Cambridge IGCSE Chemistry (9-1) 0971 — 2024 May/June Paper 6 · Variant 2

1 When a mixture of calcium hydroxide and ammonium chloride is heated, ammonia gas is made. calcium hydroxide + ammonium chloride → calcium chloride + water + ammonia Ammonia gas is soluble in water and toxic. Ammonia gas reacts with hot copper(II) oxide to make nitrogen. ammonia + copper(II) oxide → copper + water + nitrogen A student makes nitrogen using the apparatus shown in Fig. 1.1. calcium hydroxide and ammonium chloride X A nitrogen copper(II) oxide B water Fig. 1.1 (a) Name the items of apparatus labelled A and B in Fig. 1.1. A ................................................................................................................................................. B ................................................................................................................................................. [2] (b) The apparatus needs to be heated in two places. On Fig. 1.1, draw arrows in two places to show where the apparatus should be heated during the experiment. [2] (c) During the reaction, a colourless liquid collects at the point marked X in Fig. 1.1. Suggest the identity of the colourless liquid. .............................................................................................................................................. [1] (d) Some of the ammonia gas passes over the copper(II) oxide without reacting. Suggest why none of this ammonia gas is collected in the item of apparatus labelled B in Fig. 1.1. .................................................................................................................................................... .............................................................................................................................................. [1] (e) The student does not collect the first few bubbles of gas. Suggest why the first few bubbles of gas are not collected. .................................................................................................................................................... .............................................................................................................................................. [1] (f) Explain why this experiment should be carried out in a fume cupboard. .................................................................................................................................................... .............................................................................................................................................. [1] [Total: 8]

Mark scheme: 1(a) A boiling tube / test-tube 1 B measuring cylinder 1 1(b) one arrow in each region shown 2 1(c) water / H2O 1 1(d) ammonia dissolves in the water 1 1(e) it is air 1 1(f) ammonia is toxic / poisonous 1

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2 A student investigates the reaction between aqueous aluminium chloride and two aqueous solutions of sodium hydroxide, solution F and solution G. Solution F and solution G have different concentrations. The student does three experiments. Experiment 1 ● Rinse a burette with distilled water and then with aqueous aluminium chloride. ● Rinse a conical flask with distilled water. ● Fill the burette with aqueous aluminium chloride. Run some of the aqueous aluminium chloride out of the burette so that the level of the aqueous aluminium chloride is on the burette scale. ● Record the initial burette reading. ● Use a measuring cylinder to pour 25 cm3 of solution F into the conical flask. ● Stand the conical flask on a black or dark-coloured sheet of paper. ● Slowly add aqueous aluminium chloride from the burette to the conical flask, while swirling the flask, until the mixture in the conical flask just starts to become cloudy. ● Record the final burette reading. Experiment 2 ● Refill the burette with aqueous aluminium chloride. Run some of the aqueous aluminium chloride out of the burette so that the level of the aqueous aluminium chloride is on the burette scale. ● Record the initial burette reading. ● Rinse the conical flask with distilled water. ● Rinse the measuring cylinder with distilled water and then with solution G. ● Use the measuring cylinder to pour 25 cm3 of solution G into the conical flask. ● Stand the conical flask on a black or dark-coloured sheet of paper. ● Slowly add aqueous aluminium chloride from the burette to the conical flask, while swirling the flask, until the mixture in the conical flask just starts to become cloudy. ● Record the final burette reading. Experiment 3 ● Refill the burette with aqueous aluminium chloride. Run some of the aqueous aluminium chloride out of the burette so that the level of the aqueous aluminium chloride is on the burette scale. ● Record the initial burette reading. ● Rinse the conical flask with distilled water. ● Use the measuring cylinder to pour 25 cm3 of solution G into the conical flask. ● Add 5 drops of thymolphthalein indicator to the conical flask. ● Stand the conical flask on a white tile. ● Slowly add aqueous aluminium chloride from the burette to the conical flask, while swirling the flask, until the thymolphthalein indicator changes colour. ● Record the final burette reading. (a) Use the burette diagrams in Fig. 2.1, Fig. 2.2 and Fig. 2.3 to record the readings for Experiments 1, 2 and 3 in Table 2.1 and complete Table 2.1. Experiment 1 0 14 1 15 2 16 initial reading final reading Fig. 2.1 Experiment 2 2 28 3 29 4 30 initial reading final reading Fig. 2.2 Experiment 3 0 27 1 28 2 29 initial reading final reading Fig. 2.3 Table 2.1 Experiment 1 Experiment 2 Experiment 3 final burette reading / cm3 initial burette reading / cm3 volume of aqueous aluminium chloride added / cm3 [4] (b) In Experiment 3, the aqueous sodium hydroxide in the conical flask is alkaline. At the end‑point, the mixture in the flask is no longer alkaline. State the colour change seen at the end-point in Experiment 3. from ................................................................ to ................................................................. [1] (c) State why the conical flask is swirled as solution F is added in Experiment 1. .................................................................................................................................................... .............................................................................................................................................. [1] (d) Suggest why the conical flask is placed on black or dark-coloured paper in Experiments 1 and 2. .................................................................................................................................................... .............................................................................................................................................. [1] (e) (i) Explain why the measuring cylinder is rinsed between Experiment 1 and Experiment 2. ....................................................................................................................................... [1] (ii) Explain why the measuring cylinder does not need rinsing between Experiment 2 and Experiment 3. ....................................................................................................................................... [1] (f) Compare the concentration of solution F used in Experiment 1 with the concentration of solution G used in Experiment 2. Explain your answer. .................................................................................................................................................... .................................................................................................................................................... .............................................................................................................................................. [3] (g) Calculate the volume of aqueous aluminium chloride required when Experiment 1 is carried out with 10 cm3 of aqueous sodium hydroxide instead of 25 cm3. .............................................................................................................................................. [2] (h) In all three experiments it is more accurate to measure the volume of the aqueous sodium hydroxide using a volumetric pipette instead of a measuring cylinder. Explain why it is not possible to use a volumetric pipette to measure the volume of aqueous aluminium chloride in these experiments. .................................................................................................................................................... .............................................................................................................................................. [1] [Total: 15]

Mark scheme: 2(a) M1 all three final readings recorded correctly (14.7, 29.5, 28.0) 1 M2 all three initial readings recorded correctly (1.3, 2.7, 0.4) 1 M3 all three titres correct (13.4, 26.8, 27.6) 1 M4 all volumes recorded to 1 d.p. or better 1 2(b) (from) blue (to) colourless 1 2(c) to mix (reactants) 1 Question Answer Marks 2(d) (white) precipitate / cloudiness easier to see 1 2(e)(i) to clean / to remove solution F 1 2(e)(ii) same solution (of NaOH) used / used for solution G in both 1 2(f) M1 solution G is more concentrated 1 M2 as larger volume (of AlCl3(aq)) required (in Experiment 2) 1 M3 quantitative relationship such as: twice as concentrated OR needed twice as much aluminium chloride 1 2(g) M1 5.36 / 5.4 1 M2 cm3 1 2(h) volume used is not fixed / volume needed is not the same in each experiment. 1

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3 A student tests two substances: solid H and solution I. Tests on solid H Solid H is barium carbonate. Complete the expected observations. (a) (i) The student adds an excess of dilute nitric acid to the sample of solid H in a boiling tube and tests any gas produced. observations ........................................................................................................................ ............................................................................................................................................. ....................................................................................................................................... [2] (ii) Identify the gas made in (a)(i). ....................................................................................................................................... [1] The solution produced in (a)(i) is solution J. The student divides solution J into four approximately equal portions. (b) The student carries out a flame test on the first portion of solution J. observations ......................................................................................................................... [1] (c) To the second portion of solution J, the student adds a few drops of acidified aqueous potassium manganate(VII). observations ............................................................................................................................... .............................................................................................................................................. [1] (d) To the third portion of solution J, the student adds a few drops of dilute sulfuric acid. observations ............................................................................................................................... .............................................................................................................................................. [1] (e) To the fourth portion of solution J, the student adds about 1 cm depth of dilute nitric acid followed by a few drops of aqueous barium nitrate. observations ............................................................................................................................... .............................................................................................................................................. [1] Tests on solution I Table 3.1 shows the tests and the student’s observations for solution I. The student divides solution I into two portions. Table 3.1 tests observations test 1 To the first portion of solution I in a boiling tube, damp red litmus paper turns blue add 2 cm3 of aqueous sodium hydroxide and warm the mixture. Test any gas produced, using damp red litmus paper. test 2 To the second portion of solution I in a boiling a white precipitate forms tube, add 1 cm3 of dilute nitric acid followed by a few drops of aqueous silver nitrate. (f) (i) Identify the gas produced in test 1. ....................................................................................................................................... [1] (ii) State what is observed when the gas produced in test 1 is tested using damp blue litmus paper. ....................................................................................................................................... [1] (g) Identify solution I. .................................................................................................................................................... .............................................................................................................................................. [2] [Total: 11]

Mark scheme: 3(a)(i) limewater turns milky (when gas passed through it) and any one from  effervescence / fizzing / bubbles  solid disappears / dissolves 2 3(a)(ii) carbon dioxide / CO2 1 3(b) (pale / light) green (flame) 1 3(c) (solution becomes) pink / pale purple / lilac 1 3(d) white precipitate 1 Question Answer Marks 3(e) no change 1 3(f)(i) ammonia / NH3 1 3(f)(ii) no change / stays blue 1 3(g) ammonium chloride / NH4Cl M1 ammonium / NH4+ M2 chloride / Cl– 2

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4 Bismuth is a metal that has a reactivity similar to that of copper. The ore bismite contains the compound bismuth(III) oxide, Bi2O3. Bismuth(III) oxide is insoluble in water and reacts with dilute acids to form an aqueous solution of a salt. The ore bismite contains no other compounds that are insoluble in water and no other compounds that react with acids to form aqueous solutions. Describe how you could obtain a sample of bismuth metal starting with a large lump of the ore bismite. You have access to common laboratory apparatus and chemicals. ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ..................................................................................................................................................... [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 Tests for gases gas test and test result ammonia, NH3 turns damp red litmus paper blue carbon dioxide, CO2 turns limewater milky chlorine, Cl 2 bleaches damp litmus paper hydrogen, H2 ‘pops’ with a lighted splint oxygen, O2 relights a glowing splint sulfur dioxide, SO2 turns acidified aqueous potassium manganate(VII) from purple to colourless Flame tests for metal ions metal ion flame colour lithium, Li+ red sodium, Na+ yellow potassium, K+ lilac calcium, Ca2+ orange-red barium, Ba2+ light green copper(II), Cu2+ blue-green

Mark scheme: 4 any 6 from MP1 crush the ore / lumps / powder the ore / lumps / make the ore / lumps into smaller pieces MP2 using a suitable method e.g. pestle and / or mortar, hammer MP3 adds water (stirs) and filters then either: displacement in solid state method MP4 add more reactive element / suitable reducing agent (to residue / ore) MP5 identified as carbon / coke / iron / zinc / aluminium / magnesium / hydrogen / CO / ammonia / (subsumes MP4) MP6 heat (the ore or Bi2O3) (to form bismuth) MP7 bismuth displaced / reduced or bismuth formed by displacement OR electrolysis method MP4 adds suitable named (A correct formula) strong acid (to residue / ore) R adding acid to filtrate MP5 electrolysis (of solution) MP6 using inert electrodes / C or Pt electrodes MP7 bismuth forms at cathode OR displacement from aqueous solution MP4 adds suitable named strong acid (to residue / ore) R adding acid to filtrate MP5 add more reactive metal MP6 suitable more reactive metal identified (and added to solution of salt) (subsumes MP5) (e.g. Zn, Fe, Mg, Al but not K, Na, Ca) MP7 bismuth displaced / reduced or bismuth formed by displacement 6

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