Cambridge IGCSE Sciences - Co-ordinated (Double) 0654 — 2019 Oct/Nov Paper 5 · Variant 3

1 You are going to investigate an enzyme-catalysed reaction. Hydrogen peroxide is broken down by catalase, an enzyme found in living cells such as yeast cells. Oxygen gas is released during the reaction and a foam is produced. (a) (i) Procedure • Stir the yeast suspension. • Pour yeast suspension into the measuring cylinder up to the 3 cm3 graduation. • Using the syringe, quickly add 1 cm3 of hydrogen peroxide to the yeast in the measuring cylinder. • Immediately start the stopclock. • Read the total volume of the liquid and foam produced every 30 seconds for 150 seconds. • Record in Table 1.1 your values to the nearest 0.5 cm3. The volume at time = 0 has been recorded for you. • Empty out the measuring cylinder and rinse with the distilled water provided. [2] Table 1.1 total volume of liquid and foam / cm3 time / s 1 cm3 hydrogen peroxide 2 cm3 hydrogen peroxide 0 4.0 5.0 30 60 90 120 150 (ii) Repeat the procedure in (a)(i) using 2 cm3 hydrogen peroxide instead of 1 cm3 hydrogen peroxide. [2] (b) On the grid provided, plot graphs of the total volume of liquid and foam against time for both 1 cm3 and 2 cm3 hydrogen peroxide. • Choose a suitable scale. • Plot a graph of total volume of liquid and foam against time for 2 cm3 hydrogen peroxide. • Draw the best-fit line and label this line 2 cm3. • On the same axes, plot a graph of total volume of liquid and foam against time for 1 cm3 hydrogen peroxide. • Draw the best-fit line and label this line 1 cm3. total volume of liquid and foam / cm3 time / s [5] (c) State the effect of increasing the volume of hydrogen peroxide used on the rate of this reaction during the first 90 seconds. ............................................................................................................................................. [1] (d) Identify a source of inaccuracy in obtaining your volume readings of the liquid and foam. Suggest an improvement to increase the accuracy of these readings. source of inaccuracy ................................................................................................................. ................................................................................................................................................... improvement ............................................................................................................................. ................................................................................................................................................... [2] [Total: 12]

Mark scheme: 1(a)(i) full set of results for 1 cm3 ; results recorded to nearest 1.0 cm3 ; 2 1(a)(ii) full set of results for 2 cm3 ; greater volume produced at 150 seconds by 2 cm3 than 1 cm3 ; 2 1(b) scales linear and use at least half the grid ; plots correct ± half small square line 1 ; plots correct ± half small square line 2 ; good best fit line 1 ; good best fit line 2 ; 5 1(c) increases (rate of reaction) ; 1 1(d) Max one source from: foam not level ; foam moving ; timing and reading ; accuracy of scale ; parallax error qualified ; Max one matching improvement from: repeat and average ; use 2 people ; use burette ; read at eye level / read perpendicularly ; 2

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2 You are going to investigate the nutrient content of the yeast suspension used in Question 1. (a) Procedure • Place about 1 cm depth of the unused yeast suspension in each of two test-tubes. • To one test-tube, add an equal volume of biuret solution and stir well. • To the other test-tube, add a few drops of iodine solution. Complete Table 2.1 by recording the final colour observed in each test-tube after adding the testing solutions. State the conclusions from your observations. Table 2.1 test solution final colour observed conclusion biuret solution iodine solution [4] (b) The teacher says that the yeast produces carbon dioxide during respiration. To test for carbon dioxide the gas produced is bubbled through limewater. (i) Draw the assembled apparatus that should be used for this test. [1] (ii) Label the apparatus and chemicals in your diagram in (b)(i). [1] (iii) State the observation that confirms carbon dioxide is produced. ..................................................................................................................................... [1] (c) Before adding the yeast, the liquid used to make the yeast suspension in (a) is tested with biuret solution and iodine solution. Suggest why this is done. ............................................................................................................................................. [1] [Total: 8]

Mark scheme: 2(a) final colour observed conclusion biuret solution purple ; contains protein ; iodine solution brown / yellow / orange ; does not contain starch ; 4 2(b)(i) delivery tube under the limewater ; 1 2(b)(ii) delivery tube and limewater labelled ; 1 2(b)(iii) milky ; 1 2(c) To check it does not contain (named) nutrient / protein / starch / control ; 1

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3 Magnesium ribbon reacts with dilute sulfuric acid to produce magnesium sulfate solution and hydrogen gas. (a) Plan an experiment to investigate the effect of temperature on the rate of this reaction. You are not required to carry out this experiment. Your plan should include: • a labelled diagram of the apparatus • values of temperature you will use • variables you will keep constant • measurements you will take • how the measurements will be used to find the rate of reaction • one safety precaution. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [7] (b) Identify two possible sources of error in your experiment. Explain an improvement to reduce the effect of one of these errors. source of error 1 ....................................................................................................................... ................................................................................................................................................... source of error 2 ....................................................................................................................... ................................................................................................................................................... improvement ............................................................................................................................. ................................................................................................................................................... [3] [Total: 10]

Mark scheme: 3(a) MP1 apparatus and safety labelled diagram of apparatus gas collection: • flask with delivery tube ; • graduated receiving vessel ; • air tight / will work ; • thermometer ; • means to change T ; OR mass decrease: • flask and contents ; • on balance ; • balance at least 1dp ; • thermometer ; • means to change T ; OR to end: • container and acid and Mg ; • thermometer ; • means to change T ; no naked flame / limit concentration of sulfuric as corrosive / goggles as sulfuric acid corrosive / burns ; MP2 variables minimum 2 temperatures stated ; 5 stated values of temperature ; MP3 control variables same size / length / surface area of magnesium ; same volume of acid / same amount of magnesium ; same concentration of acid ; 7 Question Answer Marks 3(a) MP4 measurements (measure) volume of gas ; OR mass loss ; in a certain time ; OR time ; for certain volume of gas ; OR mass loss ; OR time ; to end / bubbles stop / Mg all gone ; MP5 processing graph of volume against time / mass against time ; rate = volume ÷ time ; mass ÷ time ; more gas in set time is fastest / same gas in less time is fastest ; Question Answer Marks 3(b) suitable error ; improvement for stated error ; any misreadings / mis-measurements ; repeat ; OR (misread because of) parallax ; eye level ; OR surface area of magnesium ; same size / shape ; OR conc of acid ; use same batch ; OR temperature ; water-bath ; OR mass loss is small ; balance to more dp ; OR loss of gas as assembled ; have tube in flask ; 2 1

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4 Notes for use in Qualitative Analysis for this question are printed on page 16. H is a solution which contains two cations and one anion. You are going to carry out some tests and identify the ions in H. (a) Identify the anion in H by carrying out the tests shown in Table 4.1. Use fresh samples of H for each test. Record in Table 4.1 your observations and conclusions, including negative conclusions to eliminate ions. All boxes should be completed. Table 4.1 test observations conclusion add dilute hydrochloric acid add dilute nitric acid followed by aqueous silver nitrate add dilute nitric acid followed by aqueous barium nitrate [3] (b) Identify the two cations in H by carrying out suitable tests on H with sodium hydroxide solution. You can heat gently and test any gases with damp litmus paper. Record in Table 4.2 your observations and conclusions. Table 4.2 test observations conclusion [5] (c) J is a solid sample of H. Procedure • Remove the stopper from the sample of solid J in the hard glass test-tube. • Heat the hard glass test-tube in a flame. • Do not heat strongly and do not heat for more than a few minutes. • Record your observations. ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [2] [Total: 10]

Mark scheme: 4(a) test observations conclusions (add dilute hydrochloric acid) no reaction not a carbonate (add dilute nitric acid followed by silver nitrate solution) no reaction / slight white ppt. not a chloride (add dilute nitric acid followed by barium nitrate solution) white ppt. sulfate 2 or 3 boxes correct ; 4 or 5 boxes correct ;; 6 boxes correct ;;; 3 4(b) test observations conclusions (add sodium hydroxide solution) AND green ppt. ; (1) Iron (II) / Fe2+ ; (1) (add sodium hydroxide solution) and heat ; (1) red litmus turns blue ; (1) ammonium / NH4+ ; (1) 5 4(c) moisture ; smell of ammonia ; 2

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5 You are going to determine the volume of a drinks cup using two methods. (a) (i) Method 1 • Place the cup with its open end facing down in the space provided below. • Draw around the circumference of the open end of the cup with a pencil. Measure and record to the nearest 0.1 cm, the diameter D of the circle you have drawn. D = .................................................... cm [1] (ii) • Turn the cup over and place it with its closed end facing down in the space provided below. • Draw around the circumference of the closed end of the cup with a pencil. Measure and record to the nearest 0.1 cm, the diameter d of the circle you have drawn. d = .................................................... cm [1] (b) Measure and record to the nearest 0.1 cm, the vertical height h of the cup. Fig. 5.1 shows h, but you should measure the height on your cup. cup h Fig. 5.1 h = .................................................... cm [1] (c) (i) Use your measurements from (a)(i) and (a)(ii) to calculate the average diameter dAV of the cup. Use the equation shown. dAV = (D + d) 2 dAV = .................................................... cm [1] (ii) Use your values from (b) and (c)(i) to calculate the volume V of the cup. Use the equation shown. Give your answer to 3 significant figures. × h V = 0.785 × dAV2 V = .................................................. cm3 [2] (d) (i) Method 2 Pour approximately 240 cm3 of water into the measuring cylinder. Record this volume V1. V1 = ........................................................ cm3 Pour water from the measuring cylinder into the cup until the cup is full. Record the volume V2 of water remaining in the measuring cylinder. V2 = ........................................................ cm3 Calculate the volume of water VW that the cup can hold. VW = ........................................................ cm3 [1] (ii) Describe how you read the scale of the measuring cylinder to ensure that your values for volume are as accurate as possible. ........................................................................................................................................... ..................................................................................................................................... [1] (e) (i) Suggest one practical difficulty in determining an accurate value for the volume V of the cup in method 1. ........................................................................................................................................... ..................................................................................................................................... [1] (ii) Suggest one practical difficulty in determining an accurate volume VW of water that the cup can hold in method 2. ........................................................................................................................................... ..................................................................................................................................... [1] [Total: 10]

Mark scheme: 5(a)(i) D recorded (to the nearest 0.1 cm) ; 1 5(a)(ii) d recorded and smaller than D and to nearest 0.1 cm ; 1 5(b) h recorded to nearest 0.1 cm ; 1 5(c)(i) dAV calculated correctly ; 1 5(c)(ii) V correct ; answer to 3 sf ; 2 5(d)(i) VW determined correctly by subtraction ; 1 5(d)(ii) read scale at right angles / eye level / read scale at bottom of meniscus ; 1 5(e)(i) h to the inside bottom of the cup / difficult to measure h / thickness of cup / determining the widest part to measure d ; 1 5(e)(ii) cup not completely full / cup overfilled / water spilled on transfer / poor precision of measuring cylinder ; 1

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6 You are going to determine the focal length of a convex lens. Set up the apparatus as shown in Fig. 6.1. illuminated object convex lens in holder screen u dA Fig. 6.1 (a) (i) Procedure • Switch on the lamp and place the lens a distance u = 30.0 cm from the illuminated object. • Adjust the position of the screen by moving it backwards and forwards along the bench until a sharp triangular image of the illuminated object is formed on the screen. • Measure and record to the nearest 0.1 cm the distance dA from the illuminated object to the screen. dA = .................................................... cm [1] (ii) Calculate the focal length fA of the lens. Use the equation shown. fA = 30.0 × (dA − 30.0) dA fA = .................................................... cm [1] (b) (i) Repeat the procedure in (a)(i) but place the lens a distance u = 40.0 cm from the illuminated object. Measure and record to the nearest 0.1 cm, the distance dB from the illuminated object to the screen. dB = .................................................... cm [1] (ii) Calculate the focal length f B of the lens. Use the equation shown. f B = 40.0 × (dB − 40.0) dB f B = .................................................... cm [1] (c) Use your results from (a)(ii) and (b)(ii) to calculate an average value for the focal length f of the lens. Give your answer to an appropriate number of significant figures. Use the equation shown. f = (f A + f B) 2 f = .................................................... cm [2] (d) State one precaution that you should take to obtain accurate results in this experiment. ................................................................................................................................................... ............................................................................................................................................. [1] (e) A student wishes to obtain more results to plot a graph to determine the focal length f of the lens. Suggest additional values of u that the student could use. ............................................................................................................................................. [2] (f) On Fig. 6.1 draw a line to show the image distance. Label this line v. [1] [Total: 10] NOTES FOR USE IN QUALITATIVE ANALYSIS Tests for anions anion test test result carbonate (CO32–) add dilute acid effervescence, carbon dioxide produced chloride (Cl –) acidify with dilute nitric acid, then white ppt. [in solution] add aqueous silver nitrate bromide (Br–) acidify with dilute nitric acid, then cream ppt. [in solution] add aqueous silver nitrate nitrate (NO3–) add aqueous sodium hydroxide, then ammonia produced [in solution] aluminium foil; warm carefully sulfate (SO42–) acidify, then add aqueous barium white ppt. [in solution] nitrate Tests for aqueous cations cation effect of aqueous sodium hydroxide effect of aqueous ammonia ammonium (NH4+) ammonia produced on warming – calcium (Ca2+) white ppt., insoluble in excess no ppt., or very slight white ppt. copper (Cu2+) light blue ppt., insoluble in excess light blue ppt., soluble in excess, giving a dark blue solution iron(II) (Fe2+) green ppt., insoluble in excess green ppt., insoluble in excess iron(III) (Fe3+) red-brown ppt., insoluble in excess red-brown ppt., insoluble in excess zinc (Zn2+) white ppt., soluble in excess, giving a white ppt., soluble in excess, giving a colourless solution colourless solution Tests for gases Flame tests for metal ions gas test and test result metal ion flame colour ammonia (NH3) turns damp, red litmus paper blue lithium (Li+) red carbon dioxide (CO2) turns limewater milky sodium (Na+) yellow chlorine (Cl 2) bleaches damp litmus paper potassium (K+) lilac hydrogen (H2) ‘pops’ with a lighted splint copper(II) (Cu2+) blue-green oxygen (O2) relights a glowing splint

Mark scheme: 6(a)(i) dA = (60.0 ± 2.0) (cm) ; 1 6(a)(ii) fA in the range 14.0 to 16.0 (cm) ; 1 6(b)(i) dB = (64.0 ± 2.0) (cm) ; 1 6(b)(ii) fB within 10% of fA ; 1 6(c) f correct ; to 2 / 3 / 4 significant figures only ; 2 6(d) Max one from: move screen slowly to and fro until sharpest focus obtained ; object / lens / screen perpendicular to bench ; object and lens same height above the bench ; carry out experiment away from other bright light sources / darkened room / use brighter lamp ; repeat (and average) ; 1 6(e) at least 3 values suggested ; all values > 15 (cm) ; 2 6(f) correct line, labelled v ; 1

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