Cambridge IGCSE Chemistry (9-1) 0971 — 2023 May/June Paper 6 · Variant 2

1 Hot powdered lead(II) oxide is reduced by methane, a flammable gas. The products are lead, steam and carbon dioxide gas. Fig. 1.1 shows the apparatus used to reduce lead(II) oxide using excess methane. powdered lead(II) oxide methane waste gases A B ice Fig. 1.1 (a) Name the item of apparatus labelled A. .............................................................................................................................................. [1] (b) Draw an arrow on Fig. 1.1 to show where the apparatus should be heated. [1] (c) Explain why powdered lead(II) oxide is used and not a large lump of lead(II) oxide. .................................................................................................................................................... .............................................................................................................................................. [1] (d) Explain what happens at the point labelled B, on Fig. 1.1. .................................................................................................................................................... .................................................................................................................................................... .............................................................................................................................................. [2] (e) The waste gases contain methane. State why the waste gases should not be released into the laboratory. .................................................................................................................................................... .............................................................................................................................................. [1] [Total: 6]

Mark scheme: 1(a) beaker 1 1(b) arrow pointing upwards towards lead oxide 1 1(c) (the powder has) larger surface area / reacts faster / rate increases 1 1(d) M1 (ice) cools (steam / vapour / gas) 1 M2 (steam / vapour / gas) condenses / water (collects / forms) 1 1(e) (methane is) flammable 1

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2 A student investigates how the rate of the reaction between aqueous iron(III) nitrate and aqueous sodium thiosulfate changes with temperature. The student does five experiments using the apparatus shown in Fig. 2.1. eye 5 cm3 of aqueous sodium thiosulfate 100 cm3 beaker 50 cm3 of aqueous iron(III) nitrate printed sheet printed text Fig. 2.1 (a) Experiment 1 ● Use a 50 cm3 measuring cylinder to pour 50 cm3 of aqueous iron(III) nitrate into a 100 cm3 beaker. ● Stand the beaker on a printed sheet as shown in Fig. 2.1. ● Use a 10 cm3 measuring cylinder to pour 5 cm3 of aqueous sodium thiosulfate into the beaker and at the same time start a stop-clock. ● Use a thermometer to stir the contents of the beaker. ● Look down from above the beaker and when the text on the printed sheet becomes visible, stop the stop-clock. ● Use the thermometer to measure the temperature of the solution when the text becomes visible. ● Rinse the beaker and thermometer with water. Experiment 2 ● Use the 50 cm3 measuring cylinder to pour 50 cm3 of aqueous iron(III) nitrate into the 100 cm3 beaker. ● Heat the beaker on a gauze over a Bunsen burner until the temperature of the iron(III) nitrate has increased by about 5 °C. ● Stand the beaker on the printed sheet as shown in Fig. 2.1. ● Use the 10 cm3 measuring cylinder to pour 5 cm3 of aqueous sodium thiosulfate into the beaker and at the same time start a stop-clock. ● Use the thermometer to stir the contents of the beaker. ● Look down from above the beaker and when the text on the printed sheet becomes visible, stop the stop-clock. ● Use the thermometer to measure the temperature of the solution when the text becomes visible. ● Rinse the beaker and thermometer with water. Experiment 3 ● Repeat Experiment 2, this time heating the aqueous iron(III) nitrate until the temperature has increased by about 10 °C. Experiment 4 ● Repeat Experiment 2, this time heating the aqueous iron(III) nitrate until the temperature has increased by about 15 °C. Experiment 5 ● Repeat Experiment 2, this time heating the aqueous iron(III) nitrate until the temperature has increased by about 25 °C. Use the thermometer diagrams and stop-clock diagrams to complete Table 2.1. Table 2.1 time taken for temperature of the the text to thermometer solution when theexperiment stop-clock diagram become visible diagram text becomes / s visible / C 0 seconds 0 30 1 45 15 5 15 25 10 minutes 20 30 0 0 30 2 45 15 5 15 25 10 20 30 0 0 30 3 45 15 5 15 25 10 20 30 0 0 40 4 45 15 5 15 35 10 30 30 0 0 50 5 45 15 5 15 45 10 40 30 [4] (b) Write a suitable scale on the y-axis and plot your results from Experiments 1 to 5 on Fig. 2.2. Draw a smooth curve of best fit. time taken for the text to become visible / s 10 20 30 40 50 60 temperature of the solution when the text becomes visible / C Fig. 2.2 [4] (c) Deduce the experiment in which the rate of reaction is fastest. .............................................................................................................................................. [1] (d) Use your graph to predict the temperature of the solution when the text becomes visible after 55 seconds. Show your working on Fig. 2.2. temperature = .............................. °C [2] (e) Explain why wrapping the beaker in cotton wool after it has been heated will improve the accuracy of the results obtained. .................................................................................................................................................... .............................................................................................................................................. [2] (f) (i) Explain why it would be an improvement to measure the volume of aqueous iron(III) nitrate in a burette rather than a measuring cylinder. ............................................................................................................................................. ....................................................................................................................................... [1] (ii) Suggest why it would not be an improvement to add the aqueous sodium thiosulfate using a pipette. ............................................................................................................................................. ....................................................................................................................................... [1] (g) Suggest why the aqueous sodium thiosulfate must be added after the aqueous iron(III) nitrate has been heated and not before it is heated. .................................................................................................................................................... .............................................................................................................................................. [1] (h) Describe how the results of the experiment would change when the experiment is repeated using a 250 cm3 beaker in place of the 100 cm3 beaker. Explain your answer. change in results ........................................................................................................................ explanation ................................................................................................................................. .................................................................................................................................................... [2] [Total: 18]

Mark scheme: 2(a) M1 all five times correct (116, 80, 69, 46, 21) 1 M2 all times shown in seconds only 1 M3 all temperatures correct (20.5, 27.0, 30.0, 37.0, 46.5) 1 M4 all temperatures shown to 1 dp 1 Question Answer Marks 2(b) M1 y-axis scale in linear and points extend over halfway up scale 1 M2 and M3 all points plotted correctly 2 M4 best fit line 1 2(c) experiment 5 1 2(d) M1 working shown on graph at 55 s 1 M2 correct value for temperature from their graph 1 2(e) M1 insulation / reduces heat loss 1 M2 temperature remains (more) constant / changes less / does not change / is maintained 1 2(f)(i) (burette) (more) accurate (than a measuring cylinder) 1 2(f)(ii) reaction starts while still adding the sodium thiosulfate / slow (to add) 1 2(g) otherwise it will react while it is being heated / temperature increases while it is reacting / reaction starts at a lower temperature 1 2(h) M1 times shorter / decrease 1 M2 less depth to look through 1

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3 A student tests two substances: solution F and solid G. Tests on solution F Table 3.1 shows the tests and the student’s observations for solution F. The student divides solution F into three portions. Table 3.1 tests observations test 1 Do a flame test on the first portion of solution F. light green colour test 2 To the second portion of solution F, add a effervescence was seen; 1 cm depth of aqueous sodium hydroxide and the gas turned damp red litmus paper blue a piece of aluminium foil. Warm the mixture gently and test any gas produced. test 3 To the third portion of solution F, add a 1 cm no change depth of dilute nitric acid followed by a few drops of aqueous silver nitrate. (a) Describe how to do the flame test used in test 1. .................................................................................................................................................... .................................................................................................................................................... .............................................................................................................................................. [2] (b) Identify the gas given off in test 2. .............................................................................................................................................. [1] (c) Identify solution F. .................................................................................................................................................... .............................................................................................................................................. [2] (d) State what would be observed if the student adds dilute sulfuric acid to another portion of solution F. observations ............................................................................................................................... .............................................................................................................................................. [1] Tests on solid G Solid G is iron(II) carbonate. (e) About 10 cm3 of dilute sulfuric acid is added to solid G. Any gas given off is tested. observations ............................................................................................................................... .................................................................................................................................................... .............................................................................................................................................. [2] (f) To the product from (e), aqueous sodium hydroxide is added dropwise until in excess. observations adding dropwise .................................................................................................... observations in excess ............................................................................................................... [2] [Total: 10]

Mark scheme: 3(a) M1 use of a wire / splint to get substance into a flame 1 M2 putting sample INTO flame and identifying (Bunsen) flame as roaring / blue / non-luminous / hot 1 3(b) ammonia / NH3 1 Question Answer Marks 3(c) M1 barium / Ba2+ 1 M2 nitrate / NO3– 1 3(d) white precipitate 1 3(e) M1 fizzing / bubbles / effervescence 1 M2 limewater becomes milky 1 3(f) M1 green precipitate 1 M2 remains in excess / does not dissolve / green precipitate 1

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4 A metal polish is a mixture of four substances. The properties of these substances are shown in Table 4.1. Table 4.1 name of substance solubility in water reaction with dilute nitric acid propanol soluble dissolves ethanoic acid soluble dissolves iron(III) oxide insoluble reacts when warmed to form a soluble salt silicon(IV) oxide insoluble no reaction Plan an experiment to find the percentage by mass of silicon(IV) oxide in the mixture. Your plan should include how you will calculate the percentage of silicon(IV) oxide in the mixture. You are provided with a sample of the metal polish, dilute nitric acid and common laboratory apparatus. ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ..................................................................................................................................................... [6] Notes for use in qualitative analysis Tests for anions anion test test result carbonate, CO32– add dilute acid, then test for carbon effervescence, carbon dioxide dioxide gas 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 iodide, I– acidify with dilute nitric acid, then yellow ppt. [in solution] add aqueous silver nitrate nitrate, NO3– add aqueous sodium hydroxide, ammonia produced [in solution] then aluminium foil; warm carefully sulfate, SO42– acidify with dilute nitric acid, then white ppt. [in solution] add aqueous barium nitrate sulfite, SO32– add a small volume of acidified the acidified aqueous potassium aqueous potassium manganate(VII) manganate(VII) changes colour from purple to colourless Tests for aqueous cations cation effect of aqueous sodium hydroxide effect of aqueous ammonia aluminium, Al 3+ white ppt., soluble in excess, giving white ppt., insoluble in excess a colourless solution ammonium, NH4+ ammonia produced on warming – calcium, Ca2+ white ppt., insoluble in excess no ppt. or very slight white ppt. chromium(III), Cr3+ green ppt., soluble in excess green ppt., insoluble in excess copper(II), 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, ppt. turns brown near surface on ppt. turns brown near surface on standing standing iron(III), Fe3+ red-brown ppt., insoluble in excess red-brown ppt., insoluble in excess zinc, Zn2+ white ppt., soluble in excess, giving white ppt., soluble in excess, giving a colourless solution a colourless solution

Mark scheme: 4 any 6 from: MP1 stated / known mass of polish / weigh polish MP2 add nitric acid MP3 nitric acid and polish / solid combined in a suitable container MP4 warm / heat (polish and acid / water) MP5 filter (wash) and dry residue / solid MP6 find the mass of the silicon(IV) oxide MP7 percentage = (mass of SiO2 / mass of polish)  100 max 6

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