2021 EJC Prelim H2 Chemistry Paper 4 QP

© EJC 9729/04/J2PE/21 [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 sulfuric 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 adding FA 2 until the equivalence point is reacted and passed. Throughout the experiment you will note and record the temperature of the mixture after each addition. You will then analyse your results graphically in order to determine the • titration volume at the equivalence point, Vequivalence, • maximum temperature change, DTmaximum 1, • molar enthalpy change, DHreaction 1, for reaction 1. In your second experiment, you will mix together a given volume of FA 1 with a suitable volume of FA 3. You will then determine the • maximum temperature change, DTmaximum 2, • molar enthalpy change, DHreaction 2, for reaction 2. 1212

3 © EJC 9729/04/J2PE/21 [Turn Over For Examiner’s Use (a) The reaction between FA 1 and FA 2 In this task you will need to record the maximum temperature of the reaction mixture when specified volumes of FA 2 have been added. It is important that the volume of FA 2 recorded is the total volume you have added up to that point when the temperature reading was made. Note: If you overshoot on an addition, record the actual total volume of FA 2 added up to that point. In an appropriate format in the space provided on page 4, record all values of temperature, T, and each total volume of FA 2 added. (i) 1. Fill a burette with FA 2. 2. Place a Styrofoam cup inside a second Styrofoam cup which is held in a glass beaker to prevent it tipping over. 3. Using a pipette, transfer 25.0 cm3 of FA 1 to the first Styrofoam cup. 4. Stir the FA 1 solution in the cup with the thermometer. Read and record its temperature. 5. From the burette, add 2.00 cm3 of FA 2 to the cup and stir the mixture thoroughly. 6. Read and record the maximum temperature of the mixture, T, and the volume of FA 2 added. 7. Repeat points 5 and 6 until a total of 30.00 cm3 of FA 2 has been added. After each addition of FA 2, record the maximum temperature of the mixture and the total volume of FA 2 added up to that point.

4 © EJC 9729/04/J2PE/21 For Examiner’s Use Results [2]

5 © EJC 9729/04/J2PE/21 [Turn Over For Examiner’s Use (ii) On the grid below, plot a graph of temperature, T (y-axis) against volume of FA 2 added (x-axis). [4] (iii) Draw two smooth lines of best fit. • The first best-fit line should be drawn using the plotted points where the temperature is rising. • The second best-fit line should be drawn using the plotted points where the temperature is falling. • Extrapolate these lines until they cross. Note: Each line should have a shape best suited to its plotted points.

6 © EJC 9729/04/J2PE/21 For Examiner’s Use (iv) Determine from your graph • the maximum temperature reached, Tmaximum, • the maximum temperature change, DTmaximum 1, • the volume, Vequivalence, of FA 2 needed to completely react with 25.0 cm3 of FA 1. Show on your graph how you obtained these values. Record these values in the spaces provided below. maximum temperature reached, Tmaximum = ............................................ maximum temperature change, DTmaximum 1 = ............................................ volume of FA 2 used, Vequivalence = ............................................ [3] (b) Ideally, the graph line before the equivalence point should be an increasing curve that concaves downward (that is, gradient of the curve decreases). (i) Explain why the graph line is increasing. ................................................................................................................................ ................................................................................................................................ ................................................................................................................................ ............................................................................................................................ [1] (ii) Explain why the graph line concaves downward. ................................................................................................................................ ................................................................................................................................ ................................................................................................................................ ............................................................................................................................ [1]

7 © EJC 9729/04/J2PE/21 [Turn Over For Examiner’s Use (c) The reaction between FA 1 and FA 3 The molar enthalpy change for reaction 2, DHreaction2, is the enthalpy change when 1.00 mol of NaHCO3 reacts completely with H2SO4. In this task you will calculate a value for the molar enthalpy change, DHreaction 2. To do this, you will need to determine the maximum temperature change produced when measured volumes of FA 1 and FA 3 are mixed. Upon considering the concentrations of FA 1 and