot water) temperature ; higher room temperature ; more water ; 2

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