2025 Prelim 9729 P4 final MS H2 Chem CJC

[Turn over 9729/04/CJC JC2 Preliminary Examinations 2025 CANDIDATE NAME CLASS 2T CHEMISTRY 9729/04 Paper 4 Practical 26 August 2025 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 17 and 18. 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 18 printed pages. Instruction Catholic Junior College JC2 Preliminary Examinations Higher 2 Shift Laboratory For Examiner’s Use 1 / 13 2 / 11 3 / 19 4 / 12 Total / 55

2 9729/04/CJC JC2 Preliminary Examinations 2025 Answer all the questions in the spaces provided. 1 Investigation of an organic compound and an inorganic compound FA 1 is an aqueous solution that contains a mixture of salts with two cations and one anion listed in the Qualitative Analysis Notes. FA 2 is an aqueous solution of an organic compound, X, with only one functional group present. You will perform tests to identify: • the ions present in FA 1. • the functional group of X in FA 2. (a) (i) Carry out the following tests. Carefully record your observations in Tables 1.1 and 1.2. The volumes given below are approximate and should be estimated rather than measured. Test and identify any gases evolved. If there is no observable change, write no observable change. Table 1.1 tests observations 1 To 1 cm depth of FA 1 in a boiling tube, add aqueous sodium hydroxide until there is no further change. Heat the boiling tube gently. 2 To 1 cm depth of FA 1 in a test-tube, add a few drops of Ba(NO3)2 (aq). Then, add excess nitric acid. 3 To 1 cm depth of FA 1 in a test-tube, add excess aqueous hydrogen peroxide until no further change. From your observations, identify the ions present in FA 1. The cations are ......................... and ...................... . The anion is ..................................... . [7] Fe2+ NH4+. SO42 – Pale green solution turned brown/ orange- yellow. Effervescence observed. O2 gas relighted a glowing splint. White ppt formed, insoluble in excess HNO3. Green ppt formed, turned brown on contact with air, insoluble in excess NaOH (aq). Gas evolved on heating turned moist red litmus paper blue. NH3 (g) evolved.

3 [Turn over 9729/04/CJC JC2 Preliminary Examinations 2025 (ii) Explain the observation for the reaction between FA 1 and aqueous hydrogen peroxide in Test 3. …………………………………………………………………………………………............. ………………………………………………………………………………………………… [1] Table 1.2 tests observations 1 To 1 cm depth of FA 2 in a test tube, add 2 cm of depth of water. Test this solution with Universal Indicator paper. Hence conclude the pH of the resultant solution of FA 2. Keep this solution for test 2 below. 2 To the resultant solution in test 1, add 1 full spatula of solid Na2CO3. 3 To a 1 cm depth of FA 2 in a test-tube, add 1 cm depth of aqueous silver nitrate. [3] (b) (i) Use your results of Test 3 in Table 1.2 to identify the anion present in FA 2. Anion present: …………………………… (ii) Suggest a possible functional group that could be present in X in FA 2 and state the evidence by completing Table 1.3. Table 1.3 Functional group evidence [2] [Total: 13] In Test 3, H2O2 oxidises Fe2+ to Fe3+ which explains for the change in colour of the solution from pale green to brown/ orange-yellow. No observable change UI paper turns red. pH = 1 or 2 Effervescence observed Gas evolved forms white ppt with limewater. CO2(g) evolved. An immediate white precipitate of AgCl is obtained. FA 2 reacts with water to form an acidic solution and it also reacts with aqueous AgNO 3 to form white ppt of AgCl(s). Acyl chloride. Cl–

4 9729/04/CJC JC2 Preliminary Examinations 2025 2 Determination of the amount of water of crystallisation in CuSO4. nH2O. In this experiment, you are to determine the amount of water of crystallisation (value of n) in a sample of hydrated copper(II) sulfate, CuSO4. nH2O by titration. When excess aqueous potassium iodide is added to the aqueous Cu2+ ions, iodine and a white precipitate of copper(I) iodide are produced. equation 1 2Cu2+ + 4I ‒ → 2CuI + I2 The amount of iodine produced is found by titration with aqueous thiosulfate ions, S2O32–. equation 2 2S2O32– + I2 → S4O62– + 2I– You are provided with FA 3 is a solution of aqueous hydrated copper(II) sulfate of concentration 20.0 g dm−3. FA 4 is a solution of aqueous potassium iodide, KI. FA 5 is 0.100 mol dm–3 aqueous sodium thiosulfate, Na2S2O3. Starch indicator (a)(i) Titration of FA 3 against FA 5 1. Fill a burette with FA 5. 2. Use a pipette to transfer 25.0 cm3 of FA 3 into a 250 cm3 conical flask. 3. Use a measuring cylinder to add about 15 cm 3 of FA 4 to this flask. A white precipitate forms in a brown solution. 4. Run FA 5 from the burette into this flask. Near the end -point, when the brown solution becomes pale, add about 1 cm3 of starch indicator. 5. Continue adding FA 5 slowly. The end-point is reached when the solution first becomes colourless. The white precipitate remains. 6. Record your titration results, to an appropriate level of precision, in the space provided below. 7. Repeat points 2 to 6 until consistent results are obtained. Titration Results [3] 1 2 Final burette reading / cm3 20.00 40.00 Initial burette reading / cm3 0.00 0.00 Volume of FA 5 used / cm3 20.00 20.00 ✓ ✓

5 [Turn over 9729/04/CJC JC2 Preliminary Examinations 2025 (ii) From your titrations, obtain a suitable volume of FA 5, VFA5, to be used in your calculations. Show clearly how you obtained this volume and place a tick ( ✓) under the readings used. VFA 5 = ………..........… [3] (b) (i) Calculate the concentration of CuSO4.nH2O in FA 3. 2Cu2+ ≡ I2 ≡ 2S2O32- Cu2+ ≡ S2O32- concentration of CuSO4.nH2O = …........…………. [1] 20.00 cm3 average titre = 20.00 + 20.00 2 = 20.00 cm3 25.0 cm3 of FA 3 (Cu2+) reacts with 20.00 cm3 of FA 5 (S2O32–) amt of Cu2+ in 25.0 cm3 of FA 3 = amt of S2O32– in 20.00 cm3 of FA 5 = 0.100 × 𝟐𝟎.𝟎𝟎 𝟏𝟎𝟎𝟎 = 2.00 × 10–3 mol conc of CuSO4 in FA 3 = 1000 25.00 × 2.00 × 10–3 = 0.0800 mol dm–3 0.0800 mol dm–3

6 9729/04/CJC JC2 Preliminary Examinations 2025 (ii) Determine the relative molecular mass of CuSO4.nH2O in FA 3 and hence calculate the value of n. You must show your working. [Ar: H, 1.0; O, 16.0; S, 32.1; Cu, 63.5] relative molecular mass, Mr, of CuSO4.nH2O = …........……… value of n = ……….....…....... [2] (c) Calculate the maximum total percentage uncertainty for your titration in 2(a)(i) if the uncertainty associated with each reading using a 25.0 cm 3 pipette and a burette are ±0.06 cm3 and ±0.05 cm3 respectively.