VJC 2026 H2 Chem Prelim P4 Ans

1 © VJC 2026 9476/04/PRELIM/26 [Turn over CANDIDATE NAME CT GROUP VICTORIA JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION Higher 2 ……………………………………………….………….. …………………………….. CHEMISTRY 9476/04 Paper 4 Practical You must answer on the question paper. 19 August 2026 2 hours 30 minutes You will need: The materials and apparatus listed in the confidential instructions INSTRUCTIONS • Answer all questions. • Use a black or dark blue pen. You may use an HB pencil for any diagrams or graphs. • Write your name and CT group on the lines at the top of the page. • Write your answer to each question in the space provided. • Do not use an erasable pen. Do not use correction fluid or tape. • You may use an approved calculator. • Qualitative analysis notes are printed in the question paper. • Write the details of the shift and laboratory in the boxes provided. • You may lose marks if you do not show your working or if you do not use appropriate units. INFORMATION • The total mark for this paper is 50. • The number of marks for each question or part question is shown in brackets [ ]. Shift Laboratory For Examiner’s Use 1 / 13 2 / 15 3 / 12 4 / 10 Total / 50 This document consists of 16 printed pages.

2 © VJC 2026 9476/04/PRELIM/26 Answer all the questions in the spaces provided. 1 Determination of the percentage purity of a sample of calcium carbonate, CaCO3 FA 1 is impure calcium carbonate, CaCO3. FA 2 is 2.00 mol dm–3 hydrochloric acid, HCl. FA 4 is 0.150 mol dm–3 sodium hydroxide, NaOH. Thymolphthalein indicator is also provided. This experiment involves three steps. Step 1: A known mass of the impure calcium carbonate, FA 1, is reacted with an excess of hydrochloric acid, FA 2. Step 2: You will dilute the products of step 1 to 250 cm 3 in a volumetric flask. This solution is FA 3. Step 3: You will carry out titrations to find out how much acid remains after the reaction in step 1. (a) (i) In the space provided on page 3, prepare tables in which to record for your experiment: • all weighings, to an appropriate level of precision • the mass of FA 1 used in the reaction • titration results, to an appropriate level of precision Procedure 1. Pipette 25.0 cm3 of FA 2 into a 250 cm3 beaker. 2. Weigh the capped container containing solid FA 1. Record the mass. 3. Transfer all the solid FA 1 gradually into the 250 cm3 beaker. Vigorous effervescence and some spraying of the acid on the sides of the beaker will occur. Stir the mixture with a glass rod to dissolve FA 1 completely. Reweigh and record the mass of the emptied capped container. 4. Transfer the solution into a 250 cm3 volumetric flask quantitatively. Rinse the beaker and the glass rod with deionised water and pour the washings into the volumetric flask. 5. Make the solution up to the mark with deionised water. Thoroughly mix the contents of the volumetric flask. Label this solution FA 3. 6. Fill a burette with FA 4. 7. Rinse the 10.0 cm3 pipette with deionised water and then with FA 3. 8. Pipette 10.0 cm3 of FA 3 into a 250 cm3 conical flask. 9. Add 2 to 3 drops of thymolphthalein. 10. Run FA 4 from the burette into the conical flask. The end-point is reached when the first permanent blue colour , lasting at least 15 seconds , is seen throughout the solution. 11. Record your titration results, to an appropriate level of precision.

3 © VJC 2026 9476/04/PRELIM/26 [Turn over 12. Discard the reaction mixture via the sink. 13. Repeat steps 8 to 12 until consistent results are obtained. Results Mass of FA 1 and capped container / g 5.960 Mass of emptied capped container / g 4.760 Mass of FA 1 used / g 1.200 Initial burette reading / cm3 3.00 13.50 Final burette reading / cm3 13.40 23.90 Volume of FA 4 used / cm3 10.40 10.40 • Tables with appropriate headers and units • Record mass weighings to 3 d.p. and burette readings to nearest 0.05 cm3 • At least two consistent readings ±0.10 cm3 • Correct subtraction to find mass of FA 1 and titre To compute student result using mFA1 + 0.05titre Supervisor value is 1.736 Accuracy: •• ± 0.015, OR •· ± 0.030 [6] (ii) From your titrations, obtain a suitable volume of FA 4 to be used in your calculations. Show clearly how you obtained this volume. • Average volume of FA 4 used = (10.40 + 10.40) ÷ 2 = 10.40 cm3 [The volume of FA 4 used is calculated by taking the average of readings which are consistent within ± 0.10 cm3.] Volume of FA 4 = …………………….…… cm3 [1] (b) (i) Calculate the amount, in mol, of sodium hydroxide in the volume of FA 4 in (a)(ii). • Amount of NaOH used = 0.150 × 10.40 1000 = 0.00156 mol amount of NaOH = ………………………… mol [1] (ii) Use your answer to (b)(i) to calculate the amount, in mol, of hydrochloric acid in 250 cm3 of FA 3. Amount of HCl in 10.0 cm3 of FA 3 = amount of NaOH used = 0.00156 mol • Amount of HCl in 250 cm3 of FA 3 = 0.00156 × 250 10.0 = 0.0390 mol amount of HCl in 250 cm3 of FA 3 = ………………………. mol [1] 10.40 0.00156 0.0390

4 © VJC 2026 9476/04/PRELIM/26 (iii) Use your answers to (b)(ii) to calculate the amount, in mol, of hydrochloric acid that reacted with the FA 1 in step 1. Amount of HCl in 25.0 cm3 of FA 2 = 2.00 × 25.0 1000 = 0.0500 mol • Amount of HCl that reacted with FA 1 = 0.0500 – 0.0390 = 0.0110 mol amount of HCl that reacted with FA 1 = …………………… mol [1] (iv) Use your answer to (b)(iii) and the mass of FA 1 used to calculate the percentage purity of calcium carbonate. Show your working. [Ar: Ca, 40.1; C, 12.0; O, 16.0] CaCO3(s) + 2HCl(aq) → CaCl2(aq) + H2O(l) +CO2(g) Amount of CaCO3 in FA 1 = 0.0110 ÷ 2 = 0.00550 mol  Mass of CaCO3 in FA 1 = 0.00550 × (40.1 + 12.0 + 3 × 16.0) = 0.551 g • Percentage purity of CaCO3 = 𝟎.551 1.200 × 100% = 45.9%  3sf, clear statements and workings for 1(b) percentage purity of CaCO3 = …………………… % [3] [Total: 13] 0.0110 45.9

5 © VJC 2026 9476/04/PRELIM/26 [Turn over 2 Investigation of the kinetics of an acid-catalysed reaction between propanone and iodine FA 2 is 2.00 mol dm–3 hydrochloric acid, HCl. FA 5 is 1.00 mol dm–3 propanone, CH3COCH3. FA 6 is an aqueous solution of iodine, I2. FA 7 is 0.0100 mol dm–3 sodium thiosulfate, Na2S2O3. FA 8 is aqueous sodium carbonate, Na2CO3. Starch indicator is also provided. The iodination of propanone to form iodopropanone proceeds as shown in equation 1. This reaction is catalysed by hydrogen ions. equation 1 CH3COCH3(aq) + I2(aq) → CH3COCH2I(aq) + HI(aq) You are to investigate the order of reaction with respect to I2. A reaction mixture containing FA 2, FA 5 and FA 6 is first prepared. At different chosen times, aliquots (portions) of this reaction mixture are removed and quenched with excess FA 8. The remaining I2 in the aliquot reacts with S2O32− as shown in equation 2. equation 2 2S2O32−(aq) + I2(aq) → 2I−(aq) + S4O62−(aq) It is necessary that you titrate each aliquot against FA 7 before transferring the next aliquot. The required order of reaction can