Cambridge IGCSE Chemistry (9-1) 0971 — 2021 Oct/Nov Paper 5 · Variant 2

1 You are going to investigate the reaction between two different solutions of aqueous sodium carbonate, labelled solution K and solution L, and two different solutions of dilute hydrochloric acid, labelled acid M and acid N. Read all of the instructions carefully before starting the experiments. Instructions You are going to do three experiments. (a) Experiment 1 ● Fill the burette with solution K. Run some of solution K out of the burette so that the level of solution K is on the burette scale. ● Use the measuring cylinder to pour 25 cm3 of acid M into the conical flask. ● Add five drops of methyl orange indicator to the conical flask. ● Stand the conical flask on a white tile. ● Slowly add solution K from the burette to the conical flask, while swirling the flask, until the solution just changes colour. ● Record the burette readings in the table and complete the table. Experiment 1 final burette reading / cm3 initial burette reading / cm3 volume of solution K added / cm3 Experiment 2 ● Empty the conical flask and rinse it with distilled water. ● Refill the burette with solution K. Run some of solution K out of the burette so that the level of solution K is on the burette scale. ● Use the measuring cylinder to pour 25 cm3 of acid N into the conical flask. ● Add five drops of methyl orange indicator to the conical flask. ● Stand the conical flask on a white tile. ● Slowly add solution K from the burette to the conical flask, while swirling the flask, until the solution just changes colour. ● Record the burette readings in the table and complete the table. Experiment 2 final burette reading / cm3 initial burette reading / cm3 volume of solution K added / cm3 Experiment 3 ● Empty the burette and rinse it with distilled water. ● Empty the conical flask and rinse it with distilled water. ● Fill the burette with solution L. Run some of solution L out of the burette so that the level of solution L is on the burette scale. ● Use the measuring cylinder to pour 25 cm3 of acid N into the conical flask. ● Add five drops of methyl orange indicator to the conical flask. ● Stand the conical flask on a white tile. ● Slowly add solution L from the burette to the conical flask, while swirling the flask, until the solution just changes colour. ● Record the burette readings in the table and complete the table. Experiment 3 final burette reading / cm3 initial burette reading / cm3 volume of solution L added / cm3 [5] (b) State the colour change observed at the end-point in the conical flask in Experiment 1. from ................................................................... to ������������������������������������������������������������������� [1] (c) Describe one other observation made when solution K is added to acid M in Experiment 1. .............................................................................................................................................. [1] (d) (i) Compare the volumes of solution K used in Experiment 1 and Experiment 2. ............................................................................................................................................. ....................................................................................................................................... [2] (ii) Suggest why different volumes of solution K were needed in Experiment 1 and Experiment 2. ....................................................................................................................................... [1] (e) Deduce the volume of solution L required to reach the end-point if Experiment 3 is repeated using acid M in place of acid N. volume of solution L = .............................. cm3 [1] (f) Explain why the conical flask was rinsed with water at the start of Experiment 2 and Experiment 3. .............................................................................................................................................. [1] (g) At the start of Experiment 3 the burette was rinsed with water. Describe an additional step that should have been done after rinsing the burette with water but before filling the burette with solution L. Explain your answer. .................................................................................................................................................... .............................................................................................................................................. [2] (h) Explain why the conical flask is placed on a white tile. .............................................................................................................................................. [1] (i) Describe how the reliability of the results of the experiments can be confirmed. .................................................................................................................................................... .............................................................................................................................................. [1] (j) State one source of error in Experiment 1. Suggest an improvement to reduce this error. source of error ............................................................................................................................ improvement .............................................................................................................................. [2] [Total: 18]

Mark scheme: 1(a) all readings/volumes for all three experiments recorded to 1 dp or better 1 all three tables completed correctly with final > initial 1 all three subtractions to get volume added correct 1 Experiment 1 volume comparable to supervisors. 1 Experiment 2 volume is half Experiment 1 volume 1 1(b) (from) red (to) orange 1 1(c) effervescence/fizzing/bubbles 1 1(d)(i) greater volume used in Experiment 1 / smaller volume used in Experiment 2 1 twice as much in experiment 1 / half as much in Experiment 2 1 1(d)(ii) solution M is more concentrated than solution N 1 1(e) correct evaluation of (vol expt 1 / vol exp 2) × vol expt 3 1 1(f) to clean / to remove residue from previous experiment 1 1(g) rinse with solution L 1 to remove water / avoid diluting solution L / avoid changing concentration (of L) 1 1(h) to see colour change clearly/easily/accurately/better 1 1(i) repeat the experiments and compare the results 1 1(j) source of error: measuring cylinder / error in volume of solution M 1 improvement: use a pipette 1

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2 You are provided with solid O and liquid P. Do the following tests on the two substances, recording all of your observations at each stage. tests on solid O (a) Use a spatula to transfer approximately one third of solid O to a boiling tube. Heat the boiling tube gently and then strongly. Record your observations. .................................................................................................................................................... .............................................................................................................................................. [2] Place the remaining solid O in a boiling tube. Add about 10 cm3 of distilled water to the boiling tube. Place a stopper in the boiling tube and shake the tube to dissolve solid O and form solution O. Divide solution O into three approximately equal portions in one boiling tube and two test‑tubes. (b) To the first portion of solution O, in the boiling tube, add approximately 2 cm3 of aqueous sodium hydroxide. Keep the product for part (c). Record your observations. .............................................................................................................................................. [1] (c) Warm the product from (b). Test any gas produced. Record your observations. Identify the gas produced. observations ............................................................................................................................... identity of gas ............................................................................................................................. [2] (d) To the second portion of solution O add about 1 cm depth of dilute nitric acid followed by a few drops of aqueous silver nitrate. Record your observations. .............................................................................................................................................. [1] (e) To the third portion of solution O, add the aqueous chlorine. Record your observations. .............................................................................................................................................. [1] (f) Identify solid O. .................................................................................................................................................... .............................................................................................................................................. [2] tests on liquid P (g) Add a few drops of liquid P to the test‑tube containing aqueous bromine. Replace the stopper in the test‑tube and shake the test‑tube. Record your observations. .................................................................................................................................................... .............................................................................................................................................. [2] (h) Add a few drops of liquid P to a crucible. Apply a lighted splint to the surface of liquid P in the crucible. Record your observations. .................................................................................................................................................... .............................................................................................................................................. [1] (i) To the remaining liquid P add a few drops of aqueous alkaline potassium manganate(VII). Replace the stopper in the test‑tube and shake the test‑tube. Leave the test‑tube to stand for a few minutes. Record your observations. .............................................................................................................................................. [2] (j) State what conclusions can be made about liquid P. .................................................................................................................................................... .............................................................................................................................................. [2] [Total: 16]

Mark scheme: 2(a) any two from: • White smoke / gas / fumes / vapour • Solid/powder deposited on sides / near mouth of tube • Solid disappears (from bottom of tube) max 2 2 2(b) no change / colourless / no reaction 1 2(c) (red) litmus becomes blue. 1 ammonia 1 2(d) cream precipitate 1 2(e) (solution becomes) yellow 1 2(f) ammonium / NH4 1 bromide / Br- 1 Tests on liquid P 2(g) any two from: • orange changes to • colourless/decolourises • two layers max 2 2 Question Answer Marks 2(h) any one from: • burns/flame/ignites • yellow flame • smoke max 1 1 2(i) any two from: • purple changes to • green • and then brown (precipitate) max 2 2 2(j) any two from: • flammable / fuel • unsaturated / alkene / any named alkene • organic / contains carbon / hydrocarbon max 2 2

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3 Cobalt is a metal. Cobalt is between copper and iron in the reactivity series. The mineral spherocobaltite contains the compound cobalt(II) carbonate and no other metal ions. Cobalt(II) carbonate is insoluble in water and reacts with dilute acids to form an aqueous solution of a salt. Describe how you would obtain a sample of cobalt metal starting with a large lump of spherocobaltite. You have access to all normal laboratory apparatus and chemicals. ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ..................................................................................................................................................... [6]

Mark scheme: 3 reduction method any 6 from: • crush rock / break into smaller pieces/powder • using a suitable method e.g. pestle and/or mortar, hammer • add more reactive metal/suitable gas • carbon/coke/zinc/aluminium/magnesium/CO/hydrogen specified • heat • In a suitable container (eg crucible, evaporating basin) • cobalt displaced / cobalt formed electrolysis method any 6 from: • crush rock / break into smaller pieces/powder • using a suitable method e.g. pestle and/or mortar, hammer • add a (dilute) acid • suitable strong acid named (eg. HCl, H2SO4, HNO3) • electrolysis (of solution) • specified inert material for electrodes (eg. carbon, platinum) • cobalt obtained at the negative electrode/cathode displacement method any 6 from: • crush rock / break into smaller pieces/powder • using a suitable method e.g. pestle and/or mortar, hammer • add a (dilute) acid • suitable strong acid named (eg. HCl, H2SO4, HNO3) • add metal more reactive than cobalt • name of metal added specified (eg. iron, zinc, magnesium) • Cobalt displaced / cobalt formed max 6 6

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