2024 CJC H2 Chemistry Prelim P4 (QP)

[Turn over 9729/04/CJC JC2 Preliminary Examinations 2024 CANDIDATE NAME CLASS 2T CHEMISTRY 9729/04 Paper 4 Practical 21 August 2024 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 19 and 20. 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 19 printed pages and 1 blank page. Instruction Catholic Junior College JC2 Preliminary Examinations Higher 2 Shift Laboratory For Examiner’s Use 1 / 16 2 / 15 3 / 16 4 / 8 Total / 55

2 9729/04/CJC JC2 Preliminary Examinations 2024 Answer all the questions in the spaces provided. 1 Part 1: Qualitative analysis of an inorganic solid mixture FA 1 is a solid mixture that contains two cations and two anions listed in the Qualitative Analysis Notes on pages 19 and 20. Unless otherwise stated, the volumes given below are approximate and should be estimated rather than measured. 1. Add 3 full spatulas of FA 1 into a boiling tube and add 3 cm depth of deionised water. 2. Using a glass rod, stir the mixture for one minute until no more of the solid mixture can dissolve. 3. Filter the mixture into another clean boiling tube. This is the filtrate. While waiting, you may wish to proceed to Question 2 first. 4. When the filtration is completed, p lace 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) To 1 cm depth of the filtrate in a test - tube, add aqueous sodium hydroxide dropwise, with shaking, until no further change is observed.

3 [Turn over 9729/04/CJC JC2 Preliminary Examinations 2024 (ii) To 1 cm depth of the filtrate in a test - tube, add aqueous ammonia dropwise, with shaking, until no further change is observed. (iii) To 1 cm depth of the filtrate in a test - tube, add 5 drops of aqueous barium nitrate, followed by aqueous nitric acid. (b) Tests on the residue. Table 1.2 test observations (i) Place the filter 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 filter funnel and return it to the conical flask. (ii) To 1 cm depth of the filtrate from (b)(i) in a test -tube, add aqueous ammonia dropwise, with shaking, until no further change is observed. • Blue ppt insoluble in excess

4 9729/04/CJC JC2 Preliminary Examinations 2024 (iii) To 1 cm depth of aqueous potassium iodide, add 5 drops of the filtrate from (b)(i) and shake well. Then add 1 cm depth of aqueous sodium thiosulfate dropwise, with shaking. [6] (c) (i) Identify the two cations and two anions in FA 1 and state the evidence for each cation/anion by completing Table 1.3. Table 1.3 identity of cation or anion evidence [4] (ii) State the type of reaction occurring in test (b)(iii) when the filtrate from (b)(i) is added to potassium iodide, writing a suitable equation to illustrate your answer. Type of reaction………………………… [1] (iii) Write an equation for the reaction that occurs when sodium thiosulfate is added in test (b)(iii). ………………………………………………………………………………………………..[1]

5 [Turn over 9729/04/CJC JC2 Preliminary Examinations 2024 Part 2: Planning (d) Consider the following organic compounds. butanal benzaldehyde propan-1-ol 2-methylpropan-2-ol Plan an investigation, using test-tube reactions, which would enable you to identify each of these four compounds. Each compound should be identified by at least one positive test result. Hence, four different tests are required. Your plan should include: • details of the reagents and conditions to be used • an outline of the sequence of steps you would follow • an explanation of how you w ould analyse your results in ord er to identify each compound. Once a compound has been clearly identified, your plan should concentrate on distinguishing the remaining compounds. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. …………………………………………………………………………………………………….. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. ……………………………………………………………………………………………………. ………………………………………………………………………………………………….[4] [Total: 16]

6 9729/04/CJC JC2 Preliminary Examinations 2024 2 Determination of the percentage of sodium carbonate in a mixture of sodium carbonate and sodium hydrogen carbonate Sodium carbonate reacts with hydrochloric acid in two separate stages: Stage 1: Na2CO3 + HCl → NaHCO3 + NaCl Stage 2: NaHCO3 + HCl → NaCl + CO2 + H2O The overall reaction at the end of the two stages is Na2CO3 + 2 HCl → 2 NaCl + CO2 + H2O The percentage by mass of sodium carbonate in a mixture of sodium carbonate and sodium hydrogen carbonate can thus be determined in a double-indicator titration experiment, where two different indicators are used in the same titration experiment, as described below. With hydrochloric acid as the titrant and the use of thymolphthalein indicator, the end -point for Stage 1 can be determined to be when the solution turns from blue to colourless. Continuing the titration with the subsequent addition of methyl orange indicator, the end-point for Stage 2 can be determined to be when the solution turns from yellow to orange. FA 2 is an aqueous solution prepared by dissolving a solid mixture of sodium carbonate, Na2CO3, and sodium hydrogen carbonate, NaHCO3, in deionised water. FA 3 is an aqueous solution containing 0.50 mol dm‒3 of hydrochloric acid, HCl. (a) Titration of FA 2 against FA 3 1. Fill the unlabelled burette with FA 3. (Do not use the burette labelled “FA 4”.) 2. Using a pipette, transfer 25.0 cm3 of FA 2 into a conical flask. 3. Add 3 to 4 drops of thymolphthalein indicator and titrate with FA 3. The first end-point is reached when the solution turns from blue to colourless. Record your titration results on the next page. Do not discard this solution. 4. To the same solution, add 3 drops of methyl orange indicator and conti