Cambridge IGCSE Chemistry (9-1) 0971 — 2022 Oct/Nov Paper 6 · Variant 2

1 A mixture of three coloured compounds was separated using the apparatus shown in the diagram. lid paper A baseline (a) Give the name of the item of apparatus labelled A. .............................................................................................................................................. [1] (b) One drop of the mixture of coloured compounds was placed on the paper and some solvent was poured into A. Draw on the diagram: ● a spot (●) to show where the drop of the mixture of coloured compounds should be placed on the paper at the start of the experiment ● a line to show the level of the solvent in A at the start of the experiment. [2] (c) Name an item of apparatus that should be used to place a drop of the mixture of coloured compounds onto the paper. .............................................................................................................................................. [1] (d) State when the paper should be removed from the solvent in A. .............................................................................................................................................. [1] (e) Name this method of separation of coloured compounds. .............................................................................................................................................. [1] [Total: 6]

Mark scheme: Question Answer Marks 1(a) beaker 1 1(b) 1 M1 ‘∙’ shown anywhere on base line M2 horizontal line drawn between bottom of paper and baseline. Line must not touch spot drawn on baseline or the 1 baseline 1(c) (dropping / teat) pipette / capillary tube / glass rod 1 1(d) when the solvent is near the top of the paper 1 1(e) (paper) chromatography 1

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2 A student investigated the temperature change when two different aqueous solutions of sodium hydroxide, solution G and solution H, reacted with dilute hydrochloric acid. Two experiments were done. (a) Experiment 1 ● A burette was rinsed with distilled water and then with dilute hydrochloric acid. ● The burette was filled with the dilute hydrochloric acid. The hydrochloric acid was then run out through the tap until the level was on the 0.00 cm3 mark. ● A 50 cm3 measuring cylinder was used to pour 20 cm3 of solution G into a beaker. ● A thermometer was used to measure the initial temperature of solution G. ● 5 cm3 of dilute hydrochloric acid was added from the burette into the beaker. ● The mixture in the beaker was stirred using the thermometer and the temperature of the mixture was measured. ● Another 5 cm3 of dilute hydrochloric acid was added from the burette into the beaker. ● The mixture in the beaker was stirred using the thermometer and the temperature of the mixture was measured. ● 5 cm3 portions of dilute hydrochloric acid continued to be added and the temperature measured until a total of 35 cm3 of dilute hydrochloric acid had been added. Experiment 2 ● Experiment 1 was repeated using solution H instead of solution G. Use the thermometer diagrams to complete the t Experiment 1 using solution G total volume temperature of dilute thermometer temperature changehydrochloric diagram / C since start acid added / C / cm3 30 0 25 20 30 5 25 20 30 10 25 20 30 15 25 20 30 20 25 20 30 25 25 20 30 30 25 20 30 35 25 20 (b) Complete a suitable scale on the y-axis and plot the results from Experiments 1 and 2 on the grid. Draw two smooth line graphs. Both curves must start at (0,0). Clearly label your lines. temperature change / C 0 0 5 10 15 20 25 30 35 total volume of dilute hydrochloric acid added / cm3 [5] (c) From your graph, deduce the temperature change obtained when a total volume of 13 cm3 of dilute hydrochloric acid is added in Experiment 1. Show clearly on the grid how you worked out your answer. temperature change = .............................. °C [2] (d) Explain why the temperature change decreases towards the end of each experiment. .................................................................................................................................................... .............................................................................................................................................. [1] (e) Explain what conclusion about the concentrations of solution G and solution H can be made from the results of Experiments 1 and 2. .................................................................................................................................................... .................................................................................................................................................... .................................................................................................................................................... .............................................................................................................................................. [2] (f) Explain how the results obtained would be different if a polystyrene cup is used instead of the beaker. .................................................................................................................................................... .................................................................................................................................................... .................................................................................................................................................... .............................................................................................................................................. [2] (g) Give an advantage and a disadvantage of using a burette rather than a measuring cylinder to add the dilute hydrochloric acid to solution G and solution H. advantage .................................................................................................................................. .................................................................................................................................................... disadvantage .............................................................................................................................. .................................................................................................................................................... [2] [Total: 19]

Mark scheme: 2(a) M1 all eight temperatures recorded for Experiment 1 correct (21.0, 24.0, 26.5, 28.0, 29.0, 28.5, 28.0, 27.5) 1 M2 all eight temperatures recorded for Experiment 2 correct (22.0, 25.0, 27.5, 28.0, 27.5, 27.0, 26.5, 26.0) 1 M3 all 7 temperature changes in Experiment 1 calculated correctly (3.0, 5.5, 7.0, 8.0, 7.5, 7.0, 6.5) 1 M4 all 7 temperature changes in Experiment 2 calculated correctly (3.0, 5.5, 6.0, 5.5, 5.0, 4.5, 4.0) 1 M5 all temperature changes recorded to one decimal place 1 2(b) M1 y-axis scale in linear with scale of 2 cm = 2 °C 1 M2 all points for Experiment 1 plotted correctly. (0,0) not required 1 M3 all points for Experiment 2 plotted correctly. (0,0) not required 1 M4 two acceptable smooth curves drawn which are both extended to (0,0) 1 M5 lines labelled or key 1 2(c) M1 correct working shown on graph for 13 cm3 of acid to Experiment 1 line 1 M2 correct reading from their working shown on graph 1 2(d) excess / too much (hydrochloric) acid 1 or reaction over / stopped / finished / all NaOH / G / H has been used up 2(e) M1 solution G is more concentrated (than solution H) 1 M2 as maximum temperature change higher in Experiment 1 1 OR M2 (maximum temperature change) needs more (hydrochloric acid) in Experiment 1 2(f) M1 temperature (changes) higher 1 M2 as less heat lost / polystyrene is a (better) insulator 1 2(g) advantage: (burette is) (more) accurate / precise 1 disadvantage: slow / takes more time (to add) / can overshoot required volume 1

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3 Solid I and solid J were analysed. Tests were done on each substance. tests on solid I tests observations test 1 Dilute hydrochloric acid was added to a effervescence was seen, the solid dissolved boiling tube containing solid I. to form a colourless solution Any gas produced was tested. the gas turned limewater milky test 2 A flame test was carried out on the solution a red flame was seen formed in test 1. (a) Identify the gas made in test 1. .............................................................................................................................................. [1] (b) Identify solid I. .................................................................................................................................................... .............................................................................................................................................. [2] tests on solid J Solid J was aluminium chloride. Solid J was dissolved in water to form solution J. Solution J was divided into four approximately equal portions in four test-tubes. (c) Aqueous sodium hydroxide was added dropwise and then in excess to the first portion of solution J. observations ............................................................................................................................... .............................................................................................................................................. [2] (d) Aqueous ammonia was added dropwise and then in excess to the second portion of solution J. observations ............................................................................................................................... .............................................................................................................................................. [2] (e) About 1 cm depth of dilute nitric acid followed by a few drops of aqueous barium nitrate were added to the third portion of solution J. observations ......................................................................................................................... [1] (f) About 1 cm depth of dilute nitric acid followed by a few drops of aqueous silver nitrate were added to the fourth portion of solution J. observations ......................................................................................................................... [1] [Total: 9]

Mark scheme: 3(a) carbon dioxide / CO2 1 3(b) lithium / Li+ 1 carbonate / CO32– 1 3(c) M1 white precipitate 1 M2 dissolves 1 3(d) M1 white precipitate 1 M2 remains / does not redissolve / no change 1 3(e) no change / (remains) colourless 1 3(f) white precipitate 1

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4 Hydrogels are powders that absorb water to form hydrated solids. Hydrogels and the hydrated solids formed are insoluble in water. Plan an investigation to find which hydrogel, hydrogel A or hydrogel B, is able to absorb the greater mass of water. You are provided with samples of hydrogel A, hydrogel B, water and common laboratory apparatus. ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ..................................................................................................................................................... [6]

Mark scheme: 4 any 6 from 6 mass increase method MP1 known / stated / find mass of hydrogel MP2 repeat experiment for second hydrogel MP3 add excess water MP4 stir / mix with water MP5 filter (to obtain solid hydrogel / excess water) MP6 weigh hydrogel MP7 mass of water absorbed = final mass – initial mass OR add gradually method MP1 known / stated / find mass of hydrogel MP2 repeat experiment for second hydrogel MP3 add water gradually to hydrogel MP4 stir / mix MP5 until no more absorbed MP6 find mass of hydrated hydrogel MP7 mass of water absorbed = final mass – initial mass max 6

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