2023 CJC H2 Chem Prelim P4 QP

[Turn over 9729/04/CJC JC2 Preliminary Examinations 2023 CANDIDATE NAME CLASS 2T CHEMISTRY 9729/04 Paper 4 Practical 23 August 2023 2 hours 30 minutes Candidates answer on the Question Paper. Additional Materials: As listed in the Confidential Instructions READ THESE INSTRUCTIONS FIRST Write your name and class in the boxes above. 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 21 and 22. 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. This document consists of 21 printed pages and 1 blank page. Instruction Catholic Junior College JC2 Preliminary Examinations Higher 2 Shift Laboratory For Examiner’s Use 1 / 11 2 / 18 3 / 16 4 / 10 Total / 55

2 [Turn over 9729/04/CJC JC2 Preliminary Examinations 2023 Answer all the questions in the spaces provided. 1 Qualitative analysis of an inorganic solid mixture FA 8 is a solid mixture that contains two cations and two anions listed in the Qualitative Analysis Notes on pages 21 and 22. Unless otherwise stated, the volumes given below are approximate and should be estimated rather than measured. 1. Transfer the FA 8 provided into a boiling tube and add in 3 cm depth of deionised water. 2. Using a glass rod, stir the mixture well for one minute until no more of the solid mixture can dissolve. 3. Filter the mixture into another clean boiling tube. While waiting, proceed to Question 2 first. 4. When the filtration is completed, place the filter funnel containing the residue on a conical flask and wash the residue with a little deionised water. Keep both filtrate and residue for tests (a) and (b) below. Test and identify any gases evolved. At each stage of any test, you are to record details of the following: • colour changes seen • the formation of any precipitate • the solubility of such precipitates in an excess of the reagent added If there is no observable change, write no observable change. Record your observations in Tables 1.1 and 1.2 below. No additional tests for ions present should be attempted. (a) Tests on the filtrate. Table 1.1 test observations (i) Test the filtrate using Universal indicator paper. Hence conclude pH of the filtrate.

3 [Turn over 9729/04/CJC JC2 Preliminary Examinations 2023 (ii) To 1 cm depth of the filtrate in a test - tube, add aqueous sodium hydroxide dropwise, with shaking, until no further change is observed. (b) Tests on the residue. Table 1.2 test observations (i) Place the funnel containing the residue (on the filter paper) into a clean boiling tube. Pour about 5 cm 3 of dilute nitric acid onto the residue. Collect 1 cm depth of the solution in the boiling tube. Remove the funnel and return it to the conical flask.

4 [Turn over 9729/04/CJC JC2 Preliminary Examinations 2023 (ii) To this solution in the boiling tube, add aqueous sodium hydroxide dropwise, with shaking, until no further change is observed. Keep this resultant mixture for test (iii) below. (iii) To 1 cm depth of the mixture from (ii), carefully add 1 cm depth of aqueous hydrogen peroxide. [6] (c) (i) One of the cations in FA 8 is responsible for the nature of the filtrate in test 1(a)(i). It is formed from a Period 3 element. This cation present in FA 8 is: …………………………………………………………… [1] (ii) Write an equation to account for the nature of the filtrate in test 1(a)(i). ……………………………………………………………………………………………… [1] (d) (i) The second cation present in FA 8 is ……………… evidence ...…………………………………………………………………………………… ….……………………………………………………………………………………………… ………………………………………………………………………………………………...[1]

5 [Turn over 9729/04/CJC JC2 Preliminary Examinations 2023 (ii) One anion present in FA 8 is ………………. evidence ………………………………………………………………………………………. ……………………………………………………………………………………………….… ………………………………………………………………………………………………… ………………………………………………………………………………………….…… [1] (iii) Suggest what type of reaction takes place when hydrogen peroxide is added in test 1(b)(iii). ……………………………………………………………………………………………....[1] [Total: 11]

6 [Turn over 9729/04/CJC JC2 Preliminary Examinations 2023 2 Determination of the molar enthalpy changes of two reactions by indirect methods. Sodium carbonate, Na 2CO3 reacts with water and carbon dioxide to form sodium hydrogencarbonate, NaHCO3, according to equation 1. equation 1 Na2CO3(s) + H2O(l) + CO2(g) → 2NaHCO3(s) H1 The enthalpy change of this reaction cannot be determined directly. Both Na2CO3(s) and NaHCO3(s) react with dilute sulfuric acid. equation 2 Na2CO3(s) + H2SO4(aq) → Na2SO4(aq) + H2O(l) + CO2(g) H2 equation 3 NaHCO3(s) + ½ H2SO4(aq) → ½ Na2SO4(aq) + H2O(l) + CO2(g) H3 In this experiment, you will determine the values for H2 and H3, and then use your results to calculate a value for H1. You are provided with: FA 1 is sodium carbonate, Na2CO3. FA 2 is sodium hydrogen carbonate, NaHCO3. FA 3 is 1.00 mol dm−3 sulfuric acid, H2SO4 (FA 3 will also be used in Q3). (a) Method Experiment 1: Na2CO3(s) + H2SO4(aq) → Na2SO4(aq) + H2O(l) + CO2(g) 1. Use a measuring cylinder to transfer 25 cm 3 of the acid, FA 3, into a polystyrene cup supported in a 250 cm3 beaker. The acid is in excess. 2. Weigh the capped bottle containing FA 1 and record the balance reading. 3. Place the thermometer in the acid and record its initial temperature. 4. Carefully tip all the FA 1, in small portions, into the acid and stir to dissolve. 5. Read and record the highest temperature reached. 6. Reweigh the emptied bottle and its cap and record the balance reading and the mass of FA 1 used. Experiment 2: NaHCO3(s) + ½ H2SO4 (aq) → ½ Na2SO4(aq) + H2O(l) + CO2(g) 7. Replace the wet polystyrene cup with a clean, dry polystyrene cup. 8. Repeat Steps 1 to 4 in Experiment 1 but use FA 2 in place of FA 1. 9. Read and record the lowest temperature reached. 10. Reweigh the emptied bottle and its cap and record the balance reading and the mass of FA 2 used.

7 [Turn over 9729/04/CJC JC2 Preliminary Examinations 2023 Results Record all weighings and temperature readings to an appropriate level of precision in the table below. Table 2.1 [5] (b) For the purpose of calculations, you should assume that the specific heat capacity of the solution is 4.18 J g–1K–1, and that the density of the solution is 1.0 g cm–3. (i) Use relevant results from Table 2.1 to calculate the heat energy produced when FA 1 was added to the acid in Experiment 1. Hence, calculate the enthalpy change, in kJ mol –1, when 1 mol of FA 1, Na2CO3, reacts with the acid. Include the sign of H2 in your answer. [Ar: C, 12.0; O, 16.0; Na, 23.0]. heat energy produced =…………...… J enthalpy change, H2 = ...................... kJ mol–1 [3] Experiment 1 Experiment 2 mass of capped bottle + solid / g mass of capped bottle + residual solid / g mass of solid added / g initial temperature, Ti, of FA 3 / °C final temperature, Tf / °C temperature change, T / °C

8 [Turn over 9729/04/CJC JC2 Preliminary Examinations 2023 (ii) Use relevant results from Table 2.1 to calculate