Cambridge IGCSE Chemistry (9-1) 0971 — 2022 Oct/Nov Paper 5 · Variant 2

1 You are going to investigate the temperature change when two different aqueous solutions of sodium hydroxide, solution G and solution H, react with dilute hydrochloric acid. Read all of the instructions carefully before starting the experiments. Instructions You are going to do two experiments. (a) Experiment 1 ● Rinse a burette with distilled water and then with the dilute hydrochloric acid for Question 1. ● Fill the burette to the 0.00 cm3 mark with the dilute hydrochloric acid. ● Use a 50 cm3 measuring cylinder to pour 20 cm3 of solution G into a beaker. ● Use a thermometer to measure the initial temperature of solution G. Record the initial temperature in the table. ● Add 5 cm3 of dilute hydrochloric acid from the burette into the beaker. ● Stir the mixture in the beaker using the thermometer and measure the temperature of the mixture. Record the temperature in the table. ● Add another 5 cm3 of dilute hydrochloric acid from the burette into the beaker. ● Stir the mixture in the beaker using the thermometer and measure the temperature of the mixture. Record the temperature in the table. ● Continue to add 5 cm3 portions of dilute hydrochloric acid and record the temperature of the mixture in the table until you have added a total of 35 cm3 of dilute hydrochloric acid. Experiment 2 ● Repeat Experiment 1 using solution H instead of solution G. Complete the table. Experiment 1 using solution G Experiment 2 using solution H total volume of dilute temperature temperature temperature temperature hydrochloric acid change since change since / °C /°C added / cm3 start / °C start / °C 0 5 10 15 20 25 30 35 [6] (b) Complete a suitable scale on the y-axis and plot your 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: 20]

Mark scheme: Question Answer Marks 1(a) M1 eight temperatures recorded for Experiment 1 and temperatures show an increasing trend and then a decreasing trend 1 M2 eight temperatures recorded for Experiment 2 and temperatures show an increasing trend and then a decreasing trend 1 M3 temperature changes in Experiment 1 calculated correctly 1 M4 temperature changes in Experiment 2 calculated correctly 1 M5 maximum temperature change in Experiment 1 is greater than maximum temperature change in Experiment 2 1 M6 all temperatures and temperature changes recorded to a consistent number of decimal places 1 1(b) M1 y-axis scale in linear and points extend over halfway up the scale 1 M2 all points for Experiment 1 plotted correctly 1 M3 all points for Experiment 2 plotted correctly 1 M4 two acceptable curves drawn which are both extended to (0,0) 1 M5 lines labelled or key 1 1(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 1(d) excess / too much (hydrochloric) acid 1 or reaction over / stopped/finished / all NaOH / G / H has been used up 1(e) M1 solution G is more concentrated (than solution H) 1 M2 as max temperature change higher in Experiment 1 1 OR M2 (max temperature change) needs more (hydrochloric acid) in Experiment 1 1(f) M1 temperature (changes) higher 1 M2 as less heat lost / polystyrene is a (better) insulator 1 1(g) advantage: (burette is) (more) accurate / precise 1 disadvantage: slow / takes more time (to add) / can overshoot required volume 1

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2 You are provided with solid I and solid J. Do the following tests on the substances, recording all of your observations at each stage. tests on solid I (a) To the boiling tube containing solid I add 15 cm3 of the dilute hydrochloric acid for Question 2. Test any gas produced. Keep the mixture in the boiling tube for (b). Record your observations. .................................................................................................................................................... .................................................................................................................................................... .............................................................................................................................................. [3] (b) Carry out a flame test on the mixture formed in the boiling tube from (a). Record your observations. .............................................................................................................................................. [1] (c) Identify solid I. .................................................................................................................................................... .............................................................................................................................................. [2] tests on solid J Add about 10 cm3 of distilled water to the boiling tube containing solid J. Replace the stopper and shake the boiling tube to dissolve solid J and form solution J. Divide solution J into four approximately equal portions in four test-tubes. (d) To the first portion of solution J add aqueous sodium hydroxide dropwise and then in excess. Record your observations. .................................................................................................................................................... .............................................................................................................................................. [2] (e) To the second portion of solution J add aqueous ammonia dropwise and then in excess. Record your observations. .................................................................................................................................................... .............................................................................................................................................. [2] (f) To the third portion of solution J 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 J add about 1 cm depth of dilute nitric acid followed by a few drops of aqueous silver nitrate. Record your observations. .............................................................................................................................................. [1] (h) Identify solid J. .................................................................................................................................................... .............................................................................................................................................. [2] [Total: 14]

Mark scheme: 2(a) M1 effervescence / bubbles / fizzing 1 M2 solid disappears / colourless (solution) 1 M3 limewater goes milky 1 2(b) red 1 2(c) lithium / Li+ 1 carbonate / CO32– 1 2(d) M1 white precipitate 1 M2 dissolves 1 2(e) M1 white precipitate 1 M2 remains / does not redissolve / no change 1 2(f) no change / (remains) colourless 1 2(g) white precipitate 1 2(h) aluminium / Al 3+ 1 chloride / Cl – 1

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3 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: 3 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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