HCI 2022 H2 Chemistry Prelim P4 QP and Ans

HWA CHONG INSTITUTION C2 Preliminary Examination Higher 2 NAME CT GROUP 21S CHEMISTRY Paper 4 Practical Candidates answer on the Question Paper 9729/04 25 August 2022 2 hours 30 minutes READ THESE INSTRUCTIONS FIRST Write your 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. 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 16 and 17. 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. Shift Laboratory For Examiner’s Use 1 2 3 4 Total This document consists of 17 printed pages.

2 © Hwa Chong Institution 2022 9729/04/C2Prelim 2022 [Turn over 1 Determination of the basicity of an acid and the strength of a base FA 1 is 1.50 mol dm–3 sodium hydroxide, NaOH. FA 2 is 0.75 mol dm–3 acid A, which is either monobasic (monoprotic) or dibasic (diprotic). FA 3 is 1.50 mol dm–3 base B, which is monoacidic (monoprotic) and is either a strong base or a weak base. You will perform experiments to determine whether acid A is monobasic or dibasic. You will then calculate the enthalpy change of neutralisation, Hneut, between NaOH and acid A. You will also design one more experiment to determine whether base B is a strong base or a weak base. (a) (i) Experiment 1 1. Place one polystyrene cup inside a second polystyrene cup. Place these in a glass beaker to prevent them from tipping over. 2. Use a measuring cylinder to transfer 40.0 cm3 of FA 1 into the first polystyrene cup. Stir the FA 1 in the polystyrene cup with the thermometer with 0.2 °C divisions. Read and record the initial temperature of FA 1 in Table 1.1. 3. Use another measuring cylinder to measure 20.0 cm3 of FA 2. Add FA 2 to FA 1 in the polystyrene cup. Stir the mixture using the same thermometer and record the maximum temperature reached. 4. Wash and dry the thermometer and the polystyrene cup. Experiment 2 Repeat experiment 1 using 20.0 cm3 of FA 1 and 40.0 cm3 of FA 2. Use your results to determine the maximum change in temperature , T, for each experiment and complete Table 1.1. You may assume that the initial temperature of FA 2 is the same as that of FA 1. Table 1.1 experiment Volume of FA 1 /cm3 Volume of FA 2 /cm3 Initial temperature of FA 1 /C Maximum temperature /C Maximum change in temperature, T /C 1 40.0 20.0 29.8 32.9 3.1 2 20.0 40.0 29.8 36.0 6.2 [2]

3 © Hwa Chong Institution 2022 9729/04/C2Prelim 2022 [Turn over (ii) Use your T results of experiments 1 and 2 to deduce whether acid A is monobasic or dibasic. Explain your deduction. ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… …………………………………………………………………………………………….. [2] (iii) Hence, calculate the enthalpy change of neutralisation, Hneut, between NaOH and acid A. Assume that the specific heat capacity of the reaction mixture is 4.18 J g–1 K–1, and that the density of the reaction mixture is 1.00 g cm–3. Hneut = ………………………………… [2] (iv) A student repeated experiment 2 but using solutions of double the concentrations (3.00 mol dm–3 NaOH and 1.50 mol dm–3 acid A). Suggest the effect this would have on the value of T for experiment 2. Hence , deduce and explain the effect this would have on the value for Hneut. ………………………………………………………………………………………………… ………………………………………………………………………………………………… …………………………………………………………………………………………….. [2]

4 © Hwa Chong Institution 2022 9729/04/C2Prelim 2022 [Turn over (b) (i) Experiment 3 FA 3 contains a monoacidic base, base B, that has the same concentration as the NaOH in FA 1. Design one more experiment, the results of which, when compared against your experiment 2, will allow you to deduce whether base B is a strong or weak base. Fill Table 1.2 with your chosen volumes of FA 3 and FA 2. Carry out this experiment. Complete Table 1.2. Table 1.2 experiment Volume of FA 3 /cm3 Volume of FA 2 /cm3 Initial temperature of FA 3 /C Maximum temperature /C Maximum change in temperature, T /C 3 20.0 40.0 29.0 34.0 5.0 [1] (ii) Use your T results of experiment 3 and experiment 2 to deduce whether base B is a strong base or a weak base. Explain your deduction. ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… …………………………………………………………………………………………….. [1] [Total: 10]

5 © Hwa Chong Institution 2022 9729/04/C2Prelim 2022 [Turn over 2 Investigation of the kinetics of the catalysed decomposition of hydrogen peroxide Hydrogen peroxide decomposes very slowly to form water and oxygen as shown in equation 1. equation 1 2H2O2 → 2H2O + O2 Many transition element ions are able to catalyse the decomposition of hydrogen peroxide. Iron(III) nitrate, Fe(NO3)3, is an effective catalyst for this reaction. FA 4 is iron(III) nitrate, Fe(NO3)3. FA 5 is 0.0200 mol dm–3 potassium manganate(VII), KMnO4. FA 6 is aqueous hydrogen peroxide, H2O2. FA 7 is 0.2 mol dm–3 sulfuric acid, H2SO4. (FA 7 is also used in Question 3.) You will add a measured volume of FA 4 to a measured volume of FA 6 and, at timed intervals, you will transfer aliquots (portions) of the reaction mixture. It is necessary that you titrate each aliquot against FA 5 before transferring the next aliquot. Acidified KMnO4 and H2O2 react as shown in equation 2. equation 2 2MnO4–(aq) + 5H2O2(aq) + 6H+(aq) → 2Mn2+(aq) + 8H2O(l) + 5O2(g) (a) (i) 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. You should transfer your first aliquot within the first three minutes of starting the reaction. The titre volume for your first titration is expected to be greater than 30 cm3. You should not exceed a maximum reaction time of 25 minutes for this experiment. In an appropriate format in the space provided on the next page, prepare a table in 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 = 4 min 33 s then td = 4 min + 33/60 min = 4.6 min, • the burette readings and the volume of FA 5 added.

6 © Hwa Chong Institution 2022 9729/04/C2Prelim 2022 [Turn over 1. Fill a burette with FA 5. 2. Using a measuring cylinder, add 100.0 cm 3 of FA 6 to the conical flask labelled reaction mixture. Do not use the H2O2 bench reagent for this step. 3. Using a measuring cylinder, add 2.0 cm3 of FA 4 to the same conical flask. Start the stopwatch and swirl the mixture thoroughly to mix its contents. 4. Using a measuring cylinder, add 50.0 cm3 of FA 7 to a second conical flask. 5. Before 3 minutes, withdraw a 10.0 cm3 aliquot (portion) of the reaction mixture to