Cambridge IGCSE Science - Combined 0653 — 2024 May/June Paper 5 · Variant 2

1 You are going to investigate the effect of enzyme concentration on the breakdown of a substance. Catalase is an enzyme found in peas that breaks down hydrogen peroxide into water and oxygen gas. The word equation for the reaction is shown. catalase hydrogen peroxide water + oxygen When peas are added to a solution of hydrogen peroxide and detergent, the oxygen gas causes a frothy layer of bubbles to form on top. The rate of this reaction can be estimated by measuring the height of the layer of bubbles formed. This is shown as h in Fig. 1.1. layer of bubbles height h peas, hydrogen peroxide and detergent Fig. 1.1 You are provided with peas soaked in distilled water. (a) Procedure Step 1 Label five boiling tubes 0, 1, 2, 4 and 8. Step 2 Use the 10 cm3 syringe to add 10.0 cm3 of hydrogen peroxide to each labelled boiling tube. Step 3 Use the 1 cm3 syringe to add 1.0 cm3 of detergent to the five boiling tubes and stir gently to mix. Step 4 Add the number of peas shown in Table 1.1 to the five labelled boiling tubes. Table 1.1 boiling tube number of peas added height h / mm 0 0 1 1 2 2 4 4 8 8 Step 5 Start the stop-clock and wait for 5 minutes. Step 6 At 5 minutes, measure the height h of the layer of bubbles formed. (i) Record in Table 1.1 the value of h in each of the five boiling tubes. [3] (ii) On the grid, plot a graph of height h (vertical axis) against the number of peas added. [3] (iii) Draw the line of best fit. [1] (iv) Use your graph to estimate the height h when six peas are used. Show on the graph how you obtain your value. height h = ...................................................mm [2] (v) Describe the relationship between height h and the number of peas added. ........................................................................................................................................... ..................................................................................................................................... [1] (vi) Use your answer to (a)(v) to determine the relationship between the concentration of catalase and the rate of breakdown of hydrogen peroxide. ........................................................................................................................................... ..................................................................................................................................... [1] (b) Identify one source of error when measuring height h in step 6. ................................................................................................................................................... ............................................................................................................................................. [1] (c) A student does the same investigation. The student repeats the procedure several times for each boiling tube. Suggest how repeating the procedure allows the student to evaluate the quality of the data. ................................................................................................................................................... ............................................................................................................................................. [1] [Total: 13]

Mark scheme: 1(a)(i) all results recorded ; all values in mm ; h increases going down the table ; 3 1(a)(ii) vertical axis labelled height or h in mm AND horizontal axis labelled number of peas ; linear scales so that plotted points occupy at least half the grid ; plots correct  half a small square ; 3 1(a)(iii) line of best fit ; 1 1(a)(iv) correct estimate from graph ; horizontal and vertical lines shown on graph ; 2 1(a)(v) as the (number of) peas increases, the height (of bubbles) increases ; 1 1(a)(vi) the higher the concentration of catalase, the higher the rate of breakdown of hydrogen peroxide ; 1 1(b) difficult to determine exact height / bubbles not level / bubbles moving AW ; 1 1(c) can identify / check for / exclude, anomalous results ; 1

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2 You are going to investigate the identity of unknown solution X. (a) Procedure • Pour approximately 2 cm depth of solution X into test-tubes 1 to 4. • Place a clean wooden splint into test-tube 4 and leave it to soak. • Do each test as described in Table 2.1. • Record your observations in Table 2.1. Table 2.1 test-tube test observations 1 Add approximately 2 cm depth of aqueous sodium carbonate to solution X. Leave for one minute. 2 Add approximately 2 cm depth of dilute nitric acid followed by a further 2 cm depth of aqueous barium nitrate to solution X. Leave for one minute. 3 Add approximately 2 cm depth of dilute nitric acid followed by five drops of aqueous silver nitrate to solution X. Leave for one minute. 4 Take the splint soaking in solution X and place it into a blue Bunsen burner flame. Record the immediate colour seen. If you do not see any colour, dip the splint in the solution and replace into the flame. [4] (b) Explain why it is difficult to identify the positive ion (cation) present in solution X using the procedure for test-tube 4. ................................................................................................................................................... ............................................................................................................................................. [1] (c) Identify the negative ion (anion) present in solution X. State which test you use to make this identification. negative ion is ........................................................................................................................... test ............................................................................................................................................ [2] [Total: 7]

Mark scheme: 2(a) test 1 – (light) blue ppt. ; test 2 – (stays) blue solution / stays green solution ; test 3 – white ppt. ; test 4 – green / green-blue / blue flame ; 2(b) mixture of colours seen / subjective AW / difficult to distinguish from colour of burning splint / green-blue colour only appears for a short time ; 1 2(c) chloride ; test 3 / (dilute) nitric acid and (aqueous) silver nitrate ; 2

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3 When an aqueous salt solution is left in an open container, the mass of the solution decreases. This is because some of the water evaporates. Plan an investigation to determine the relationship between the concentration of salt solution and the rate of evaporation of water from the salt solution. You are provided with: • distilled water • solid salt. You may use any other common laboratory apparatus in your plan. You are not required to do this investigation. In your plan, include: • the apparatus you will use • 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 labelled diagram if you wish. You may include a table that can be used to record the results if you wish. You do not need to include any results in the table. .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .................................................................................................................................................... [7]

Mark scheme: 3 One mark from each section and any two other marking points: (If one section is missing max 6 etc.) 1 Apparatus balance AND measuring cylinder ; stop-clock ; 2 Method description of making different concentrations of salt solution ; leave different concentrations of salt solution to evaporate for a fixed time (not to dryness / crystallisation) ; at least five different concentrations of salt solution ; 3 Measurements states values of mass of salt added to make solutions (if they use increments, must include the starting mass) / states volumes used in serial dilution ; measure mass / volume of salt solution at start and at end ; measure time (for fixed change in, mass / volume) ; 4 Control variables temperature of liquid or room ; (initial) volume of salt solution ; 5 Processing results calculate rate / divide mass by time ; plot a graph of change of mass against concentration of salt solution / graph of time for fixed change in mass against concentration of salt solution / graph of rate against concentration ; idea of repeat measurements at each concentration and averaging results / repeat measurements at each concentration to, identify / check for / exclude anomalous results ; 7

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4 You are going to compare the rate at which hot water cools in a beaker with and without a lid. You have a cardboard disc with a small circular hole in the centre to use as a lid. Arrange the equipment as shown in Fig. 4.1. clamp thermometer boss beaker stand lid bench Fig. 4.1 (a) (i) Procedure • Remove the lid from the beaker and carefully add 100 cm3 of hot water to the empty beaker. • Put the cardboard lid on top of the beaker. • Put the thermometer through the hole in the lid into the hot water in the beaker. • Wait for 30 s after placing the thermometer in the hot water. • Record in Table 4.1 the temperature on the thermometer θA at time t = 0 to one decimal place. • Start the stop-clock. • Measure θA every 30 s for 180 s and record the results in Table 4.1. • Move the clamp and thermometer away from the beaker. Table 4.1 temperature θA temperature θB time t (with a lid) (without a lid) / s / °C / °C 0 30 60 90 120 150 180 [2] (ii) Repeat the procedure in (a)(i) but without using the lid. Record in Table 4.1 the temperatures θB for the beaker without the lid. [2] (b) (i) Calculate the total change in temperature between t = 0 and t = 180 s for the beaker with a lid ΔθA and for the beaker without a lid ΔθB. ΔθA = .......................................................... °C ΔθB = .......................................................... °C [1] (ii) Calculate the average rate of cooling R of the water for each experiment. Use the equation shown. Δθ R = where Δt = 180 s Δt Give your answers to two significant figures. Determine the unit for the rate of cooling. RA = ............................................................... RB = ............................................................... unit = ............................................................... [3] (iii) Two results are equal within the limits of experimental accuracy if the values are within 10% of each other. Use your answers to (b)(ii) to state whether the rate of cooling RA in the beaker with a lid is equal to the rate of cooling RB in the beaker without a lid. Support your answer with a calculation. calculation statement .......................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... [2] (c) (i) State how to avoid parallax (line of sight) error when reading the thermometer. ........................................................................................................................................... ..................................................................................................................................... [1] (ii) Suggest two improvements to the procedure described in (a). 1 ........................................................................................................................................ ........................................................................................................................................... 2 ........................................................................................................................................ ........................................................................................................................................... [2] [Total: 13]

Mark scheme: 4(a)(i) values decreasing from t = 0 to t = 180 ; 2 4(a)(ii) full set of results for column  B all to nearest 0.5 °C ;  B >  A ; 2 4(b)(i)  A and  B correct ; 1 4(b)(ii) RA (and RB) calculated correctly ; both values recorded to 2 sig fig ; unit = °C / s ; 3 4(b)(iii) statement must be consistent with candidate results expect rates are different (no mark) evidence of 10% calculation ; because they differ by more than 10% / are not within experimental accuracy ; OR rates are the same (no mark) evidence 10% calculation ; because they are within 10% of each other / are within experimental accuracy ; 2 4(c)(i) read (with eye) perpendicular (to the reading) ; 1 4(c)(ii) any two from: same starting temperature of water (in both beakers) ; stir the water before each temperature reading ; thermometer bulb not touching, sides / base of the beaker ; thermometer bulb, immersed in / covered by water ; 2

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