Cambridge IGCSE Sciences - Co-ordinated (Double) 0654 — 2020 Oct/Nov Paper 5 · Variant 2

1 You are going to estimate the concentration of reducing sugar in a sample of food U. You will do this by comparing sample U with glucose solutions of known concentrations. (a) Procedure • Label five test-tubes A, B, C, D and U. • Use a syringe to add 2 cm3 of testing solution G to each of the five test-tubes. • Use a clean syringe to add 1 cm3 of the 0.0% glucose solution into test-tube A. • With the same syringe add 1 cm3 of the 0.5% glucose solution into test-tube B. • With the same syringe add 1 cm3 of the 1.0% glucose solution into test-tube C. • With the same syringe add 1 cm3 of the 2.0% glucose solution into test-tube D. • Use a clean syringe to add 1 cm3 of the food sample U into test-tube U. • Place the test-tubes in a hot water-bath and start the stop-clock. • The test-tubes need to be in the hot water-bath for three minutes, so you may continue with parts (b), (c) and (d) while you are waiting. • After three minutes remove the test-tubes from the water-bath and immediately observe the final colours. (i) Record in Table 1.1 the final colour in each test-tube. Table 1.1 percentage concentration of test-tube final colour observed glucose solution A 0.0 B 0.5 C 1.0 D 2.0 U unknown [5] (ii) Suggest the concentration of the glucose solution in test-tube U. Explain your answer using Table 1.1. concentration ..................................................................... % explanation ........................................................................................................................ ..................................................................................................................................... [1] (b) Name the test solution G. ............................................................................................................................................. [1] (c) State and explain a safety precaution taken when carrying out this investigation. precaution ................................................................................................................................. explanation ............................................................................................................................... [1] (d) (i) Suggest why it would be better to use clean syringes for adding the different glucose solutions. ........................................................................................................................................... ..................................................................................................................................... [1] (ii) Suggest how you could get a more accurate estimate for the concentration of reducing sugar in the food sample U. ........................................................................................................................................... ..................................................................................................................................... [1] (e) A food sample is tested for fat. (i) Name the two substances used to test a food sample for the presence of fat. .............................................................. and ............................................................... [1] (ii) State the observation for a positive result. ..................................................................................................................................... [1] (iii) Explain why there should be no flames in the laboratory when doing this test. ..................................................................................................................................... [1] [Total: 13]

Mark scheme: 1(a)(i) blue recorded for 0.0; full set of results; yellow / green recorded for 0.5; red recorded for 2.0; colour recorded for U; 5 1(a)(ii) correct estimate and explanation from Table 1.1; 1 1(b) Benedict’s ; 1 1(c) 1 from: tongs / glove AND protect hands / skin AND from burns / hot water ; goggles AND protect eyes AND from corrosive / liquids / Benedict’s / solution / chemical / substance / hot water ; water bath AND protect from fire / burns AND flammable ; 1 1(d)(i) prevent contamination AW; 1 1(d)(ii) use colour chart / more intermediate glucose concentrations / examples ; 1 1(e)(i) ethanol / alcohol and water ; 1 1(e)(ii) White emulsion ; 1 1(f) ethanol / alcohol and flammable; 1 Question Answer Marks

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2 A teacher says that the shoots of germinated seeds grow more quickly in a warmer environment. Plan an investigation to test if the teacher’s statement is correct. You are provided with germinated seeds. You may also use any other common laboratory apparatus. In your answer, you should include: • the apparatus needed, including a labelled diagram if you wish • a brief description of the method including the measurements you will make • the variables you will control • how you will process your results to draw a conclusion. You are not required to do this experiment. .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... [Total: 7]

Mark scheme: 2(a) 1 mark from each section and any 2 others If one section is missed max 6 etc. apparatus ruler; temperature changing apparatus ; method of illumination; soil / cotton substrate; method seedling in pots; at least two temperatures measured / hot and cold ; water them (not just water at the strat); measurement (and accuracy) measure height / length / size of shoot; after at least 5 days ; repeats / lots of seedlings; 4 or more different temperatures ; control variables same amount of water / specified amount ; same amount of light; same amount of nutrients / soil ; same amount of carbon dioxide; same species of plant; Process results and draw a conclusion calculate a mean / average ; plot graph of temperature against height ; see if higher / lower temperature increases / decreases the heights ; 7 Question Answer Marks

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3 You are provided with solid J which is a mixture of two compounds. Solid J contains one anion and two cations. One compound is soluble and the other is insoluble in water. You are going to do a series of experiments to identify the ions in J. (a) Place a spatula load of J into a test-tube. Add 3 cm depth of dilute hydrochloric acid to the test-tube. (i) Record your observations. ..................................................................................................................................... [1] (ii) Identify the gas that is produced. State the test used to identify the gas and give the positive result for this test. test used ............................................................................................................................ positive result .................................................................................................................... identity of gas .................................................................................................................... [1] (iii) Identify the anion shown to be present in J. ..................................................................................................................................... [1] (b) Place a spatula load of J into a boiling tube. Add about 2 cm depth of aqueous sodium hydroxide into the boiling tube. Carefully warm the mixture. (i) Identify the gas that is produced. State the test used to identify the gas and give the positive result for this test. test used ............................................................................................................................ positive result .................................................................................................................... identity of gas .................................................................................................................... [1] (ii) Identify a cation shown to be present in J. ..................................................................................................................................... [1] (iii) State and explain one safety precaution you took during this experiment. safety precaution ............................................................................................................... explanation ........................................................................................................................ ........................................................................................................................................... [1] (c) Procedure • Place two spatula loads of J into a 100 cm3 glass beaker. • Add about 20 cm3 of distilled water to J and stir for about one minute. • Filter the mixture and keep the residue in the filter paper. • Wash the residue with a dropping pipette full of distilled water. • Place a small sample of the residue into a test-tube. • Add about 3 cm depth of dilute hydrochloric acid into this test-tube. • Stir the mixture to make a solution. Ignore any formation of a gas. • Split this solution between two test-tubes. (i) Do the tests shown and record your observations in Table 3.1. Table 3.1 test observations to the first test-tube, add aqueous sodium hydroxide drop by drop … … until it is in excess. to the second test-tube, add aqueous ammonia drop by drop … … until it is in excess. [3] (ii) Suggest why it is important to wash the residue with distilled water. ........................................................................................................................................... ..................................................................................................................................... [1] (iii) Use your results from (c)(i) to identify the other cation shown to be present in J. ..................................................................................................................................... [1] [Total: 11]

Mark scheme: 3(a)(i) fizzes / colourless solution ; 1 3(a)(ii) carbon dioxide AND (bubble through) limewater goes milky ; 1 3(a)(iii) carbonate (ions) / CO32– ; 1 3(b)(i) ammonia AND turns (moist) red litmus paper blue ; 1 3(b)(ii) ammonium (ions) / NH4+ ; 1 3(b)(iii) wear goggles AND sodium hydroxide is corrosive ; OR point test-tube away from people ; AND if liquid spits out it will not become in contact with someone ; OR hold test-tube in a holder AND so you do not burn yourself holding with your hand ; 1 3(c)(i) white precipitate ; soluble / dissolves / colourless solution or … white precipitate ; … soluble / dissolves / colourless solution ; 3 3(c)(ii) to remove any soluble material ; 1 3(c)(iii) zinc ions / Zn2+ ; 1 Question Answer Marks 4

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4 You are going to investigate the effect of increasing the length of magnesium ribbon on the temperature rise in the reaction between magnesium and dilute hydrochloric acid. (a) Procedure • Cut a 10 mm length of magnesium ribbon. • Measure 25 cm3 of dilute hydrochloric acid using a measuring cylinder. • Pour the acid into a 100 cm3 glass beaker. • Measure and record in Table 4.1 the temperature of the dilute hydrochloric acid to the nearest 0.5 °C. • Add the magnesium ribbon into the beaker and keep the magnesium ribbon under the surface of the acid using the thermometer. • Record in Table 4.1 the highest temperature of the reaction mixture to the nearest 0.5 °C. • Rinse the beaker with water. Repeat the procedure using fresh dilute hydrochloric acid and the different lengths of magnesium ribbon shown in Table 4.1. Table 4.1 length of temperature of highest temperature of temperature rise of magnesium ribbon acid at start the reaction mixture the reaction / mm / °C / °C / °C 10 20 30 40 50 [4] (b) Calculate the temperature rise for each experiment. Record your answers in Table 4.1. [1] (c) State the relationship between the length of magnesium ribbon and the temperature rise of the reaction. ................................................................................................................................................... ............................................................................................................................................. [1] (d) State one variable that must be controlled in this investigation. ............................................................................................................................................. [1] (e) A teacher says that the highest temperature measured in each experiment is lower than expected. (i) Suggest one reason why the highest temperature measured is lower than expected. ........................................................................................................................................... ..................................................................................................................................... [1] (ii) Suggest one improvement to the investigation which will make the highest temperature measured closer to the expected value. ........................................................................................................................................... ..................................................................................................................................... [1] [Total: 9]

Mark scheme: 4(a) temperature and lowest temperature for 10 mm of magnesium ; all ten temperatures recorded ; all temperatures quoted to nearest 0.5 °C ; the temperature rise increases as the length of ribbon increases ; 4(b) all temperature rises correctly calculated ; 1 4(c) as length increases the temperature rise increases ; 1 4(d) Any one from: concentration of acid ; volume of acid ; thickness of magnesium ribbon ; 1 4(e)(i) loss of energy (to surroundings) ; 1 4(e)(ii) insulate beaker / use a plastic beaker or cup / use a lid ; 1 Question Answer Marks l0 recorded to the nearest 0.1 cm ;

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5 You are going to use two different methods to measure the spring constant k of a spring. The spring constant k of a spring is a measure of the stiffness of the spring. (a) Method 1 Measure the unstretched length l0 of the spring to the nearest 0.1 cm. Do not include the loops at the end of the spring in your measurement. l0 = ................................................... cm [1] (b) • Attach the spring to the clamp as shown in Fig. 5.1. clamp spring mass Fig. 5.1 • Suspend a 200 g mass on the spring. Measure the new length l1 of the spring. l1 = ......................................................... cm Calculate the extension e of the spring produced by the mass. Use the equation shown. e = l1 – l0 e = ......................................................... cm [1] (c) Calculate the spring constant k of the spring. Use the equation shown. 2 k = e k = ............................................... N / cm [1] (d) Method 2 When the 200 g mass is pulled down a small distance and released, it oscillates up and down. The period T of the oscillations is the time taken for one oscillation. One complete oscillation of the mass is shown in Fig. 5.2. highest position of mass rest position of mass lowest position of mass One complete oscillation is from the lowest position to the highest position and back to the lowest position. Fig. 5.2 • Pull the 200 g mass down a small distance and release it. (i) Measure the time t taken for 20 oscillations. Record this time in Table 5.1. [1] (ii) Repeat (d)(i) for a mass of 300 g. Record the time t in Table 5.1. [1] Table 5.1 time t for 20 2 mass m period T T oscillations / g / s / s2 / s 200 300 (e) (i) Calculate the period T, the time for one oscillation, for each of the masses. Record these values in Table 5.1. [1] (ii) Calculate the values of T 2. Record your answers in Table 5.1. [1] (f) Use your results for the 200 g mass in Table 5.1 to calculate the spring constant k of the spring. Use the equation shown. 0.08 k = T 2 k = ............................................... N / cm [1] (g) Compare your values of k from (c) and (f). State whether they agree within the limits of experimental error. Explain your answer. ................................................................................................................................................... ............................................................................................................................................. [1] (h) It is important to avoid line-of-sight (parallax) errors when measuring the length of the spring in Method 1. Describe how you avoided this error. ................................................................................................................................................... ............................................................................................................................................. [1] [Total: 10]

Mark scheme: 5(a) 1 5(b) l1 recorded and > l0 and e correctly calculated ; 1 5(c) correct calculation of k ; 1 5(d)(i) t recorded in Table 5.1 ; 1 5(d)(ii) t recorded in Table 5.1 and > value in (i) ; 1 5(e)(i) both values of T correct ; 1 5(e)(ii) both values of T2 correct ; 1 5(f) k = 0.25 ± 0.05 (N / cm) ; 1 5(g) (expect YES) values are (very) close / not (very) far apart / within 10% of each other / the same ; 1 5(h) view perpendicularly to scale / rule close to spring / use a fiducial aid ; 1 Question Answer Marks

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6 You are going to investigate the cooling of hot water in a beaker. A thermometer has been set up in a clamp for you as shown in Fig. 6.1. clamp thermometer stand beaker of hot water Fig. 6.1 • Pour approximately 200 cm3 of hot water into the beaker. • Lower the thermometer into the hot water. • When the reading on the thermometer stops rising, measure the temperature θ of the hot water. This is time t = 0. (a) Record in Table 6.1 the value of the temperature θ to the nearest 0.5 °C at time t = 0 and start the stop-watch. [1] Table 6.1 time t temperature θ / s / °C 0 300 (b) Record in Table 6.1 the temperature θ of the water and the time t every 60 s for 300 s. [2] (c) (i) On the grid provided, plot a graph of temperature θ (vertical axis) against time t. The vertical axis starts at θ = 50 °C. [3] 50 0 (ii) Draw the best-fit curve. [1] (d) Calculate the average rate of cooling of the hot water during the whole investigation. Use the equation shown. total temperature decrease average rate of cooling = time taken average rate of cooling = ................................................ °C / s [1] (e) (i) State one safety precaution taken during the investigation. Explain your answer. safety precaution ............................................................................................................... explanation ........................................................................................................................ ..................................................................................................................................... [1] (ii) Suggest one change that you can make to your investigation to reduce the rate of cooling of the hot water. ........................................................................................................................................... ..................................................................................................................................... [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) temperature recorded at t = 0 to nearest 0.5 °C ; 1 6(b) all temperatures recorded and all times correct ; temperatures decreasing ; 2 6(c)(i) axes labelled with units ; suitable scale (⩾ half the grid used) ; minimum of 4 plots correct ± ½ small square ; 3 6(c)(ii) best-fit curve drawn within ½ square of points ; 1 6(d) answer correct from candidates’ results ; 1 6(e)(i) gloves AND protect hand AND from burns / hot water OR goggles AND to protect eyes AND from hot water / burns OR pour slowly / no splashes when pouring AND protect hands / skin AND from burns / hot water OR tongs AND protect hand AND from burns / hot water 1 6(e)(ii) use a lid (between readings) / thicker beaker / insulate the beaker / use a plastic beaker ; 1

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