Cambridge IGCSE Chemistry (9-1) 0971 — 2023 May/June Paper 5 · Variant 1

1 You are going to investigate the reaction between aqueous ammonia and two different aqueous solutions of copper(II) sulfate labelled A and B. Solutions A and B have different concentrations. Read all of the instructions carefully before starting the experiments. Instructions You are going to do two experiments. (a) Experiment 1 ● Fill a burette with solution A. Run some of solution A out of the burette so that the level of solution A is on the burette scale. ● Record the initial burette reading in Table 1.1. ● Use the measuring cylinder to pour 25 cm3 of the aqueous ammonia into the conical flask. ● Stand the conical flask on a white tile. ● Slowly add solution A 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 in Table 1.1. Experiment 2 ● Empty the conical flask and rinse it with distilled water. ● Empty the burette and rinse it with distilled water. ● Rinse the burette with solution B. ● Repeat Experiment 1 using solution B instead of solution A. ● Complete Table 1.1. Table 1.1 Experiment 1 Experiment 2 using solution A using solution B final burette reading / cm3 initial burette reading / cm3 volume of aqueous copper(II) sulfate added / cm3 [4] (b) Explain why a white tile is used during the titration. .................................................................................................................................................... .............................................................................................................................................. [1] (c) In Experiment 2 the burette and the conical flask are both rinsed with water. The burette is then rinsed with solution B. (i) State why both the burette and the conical flask are rinsed with water. ....................................................................................................................................... [1] (ii) Explain why the burette is then rinsed with solution B. ............................................................................................................................................. ....................................................................................................................................... [1] (iii) Describe how the result of Experiment 2 would be different if the conical flask is rinsed with aqueous ammonia after rinsing with water. Explain your answer. ............................................................................................................................................. ....................................................................................................................................... [2] (d) (i) Deduce which solution of copper(II) sulfate, A or B, is more concentrated. Explain your answer. ............................................................................................................................................. ....................................................................................................................................... [1] (ii) Deduce how many times more concentrated this solution of copper(II) sulfate is than the other solution of copper(II) sulfate. ....................................................................................................................................... [1] (e) Describe how the reliability of the results obtained can be checked. .................................................................................................................................................... .............................................................................................................................................. [1] (f) Deduce the volume of solution A required when Experiment 1 is carried out with 10 cm3 of aqueous ammonia. .............................................................................................................................................. [2] (g) In Experiments 1 and 2, the volume of aqueous ammonia is measured using a measuring cylinder. Give an advantage and a disadvantage of using a volumetric pipette instead of a measuring cylinder to measure the volume of aqueous ammonia. advantage .................................................................................................................................. disadvantage .............................................................................................................................. [2] [Total: 16]

Mark scheme: 1(a) M1 all burette readings recorded correctly with final reading > initial reading in both tables 1 M2 both titres calculated correctly 1 M3 all values to 1dp 1 M4 titre for experiment 1 is 1.5 the titre for experiment 2 1 1(b) to make solid easier to see / so colour (change) easier to see 1 1(c)(i) to clean / remove solution A 1 1(c)(ii) to remove water (from the burette) 1 1(c)(iii) M1 more solution B needed 1 M2 as more (than 25 cm3 of) aqueous ammonia in flask 1 1(d)(i) solution B and as a smaller volume (of solution B/copper(II) sulfate) was needed / smaller titre 1 1(d)(ii) correct evaluation of ‘bigger titre  smaller titre’ 1 1(e) repeat experiment and compare 1 1(f) M1 correct evaluation of titre 1  2.5 1 M2 cm3 1 1(g) advantage: (more) accurate 1 disadvantage: slower / takes longer 1

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2 You are provided with solid E. Do the following tests on solid E, recording all of your observations at each stage. Tests on solid E Divide solid E into two approximately equal portions in two boiling tubes. (a) Gently heat the first portion of solid E. Record your observations. .................................................................................................................................................... .............................................................................................................................................. [2] (b) State what conclusion can be made about solid E from the observations in (a). .................................................................................................................................................... .............................................................................................................................................. [1] Add about 15 cm3 of distilled water to the boiling tube containing the second portion of solid E. Place a stopper in the boiling tube and shake the tube to dissolve solid E and form solution E. Divide solution E into seven approximately equal portions in one boiling tube and six test-tubes. (c) To the first portion of solution E in the boiling tube, add aqueous sodium hydroxide dropwise and then in excess. Keep the product for use in (d). Record your observations. dropwise ..................................................................................................................................... in excess .................................................................................................................................... [2] (d) Transfer about 2 cm depth of the product from (c) into a clean boiling tube. Warm the mixture gently. Test and identify the gas produced. .................................................................................................................................................... .................................................................................................................................................... identity of gas ............................................................................................................................. [2] (e) To the second portion of solution E, add about 1 cm depth of aqueous sodium thiosulfate. Leave the mixture to stand for about three minutes. Record your observations. .................................................................................................................................................... .............................................................................................................................................. [2] (f) To the third portion of solution E, add about 1 cm depth of dilute nitric acid followed by a few drops of aqueous barium nitrate. Record your observations. .................................................................................................................................................... .............................................................................................................................................. [1] (g) To the fourth portion of solution E, add about 1 cm depth of dilute nitric acid followed by a few drops of aqueous silver nitrate. Record your observations. .................................................................................................................................................... .............................................................................................................................................. [1] (h) To the fifth portion of solution E, add about 2 cm depth of aqueous sodium carbonate. Record your observations. .................................................................................................................................................... .............................................................................................................................................. [1] (i) To the sixth portion of solution E, add about 1 cm depth of aqueous potassium iodide followed by about 1 cm depth of starch solution. Record your observations. .................................................................................................................................................... .............................................................................................................................................. [2] (j) To the seventh portion of solution E add a few drops of acidified aqueous potassium manganate(VII). Record your observations. .................................................................................................................................................... .............................................................................................................................................. [1] (k) Identify the three ions in solid E. .................................................................................................................................................... .............................................................................................................................................. [3] [Total: 18]

Mark scheme: 2(a) M1 dissolves / forms a solution 1 M2 steam given off / condensation on tube 1 2(b) hydrated / contains water 1 2(c) M1 red-brown precipitate 1 M2 remains / does not dissolve in excess / red-brown precipitate 1 2(d) M1 (red) litmus turns blue 1 M2 ammonia / NH3 1 2(e) M1 (solution) turns red/black/purple 1 M2 becomes yellow / paler / lighter on standing 1 2(f) white precipitate 1 2(g) no change / no reaction 1 2(h) red-brown ppt 1 2(i) M1 brown 1 M2 (blue)-black (when starch added) 1 2(j) pink solution 1 2(k) M1 ammonium / NH4+ 1 M2 iron(III) / Fe3+ 1 M3 sulfate / SO42– 1

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3 Solid cobalt(II) oxide is a base which is insoluble in water. It reacts very slowly with cold dilute sulfuric acid to form a solution of cobalt(II) sulfate. Describe how to make pure, dry crystals of hydrated cobalt(II) sulfate. You are provided with cobalt(II) oxide, dilute sulfuric acid and common laboratory apparatus. ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ..................................................................................................................................................... [6]

Mark scheme: 3 any 6 from MP1 adds cobalt(II) oxide to (dilute) sulfuric acid in a suitable container MP2 cobalt(II) oxide is in excess MP3 the mixture is stirred / mixed MP4 the acid/mixture is heated/warmed MP5 filter (to remove (excess) cobalt(II) oxide) MP6 heat filtrate/solution / leave to evaporate (reject heat to dryness) MP7 filter out crystals / description of drying crystals max 6 6

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