Cambridge IGCSE Chemistry (9-1) 0971 — 2020 May/June Paper 6 · Variant 1

1 A student investigated the dyes contained in different coloured inks using chromatography. Water was the solvent. The diagram shows how the student set up the apparatus. chromatography paper baseline drawn in ink water red orange yellow green blue purple black (a) Identify two errors in the way the student set up the apparatus. 1 ................................................................................................................................................. 2 ................................................................................................................................................. [2] (b) The student then carried out the chromatography correctly. The diagram shows the results. red orange yellow green blue purple black (i) Which ink contains the greatest number of soluble dyes? ....................................................................................................................................... [1] (ii) Which two inks are made of a single soluble dye? ................................................................... and .................................................................. [1] (iii) From the chromatogram it is not possible to tell if the red ink contains different dyes. Suggest how the experiment could be changed to find out if the red ink contains different dyes. ....................................................................................................................................... [1] [Total: 5]

Mark scheme: 1(a) spots / baseline below solvent level 1 baseline drawn in ink 1 1(b)(i) black 1 1(b)(ii) yellow (and) blue 1 1(b)(iii) use an organic solvent / different solvent 1

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2 A student investigated the reaction between dilute hydrochloric acid and two different aqueous solutions of sodium carbonate, solution E and solution F. Three experiments were done. (a) Experiment 1 ●● A burette was filled up to the 0.0 cm3 mark with dilute hydrochloric acid. ●● Using a measuring cylinder, 25 cm3 of solution E was poured into a conical flask. ●● Five drops of thymolphthalein indicator were added to the conical flask. ●● Dilute hydrochloric acid was slowly added from the burette to the conical flask, while the flask was swirled, until the solution just changed colour. Use the burette diagrams to complete the table for Experiment 1. 0 9 1 10 2 11 initial reading final reading final burette reading / cm3 initial burette reading / cm3 volume of dilute hydrochloric acid added / cm3 Experiment 2 ●● The conical flask was emptied and rinsed with distilled water. ●● The burette was refilled with dilute hydrochloric acid. ●● Experiment 1 was repeated using five drops of methyl orange indicator instead of thymolphthalein indicator. Use the burette diagrams to complete the table for Experiment 2. 5 24 6 25 7 26 initial reading final reading final burette reading / cm3 initial burette reading / cm3 volume of dilute hydrochloric acid added / cm3 Experiment 3 ●● The conical flask was emptied and rinsed with distilled water. ●● The burette was refilled with dilute hydrochloric acid. ●● Using a measuring cylinder, 25 cm3 of solution F was poured into the conical flask. ●● Five drops of methyl orange indicator were added to the conical flask. ●● Dilute hydrochloric acid was slowly added from the burette to the conical flask, while the flask was swirled, until the solution just changed colour. Use the burette diagrams to complete the table for Experiment 3. 1 33 2 34 3 35 initial reading final reading final burette reading / cm3 initial burette reading / cm3 volume of dilute hydrochloric acid added / cm3 [5] (b) What colour change was observed in the conical flask in Experiment 2? from .................................................................... to ................................................................... [2] (c) Compare the volumes of dilute hydrochloric acid added in Experiment 2 and Experiment 3. Explain any difference. .................................................................................................................................................... .............................................................................................................................................. [2] (d) Determine the simplest whole number ratio of volumes of dilute hydrochloric acid used in Experiments 1 and 2. ratio Experiment 1 : Experiment 2 = .............................. [1] (e) What volume of dilute hydrochloric acid would be required if Experiment 3 was repeated using thymolphthalein indicator instead of methyl orange indicator? volume = .............................. [2] (f) The conical flask was rinsed with distilled water between each experiment. (i) Why was the conical flask rinsed? ............................................................................................................................................. ....................................................................................................................................... [1] (ii) Why does it not matter if a little distilled water is left in the flask after it has been rinsed? ............................................................................................................................................. ....................................................................................................................................... [1] (g) State two sources of error in the experiments. For each error suggest an improvement that would reduce the error. source of error 1 ......................................................................................................................... improvement 1 ........................................................................................................................... .................................................................................................................................................... source of error 2 ......................................................................................................................... improvement 2 ........................................................................................................................... .................................................................................................................................................... [4] [Total: 18]

Mark scheme: 2(a) all six burette readings correct • 10.2 / 0.0 • 25.9 / 5.5 • 33.0 / 2.4 2 all readings to 1 dp 1 initial and final readings the correct way round 1 all subtractions correct to calculate volume added • 10.2 • 20.4 • 30.6 1 2(b) (from) yellow 1 (to) red / pink / orange 1 2(c) solution F more concentrated (than solution E) 1 1.5 times 1 2(d) 1:2 1 Question Answer Marks 2(e) 15.3 1 cm3 1 2(f)(i) clean / remove residues from previous experiment 1 2(f)(ii) does not change amount of E / F or volumes / amounts already measured 1 2(g) errors any two from: • using measuring cylinder • missing endpoint / misjudging colour change • not repeating improvements any two from: • use pipette (in place of measuring cylinder) • add more slowly • repeat (and find mean) 4

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3 Two solids, solid G and solid H, were analysed. Solid G was copper(II) carbonate. Tests were done on each solid. tests on solid G Complete the expected observations. (a) Solid G was placed in a boiling tube. An excess of dilute sulfuric acid was added to the boiling tube. Any gas produced was tested. observations ............................................................................................................................... .................................................................................................................................................... .............................................................................................................................................. [3] (b) Identify the gas produced in (a). .............................................................................................................................................. [1] (c) Aqueous ammonia was added slowly until in excess to the solution produced in (a). observations ............................................................................................................................... .................................................................................................................................................... .................................................................................................................................................... .............................................................................................................................................. [3] tests on solid H Tests were done and the following observations were made. tests on solid H observations test 1 Flame test yellow flame test 2 Some of solid H was placed in a boiling tube. condensation appeared near the The boiling tube was heated strongly. mouth of the boiling tube Solid H was dissolved in distilled water. The solution was divided into two equal portions. test 3 About 1 cm3 of dilute nitric acid followed by a the solution remained colourless few drops of aqueous silver nitrate were added to the first portion of the solution. test 4 About 1 cm3 of dilute nitric acid followed by white precipitate a few drops of aqueous barium nitrate were added to the second portion of the solution. (d) What conclusion can be made from the result of test 3? .................................................................................................................................................... .............................................................................................................................................. [1] (e) What conclusions can be made about solid H from the results of test 1, test 2 and test 4? .................................................................................................................................................... .................................................................................................................................................... .............................................................................................................................................. [3] [Total: 11]

Mark scheme: 3 Tests on solid G 3(a) any three from: • bubble / fizz / effervescence • blue solution formed • (gas made turns) limewater • milky 3 3(b) • carbon dioxide / CO2 1 Question Answer Marks 3(c) blue 1 precipitate 1 dark(er) / royal blue and dissolves / solution 1 3(d) not a halide 1 tests on solid H 3(e) hydrated 1 sodium / Na+ sulfate / SO42- sodium sulfate = 2 Na2SO4 = 2 1

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4 Cobalt, manganese and nickel are metals. They react with dilute hydrochloric acid to form hydrogen gas. Plan an investigation to find the order of reactivity of these three metals. You are provided with: ●● samples of each metal ●● dilute hydrochloric acid ●● common laboratory apparatus. Your plan must make it clear how your investigation will be a fair test and how you will use your results to place the metals in order of reactivity. ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ..................................................................................................................................................... [6]

Mark scheme: 4 fair test – max 4 • same volume HCl • some concentration HCl • same temperature acid • same mass / moles / amount metals • same surface area / form of metal measure • start timing when solid added • stop timing when all solid gone / reaction to stop 6 Question Answer Marks 4 OR • start timing when solid added • stop timing when collected set volume of gas OR • start timing when solid added • measure volume of gas after a set time OR • measure temperature at start • measure temperature after reaction OR highest temperature reached conclusion • shortest time is most reactive OR • biggest volume of gas most reactive OR • biggest temperature change most reactive

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