2022 XMS Chem Prelims P2

4 6092/Chemistry/Paper 2/2022 Prelim Exam For Examiner’s Use A2 Ammonium iodide, NH4I, is a white solid which decomposes when heated. NH4I(s) ® NH3(g) + HI(g) (a) A small sample of ammonium iodide is heated in a test-tube. Describe how you would know when all the ammonium iodide has decomposed. …………………………………………………………………………………………… …………………………………………………………………………………………… [1] (b) Calculate the total volume of gas, measured at room temperature and pressure, formed when 2.90 g of ammonium iodide is completely decomposed. [3] (b) Aqueous ammonium iodide reacts with three halogens, fluorine, chlorine and bromine, but not with astatine. (i) Write a general equation to show the reaction of ammonium iodide with a halogen. Use X2 as the symbol for the halogen. ……………………………………………………………………………………. [1] (ii) Explain why aqueous ammonium iodide has no reaction with astatine. ……………………………………………………………………………………. [1] (c) Solid ammonium iodide does not conduct electricity. Aqueous ammonium iodide conducts electricity. Explain these observations. …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………………… [2] [Total: 8]

5 6092/Chemistry/Paper 2/2022 Prelim Exam For Examiner’s Use A3 (a) Two students set up an experiment to investigate the rate of diffusion of gases. Concentrated hydrochloric acid produces fumes of hydrogen chloride, HCl. Concentrated hydrobromic acid produces fumes of hydrogen bromide. HBr. The students made the following observations: Four minutes after setting up the experiment, the litmus paper in tube 1 turns red. Seven minutes after setting up the experiment, the litmus paper in tube 2 turns red. One of the students makes this conclusion: ‘The rate of diffusion is inversely proportional to the relative molecular mass of each gas.’ Do the observations support this conclusion? Show by means of a calculation. [3]

6 6092/Chemistry/Paper 2/2022 Prelim Exam For Examiner’s Use (b) The students conducted another experiment to investigate the rate of decomposition of three metal carbonates, CaCO3, FeCO3 and ZnCO3. An equal mole of each metal carbonate is heated in a test-tube. The total volume of carbon dioxide formed is measured every 10 seconds, and the results are plotted. The diagram shows the typical shape of the graph for all the metal carbonates. (i) Suggest why the volume of carbon dioxide does not increase by very much when each metal carbonate is first heated. ……………………………………………………………………………………. [1] (ii) How is the graph used to find out when the decomposition has finished? ……………………………………………………………………………………. [1] The table shows the results. metal carbonate time taken for complete decomposition / s CaCO3 360 FeCO3 60 ZnCO3 70 (iii) Predict and explain the time it would take MgCO3 and PbCO3 to fully decompose. MgCO3 ........................... s PbCO3 ............................. s explanation ……………………………………………………………………… ……………………………………………………………………………………. [3] [Total: 8]

7 6092/Chemistry/Paper 2/2022 Prelim Exam For Examiner’s Use A4 (a) Cyclobutane is an organic compound with the following structure. The complete combustion of one mole of cyclobutane releases 2702 kJ of heat energy. (i) Calculate the heat energy released when 600 dm3 of cyclobutane, at room temperature, and pressure, is completely combusted. [2] (ii) Explain, in terms of the energy changes associated with bond breaking and bond making, why the combustion of cyclobutane is exothermic. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. [2] (iii) Cyclobutane has several isomers which are alkenes. Draw the structure of one of these isomers. [1]

8 6092/Chemistry/Paper 2/2022 Prelim Exam For Examiner’s Use (b) Sorrel is a small green plant. Sorrel plants contain a poisonous carboxylic acid Y. (i) What can be deduced about the chemistry of Y from each of the following pieces of information? When Y is warmed with acidified potassium manganate(VII), the solution changes from pink to colourless. ……………………………………………………………………………………. ……………………………………………………………………………………. A 0.1 mol/dm3 solution of Y has a pH of 5 whereas a 0.1 mol/dm3 hydrochloric acid solution has a pH of 1. ……………………………………………………………………………………. ……………………………………………………………………………………. [2] (ii) Analysis of 10.0 g of carboxylic acid Y shows that it contains 2.67 g carbon, 0.220 g hydrogen and 7.11 g oxygen. The relative molecular mass of Y is 90. Deduce the empirical formula and the molecular formula of Y. empirical formula ……………………………. molecular formula ……………………………. [3] [Total: 10]

9 6092/Chemistry/Paper 2/2022 Prelim Exam For Examiner’s Use A5 (a) The diagram shows the apparatus that a student sets up for the electrolysis of concentrated sodium chloride solution. Explain why (i) hydrogen, and not sodium, is formed at the cathode. ……………………………………………………………………………………. ……………………………………………………………………………………. [1] (ii) equal volumes of chlorine and hydrogen gas are produced. ……………………………………………………………………………………. ……………………………………………………………………………………. [1] (iii) the Universal Indicator turns purple during the electrolysis. ……………………………………………………………………………………. ……………………………………………………………………………………. [1]

10 6092/Chemistry/Paper 2/2022 Prelim Exam For Examiner’s Use (b) The student modifies the apparatus for the electrolysis of copper(II) sulfate solution. (i) Explain, using the reaction occurring at the cathode, the meaning of the term reduction. ……………………………………………………………………………………. [1] (ii) Over time, the electrolyte turns from blue to colourless. State one change the student could make to the apparatus so that the electrolyte remains blue during the electrolysis. Give a reason for your answer. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. [2] [Total: 6]

11 6092/Chemistry/Paper 2/2022 Prelim Exam For Examiner’s Use A6 (a) Global warming is believed to be mainly the result of increasing levels of carbon dioxide in the atmosphere. (i) How is the balance of carbon dioxide and oxygen maintained in the atmosphere? Explain why levels of carbon dioxide are increasing and how this leads to global warming. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. [3] (ii) Some scientists believe that it is changes in solar activity (i.e. changes in the brightness and warmth of the sun) that causes global warming. The graphs below show the changes in solar activity and atmospheric temperature from 1880 to 2020. Using the information from the graphs, describe how well the evidence supports the argument that solar activity is the cause of global warming. ……………………………………………………………………………………. ……………………………………………………………………………………. [2]

12 6092/Chemistry/Paper 2/2022 Prelim Exam For Examiner’s Use (b) Oxides of nitrogen are atmospheric pollutants. Nitrogen monoxide, NO, is formed in an internal combustion engine when nitrogen and oxygen react together. N2(g) + O2(g) ® 2NO(g) The diagram shows the energy profile for this reaction. (i) Identify the energy changes X and Z. X is …………………………………………. Z is …………………………………………. [2] (ii) Explain how you can tell from the diagram that the reaction is endothermic. ……………………………………………………………………………………. ……………………………………………………………………………………. [1]

13 6092/Chemistry/Paper 2/2022 Prelim Exam For Examin