Cambridge IGCSE Sciences - Co-ordinated (Double) 0654 — 2025 May/June Paper 5 · Variant 3

1 Urine tests are commonly used for the diagnosis of diseases. You are going to investigate four samples A, B, C and D that react like urine. You are going to determine if there is any indication of disease. (a) Read through the procedure and draw a table to record your observations for samples A, B and C in the space provided. [2] (b) (i) Procedure Testing samples A, B and C. • Add approximately 1 cm depth of sample A to each of two test-tubes. • Add approximately 1 cm depth of Benedict’s solution to one of the test-tubes and place in the hot water-bath for at least 2 minutes. • Add about 1 cm depth of biuret solution to the other test-tube. • Record in your results table in (a) the final colour observed for each of the test-tubes. Repeat the procedure with sample B instead of sample A. Repeat the procedure with sample C instead of sample A. [5] (ii) The tests in the procedure are used to detect chemicals in a urine sample. The reducing sugar glucose and proteins are not usually present in the urine of a healthy person. People with diabetes have glucose in their urine. People with nephritis have proteins in their urine. State if the observations indicate the presence of diabetes, nephritis or if the person is healthy. Explain your answer. sample A ........................................................................................................................... ........................................................................................................................................... sample B ........................................................................................................................... ........................................................................................................................................... sample C ........................................................................................................................... ........................................................................................................................................... [3] (c) (i) Procedure Testing sample D. • Dip the urine testing strip into sample D. • Remove the testing strip. • Compare the colour observed on the testing strip with the colour chart provided. Use the colour chart to estimate the concentration of glucose in sample D. ..................................................................................................................................... [1] (ii) People use the testing strips instead of using the test with Benedict’s solution. Give two reasons why people use testing strips instead of doing the test with Benedict’s solution. Do not include cost in your answer. 1 ........................................................................................................................................ ........................................................................................................................................... 2 ........................................................................................................................................ ........................................................................................................................................... [2] [Total: 13]

Mark scheme: Question Answer Marks 1(a) Columns / rows for reagents ; 2 headings for samples A, B, C ; 1(b)(i) full set of results ; 5 A – red / orange / yellow / green (positive for Benedicts) ; B – lilac (positive for biuret) ; A and B blue as negatives for Benedicts and biuret ;; C – blue (negative for both) 1(b)(ii) A diabetes as urine contains glucose ; 3 B nephritis as urine contains protein ; C healthy / no disease as urine doesn’t contain glucose or protein ; 1(c)(i) concentration stated matches supervisor ; 1 1(c)(ii) Any two from: 2 doesn't need heating / / doesn’t need water bath ; instant result ; need less apparatus / equipment needed ; specific for glucose ; no need to measure any volumes ; gives concentration (of the substances in urine) ; chemicals are not hazardous ; test strips easy to access / chemicals not easy to access ; less waste ;

2 The pH of urine in a healthy person is approximately 6.5. A student suggests that the pH of urine changes as the amount of water a person drinks during the day changes. Plan an investigation to determine the relationship between the volume of water a person drinks and the pH of their urine three hours later. You may use any common laboratory apparatus in your plan. You are not required to do this investigation. In your plan, include: • the apparatus and chemicals you will need • a brief description of the method • the measurements you will make and how you make them as valid as possible • the variables you will control • how you will process your results to reach a conclusion. You may include a results table if you wish. You are not required to enter any readings in the table. .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .................................................................................................................................................... [7]

Mark scheme: 2 One marking point from each section and any other two marks 7 apparatus universal indicator / test-stick and its use ; measuring cylinder and its use ; timer and 3 hours measured ; method drink water and measure pH of urine for at least 2 different volumes of water ; measurement measure pH (at start and) after ; use of a pH colour chart if UI used ; repeat each volume to exclude / identify anomalies; at least 5 volumes of water; control variables eat same meals / diet ; same activity levels ; same volume of urine tested ; same volume of Universal Indicator ; same person ; drink / test at same time of day ; water drunk has the same pH ; Process results and draw a conclusion plot graph of volume and pH / pH change ; shape of graph explained i.e. IF straight line through the origin they are proportional etc. when volume increase does pH increase, decrease (or stay the same) ;

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3 You are going to investigate the effect of concentration on the rate of a reaction. When aqueous sodium thiosulfate reacts with aqueous iron(III) nitrate, the reaction mixture immediately turns a dark brown-purple colour. This colour then starts to fade. The time taken for the colour of the mixture to fade is called the reaction time, and is used to find the rate of the reaction. Fig. 3.1 shows the experiment. aqueous sodium thiosulfate and cross on a piece of white paper aqueous iron(III) nitrate Fig. 3.1 When the colour fades, the cross on the paper becomes visible through the reaction mixture. Aqueous sodium thiosulfate is made less concentrated by adding water to it. (a) Procedure • Using the measuring cylinder labelled S, add 30 cm3 of aqueous sodium thiosulfate to a conical flask. • Place the conical flask on the piece of white paper marked with a cross. • Using the measuring cylinder labelled I, measure 25 cm3 of aqueous iron(III) nitrate. • Add the aqueous iron(III) nitrate to the flask, swirl and immediately start a stop-watch. • Look through the mixture and when the cross just becomes visible, stop the stop-watch. • Record in Table 3.1 this reaction time in seconds to the nearest second. If the time takes longer than 300 s, put > 300 s in Table 3.1. Repeat the procedure using the quantities of aqueous sodium thiosulfate, water and aqueous iron(III) nitrate shown in Table 3.1. The water needs to be added to the aqueous sodium thiosulfate before the aqueous iron(III) nitrate is added. Use the measuring cylinder labelled W to measure the volume of water. Table 3.1 volume of volume of aqueous volume of water aqueous reaction time rate of reaction sodium thiosulfate / cm3 iron(III) nitrate / s per 1000 s / cm3 / cm3 30 0 25 20 10 25 15 15 25 10 20 25 [4] (b) (i) Describe one difficulty in determining the reaction time. ........................................................................................................................................... ..................................................................................................................................... [1] (ii) State what happens to the reaction time when the volume of aqueous sodium thiosulfate is doubled. Explain your answer using data from Table 3.1. statement .......................................................................................................................... explanation ........................................................................................................................ ........................................................................................................................................... [1] (c) (i) Calculate the rate of each reaction. Use the equation shown. 1000 rate of reaction = time Record in Table 3.1 your values to two significant figures. [2] (ii) State the relationship between concentration of aqueous sodium thiosulfate and rate of reaction. ........................................................................................................................................... ..................................................................................................................................... [1] (d) (i) Name one piece of apparatus suitable for measuring 25 cm3 more accurately than a measuring cylinder. ..................................................................................................................................... [1] (ii) Suggest why the total volume in the conical flask must be the same for each experiment. Do not include fair test in your answer. ........................................................................................................................................... ..................................................................................................................................... [1] (iii) Suggest why repeating the experiment several times increases confidence in the results. ........................................................................................................................................... ..................................................................................................................................... [1] (e) A reaction happens when reactant particles collide with each other. When the concentration increases, there are more particles in the solution and they are closer together. Suggest why the rate of reaction changes as the concentration of the aqueous sodium thiosulfate changes. ................................................................................................................................................... ............................................................................................................................................. [1] [Total: 13]

Mark scheme: 3(a) time for first reaction ; 4 time for all reactions ; time increasing ; all times to nearest second ; 3(b)(i) difficult to tell when cross (just) appears ; 1 3(b)(ii) decreases AND data to show this ; 1 3(c)(i) calculations of rate correct ; 2 all to 2 sf ; 3(c)(ii) as concentration increases rate increases ; 1 3(d)(i) volumetric pipette / burette ; 1 3(d)(ii) looking through the same volume / depth of solution ; 1 3(d)(iii) identify / exclude anomalies ; 1 3(e) more collisions / more effective collisions / more frequent collisions ; 1

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4 You are going to identify the ions present in aqueous H. (a) Procedure • Put 2 cm depth of aqueous H into 5 test-tubes. • Put a splint into one of these test-tubes for use in test 5. • Do the tests shown in Table 4.1 using separate test-tubes of aqueous H for each test. • Record all observations in Table 4.1. Table 4.1 test test observations number add a few drops of aqueous sodium hydroxide 1 add excess aqueous sodium hydroxide add a few drops of aqueous ammonia 2 add excess aqueous ammonia add dilute nitric acid and 3 aqueous barium nitrate add dilute nitric acid and 4 aqueous silver nitrate 5 flame test [5] (b) State the identity of all of the ions in aqueous H. ................................................................................................................................................... ............................................................................................................................................. [1] (c) Explain why dilute nitric acid is added in tests 3 and 4. ................................................................................................................................................... ............................................................................................................................................. [1] [Total: 7]

Mark scheme: 4(a) white ppt and dissolves / colourless solution in excess ; 5 white ppt and dissolves / colourless solution in excess ; colourless solution ; white ppt ; lilac ; 4(b) zinc ions / Zn2+ and chloride ions / Cl– and potassium ions / K+ ; 1 4(c) breaks down / removes any carbonate (which would give a white ppt) ; 1

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5 You are going to investigate how the resistance of a lamp depends on the potential difference across the lamp. The circuit shown in Fig. 5.1 is assembled for you. power supply A Y V Fig. 5.1 (a) (i) State the name of component Y. ..................................................................................................................................... [1] (ii) You are going to measure the current I and the potential difference V. Component Y changes the values of I and V. Procedure • Close the switch. • Slowly adjust component Y until V is 0.3 V. • Record in Table 5.1 the current I. • Open the switch. Table 5.1 potential difference V current I resistance R / V / A / Ω 0.3 0.8 1.3 1.8 2.1 2.5 [1] (iii) Repeat the procedure in (a)(ii) for the other values of V shown in Table 5.1. Record your results in Table 5.1. [3] (iv) Calculate the resistance R for each current. Use the equation shown. V R = I Record in Table 5.1 your values of R. [1] (v) Suggest why it is good experimental practice to open the switch between readings. ........................................................................................................................................... ........................................................................................................................................... [1] (b) (i) On the grid, plot resistance R (vertical axis) against potential difference V. [3] (ii) Draw the line of best fit. [1] (iii) Use your graph to describe the relationship between R and V. ........................................................................................................................................... ..................................................................................................................................... [1] (iv) A student says R is directly proportional to V. State if the student is correct. Explain your answer. statement .......................................................................................................................... explanation ........................................................................................................................ ........................................................................................................................................... [1] [Total: 13]

Mark scheme: 5(a)(i) variable resistor ; 1 5(a)(ii) value for I in table ; 1 5(a)(iii) 6 different values of I ; 3 all values of I to 2dp ; all values of I increase ; 5(a)(iv) R correct ; 1 5(a)(v) so that current does not heat up the components ; 1 5(b)(i) axes labelled with property and unit ; 3 suitable linear scale with points covering at least half the grid and all points can be plotted ; all points correctly plotted  ½ small square ; 5(b)(ii) line of best fit ; 1 5(b)(iii) as V increases, R increases ; 1 5(b)(iv) no (no mark) 1 not a straight line going through the origin / ratio of variables not constant ;

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6 You are going to calculate the spring constant k of a spring. The spring constant is a measure of the stiffness of a spring. The apparatus in Fig. 6.1 is assembled for you. l 0 Fig. 6.1 (a) (i) Procedure • Record the length l of the unstretched spring in cm to the nearest 0.1 cm. 0 Do not include the loops at either end of the spring in your measurement. l = ......................................................... cm 0 • Suspend a mass of 200 g from the spring. • Record the length l of the stretched spring in cm to the nearest 0.1 cm as shown in 1 Fig. 6.2. l 1 Fig. 6.2 l = ................................................... cm [2] 1 (ii) Calculate the extension e of the spring. Use the equation shown. e = l – l 1 0 e = .................................................... cm [1] (iii) Calculate the spring constant k. Use the equation shown. 2.0 k = e k = ............................................... N / cm [1] (b) (i) A teacher does the same experiment and calculates the spring constant k as 0.31 N / cm. Two values are considered to be equal within the limits of experimental error if they are within 10% of each other. State if your value for k in (a)(iii) and the teacher’s value are equal within the limits of experimental error. Justify your answer with a calculation. ........................................................................................................................................... ..................................................................................................................................... [2] (ii) Another student does the same experiment using a mass of 200 g but uses a spring with a larger spring constant. Suggest a value for the extension e. Explain your answer. value .............................. cm explanation ........................................................................................................................ ........................................................................................................................................... [1] [Total: 7] NOTES FOR USE IN QUALITATIVE ANALYSIS Tests for anions anion test test result carbonate, CO32− add dilute acid, then test for carbon effervescence, carbon dioxide dioxide gas 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 iodide, I – acidify with dilute nitric acid, then yellow ppt. [in solution] add aqueous silver nitrate nitrate, NO3− add aqueous sodium hydroxide, ammonia produced [in solution] then aluminium foil; warm carefully sulfate, SO42− acidify with dilute nitric acid, then white ppt. [in solution] add aqueous barium 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(II), 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, ppt. turns brown near surface on ppt. turns brown near surface on standing standing iron(III), Fe3+ red-brown ppt., insoluble in excess red-brown ppt., insoluble in excess zinc, Zn2+ white ppt., soluble in excess, giving white ppt., soluble in excess, giving a colourless solution a 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) l0 and l1 to 1 decimal place ; 2 l0 less than l1 ; 6(a)(ii) e correct ; 1 6(a)(iii) k correct ; 1 6(b)(i) Any suitable method and statement ;; 2 10% calculation ; use of the 10% in a calculation and matching statement ; 6(b)(ii) smaller e than 6(a)(ii) 1 and larger k requires a larger force to produce same extension ;

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