Cambridge IGCSE Science - Combined 0653 — 2024 May/June Paper 6 · Variant 1

1 (a) A student investigates the effect of copper sulfate on the enzyme amylase. Amylase speeds up the breakdown of starch into the sugar maltose. The word equation is shown. amylase starch maltose The progress of this reaction can be followed by using iodine solution to test for the presence of starch. Procedure The student: Step 1 adds 2 drops of iodine solution to 12 labelled wells on a spotting tile, as shown in Fig. 1.1 iodine solution well A0 A3 C0 C3 spotting tile A1 A4 C1 C4 A2 A5 C2 C5 Fig. 1.1 Step 2 puts three test-tubes, one containing starch solution, one containing amylase solution and one containing copper sulfate solution, into a water-bath for 3 minutes Fig. 1.2 shows the reading on a thermometer in the water-bath. °C 60 50 40 Fig. 1.2 (i) Record the temperature of the water-bath to the nearest 0.5 °C. temperature = .................................................... °C [1] Step 3 puts 2 cm3 of starch solution into each of two test-tubes labelled A and C (ii) Suggest a piece of apparatus suitable for measuring 2 cm3 of starch solution. ..................................................................................................................................... [1] Step 4 adds 2 cm3 of amylase solution to each test-tube A and C Step 5 adds 1 cm3 of copper sulfate solution to test-tube C only A C 2 cm3 of starch solution 2 cm3 of starch solution with 2 cm3 of amylase with 2 cm3 of amylase solution solution and 1 cm3 of copper sulfate solution Fig. 1.3 Step 6 puts a drop of solution from test-tube A into well A0 of the spotting tile (0 min) Step 7 puts a drop of solution from test-tube C into well C0 of the spotting tile (0 min) Step 8 starts a stop-watch and repeats step 6 and step 7 for test-tubes A and C at one minute, using well A1 and C1 Step 9 repeats step 6 and step 7 for test-tubes A and C at one minute intervals for a further 4 minutes, using wells A2–A5 and C2–C5. Fig. 1.4 shows the spotting tile at the end of the investigation. A0 A3 C0 C3 Key: = blue-black colour A1 A4 C1 C4 = brown colour A2 A5 C2 C5 Fig. 1.4 (iii) Use Fig. 1.4 and the key to record in Table 1.1, the colour of the solution in each well for test-tubes A and C. Table 1.1 colour in the well after adding colour in the well after adding time solution from test-tube A solution from test-tube C / minutes well colour well colour 0 A0 C0 1 A1 C1 2 A2 C2 3 A3 C3 4 A4 C4 5 A5 C5 [2] (iv) Explain the results for test-tube A. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [2] (v) Describe the effect of copper sulfate on the reaction. ........................................................................................................................................... ..................................................................................................................................... [1] (vi) Calculate the difference in volume of the solution in test-tube A and the solution in test-tube C at the end of step 5. Use the information from steps 3, 4 and 5. volume of solution in test-tube A = ........................................................ cm3 volume of solution in test-tube C = ........................................................ cm3 difference in volume = ........................................................ cm3 [1] (vii) The difference in volume of solution you calculated in (a)(vi) identifies a limitation in this investigation. Suggest a change to the procedure that removes this limitation. ........................................................................................................................................... ..................................................................................................................................... [1] (viii) Explain why the test-tubes were left for 3 minutes in a water-bath in step 2. ........................................................................................................................................... ..................................................................................................................................... [1] (b) Amylase is extracted from the fungus Aspergillus. Fig. 1.5 shows a photograph of the fruiting body of the fungus taken using a microscope. A B magnification = ×920 Fig. 1.5 Line AB represents the diameter of the fruiting body. (i) Measure the length of line AB on Fig. 1.5. length of line AB = .................................................. mm [1] (ii) Calculate the actual diameter of the fruiting body. Use the equation shown. length of line AB actual diameter = magnification Give your answer to one significant figure. actual diameter = .................................................. mm [2] [Total: 13]

Mark scheme: 1(a)(i) 51.0 (°C) ; 1 1(a)(ii) syringe ; 1 1(a)(iii) A results recorded as A0–A2 blue-black, A3–A5 brown ; C results recorded as C0–C4 blue-black, C5 brown ; 2 1(a)(iv) blue-black means starch present and brown means starch is not present / brown is the negative result (for starch) OR idea that starch is present at the start and no starch is present at the end OR starch present in A0, A1 and A2 but no starch in A3A5 ; starch is broken down (by amylase) ; 2 1(a)(v) reduces the activity of amylase / reduces the rate / slows down the reaction ; 1 1(a)(vi) A = 4 (cm3) C = 5 (cm3) difference calculated as 1 (cm3) ; 1 1(a)(vii) add 1 cm3 water to tube A ; 1 1(a)(viii) so that all solutions are at same temperature / at same temperature as the water bath ; 1 1(b)(i) 58 (mm) ; 1 1(b)(ii) 58 ÷ 920 or 0.063 ; answer to one sf / 0.06 (mm) ; 2

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2 A student investigates the reaction of sodium hydrogencarbonate with dilute sulfuric acid. This reaction produces carbon dioxide gas. Procedure The student: Step 1 pours 50.0 cm3 of dilute sulfuric acid into a beaker Step 2 adds one spatula of sodium hydrogencarbonate to the acid Step 3 immediately starts a stop-watch Step 4 stirs the mixture until it stops fizzing Step 5 stops the stop-watch Step 6 records in Table 2.1 this reaction time. The student repeats the procedure four more times with the number of spatulas of sodium hydrogencarbonate shown in Table 2.1. Table 2.1 number of spatulas of sodium reaction time hydrogencarbonate / s 1 2 37 3 55 4 75 5 (a) Fig. 2.1 shows the stop-watch readings for 1 spatula and 5 spatulas of sodium hydrogencarbonate. 0 : 21 . 32 1 : 36 . 88 min sec min sec 1 spatula 5 spatulas Fig. 2.1 Record in Table 2.1 these reaction times to the nearest second. [2] (b) (i) On the grid, plot reaction time (vertical axis) against the number of spatulas of sodium hydrogencarbonate. The x-axis must include 6 spatulas of sodium hydrogencarbonate. You should also extend your y-axis. [3] (ii) Draw the line of best fit. [1] (iii) Describe the relationship between the number of spatulas of sodium hydrogencarbonate and the reaction time. ........................................................................................................................................... ..................................................................................................................................... [1] (iv) Use your graph to predict the reaction time for 6 spatulas of sodium hydrogencarbonate. Show your working on the graph. reaction time = ...................................................... s [2] (c) (i) Suggest why it is difficult to measure the reaction time accurately. ........................................................................................................................................... ..................................................................................................................................... [1] (ii) The student repeats the measurement for each number of spatulas of sodium hydrogencarbonate. Suggest how repeating the measurements allows the student to evaluate the quality of the data. ........................................................................................................................................... ..................................................................................................................................... [1] (iii) Suggest a change to step 2 to improve the procedure. ........................................................................................................................................... ..................................................................................................................................... [1] (d) The gas given off is carbon dioxide. Describe the test for carbon dioxide. Include the observation for a positive result. test ............................................................................................................................................ observation ............................................................................................................................... [1] [Total: 13]

Mark scheme: 2(a) 21 ; 97 ; 2 2(b)(i) vertical axis labelled (reaction) time in s and horizontal axis labelled with number of spatulas (of sodium hydrogencarbonate) ; linear scales so that plotted points occupy at least half the grid ; plots correct to  ½ small square ; 3 2(b)(ii) line of best fit ; 1 2(b)(iii) as number of spatulas increases the reaction time increases ; 1 2(b)(iv) straight line extrapolation to 6 spatulas shown on graph ; reaction time read from correct extrapolation to nearest half a square ; 2 2(c)(i) cannot easily tell when it stops fizzing ; 1 2(c)(ii) can identify / check for / exclude, anomalous results ; 1 2(c)(iii) measure the mass (of the sodium hydrogencarbonate) ; 1 2(d) (test) (bubble through) limewater and (observation) turns milky ; 1

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3 A student determines the density of a wooden block. (a) The student determines the volume of the wooden block. Fig. 3.1 shows the wooden block drawn to actual size. wooden block height h width w length l Fig. 3.1 (i) Measure the height h, width w and length l of the wooden block. Record each measurement to the nearest 0.1 cm. h = ......................................................... cm w = ......................................................... cm l = ......................................................... cm [1] (ii) Calculate the volume Vblock of the wooden block. Use the equation shown. Vblock = h × w × l Vblock = .................................................. cm3 [1] (b) The student uses a displacement method to measure the mass of the wooden block. The student has two identical beakers labelled A and B, each containing 100 cm3 of water. The student also has a measuring cylinder containing water. Procedure The student: • carefully places the wooden block in beaker A. The water level in beaker A rises as the wooden block displaces water and the block floats as shown in Fig. 3.2. floating wooden block water A B Fig. 3.2 The student: • records the initial volume of water V1 in the measuring cylinder • slowly pours water from the measuring cylinder into beaker B until the water level is the same in both beakers • records the final volume of water V2 in the measuring cylinder. (i) Fig. 3.3 shows the water level in the measuring cylinder before and after pouring the water into beaker B. cm3 cm3 100 100 90 90 80 80 70 70 V1 V2 Fig. 3.3 Record V1 and V2 as shown in Fig. 3.3. V1 = ........................................................ cm3 V2 = ........................................................ cm3 [2] (ii) The mass M of the wooden block is equal to the mass of water displaced by the block when it is placed in beaker A. 1.0 cm3 of water has a mass of 1.0 g. Calculate the mass M. Use the equation shown. M = (V1 – V2) × 1.0 M = ...................................................... g [1]

Mark scheme: 3(a)(i) h = 2.5 (cm) and w = 3.2 (cm) and l = 4.0 (cm) ; 1 3(a)(ii) 32(.0) (cm3) ; 1 3(b)(i) V1 97.0 (cm3) ; V2 73.5 (cm3) ; 2 3(b)(ii) 23.5 (g) ; 1 3(c) correct calculation of  / 0.73 (g / cm3) ; 1 3(d) (effect)  is greater AND (reason) (V1–V2) is greater / M is greater ; 1

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4 A thermistor is a type of variable resistor. A thermistor is used to measure changes in the temperature of water in a beaker. The resistance of the thermistor changes as the water temperature changes. The resistance R of the thermistor at temperature T is calculated using the equation: V RT = I where V is the potential difference across the thermistor and I is the current through the thermistor. Plan an investigation to find the relationship between the temperature of the water and the resistance of the thermistor. You are provided with: • a supply of hot and cold water • extra connecting wires (or leads) • the assembled apparatus shown in Fig. 4.1. power supply switch ammeter A thermistor glass beaker water Fig. 4.1 You may use any common laboratory apparatus in your plan. In your plan, include: • a brief description of how you will use the assembled apparatus shown in Fig. 4.1 • any other apparatus needed • what you will measure and how you will make sure your measurements are accurate • a results table to record your measurements (you do not need to enter any readings in the table) • how you will process your results to draw a conclusion. .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... ..........................................................................................................................................................

Mark scheme: 4 One mark from each section and any two other marking points: (If one section is missing max 6 etc.) 1 Apparatus thermometer ; voltmeter ; 2 Method method of varying temperature of water, e.g. mix hot and cold water / using ice cubes to cool the water / allow hot water to cool to different temperatures ; use at least five different temperatures ; ensure thermistor is not touching beaker / stir to make sure temperature is evenly distributed ; 3 Measurements measure temperature of water and the current / I and measure / check / use, fixed value of voltage / V ; 4 Table of results columns for temperature / T, (voltage / V) and current / I ; with units for temperature (°C) and current (amps / A) ; 5 Processing results calculate resistance from voltage and current / use R = V / I ; plot graph of resistance against temperature ; idea of repeating at the same temperature and averaging results / repeating at the same temperature to, identify / check for / exclude anomalous results ;

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