Cambridge IGCSE Science - Combined 0653 — 2025 May/June Paper 6 · Variant 1

1 A student investigates the nutrient content of three colourless drinks, A, B and C. Procedure The student: step 1 adds 2 cm3 of drink A, drink B and drink C to separate clean test‑tubes step 2 adds a few drops of iodine solution to each of the test‑tubes step 3 records the results step 4 repeats step 1 to step 3 but adds 1 cm3 of biuret solution in step 2 instead of iodine solution. Fig. 1.1 shows the results the student records. with iodine: A no change B gives a positive result C is a negative result with biuret: A gives a positive result B gives a positive result C does not change colour Fig. 1.1 (a) Record in Table 1.1 the colours the student observes in each test‑tube. Table 1.1 drink colour with iodine solution colour with biuret solution A B C [3] (b) Use Table 1.1 to state conclusions about the nutrient content for each of the drinks. drink A ...................................................................................................................................... ................................................................................................................................................... drink B ...................................................................................................................................... ................................................................................................................................................... drink C ...................................................................................................................................... ................................................................................................................................................... [3] (c) State the reagent used to test for fats and oils. ............................................................................................................................................. [1] [Total: 7]

Mark scheme: Question Answer Marks 1(a) 3 drink colour with iodine solution colour with biuret solution A brown lilac B blue-black lilac C brown blue ;;; brown 2 = 1 mark blue-black = 1 mark all of colour with biuret lilac, lilac, blue = 1 mark 1(b) A contains no starch but does contain protein ; 3 B contains starch and protein ; C does not contain starch or protein ; 1(c) ethanol ; 1

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2 Invertase is an enzyme. Invertase breaks down the non‑reducing sugar sucrose into reducing sugars. invertase non‑reducing sugar sucrose reducing sugars Benedict’s solution is used to test for reducing sugars. The activity of invertase can be determined by measuring the time it takes for reducing sugars to form. Plan an investigation to determine the relationship between the activity of invertase and temperature. You are provided with: • a solution of invertase enzyme • a solution of sucrose • Benedict’s solution. You may use any common laboratory apparatus. In your plan, include: • the apparatus you will need • a brief description of the method • what you will measure • which variables you will keep constant • how you will process your results to draw a conclusion. You may include a results table (you are not required to enter any readings in the table). .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .................................................................................................................................................... [7]

Mark scheme: 2 One marking point from each section and any two others (if one section is missing max 6 etc.): 7 1. Apparatus (thermostatically controlled) water-bath ; stop-watch ; thermometer / measuring cylinder ; 2. Method allow both invertase and sucrose to reach (required) temperature before mixing ; mix together invertase and sucrose for at least two temperatures and use Benedict’s solution ; start stop-watch when invertase and sucrose are mixed ; take samples at intervals (for testing) ; repeat at five or more different temperatures all below 100 °C ; 3. Measurements measure volume of, invertase / sucrose / provides stated value with units (cm3) ; measure time to colour change / time to (brick-)red ; measure temperature/provides stated value with units (°C) ; 4. Constant variables constant volume / amount of, invertase (solution) / control the volume / amount of, invertase / repeat with stated volume ; constant volume / amount of, sucrose (solution) / control the volume / amount of, sucrose repeat with stated volume ; 5. Processing results plot a graph of time (to colour change) against temperature ; idea of shorter time equals greater activity (of enzyme / invertase) ;

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3 A student investigates aqueous H. (a) Investigating the rate of reaction of aqueous H with magnesium. Procedure The student: step 1 pours 25 cm3 of aqueous H into a beaker step 2 adds a 30 mm length of magnesium ribbon to the aqueous H step 3 immediately starts a stop‑watch step 4 stirs the reaction mixture making sure that the magnesium ribbon is always under the surface of the aqueous H step 5 stops the stop‑watch as soon as all of the magnesium ribbon has reacted step 6 records in Table 3.1 this reaction time step 7 empties the reaction mixture into a waste container and then rinses the beaker and stirrer with water step 8 pours 20 cm3 of aqueous H into the beaker step 9 adds 5 cm3 of water into the beaker of aqueous H and stirs the mixture step 10 repeats step 2 to step 7 step 11 repeats step 8 to step 10 using the volumes of aqueous H and water shown in Table 3.1. Table 3.1 volume of aqueous H volume of water reaction time rate of reaction / cm3 / cm3 / s in mm / s 25 0 12 2.5 20 5 18 1.7 15 10 10 15 5 20 280 0.11 (i) Fig. 3.1 shows the readings from the stop‑watch for 15 cm3 and 10 cm3 of aqueous H. 15 cm3 of aqueous H 10 cm3 of aqueous H 0:42.61 1:52.34 min sec min sec Fig. 3.1 Record in Table 3.1 these reaction times to the nearest second. [2] (ii) State the relationship between the volume of aqueous H and the reaction time. Use information from Table 3.1. ........................................................................................................................................... ..................................................................................................................................... [1] (iii) Calculate the rate of reaction for 15 cm3 and 10 cm3 of aqueous H. Use the equation shown. 30 rate of reaction = reaction time Record in Table 3.1 these values to two significant figures. [2] (iv) State the relationship between the volume of aqueous H and the rate of reaction. Use information from Table 3.1. ........................................................................................................................................... ..................................................................................................................................... [1] (v) State the name of a piece of apparatus suitable to measure the volumes of aqueous H. ..................................................................................................................................... [1] (vi) Explain why in step 4 it is important that all the magnesium is under the surface of aqueous H. ........................................................................................................................................... ..................................................................................................................................... [1] (vii) Explain why in step 7 it is important the beaker and stirrer are rinsed. ........................................................................................................................................... ..................................................................................................................................... [1] (b) Investigation of some reactions of aqueous H. Procedure The student: • pours 2 cm depth of aqueous H into each of four test‑tubes • does each of the tests shown in Table 3.2 to a different test‑tube of aqueous H • records the observations in Table 3.2. Table 3.2 test observation add 1 cm depth of dilute nitric acid followed by remains a colourless solution 1 cm depth of aqueous barium nitrate add 1 cm depth of dilute nitric acid followed by white precipitate 1 cm depth of aqueous silver nitrate add 5 drops of universal indicator red colour mixture fizzes and a blue solution add a small amount of copper(II) carbonate forms (i) Identify the anion (negative ion) shown to be present in aqueous H. ..................................................................................................................................... [1] (ii) Identify what type of substance is aqueous H. Explain your answer using information from Table 3.2. type of substance .............................................................................................................. explanation ........................................................................................................................ ........................................................................................................................................... [2] (iii) State the name of the gas produced in the test with copper(II) carbonate. ..................................................................................................................................... [1] [Total: 13]

Mark scheme: 3(a)(i) 43 ; 2 112 ; 3(a)(ii) as volume (of H) decreases the (reaction) time increases ; 1 3(a)(iii) 0.70 : 2 0.27 ; 3(a)(iv) as volume (of H) increases the rate (of reaction) increases ; 1 3(a)(v) measuring cylinder ; 1 3(a)(vi) ensure all of magnesium is in contact with H ; 1 3(a)(vii) to remove, (leftover) H / reaction mixture / so that there is no extra H / reaction mixture, in next experiment / to avoid 1 changing concentration of H in next experiment ; 3(b)(i) chloride / Cl − ; 1 3(b)(ii) acid ; 2 (because acid) fizzes with carbonate / red with universal indicator ; 3(b)(iii) carbon dioxide ; 1

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4 A student investigates the period T of a pendulum. (a) Fig. 4.1 shows a bob attached to a string. The string is clamped so that the centre of the bob is a distance x above the bench. clamp stand string bob x bench Fig. 4.1 (i) Measure the distance x on Fig. 4.1. Record your value to the nearest 0.1 cm. x = .................................................... cm [1] (ii) Fig. 4.1 is drawn to one‑tenth scale. Calculate the actual distance of the bob above the bench, X. Record this value of X in Table 4.1. Table 4.1 distance X time for 10 oscillations average time for period T T 2 / cm / s 10 oscillations for / s / s2 trial 1 and trial 2 trial 1 trial 2 / s 10.0 13.6 13.2 13.4 1.34 1.80 20.0 11.6 12.0 11.8 1.18 1.39 25.0 11.1 10.9 11.0 1.10 1.21 30.0 9.9 10.3 10.1 1.01 1.02 [1] (b) Procedure The student: • measures the time for 10 complete oscillations of the pendulum for each of the values of X shown in Table 4.1 • repeats each measurement. Fig. 4.2 shows repeated readings on the stop‑watch, in seconds, for your value of X in (a)(ii). reading 1 reading 2 reading 3 12.78 10.08 12.42 Fig. 4.2 (i) Suggest one reason why the student needs to take the third reading. ........................................................................................................................................... ..................................................................................................................................... [1] (ii) The student decides to use reading 1 and reading 3. Record in Table 4.1 these readings to one decimal place. [1] (iii) Calculate the average time for 10 oscillations. Record this time in Table 4.1. [1] (iv) Calculate the period T. Use the equation shown. average time for 10 oscillations T = 10 Record in Table 4.1 this value of T. Calculate T 2. Record in Table 4.1 this value of T 2. [1] (v) For X = 30.0 cm, the times for the trials are 9.9 s and 10.3 s. Two values are considered equal within the limits of experimental accuracy if they are within 10% of each other. Explain if the two values are equal within the limits of experimental accuracy. Include a calculation in your answer. ........................................................................................................................................... ..................................................................................................................................... [2] (c) (i) On the grid, plot a graph of T 2 (vertical axis) against X. 2.4 2.2 2.0 T 2 / s2 1.8 1.6 1.4 1.2 1.0 0 [2] (ii) Draw the line of best fit. [1] (iii) Extend your line so that it meets the vertical axis. Determine the value of T 2 at this point. T 2 = ......................................................s2 [1]

Mark scheme: 4(a)(i) 1.5 (cm) ; 1 4(a)(ii) 15.0 (cm) ; 1 4(b)(i) reading 1 and reading 2 are, too far apart / too different ; 1 4(b)(ii) 12.8 and 12.4 (either order) ; 1 4(b)(iii) 12.6 ; 1 4(b)(iv) 2 1 T 1.26 and T 1.59 ; 4(b)(v) correct calculation of 10%, e.g. 2 difference is (10.3 – 9.9) ÷ 10.3  100 = 3.88 or 3.9 or 4% or (10.3 – 9.9)  9.9  100 = 4.04 or 4% ; (correct calculation plus statement that) yes / this is within 10% / they are equal ; 4(c)(i) horizontal axis (distance) labelled X in cm and linear scale so that plotted points occupy at least half the grid ; 2 correct plots to  ½ small square ; 4(c)(ii) thin straight line of best fit drawn with even distribution of points ; 1 4(c)(iii) extrapolation to determine intercept and correct read-off to  ½ small square ; 1 4(d) bob drawn with its centre at the same level as the top of the bench and string connected ; 1

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