2023 YIJC H2 Chem Prelim P4 Students Copy

1 YIJC [Turn over YISHUN INNOVA JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION CANDIDATE NAME CLASS DATE H2 CHEMISTRY 9729/04 Paper 4 Practical Paper 22 August 2023 2 hours 30 minutes Candidates answer on question paper. No Additional Materials are required READ THESE INSTRUCTIONS FIRST This document consists of 19 printed pages and 5 blank pages. Write your name and class in the spaces at the top of this page. 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 23 and 24. 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 13 2 18 3 12 4 12 Total 55 Shift Laboratory

2 YIJC Answer all the questions in the spaces provided. 1 Determination of enthalpy change of reaction FA 1 is solid sodium hydrogencarbonate, NaHCO3. FA 2 is 2.00 mol dm–3 hydrochloric acid, HCl. equation 1 NaHCO3(s) + HCl(aq)  NaCl(aq) + H2O(l) + CO2(g) ∆Hr(NaHCO3(s)) The molar enthalpy change of reaction of solid sodium hydrogencarbonate wit h hydrochloric acid in equation 1 is the enthalpy change when one mole of solid sodium hydrogencarbonate reacts with excess hydrochloric acid. equation 2 Na2CO3(s) + 2HCl(aq)  2NaCl(aq) + H2O(l) + CO2(g) ∆Hr(Na2CO3(s)) The molar enthalpy change of reaction of sodium carbonate with hydrochloric acid in equati on 2 is the enthalpy change when one mole of sodium carbonate reacts with excess hydrochloric acid. You are to perform an experiment by which you will determine the enthalpy change ∆Hr(NaHCO- 3(s)). You will also determine the enthalpy change ∆Hr(Na2CO3(s)) using the data provided. You will then use your results in a Hess ’ Law calculation to determine the enthalpy change, ∆H, for the reaction of sodium carbonate, Na 2CO3, with water and carbon dioxide to form sodium hydrogencarbonate, NaHCO3, as shown in equation 3. equation 3 Na2CO3(s) + H2O(l) + CO2(g)  2NaHCO3(s) ∆H (a) Follow the instructions below to determine the maximum temperature change when a known mass of solid sodium hydrogencarbonate, FA 1, reacts with hydrochloric acid. In an appropriate format in the space provided below, record  all weighings to an appropriate level of precision,  all values of temperature to an appropriate level of precision. Procedure 1. Weigh the capped bottle containing FA 1. 2. Place one polystyrene cup inside a second polystyrene cup. Place these in a g lass beaker to prevent them from tipping over. 3. Use a measuring cylinder to transfer 25 .0 cm3 of the acid, FA 2, into the first polystyrene cup. 4. Stir the solution in the cup with the thermometer. Read and record its temperature. 5. Transfer all the FA 1 to the polystyrene cup. Stir the mixture. Note: This reaction is very vigorous. Be careful when you pour in the solid. Minim ise inhalation of gas produced. 6. Continue to stir the mixture. Observe the temperature and record the val ue that shows

3 YIJC the maximum change from the initial temperature. 7. Reweigh the empty bottle and its cap. Determine the maximum temperature change and the mass of FA 1 used. Results [4] (b) In the following calculations, you should assume that the specific heat capacity of the solution is 4.18 J g–1 K–1, and the density of the solution is 1.00 g cm–3. (i) Use your results from 1(a) to calculate the heat change for your experiment. Heat change = ……………………………... [1] (ii) Hence, determine a value for ∆Hr(NaHCO3(s)).

4 YIJC Include the sign of ∆Hr(NaHCO3(s)) in your answer. [Ar: H, 1.0; C, 12.0; O, 16.0; Na, 23.0] ∆Hr(NaHCO3(s)) = ………………………………………. [1] (iii) The results of an experiment where sodium carbonate, Na2CO3(s), was reacted completely with an excess of dilute hydrochloric acid, FA 2, are shown in Table 1.1. Table 1.1 mass of Na2CO3 (s) used / g 5.235 volume of FA 2 used / cm3 50.0 initial temperature of FA 2 / oC 33.5 maximum temperature reached / oC 41.8 Use the results given in Table 1.1 to calculate a value for ∆Hr(Na2CO3(s)). [Ar: C, 12.0; O, 16.0; Na, 23.0] ∆Hr(Na2CO3(s)) = ………………………………………. [2] (iv) Use your answers from 1(b)(ii) and 1(b)(iii) and the equations 1 and 2 to determine the enthalpy change for the following reaction, ∆H. Show your working clearly.

5 YIJC Na2CO3(s) + H2O(l) + CO2(g)  2NaHCO3(s) ∆H If you are not able to determine a value for 1(b)(ii) and/or 1(b)(iii), you may use x and y to represent the respective enthalpy changes and proceed with this part of the question. ∆H = ………………………………………. [3] (c) A student repeated 1(b)(iii) using ethanoic acid in place of hydrochloric acid. Explain how the temperature rise when using ethanoic acid would compare to the temperature rise recorded in 1(b)(iii). Assume all volumes and concentrations of solutions are the same. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ………………………………………………………………………………………………………… [2] [Total:13]

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7 YIJC 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 3 is 0.0100 mol dm−3 sodium thiosulfate, Na2S2O3. FA 4 is aqueous iodine, I2. FA 5 is 1.50 mol dm−3 propanone, CH3COCH3. FA 6 is 0.50 mol dm−3 sodium hydrogen carbonate, NaHCO3. You are also provided with a starch indicator. The iodination of propanone to form iodopropan one proceeds as shown in the equation below. This reaction is catalysed by hydrogen ions. equation 4 CH3COCH3(aq) + I2(aq) CH3COCH2I(aq) + HI(aq) This reaction is first order with respect to both CH3COCH3 and H+ ions. You are to investigate the order of reaction with respect to I2. A reaction mixture containing FA 2, FA 4 and FA 5 is first prepared. At different chosen times, aliquots (portions) of this reaction mixture are removed and added to excess FA 6. It is necessary that you titrate each aliquot against FA 3 before transferring the next aliquot. I2 and S2O3 2− react as shown in equation 5. equation 5 2S2O3 2−(aq) + I2(aq)  2I−(aq) + S4O6 2−(aq) The required order of reaction can be obtained by graphical analysis of your results. (a) (i) Preparation and titration of the reaction mixture Notes:  Please cap FA 4 and FA 5 after use.  You will perform each titration once only. Great care must be taken that you do not overshoot the end-point.  Once you have started the stopwatch, it must continue running for the duration of the experiment. You must not stop it until you have finished this experiment.  You should aim to transfer your first aliquot within the first three m inutes of starting the reaction.  You