2021 EJC Prelim H2 Chemistry Paper 4 Answer Scheme

© EJC 9729/04/J2PE/20 [Turn Over EUNOIA JUNIOR COLLEGE JC2 Preliminary Examination 2021 General Certificate of Education Advanced Level Higher 2 CANDIDATE NAME CIVICS GROUP 2 0 – INDEX NUMBER CHEMISTRY Paper 4 Practical 9729/04 31 August 2021 2 hours 30 minutes Candidates answer on the Question Paper. Additional Materials: As listed in the Confidental Instructions READ THESE INSTRUCTIONS FIRST Write your name, civics group and registration number on the work you hand in. Give details of the practical shift and laboratory, where appropriate, in the boxes provided. Write in dark blue or black pen. You may use an HB pencil for any diagrams or graphs. Do not use paper clips, highlighters, glue or correction fluid. Answer all questions in the spaces provided on the Question paper. The use of an approved scientific calculator is expected, where appropriate. You may lose marks if you do not show your working or if you do not use appropriate units. Qualitative Analysis Notes are printed on pages 23 and 24. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. Shift Laboratory For Examiner’s Use 1 / 22 2 / 22 3 / 11 Total / 55 This document consists of 22 printed pages and 2 blank pages.

2 © EJC 9729/04/J2PE/21 For Examiner’s Use Answer all the questions in the spaces provided. 1 Investigation on the behaviour of acids and bases in aqueous solution FA 1 is 1.00 mol dm–3 sodium hydrogencarbonate, NaHCO3 FA 2 is sodium hydroxide, NaOH, of concentration between 1.5 mol dm–3 and 2.0 mol dm–3 FA 3 is 2.00 mol dm–3 sulfuric acid, H2SO4 According to the Arrhenius theory, an acid-base neutralisation reaction involves reacting together H+(aq) and OH–(aq) to produce water molecules. H+(aq) + OH–(aq) ® H2O(l) DHneutralisation = –57.1 kJ mol–1 This task involves two different acid-base reactions. The first reaction is between sodium hydrogencarbonate, FA 1, and sodium hydroxide, FA 2. reaction 1 NaHCO3(aq) + NaOH(aq) ® Na2CO3(aq) + H2O(l) DHreaction 1 The molar enthalpy change for reaction 1, DHreaction 1, is the enthalpy change when 1.00 mol of NaHCO3 reacts completely with NaOH. Instead of using an indicator to determine the endpoint, you will perform a thermometric titration to determine the equivalence point of the reaction. The equivalence point is that point where H+(aq) from the acid and OH–(aq) from the base are present in equal molar amounts. The second reaction is between sodium hydrogencarbonate, FA 1, and sulphuric acid, FA 3. reaction 2 NaHCO3(aq) + H2SO4(aq) ® Na2SO4(aq) + H2O(l) + CO2(g) DHreaction 2 The molar enthalpy change for reaction 2, DHreaction 2, is the enthalpy change when 1.00 mol of NaHCO3 reacts completely with H2SO4. In your first experiment, you will perform a thermometric titration by adding portions of FA 2 progressively to a known volume of FA 1. You will continue addi