2024 MI PU3 H2 Chem EOY P4 student (final)

Class Adm No Candidate Name: This question paper consists of 20 printed pages. 2024 Preliminary Examination Pre-University 3 H2 CHEMISTRY 9729/04 Paper 4 Practical 27 Aug 2024 2 hours 30 minutes Candidates answer on the Question paper. READ THESE INSTRUCTIONS FIRST Do not turn over this question paper until you are told to do so Write your name, class and admission number 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. You may lose marks if you do not show your working or if you do not use appropriate units. Qualitative Analysis Notes are printed at the back of the Question Paper. 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. Question 1 2 3 4 Total Marks 14 18 14 9 55 Shift Laboratory

2 1 Determination of enthalpy change of reaction FA 1 is solid sodium hydrogencarbonate, NaHCO3 FA 2 is 1.50 mol dm-3 sulfuric acid, H2SO4 (also required in both question 2 and 3) Sodium hydrogencarbonate is commonly known as baking soda and is used as a reagent in various reactions. It is soluble in water according to equation 1. equation 1 NaHCO3(s) + aq ⟶ Na+(aq) + HCO3–(aq) H1 It can also react with acids in both solid and aqueous state. equation 2 2NaHCO3(s) + H2SO4(aq) ⟶ Na2SO4(aq) + 2H2O(l) + 2CO2(g) H2 equation 3 2NaHCO3(aq) + H2SO4(aq) ⟶ Na2SO4(aq) + 2H2O(l) + 2CO2(g) H3 In this question, you will carry out experiments to determine H1 and H2, then use Hess’s Law to determine H3. (a) In this experiment, you will determine the maximum temperature change when a known mass of solid sodium hydrogencarbonate, FA 1, reacts with sulfuric acid, FA 2. Then, you will determine H2. 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 glass beaker to prevent them from tipping over. 3. Use a measuring cylinder to transfer 25 cm3 of FA 2 into the first polystyrene cup. Cover the cup with the lid provided. 4. Stir FA 2 in the cup gently with the thermometer. Read and record its temperature. 5. Transfer all the FA 1 to the polystyrene cup. Stir the mixture. 6. Continue to stir the mixture. Observe the temperature and record the value that shows the maximum change from the initial temperature. 7. Reweigh the empty bottle and its cap. 8. Record the maximum temperature change and the mass of FA 1 used.

3 [Turn over (i) Results [5]

4 (ii) Calculate the heat change, q, using the values you obtained in (a)(i). You should assume that the specific heat capacity of the solution is 4.18 J g1 K1, and that the density of the solution is 1.00 g cm3. heat change = …………………………. [1] (iii) Hence, determine the enthalpy change of reaction, H2. [Ar: Na, 23.0; H, 1.0; C, 12.0; O, 16.0] H2 = …………………………. [2] (iv) Calculate the percentage error of the temperature change when using the thermometer. percentage error = …………………………. [1]

5 [Turn over (v) Suggest the effect on the value for T when 50 cm3 of FA 2 is used instead of 25 cm 3 in the experiment. …………………………………………………………………………………………………… …………………………………………………………………………………………………[1] (b) A second experiment was conducted to find out H1 and the results of the experiment are presented in Table 1.1. Table 1.1 mass of FA 1 used / g 4.00 volume of water used / cm3 50.0 initial temperature of water / °C 29.4 minimum temperature reached / °C 21.0 (i) Use the information in Table 1.1 to determine a value of H1. H1 = …………………………. [2] (ii) Use Hess’s Law and your answers from (a)(iii) and (b)(i) to determine a value for H3 for the reaction shown in equation 3. H3 = …………………………. [2] [Total: 14]

6 2 Investigation of the kinetics of the Mn2+ catalysed reaction between MnO4− and C2O42− FA 3 is 0.0200 mol dm3 potassium manganate(VII), KMnO4 FA 4 is 0.200 mol dm-3 sodium ethanedioate, Na2C2O4 FA 5 is 0.0100 mol dm–3 sodium thiosulfate, Na2S2O3 FA 6 is 0.100 mol dm–3 potassium iodide, KI FA 7 is aqueous Mn2+ Starch indicator FA 3, FA 4 and FA 7 are also required in question 3. Ethanedioate ions, C2O42-, can be oxidised by manganate(VII) ions, MnO 4- ions in acidic medium based on the equation below. 2MnO4–(aq) + 5C2O42(aq) + 16H+(aq) ⟶ 2Mn2+(aq) + 10CO2(g) + 8H2O(I) However, in the absence of a catalyst, the reaction proceeds slowly. The reaction can be catalysed through autocatalysis when Mn2+ is formed, or when Mn2+ is added at the start of the reaction. In this experiment, you will prepare investigate the kinetics of a reaction mixture containing FA 3 and FA 4 . At timed intervals, you will draw 10 cm 3 aliquots from the reaction mixture. The concentration of MnO4– ions in each aliquot will then be determined through titration against S2O32 after adding each aliquot to an excess of FA 6. Acidified potassium manganate(VII) ions oxidises I ions according to the following reaction: 2MnO4–(aq) + 10I(aq) + 16H+(aq) ⟶ 2Mn2+(aq) + 5I2(aq) + 8H2O(I) The reaction between iodine from the reaction mixture and S2O32 solution is given below. 2S2O32–(aq) + I2(aq) ⟶ 2I–(aq) + S4O62–(aq) (a) Preparation and titration of the reaction mixture Notes: 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. In an appropriate format in the space provided in page 7, prepare a table to which to record for each aliquot  the time of transfer, t, in minutes and seconds,  the decimal time, td, in minutes, to 0.1 min, for example if t = 4min 33s then td = 4min + 33/60 min = 4.6min,  the burette readings and the volume of FA 5 added.

7 [Turn over 1. Fill a burette with FA 5. 2. Label each of the boiling tubes 1 to 5. Using a measuring cylinder, add approximately 10 cm3 of FA 6 to each of these boiling tubes. 3. Using appropriate measuring cylinders, transfer 50.0 cm 3 of FA 4, 5.0 cm 3 of FA 2 , 5.0 cm3 of FA 7 and 40.0 cm3 of deionised water into a conical flask. Label the conical flask reaction mixture. 4. Using an appropriate measuring cylinder, transfer 25.0 cm 3 of FA 3 to the conical flask labelled reaction mixture. Start the stopwatch and swirl the mixture thoroughly to mix its contents. 5. At approximately t = 1 min, use a 10 cm 3 pipette to remove a 10.0 cm 3 aliquot of the reaction mixture. Immediately transfer this aliquot into the boiling tube labelled 1 and swirl the mixture. Note and record the transfer time (in minutes and seconds, to the nearest second) when half of the reaction mixture has emptied from the pipette. 6. Pour the contents of the boiling tube labelled 1 into a clean 250 cm3 conical flask. Transfer all washings from the boiling tube into the conical flask. 7. Titrate the iodine in this solution with FA 5 until