Cambridge IGCSE Science - Combined 0653 — 2019 May/June Paper 5 · Variant 2

1 You are going to investigate the amount of precipitate formed in two different reactions. (a) Barium nitrate solution and sodium sulfate solution are both colourless. They react together to form a white precipitate. Method A. Label six test‑tubes 3, 4, 5, 6, 7 and 8. Numbers 1 and 2 have been omitted deliberately. B. Using a measuring cylinder pour 3 cm3 barium nitrate solution into each test‑tube. C. Using a clean measuring cylinder add 3 cm3 sodium sulfate solution into test‑tube 3. Stir the solution with the glass rod. Rinse the glass rod with distilled water. D. Add 4 cm3 sodium sulfate solution into test‑tube 4. Stir the solution with the glass rod. Rinse the glass rod with distilled water. E. Add 5 cm3, 6 cm3, 7 cm3 and 8 cm3 sodium sulfate solution into test‑tubes 5, 6, 7 and 8 as shown in Table 1.1. Use the glass rod to stir each solution and rinse the glass rod each time with distilled water. F. Leave the test‑tubes to stand for at least six minutes to allow the precipitates to settle. While you are waiting for the precipitates to settle you should start (c). G. After six minutes, use a ruler to measure the height in mm of the solid precipitate in each test‑tube. Start at test‑tube 8. Record these heights to the nearest millimetre in Table 1.1. Table 1.1 volume of sodium height of precipitate test‑tube number sulfate solution added / mm / cm3 3 3 4 4 5 5 6 6 7 7 8 8 [2] (b) Look at the results in your experiment in Table 1.1. (i) Describe the relationship between height of precipitate and volume of sodium sulfate solution added. ..................................................................................................................................... [1] (ii) The volume of sodium sulfate solution added to the barium nitrate solution continues to be increased. Predict what happens to the height of the precipitate formed. Explain your answer. prediction ........................................................................................................................... ........................................................................................................................................... explanation ........................................................................................................................ ........................................................................................................................................... [2] (iii) State two improvements that could be made to your experiment to make the results more accurate. For each improvement explain how it increases the accuracy. 1. improvement ................................................................................................................. explanation .................................................................................................................... ....................................................................................................................................... 2. improvement ................................................................................................................. explanation .................................................................................................................... ....................................................................................................................................... [2] (c) A student performs a similar experiment to that in (a) using a fixed volume of copper sulfate solution in the test‑tube and adds ammonia solution. A blue precipitate is formed. Her results are shown in Table 1.2. Table 1.2 volume of ammonia height of precipitate test‑tube number solution added / cm3 / mm 1 1 1.1 2 2 2.6 3 3 3.5 4 4 4.6 5 5 3.7 6 6 1.9 7 7 0.1 8 8 0.0 (i) On the grid of Fig. 1.1, plot a graph of the student’s results in Table 1.2. Plot the height of precipitate (vertical axis) against volume of ammonia solution added. [3] Fig. 1.1 (ii) On Fig. 1.1, draw the best‑fit straight line for test‑tubes 1, 2, 3 and 4. On Fig. 1.1, draw a second line of best fit for test‑tubes 5, 6, 7, and 8. [1] (iii) State the volume of ammonia which needs to be added to form the maximum height of precipitate. This is the point where the two lines of best fit intersect. volume = .................................................. cm3 [1] (iv) Describe and explain what is happening in the test‑tubes numbered 5, 6, 7 and 8 in the student’s experiment. ........................................................................................................................................... ..................................................................................................................................... [1] [Total: 13]

Mark scheme: 1(a) all heights recorded ; heights clearly in mm ; 2 1(b)(i) as volume increases height of ppt increases ; 1 1(b)(ii) increases and then stays the same ; reagent(s) all used up / barium nitrate all used up / more sodium sulfate than barium nitrate idea / reaction finished ; 2 1(b)(iii) any 2 from: volumes with syringe / burette and more precise than measuring cylinder ; do experiment in a measuring cylinder to measure volume of precipitate ; ruler without dead space and difficult to get actual length due to the dead space so had to pick up tube and not level etc. ; measure at eye level to avoid parallax error ; leave to settle longer to make sure all ppt had settled ; repeat and reduces errors / spots anomalies ; 2 1(c)(i) axes labelled with units with height on vertical axis and volume of ammonia on horizontal ; reasonable linear scale more than half grid ; at least 5 points plotted correctly to within half a small square ; 3 1(c)(ii) 2 best-fit straight lines ; 1 1(c)(iii) value from graph ± ½ small square ; 1 1(c)(iv) ppt dissolves ; 1

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2 You are going to investigate the effects of the enzyme pectinase on fruit. (a) Pectinase is an enzyme that breaks down plant cell walls, and juice is released. You are provided with two beakers that have been left overnight. • Beaker A contains chopped apple with 5% pectinase solution. • Beaker B contains chopped apple with water. (i) Explain the purpose of using water instead of pectinase in beaker B. ........................................................................................................................................... ..................................................................................................................................... [1] (ii) State two variables that should have been controlled when beaker A and beaker B were left overnight. variable 1 ........................................................................................................................... variable 2 ........................................................................................................................... [2] (b) You are going to separate the juice from the chopped apple in beaker A and measure the volume of the juice collected after 5 minutes. • Separate the chopped apple from the juice in beaker A. • At the same time repeat for beaker B, using separate apparatus. • Leave for 5 minutes. (i) Draw and label the assembled apparatus you used to separate the chopped apple from the juice. [3] (ii) After 5 minutes record the volume of apple juice you have collected from beaker A and beaker B. volume of juice from beaker A = ........................................................ cm3 volume of juice from beaker B = ........................................................ cm3 [1] [Total: 7]

Mark scheme: 2(a)(i) as a control / to compare with enzyme ; 1 2(a)(ii) any 2 from: temperature ; mass / amount of apple ; pH ; volume added ; type of apple ; 2 2(b)(i) funnel and filter paper, shown with ‘V’ at bottom ; use of measuring cylinder ; at least two labels (funnel, filter paper, measuring cylinder) ; 3 2(b)(ii) volume of A greater than B ; 1

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3 A plant loses water from its leaves through transpiration. A student states: A plant in humid air will lose less water than a plant in dry air. Plan an investigation to test whether this statement is correct. You are not required to carry out this investigation. In your answer, include: • the apparatus needed, including a labelled diagram if you wish • a brief description of the method, including how you will treat variables and any safety precautions • the measurements you will make • how you will process your results • how you will use your results to draw a conclusion. .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .................................................................................................................................................... [7]

Mark scheme: 3 1 apparatus potometer / balance / shoot in water ; stop-clock ; suitable container / bell jar / bag / box (to contain moist air) ; 2 method plant in different levels of moisture ; same amount of time ; repeat experiment at each level of moisture ; safety linked to apparatus / hygiene / procedure ; 3 control of variables control size / type of plant / number / surface area / size of leaves ; control wind / temperature / (sun)light ; control amount of water given to plant ; 4 measurements, processing and use of results (dependent variable is) movement of water/bubble/meniscus in potometer / weight loss of leaves / weigh plant or leaves before and after ; measure humidity ; calculate rate of water loss / transpiration / mass lost per unit time ; graph of mass lost against humidity ; compare e.g. mass / water lost in dry and humid / compare mass at different humidities ; 7

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4 You are going to investigate ice melting in a beaker of water. (a) (i) Measure and record the mass ma of the empty measuring cylinder to the nearest 0.01 g. ma = ............................................................ g • Add 100 cm3 of water to the measuring cylinder. • Measure and record the mass mb of the measuring cylinder and water to the nearest 0.01 g. mb = ............................................................ g [1] (ii) Calculate the mass mw of the 100 cm3 of water. Use your answers to (a)(i) and the equation shown: mw = mb – ma mw = ...................................................... g [1] (iii) Measure and record the temperature Ti of the water to the nearest 0.5 °C. Ti = .................................................... °C [1] (b) (i) Take one ice cube and measure and record its mass mi to the nearest 0.01 g. mi = ...................................................... g [1] (ii) • Pour the water from the measuring cylinder into a beaker. • Add the ice cube to the beaker of water. • Immediately start the stop‑clock. • After 3 minutes, stir the water with the glass rod. • Measure and record the temperature Tf of the water. Tf = .................................................... °C [1] (iii) • Immediately remove the ice cube from the beaker. • Dry the ice cube with the paper towel provided. • Measure and record the mass mf of the ice cube. mf = ...................................................... g [1] (iv) Explain how stirring the water improves the accuracy of the temperature measurement. ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [1] (c) (i) Calculate the drop in temperature Td of the water during the experiment. Use your answers to (a)(iii) and (b)(ii) and the equation shown: Td = Ti – Tf Td = .................................................... °C [1] (ii) Calculate the thermal energy El lost by the water. Use your answers to (a)(ii) and (c)(i) and the equation shown. Give your answer to a suitable number of significant figures. El = mw × 4.2 × Td El = ...................................................... J [2] (d) (i) Calculate the mass mm of ice that melted in the experiment. Use your answers to (b)(i) and (b)(iii) and the equation shown: mm = mi – mf mm = ...................................................... g [1] (ii) 334 J of thermal energy is needed to melt 1 g of ice and change it into water. Calculate the energy Em used to melt the ice in this experiment. Use your answer to (d)(i) and the equation shown: Em = mm × 334 Em = ...................................................... J [1] (e) In this experiment the amount of thermal energy needed to melt the ice cube is greater than the thermal energy lost by the water. Suggest where the extra energy used to melt the ice comes from. ................................................................................................................................................... ............................................................................................................................................. [1] [Total: 13] 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 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 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: 4(a)(i) ma and mb recorded to 0.01 g and mb roughly 100 g more than ma ; 1 4(a)(ii) correct calculation of mw ; 1 4(a)(iii) suitable value recorded to nearest 0.5 °C ; 1 4(b)(i) mass recorded to 0.01 g ; 1 4(b)(ii) Tf < Ti ; 1 4(b)(iii) mf < mi ; 1 4(b)(iv) ensures all water at same temperature OWTTE ; 1 4(c)(i) correct calculation of Td ; 1 4(c)(ii) correct calculation of El ; correctly rounded to 2 or 3 sig figs ; 2 4(d)(i) correct calculation of mm ; 1 4(d)(ii) correct calculation of Em ; 1 4(e) energy has come from the glass / surroundings ; 1

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