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 ........