Cambridge IGCSE Chemistry (9-1) 0971 — 2022 May/June Paper 5 · Variant 1

1 You are going to investigate the rate at which hydrogen gas is made when magnesium reacts with two different solutions of dilute hydrochloric acid, C and D, with different concentrations. The dilute hydrochloric acid is in excess in both experiments. Read all of the instructions carefully before starting the experiments. Instructions You are going to do two experiments using the apparatus shown. rubber delivery tube clamp bung inverted 100 cm3 measuring cylinder conical flask trough dilute hydrochloric acid water (a) Experiment 1 ● Use a measuring cylinder to pour 50 cm3 of dilute hydrochloric acid C into a conical flask. ● Use a thermometer to measure the initial temperature of the dilute hydrochloric acid. Record the initial temperature in the space provided. ● Set the apparatus up as shown in the diagram, ensuring the inverted measuring cylinder is full of water. ● Remove the bung from the conical flask, leaving the delivery tube in the measuring cylinder. ● Add a coiled 5 cm length of magnesium ribbon to the conical flask, immediately replace the bung and start the timer. ● Measure the volume of gas collected in the inverted measuring cylinder every 20 seconds for 160 seconds. Record the volume of gas collected in the table. ● Use the thermometer to measure the final temperature of the dilute hydrochloric acid in the conical flask. Record the final temperature in the space provided. initial temperature ................................... °C final temperature ................................... °C time / s 20 40 60 80 100 120 140 160 volume of gas collected / cm3 [2] (b) Experiment 2 ● Empty and rinse the conical flask with distilled water. ● Repeat Experiment 1 using 50 cm3 of dilute hydrochloric acid D instead of dilute hydrochloric acid C. initial temperature ................................... °C final temperature ................................... °C time / s 20 40 60 80 100 120 140 160 volume of gas collected / cm3 [3] and mu (d) From your graph, deduce the volume of gas that was collected after 50 seconds in Experiment 2. Show clearly on the grid how you worked out your answer. volume of gas = .............................. [3] (e) Explain what can be deduced about the concentrations of dilute hydrochloric acid C and dilute hydrochloric acid D. .................................................................................................................................................... .................................................................................................................................................... .................................................................................................................................................... .............................................................................................................................................. [2] (f) (i) State what happens to the temperature of the dilute hydrochloric acid during Experiment 1. ....................................................................................................................................... [1] (ii) State what effect this temperature change has on the total volume of gas made when the reaction has finished. ....................................................................................................................................... [1] (iii) Describe a change that can be made to the apparatus or reagents to reduce the temperature change of the acid in Experiment 1. ....................................................................................................................................... [1] (g) Suggest why it is important to replace the bung in the conical flask immediately after adding the magnesium ribbon. .................................................................................................................................................... .............................................................................................................................................. [1] (h) State the advantage of measuring the volume of gas collected every 10 seconds rather than every 20 seconds. .............................................................................................................................................. [1] [Total: 20]

Mark scheme: 1(a) initial and final temperatures recorded and all eight volumes of hydrogen recorded 1 final temperature is greater than initial temperature 1 1(b) final temperature is greater than initial temperature and final temperature is comparable to supervisor 1 volume of hydrogen increases as time increases in BOTH experiments 1 volume of hydrogen at 40 seconds in Experiment 2 is lower than volume of hydrogen at 40 seconds in Experiment 1. 1 1(c) y-axis scale in linear and points extend over halfway up scale 1 all points for Experiment 1 and 2 plotted correctly 2 two best fit curves 1 lines both extended to (0,0) and are labelled 1 1(d) correct working shown on graph 1 correct reading from their working shown on graph. 1 cm3 1 1(e) solution C is more concentrated than solution D 1 as reaction is faster 1 1(f)(i) increases 1 1(f)(ii) none / stays the same 1 1(f)(iii) use a water bath / use a larger volume of acid 1 1(g) minimise gas loss 1 1(h) (more points / data so) better / smoother graph 1

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2 You are provided with two substances, solid E and solution F. Do the following tests, recording all of your observations at each stage. tests on solid E Add about 15 cm3 of distilled water to the boiling tube containing solid E. Replace the stopper in the boiling tube and shake the boiling tube to dissolve solid E and form solution E. Divide solution E into three approximately equal portions in one boiling tube and two test‑tubes. (a) To the first portion of solution E in the boiling tube, add aqueous sodium hydroxide dropwise until it is in excess. Keep the mixture formed for (b). Record your observations. .................................................................................................................................................... .............................................................................................................................................. [2] (b) Gently warm the mixture formed in (a). Test any gas produced and identify the gas. Record your observations. .................................................................................................................................................... .................................................................................................................................................... identity of gas ............................................................................................................................. [2] (c) To the second 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] (d) 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] (e) Identify the three ions in solution E. .................................................................................................................................................... .................................................................................................................................................... .............................................................................................................................................. [3] tests on solution F Divide solution F into two approximately equal portions in two test‑tubes. (f) Test the pH of the first portion of solution F. pH = .............................. [1] (g) Add the second portion of solution F to the boiling tube containing solid sodium carbonate. Test any gas produced. Record your observations. .................................................................................................................................................... .................................................................................................................................................... .............................................................................................................................................. [3] (h) Identify the positive ion in solution F. .............................................................................................................................................. [1] [Total: 14]

Mark scheme: 2(a) green precipitate 1 remains / does not dissolve 1 2(b) (red) litmus becomes blue 1 ammonia / NH3 1 2(c) no change / (remains) colourless 1 2(d) white precipitate 1 2(e) ammonium / NH4+ 1 iron(II) / Fe2+ 1 sulfate / SO42- 1 2(f) pH: any in range 2 to 6 1 2(g) effervescence / bubbles / fizzing 1 solid disappears / colourless (solution) 1 limewater goers milky 1 2(h) hydrogen / H+ 1

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3 A sample of muddy river water contains water, dissolved solids and insoluble solid mud. Plan an investigation to find the concentration of dissolved solids, in g / dm3, in the river water. In your answer state how you will work out the concentration of the dissolved solids in g / dm3. You are provided with a small sample (less than 1 dm3) of muddy river water and common laboratory apparatus. (1 dm3 = 1000 cm3) ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ..................................................................................................................................................... [6]

Mark scheme: 3 filter the water and any five from:  specified / known / measured volume of water / filtrate  placed in a suitable container and heated in this container (evaporating basin/beaker)  heat/warm (to evaporate water)  (heat) until all water gone / dryness / constant mass  find mass of solid left  concentration = mass  1000  volume used

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