Cambridge IGCSE Chemistry (9-1) 0971 — 2025 May/June Paper 6 · Variant 2

1 When heated, magnesium reacts with steam to make magnesium oxide and hydrogen gas. Fig. 1.1 shows the apparatus a teacher uses to react clean magnesium ribbon with steam and collect the hydrogen gas produced. water and A clean mineral wool magnesium ribbon X Fig. 1.1 (a) Name the item of apparatus labelled A in Fig. 1.1. ............................................................................................................................................. [1] (b) Suggest how the magnesium ribbon should be cleaned before use. ................................................................................................................................................... ............................................................................................................................................. [1] (c) State the purpose of the mineral wool. ................................................................................................................................................... ............................................................................................................................................. [1] (d) Draw two arrows on Fig. 1.1 to show the two places where the apparatus should be heated. [2] (e) During the reaction a colourless liquid collects at the point marked X on Fig. 1.1. Suggest the identity of liquid X. ............................................................................................................................................. [1] (f) The gas collected in A is not pure hydrogen. Suggest why the gas collected is not pure. ................................................................................................................................................... ............................................................................................................................................. [1] [Total: 7]

Mark scheme: Question Answer Marks 1(a) (gas) syringe 1 1(b) (rub with) sand / emery / abrasive paper 1 1(c) to hold / absorb the water / to prevent the water running along the tube 1 1(d) 2 1(e) water / H2O 1 1(f) contains air (that was in the apparatus at the start) 1

More questions on Experimental design

2 A student investigates the temperature change when anhydrous lithium chloride dissolves in water. The student does five experiments. Experiment 1 • Use a 50 cm3 measuring cylinder to pour 40 cm3 of distilled water into a 100 cm3 beaker. • Use a thermometer to measure the initial temperature of the water. • Add a 2.0 g sample of anhydrous lithium chloride to the water in the beaker. • Continually stir the mixture in the beaker using the thermometer. • Measure the highest temperature reached by the mixture in the beaker. • Empty the beaker and rinse the beaker with distilled water. Experiment 2 • Repeat Experiment 1 using 30 cm3 of distilled water instead of 40 cm3. Experiment 3 • Repeat Experiment 1 using 25 cm3 of distilled water instead of 40 cm3. Experiment 4 • Repeat Experiment 1 using 20 cm3 of distilled water instead of 40 cm3. Experiment 5 • Repeat Experiment 1 using 15 cm3 of distilled water instead of 40 cm3. (a) Use the information in the description of the experiments and the thermometer diagrams to complete Table 2.1. Table 2.1 thermometer mass of volume of diagram highest anhydrous initial temperature distilled for highest temperature experiment lithium temperature change water temperature reached chloride / °C / °C / cm3 reached / °C / g / °C 30 1 2.0 40 22.5 25 20 30 2 30 22.5 25 20 35 3 25 22.5 30 25 35 4 20 22.0 30 25 40 5 15 22.0 35 30 [4] (b) Complete a suitable scale on the y-axis and plot your results from Experiments 1 to 5 on Fig. 2.1. Draw a line of best fit. temperature change / °C 0 10 15 20 25 30 35 40 45 volume of water / cm3 Fig. 2.1 [4] (c) Extrapolate the line on your graph in Fig. 2.1 to deduce the temperature change when Experiment 1 is repeated with 45 cm3 of water instead of 40 cm3 of water. Show clearly on Fig. 2.1 how you worked out your answer. temperature change = .............................. [3] (d) The energy, in J, given out when 2.0 g of anhydrous lithium chloride dissolves is calculated using the equation shown. energy given out = temperature change × 4.2 × volume of water Calculate the energy given out when 2.0 g of anhydrous lithium chloride dissolves in Experiment 5. energy given out = .............................. J [1] (e) Estimate the temperature change when Experiment 1 is repeated using 4.0 g of anhydrous lithium chloride instead of 2.0 g. Give a reason for your answer. temperature change ................................................................................................................. reason ....................................................................................................................................... ................................................................................................................................................... [2] (f) Explain why the results obtained would be more accurate if the beaker used in each experiment was replaced by a polystyrene cup. ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [2] (g) (i) Explain why using a burette instead of a measuring cylinder is an improvement. ........................................................................................................................................... ..................................................................................................................................... [1] (ii) Explain why standing the beaker in a water-bath is not an improvement. ........................................................................................................................................... ..................................................................................................................................... [1] [Total: 18]

Mark scheme: 2(a) all experiments have a mass of 2.0 g of lithium chloride 1 all temperatures and temperature changes recorded to 1 dp 1 all five highest temperatures recorded correctly (27.0, 29.0, 30.5, 32.5, 35.5) 1 all temperature changes calculated correctly (4.5, 6.5, 8.0, 10.5, 13.5) 1 2(b) y-axis scale is linear and points extend over halfway up scale 1 all points plotted correctly 2 best fit line 1 2(c) extrapolation shown on graph, this must be a smooth continuation of line to at least a volume of 45 1 correct reading from their extrapolation at 45 1 °C 1 2(d) 850.5 OR 851 1 2(e) (temperature change approximately) doubled / 9 °C 1 twice as much lithium chloride dissolved / used (so twice as much energy given out) 1 2(f) polystyrene is a better insulator than glass / it is an insulator 1 less heat loss (to the surroundings) 1 2(g)(i) (burette more) accurate (than measuring cylinder) 1 2(g)(ii) water-bath would keep temperature constant 1

More questions on Experimental design

3 A student tests two solids: solid J and solid K. Tests on solid J Solid J is iron(II) iodide. The student dissolves solid J in water to form solution J. Solution J is divided into four portions. (a) To the first portion of solution J, the student adds aqueous sodium hydroxide dropwise and then in excess. observations when added dropwise ......................................................................................... observations when added in excess ......................................................................................... [2] (b) To the second portion of solution J, the student adds 1 cm3 of dilute nitric acid followed by a few drops of aqueous barium nitrate. observations ............................................................................................................................. ............................................................................................................................................. [1] (c) To the third portion of solution J, the student adds 1 cm3 of dilute nitric acid followed by a few drops of aqueous silver nitrate. observations ............................................................................................................................. ............................................................................................................................................. [1] (d) To the fourth portion of solution J, the student adds 1 cm3 of aqueous chlorine. observations ............................................................................................................................. ............................................................................................................................................. [1] Tests on solid K Table 3.1 shows the tests and the student’s observations for solid K. Table 3.1 tests observations test 1 Carry out a flame test on solid K. lilac coloured flame test 2 The remaining solid K is dissolved in water to form solution K. Solution K is divided into two portions. To the first portion of solution K in a boiling tube, the damp red litmus paper remains red add 1 cm3 aqueous sodium hydroxide. Warm the product and hold damp red litmus paper at the mouth of the boiling tube. test 3 To the second portion of solution K in a boiling effervescence is seen tube, add about 1 cm3 of aqueous sodium damp red litmus paper turns blue hydroxide and a piece of aluminium foil. Warm the mixture and test any gas given off. (e) State the conclusion about solid K that can be made from the observations in test 2. ............................................................................................................................................. [1] (f) Identify the gas given off in test 3. ............................................................................................................................................. [1] (g) Identify solid K. ................................................................................................................................................... ............................................................................................................................................. [2] [Total: 9]

Mark scheme: 3(a) dropwise: green precipitate 1 excess: no (further) change / precipitate remains / green precipitate / insoluble 1 3(b) no change 1 3(c) yellow precipitate 1 3(d) (solution / liquid becomes) yellow / orange / brown 1 3(e) does not contain ammonium / NH4+ ions / not ammonium / NH4+ 1 3(f) ammonia / NH3 1 3(g) potassium / K+ 1 nitrate / NO3– 1 KNO3 = 2

More questions on Identification of ions and gases

4 Magnesium sulfate is a salt. Magnesium sulfate is soluble in water. The solubility of a salt is the mass of the salt, in g, that dissolves in 100 cm3 of water at a specified temperature. Plan an investigation to determine the solubility of magnesium sulfate in water at 50 °C. Your plan must include how the solubility of magnesium sulfate, in g per 100 cm3 of water, can be found. You are provided with solid magnesium sulfate, distilled water and 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

Mark scheme: 4 1 mark for any 6 of: 6 • 100 cm3 of water measured using suitable apparatus and placed into a suitable container • water is heated to 50 °C • water is maintained at this temperature • magnesium sulfate is added in excess or in portions until no more dissolves • the mixture is stirred • the solution is filtered to remove undissolved magnesium sulfate or the mass used is known • the use of appropriate measurements to calculate the solubility.

More questions on Experimental design