2021 DHS H2 Prelim Paper 4_Solutions

1 This question paper consists of 18 printed pages. © DHS 2021 9729/04 [Turn over Name: Centre/Index Number: Class: DUNMAN HIGH SCHOOL Preliminary Examination Year 6 H2 CHEMISTRY 9729/04 Paper 4 Practical 24 August 2021 2 hours 30 minutes Candidates answer on the Question Paper. READ THESE INSTRUCTIONS FIRST Write your centre number, index number, name and class at the top of this page. 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 staples, paper clips, 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 5 3 15 4 13 Total 55

2 © DHS 2021 9729/Prelim/04/21 Answer all questions in the spaces provided. 1 Determination of a value for the enthalpy change of precipitation, DHppt, of barium sulfate FA 1 is 1.00 mol dm-3 sodium hydroxide, NaOH. FA 2 is a saturated solution of barium hydroxide, Ba(OH)2. FA 3 is 1.00 mol dm-3 sulfuric acid, H2SO4. The addition of FA 2 to FA 3 results in neutralisation and precipitation reactions occurring as shown in equations 1 and 2 respectively. equation 1 H+(aq) + OH-(aq) ® H2O(l) DHneut equation 2 Ba2+(aq) + SO42-(aq) ® BaSO4(s) DHppt In the first experiment, you will determine the maximum temperature change as a result of both reactions occurring in a Styrofoam cup. In the second experiment, you will measure the temperature of the resulting mixture after each addition of a fixed volume of FA 1 solution to the remaining H+ ions in the Styrofoam cup. You will analyse your results graphically in order to determine an accurate value for the temperature change of the mixture, caused by the neutralisation reaction shown in equation 1. You will use this value to calculate the heat change for the second experiment and hence determine a value for the enthalpy change of neutralisation which will then be used to determine a value for the enthalpy change of precipitation for BaSO4. (a) (i) Experiment 1 1. Use a measuring cylinder to add 20.0 cm3 of FA 3 into a Styrofoam cup. Place this cup inside a second Styrofoam cup, which is placed in a 250 cm3 glass beaker. Stir and measure the temperature of this solution, T1,initial. Record this temperature in Table 1.1. 2.