Cambridge IGCSE Chemistry (9-1) 0971 — 2024 May/June Paper 5 · Variant 1

1 You are going to investigate the temperature change when magnesium reacts with dilute sulfuric acid. Read all of the instructions carefully before starting the experiments. Instructions You are going to do five experiments. (a) Experiment 1 ● Use a 25 cm3 measuring cylinder to pour 20 cm3 of dilute sulfuric acid into a boiling tube. ● Use a thermometer to measure the initial temperature of the acid in the boiling tube. Record the initial temperature in Table 1.1. ● Add a coiled 5 cm length of magnesium ribbon to the acid in the boiling tube. At the same time start a timer. ● Continually stir the contents of the boiling tube using the thermometer. ● After 45 seconds, measure the temperature of the mixture in the boiling tube. Record this temperature in Table 1.1. ● Rinse the boiling tube with distilled water. Experiment 2 ● Use the 25 cm3 measuring cylinder to pour 20 cm3 of dilute sulfuric acid into the boiling tube. ● Use a 10 cm3 measuring cylinder to add 2.0 cm3 of distilled water to the acid in the boiling tube. ● Place a bung in the boiling tube and invert the tube to mix the acid and water. ● Use the thermometer to measure the initial temperature of the contents of the boiling tube. Record the initial temperature in Table 1.1. ● Add a coiled 5 cm length of magnesium ribbon to the contents of the boiling tube. At the same time start the timer. ● Continually stir the contents of the boiling tube using the thermometer. ● After 45 seconds, measure the temperature of the mixture. Record this temperature in Table 1.1. ● Rinse the boiling tube with distilled water. Experiment 3 ● Repeat Experiment 2, adding 4.0 cm3 of distilled water instead of 2.0 cm3. Experiment 4 ● Repeat Experiment 2, adding 6.0 cm3 of distilled water instead of 2.0 cm3. Experiment 5 ● Repeat Experiment 2, adding 10.0 cm3 of distilled water instead of 2.0 cm3. Complete Table 1.1. Table 1.1 volume of dilute volume of initial temperature temperature experiment sulfuric acid distilled water temperature after 45 s increase / cm3 / cm3 / °C / °C / °C 1 2 3 4 5 [5] (b) (i) State which Experiment, 1, 2, 3, 4 or 5, had the smallest temperature change. ....................................................................................................................................... [1] (ii) Explain why the temperature change was smallest in the experiment you have given in (b)(i). ............................................................................................................................................. ....................................................................................................................................... [1] (c) Complete a suitable scale on the y-axis and plot your results from Experiments 1 to 5 on Fig. 1.1. Draw a line of best fit. temperature increase / C 0.0 0.0 2.0 4.0 6.0 8.0 10.0 12.0 volume of distilled water / cm3 Fig. 1.1 [4] (d) Use your graph in Fig. 1.1 to deduce the temperature increase if Experiment 2 is repeated with 7.5 cm3 of distilled water instead of 2.0 cm3. Show clearly on Fig. 1.1 how you worked out your answer. .............................. °C [2] (e) The average rate of temperature increase in each experiment is calculated using the equation shown. temperature increase average rate of temperature increase = 45 seconds Calculate the average rate of temperature increase in Experiment 1. Give units for the rate you have calculated. average rate of temperature increase = .............................. units = .............................. [2] (f) (i) Explain why the results of the experiment are more accurate if the boiling tube is wrapped in cotton wool. ............................................................................................................................................. ............................................................................................................................................. ....................................................................................................................................... [2] (ii) Explain why a 25.0 cm3 volumetric pipette cannot be used to accurately measure the volume of the distilled water added. ............................................................................................................................................. ....................................................................................................................................... [1] (iii) State one other way in which the apparatus can be changed to give more accurate results. ............................................................................................................................................. ............................................................................................................................................. ....................................................................................................................................... [1] (g) Sketch on Fig. 1.1 the graph you would expect if all of the experiments were repeated using a 2 cm length of magnesium ribbon instead of the 5 cm length. Label your line g. [1] [Total: 20] Question 2 starts on the next page.

Mark scheme: 1(a) M1 all five volumes of dilute sulfuric acid (20) and water (0, 2, 4, 6, 10) are correct 1 M2 all temperatures and temperature changes are recorded to a consistent number of decimal places 1 M3 all five temperatures after 45 seconds are greater than the initial temperatures and temperature increases calculated correctly 1 M4 temperature increases decrease as table is descended 1 M5 temperature increase for experiment 1 comparable to supervisor’s result 1 1(b)(i) 5 1 1(b)(ii) larger / largest volume (being heated) 1 1(c) M1 suitable sensible scale on y-axis 1 M2 and M3 all five points plotted correctly 2 M4 best fit line 1 1(d) M1 correct working shown on graph 1 M2 correct value from their working to a point on the line 1 1(e) M1 correct evaluation of temperature change in experiment 1  45 1 M2 °C / s 1 1(f)(i) Any two from:  insulator  so reduces / prevents heat loss / traps heat  temperature (more) accurate / does not cool down / prevents temperature decreasing 2 1(f)(ii) volume used is not fixed / volume needed is not the same in each experiment / volume used is not 25 cm3 1 1(f)(iii) use a burette instead of a measuring cylinder 1 Question Answer Marks 1(g) sketch line is below results line for all volumes of water 1

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2 You are provided with one solid: 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] To the remaining portion of solid E, add about 5 cm depth of distilled water. Place a stopper in the boiling tube and shake to dissolve solid E and form solution E. Divide solution E into four approximately equal portions in one boiling tube and three test-tubes. (b) (i) To the first portion of solution E in the boiling tube, add aqueous sodium hydroxide dropwise and then in excess. Keep the product formed for use in (b)(ii). Record your observations. ............................................................................................................................................. ............................................................................................................................................. ....................................................................................................................................... [2] (ii) Transfer about 2 cm depth of the product from (b)(i) to another boiling tube. Gently warm the mixture and test any gas given off. Record your observations. ............................................................................................................................................. ....................................................................................................................................... [1] (iii) Identify the gas given off in (b)(ii). ....................................................................................................................................... [1] (c) To the second portion of solution E, add about 4 cm depth of aqueous sodium hydrogencarbonate. Record your observations. .................................................................................................................................................... .............................................................................................................................................. [2] (d) (i) To the third portion of solution E, add a few drops of acidified aqueous potassium manganate(VII). Record your observations. ............................................................................................................................................. ....................................................................................................................................... [1] (ii) State the conclusion that can be made from the result of the test in (d)(i). ............................................................................................................................................. ....................................................................................................................................... [1] (e) To the fourth portion of solution E, add about 1 cm depth of dilute nitric acid and a few drops of aqueous barium nitrate. Leave the mixture to stand for about two minutes. Record your observations. .................................................................................................................................................... .............................................................................................................................................. [1] (f) Identify the three ions in solid E. .................................................................................................................................................... .................................................................................................................................................... .............................................................................................................................................. [3] [Total: 14]

Mark scheme: 2(a) Any two from:  melts / dissolves / form a liquid  condensation on tube  becomes green 2 2(b)(i) M1 green precipitate 1 M2 dissolves / forms a solution 1 2(b)(ii) (red) litmus turns blue 1 2(b)(iii) ammonia / NH3 1 2(c) M1 green precipitate 1 M2 fizzing / effervescence / bubbles 1 2(d)(i) (solution) becomes pink 1 2(d)(ii) not a sulfite / no SO32— 1 2(e) white precipitate 1 2(f) M1 chromium ((III)) / Cr3+ 1 M2 ammonium / NH4+ 1 M3 sulfate / SO42— 1

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3 A mixture contains three compounds: ● liquid ethanol ● solid sodium chloride ● solid zinc carbonate. Table 3.1 gives some information about these three compounds. Table 3.1 name of compound solubility in water solubility in ethanol ethanol soluble sodium chloride soluble insoluble zinc carbonate insoluble insoluble Describe how to obtain a pure sample of each of the three compounds, ethanol, sodium chloride and zinc carbonate, from the mixture. You are provided with common laboratory apparatus. ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ........................................................................................................................................................... ..................................................................................................................................................... [6] Notes for use in qualitative analysis Tests for anions anion test test result carbonate, CO32– add dilute acid, then test for carbon effervescence, carbon dioxide dioxide gas produced chloride, Cl – acidify with dilute nitric acid, then white ppt. [in solution] add aqueous silver nitrate bromide, Br – acidify with dilute nitric acid, then cream ppt. [in solution] add aqueous silver nitrate iodide, I– acidify with dilute nitric acid, then yellow ppt. [in solution] add aqueous silver nitrate nitrate, NO3– add aqueous sodium hydroxide, ammonia produced [in solution] then aluminium foil; warm carefully sulfate, SO42– acidify with dilute nitric acid, then white ppt. [in solution] add aqueous barium nitrate sulfite, SO32– add a small volume of acidified the acidified aqueous potassium aqueous potassium manganate(VII) manganate(VII) changes colour from purple to colourless Tests for aqueous cations cation effect of aqueous sodium hydroxide effect of aqueous ammonia aluminium, Al 3+ white ppt., soluble in excess, giving white ppt., insoluble in excess a colourless solution ammonium, NH4+ ammonia produced on warming – calcium, Ca2+ white ppt., insoluble in excess no ppt. or very slight white ppt. chromium(III), Cr3+ green ppt., soluble in excess green ppt., insoluble in excess copper(II), Cu2+ light blue ppt., insoluble in excess light blue ppt., soluble in excess, giving a dark blue solution iron(II), Fe2+ green ppt., insoluble in excess, green ppt., insoluble in excess, ppt. turns brown near surface on ppt. turns brown near surface on standing standing iron(III), Fe3+ red-brown ppt., insoluble in excess red-brown ppt., insoluble in excess zinc, Zn2+ white ppt., soluble in excess, giving white ppt., soluble in excess, giving a colourless solution a colourless solution Tests for gases gas test and test result ammonia, NH3 turns damp red litmus paper blue carbon dioxide, CO2 turns limewater milky chlorine, Cl 2 bleaches damp litmus paper hydrogen, H2 ‘pops’ with a lighted splint oxygen, O2 relights a glowing splint sulfur dioxide, SO2 turns acidified aqueous potassium manganate(VII) from purple to colourless Flame tests for metal ions metal ion flame colour lithium, Li+ red sodium, Na+ yellow potassium, K+ lilac calcium, Ca2+ orange-red barium, Ba2+ light green copper(II), Cu2+ blue-green

Mark scheme: 3 max 6 to obtain ethanol MP1 filter the initial mixture (ethanol obtained as filtrate) 1 and then any five from: to obtain zinc carbonate MP2 add water to the residue / mixture MP3 stir/warm after adding water MP4 filter after adding water MP5 wash residue from filtration after the addition of water MP6 dry the solid zinc carbonate to obtain sodium chloride MP7 heat filtrate to remove water and obtain solid sodium chloride If candidates do not have a valid method of obtaining ethanol then MP1 cannot be awarded and the maximum score is 5. If ethanol is obtained AFTER adding more ethanol to the mixture, then do not award MP1, maximum 5 5

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