2024 CJC H2 Chemistry Prelim P4 (Ans)

[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 MARK SCHEME

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. White ppt formed; soluble in excess NaOH to give a colourless solution

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. Effervescence observed; gas gives white ppt with limewater. CO2(g) liberated. Blue filtrate obtained. White ppt formed; soluble in excess NH3 to give a colourless solution White ppt formed, insoluble in acid • Blue ppt insoluble in excess Blue ppt soluble in excess NH3(aq) to give a dark blue solution

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] White/cream/off-white ppt in brown solution Brown solution is discharged/turns colourless/ decolourised. redox White ppt with NaOH(aq) and NH3(aq), soluble in excess to give a colourless solution Zn2+ SO42‒ Cu2+ CO32‒ White ppt with Ba(NO3)2(aq), insoluble in acid Blue ppt with NH3(aq), soluble in excess to give a dark blue solution Effervescence of CO2 with HNO3(aq) which gives white ppt with limewater 2 S2O32‒ + I2 → S4O62‒ + 2 I‒

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] 1. Add Fehling’s Solution to the 4 compounds separately in a test tube. Heat gently in a water bath. Butanal, an aliphatic aldehyde will give a red ppt, the other 3 compounds will not give a red ppt. 2. Add Tollens’ Reagent to the remaining 3 compounds separately in a test -tube. Heat gently in a water bath. Benzaldehyde, an aromatic aldehyde will give a silver mirror, the other 2 compounds will not give a silver mirror. 3. Add K2Cr2O7(aq) and H 2SO4(aq) to the remaining 2 compounds separately in a test-tube. Heat gently in a water bath. Propan-1-ol being a primary alcohol, is oxidised and the orange acidified K 2Cr2O7 turns green . 2-methylpropan-2-ol, being a tertiary alcohol is not oxidised by acidified K2Cr2O7. So, the orange acidified K2Cr2O7 does not turn green. 4. Add anhydrous PCl5 to the remaining compound in a test -tube. Steamy white fumes of HCl are observed, indic