NYJC 2026 H2 Chem 9476 P4 Answers

H NANYANG JUNIOR COLLEGE JC2 PRACTICAL PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME Mark Scheme CLASS CENTRE NUMBER S INDEX NUMBER CHEMISTRY 9476/04 Paper 4 Practical 14 August 2026 2 hour 30 minutes Candidates answer on the Question Paper Additional Materials: As listed in the Confidential Instructions READ THESE INSTRUCTIONS FIRST Write your Centre number, index number, name and class on all the work you hand in. 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. Shift 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. Laboratory 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. For Examiner’s Use 1 / 12 2 / 15 3 /13 4 / 10 Total /50 This document consists of 20 printed pages and 4 blank pages.

2 1 Identification of two cations and two anions FA 1 and FA 2 each contain one cation and one anion. The ions in the two compounds are different. You will carry out tests to identify the ions in FA 1 and FA 2. The volumes given in Table 1.1 and Table 1.2 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. (a) Tests on FA1 Carry out the tests described in Table 1.1. Carefully record your observations at each stage of the tests in Table 1.1. Table 1.1 Test Observations 1 Add 1 cm depth of FA 1 into a clean test tube. Add aqueous sodium hydroxide slowly with shaking until the aqueous sodium hydroxide is in excess. Keep the reaction mixture for test 2. • White ppt formed • dissolves in excess NaOH. 2 Pour the reaction mixture from test 1 into a boiling tube. Add 1 cm depth of aqueous sodium hydroxide to the reaction mixture. Warm the mixture. Add a piece of aluminium foil to the reaction mixture. • No observable change. / No ppt • No observable change. / No gas evolved that turns red litmus blue. (No NH3 has evolved) (Vigorous / violent / Effervescence) • Gas evolved turns red litmus blue. • Gas is NH3. 3 Add 1 cm depth of FA 1 into a clean test-tube. Add aqueous ammonia slowly with shaking until the aqueous ammonia is in excess. • White ppt • soluble in excess NH3. [3] 6, 7 points: 3 marks; 4 to 5 points: 2 marks; 3 points: 1 mark

3 (b) Tests on FA2 Carry out the tests described in Table 1.2. Carefully record your observations at each stage of the tests in Table 1.2. Table 1.2 Test Observations 1 Add 1 cm depth of FA 2 into a clean test tube. Add aqueous sodium hydroxide slowly with shaking until the aqueous sodium hydroxide is in excess. • Grey-green ppt formed • dissolves in excess NaOH to give a dark green solution. 2 Add 1 cm depth of FA 2 into a clean test-tube. Add aqueous ammonia slowly with shaking until the aqueous ammonia is in excess. • Grey-green ppt • insoluble in excess NH3. 3 Add 1 cm depth of FA 2 into a clean test-tube. Add 1 cm depth of dilute nitric acid followed by aqueous silver nitrate. • No observable change. / No gas evolved. • White ppt formed (in light blue/grey-blue solution). [2] 5, 6 points: 2 marks; 3, 4 points: 1 marks (c) (i) Complete Table 1.3 to identify the ions present in FA 1 and FA2. Table 1.3 FA1 FA2 cation present Zn2+ Cr3+ anion present NO3- / NO2- Cl- (Also accept Br-) [2] (ii) Write two ionic equations to explain the chemistry of Test 3 on FA1. …………………………………………………………………………………………………………… ……………………………………………………………………………………………………….. [2] NH3 + H2O ∏ NH4+ + OH− (not required) Eqn 1: Zn2+(aq) + 2OH −(aq) → Zn(OH)2(s) (must show state symbols for precipitation reaction) Eqn 2: [Zn(H2O)6]2+ + 4NH3 Ý [Zn(NH3)4]2+ + 6H2O (preferred) OR Zn(OH)2 + 4NH3 Ý [Zn(NH3)4]2+ + 2OH− (d) (i) Carry out the following test on FA2.

4 Add 1 cm depth of FA 2 into a clean test-tube. Add FA3 slowly with shaking until FA3 is in excess. • Grey-green ppt insoluble in excess FA3. • Effervescence • Gas evolved gives white ppt in limewater. • Gas is CO2 [2] 4 points: 2 marks; 2, 3 points: 1 marks (ii) Identify the anion in FA3. CO32− ................................ ................................ ................................ ................................ .. [1] [Total: 12]

5 2 Investigating the kinetics of the reaction between peroxydisulfate ions and iodide ions Equation 1 represents the reaction between iodide ions and peroxydisulfate ions. equation 1 S2O82− + 2I‾(aq) → 2SO42−(aq) + I2(aq) When starch is added to the reaction mixture, a blue -black colour is immediately seen due to the formation of an iodine-starch complex. If a small amount of sodium thiosulfate, Na2S2O3, is also present in the reaction mixture, the formation of the blue-black colour is delayed. The Na2S2O3 reacts with I2 as shown in equation 2. equation 2 2S2O32−(aq) + I2(aq) → S4O62−(aq) + 2I‾(aq) FA 4 is 0.100 mol dm−3 potassium peroxydisulfate, K2S2O8. FA 5 is 0.20 mol dm−3 potassium iodide, KI. FA 6 is 0.0050 mol dm−3 sodium thiosulfate, Na2S2O3. Solution S is starch indicator You will perform a series of four experiments. You will add a fixed amount of FA 5 and FA 6 to each of your experiments. You will add an amount of deionised water so that the total volume is 50 cm 3. The time taken for the blue-black colour to form allows the reaction rate to be determined. You should avoid inhaling any gases produced. (a) Prepare a table on page 6 to record, to an appropriate degree of precision: • volumes of FA 4 (VFA4) and deionised water (Vwater) used • all values of t • calculated values of 100/t Experiment 1 The end-point of the reaction is the first appearance of a blue-black colour. Note: Insufficient swirling of the reaction mixture may lead to a blue -black colour appearing before the true end-point is reached. 1. Fill a burette with FA 6. 2. Use a 50 cm3 measuring cylinder, measure 25 cm3 of FA 4 and top it up to the 30 cm3 mark with deionised water. Transfer the contents in this measuring cylinder into a 250 cm3 conical flask. 3. Add to the conical flask 5.00 cm3 of FA 6 from the burette and 5 cm3 of starch indicator from a 10 cm3 measuring cylinder. 4. Use a second 10 cm3 measuring cylinder to measure 10 cm3 of FA 5. 5. Pour the FA 5 into the same conical flask, start the stopwatch during this addition. 6. Swirl the flask to ensure even mixing and place the flask on a white tile. 7. Stop the stopwatch when the solution first turns blue-black. 8. Record the time taken, t, to the nearest second in your table. 9. Wash out the flask thoroughly with tap water and then with deionised water. Stand the flask upside down on a paper towel to drain.

6 Repeat Experiments 2 – 4 Carry out three further experiments to investigate the effect of changing the concentration of S2O82−(aq) by altering the volume of K2S2O8, FA 4, used. You should not use a volume of FA 4 that is less than 10 cm3 and more than 25 cm3. In each experiment, you should adjust the volume of deionised water in step 2 to ensure the same total volume of reaction mixture is used. You should alternate the use of the two 250 cm 3 conical flasks. You should keep FA 5 and FA 6