NYJC 2020 Prelim 9729 P4

[Turn over NANYANG JUNIOR COLLEGE JC2 PRACTICAL PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME CLASS 1 9 TUTOR CENTRE NUMBER S INDEX NUMBER CHEMISTRY 9729/04 Paper 4 Practical 19 August 2020 2 hour 30 minutes Candidates answer on the Question Paper Additional Materials: As listed in the Confidential Instructions 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, highlighters, 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 17 and 18. 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(c), (d), (f) [5] 3(a) [8] 1 / 10 1(e) [5] 3(b) [2] 2 / 18 2(a) [7] 4(a)-(c) [6] 3 /10 2(b), (c) [6] 4(d)-(g) [6] 4 / 17 2(d), (e) [5] 4(h)-(k) [5] Total /55 This document consists of 18 printed pages and 2 blank pages.

2 H2 Chemistry 9729/04 NYJC J2/20 PX Answer all the questions in the spaces provided. 1 Investigation of the extraction of propanoic acid from the aqueous layer by an organic liquid Propanoic acid has different solubilities in water and in the organic liquid, FB 6. When an aqueous solution of propanoic acid is shaken with FB 6, two separate layers, an aqueous layer and an organic layer will be observed. Some of the acid dissolves in the organic layer. The amount of acid remaining in the aqueous layer can be determined by titration with aqueous sodium hydroxide. FA 1 is 0.050 mol dm–3 sodium hydroxide solution. FA 2 is 0.200 mol dm–3 propanoic acid, C2H5COOH. FB 6 is an organic liquid that does not mix with water. (a) Preparation of the mixture in Flask A. 1. Flask A is a stoppered flask that contains 40 cm3 of FB 6. 2. Use a 50 cm3 measuring cylinder to place 50 cm3 of FA 2 into Flask A. 3. Replace the stopper in the flask. 4. Shake the flask vigorously for about 1 minute. 5. Leave the flask to stand on the workbench for about 10 minutes. 6. Shake the flask vigorously again for about 1 minute during the 10 minute duration. While the flask is standing on the workbench, you may move on to the next question. (b) Titrations 1. Fill the burette with FA 1. 2. Ensure the two layers in Flask A have separated – this should take no longer than 1 minute after shaking the flask. 3. Pipette 10.0 cm 3 of the lower (aqueous) layer into a conical flask. Attach the pipette filler to the pipette before inserting it into the mixture. 4. Replace the stopper in the flask. 5. Titrate the acid in the conical flask with FA 1 , using thymolphthalein indicator. The end-point is reached when the solution in the flask becomes a permanent pale blue colour. 6. Repeat steps 3 to 5 until consistent titre values are obtained.

3 H2 Chemistry 9729/04 NYJC J2/20 PX [Turn over (c) Results Record the burette readings and volume of FA 1 added to the conical flask. [2] (d) From your titrations, obtain a suitable volume of FA 1 to be used in your calculations. Show clearly how you obtained this volume. volume of FA 1 = …………………….. cm3 [1] (e) Calculations (i) Use your answer in (c) to calculate the volume of FA 1 needed to react with the acid remaining in 50 cm3 of the aqueous layer, after shaking with the organic liquid. volume of FA 1 = ……………….. cm3 [1] (ii) It is suggested that shaking the mixture leads to the following equilibrium being established. C2H5CO2H(aq) Ý C2H5CO2H(org) Use the information given and your answer in (e)(i) to calculate the equilibrium amount of C2H5CO2H(aq) and C2H5CO2H(org). Equilibrium amount of C2H5CO2H(aq) = ……………………. mol [1] Equilibrium amount of C2H5CO2H(org) = ……………………. mol [1] (iii) The expression for the equilibrium constant is as shown below.

4 H2 Chemistry 9729/04 NYJC J2/20 PX 2 5 2 ( ) 2 5 2 ( ) [] [] org c aq C H CO HK C H CO H Using the above expression, determine a val ue for the equilibrium constant, Kc. Kc = ……………………. [2] (f) FB 6 is butan-1-ol. The above experiment is repeated using 2-methylpentane instead of FB 6. State and explain the effect on the volume of FA 1 obtained in (c). Effect on the volume of FA 1 ……………………………………...……………. [1] Explanation …………………………………………………………...……………… …………………………………………………………...…………………………….. …………………………………………………………...…………………………….. ……………………………………………………..………………………………. [1] [Total: 10]

5 H2 Chemistry 9729/04 NYJC J2/20 PX [Turn over 2 Determination of the concentration of sulfuric acid, FA 4 and its enthalpy change of reaction with aqueous sodium hydroxide. The enthalpy change of neutralisation, Hn, is the enthalpy change when one mole of water is formed during a neutralisation reaction as shown in the equation. H+(aq) + OH(aq)  H2O(l) The enthalpy change of neutralisation between an acid and an alkali can be determined by adding various volumes of acid and alkali and measuring the change in temperature. It is possible to make use of this fact to determine the equivalence point of a neutralisation reaction without the use of an indicator. The equivalence point is the point where H+(aq) from the acid and OH–(aq) from the base are present in equal molar amounts. Using this process, you are to perform a series of experiments where different volumes of alkali are added to a fixed volume of 25 cm 3 of sulfuric acid while keeping the total volume of the solution at 100 cm 3 by adding appropriate volumes of water and determining the temperature change, T, for each experiment. You will then plot a graph of T against volume of NaOH used. Volume of NaOH / cm3 T / °C 0 Tmax z You are to determine experimentally  z, the exact volume of NaOH which reacts with 25 cm3 of H2SO4  Tmax You are provided with the following reagents:  FA 3 is 1.50 mol dm3 NaOH  FA 4 is H2SO4 of approximate concentration 1.0 mol dm3  deionised water

6 H2 Chemistry 9729/04 NYJC J2/20 PX (a) Method Experiment 1 1. Using a 100 cm3 measuring cylinder, place 25 cm 3 of FA 4 and 65 cm3 of deionised water into the styrofoam cup provided. Place the cup inside a 250 cm3 glass beaker to prevent it from tipping over. 2. Measure and record the initial temperature of the mixture of FA 4 and water. 3. Using another 100 cm 3 measuring cylinder , measure 10 cm 3 of FA 3 . Measure and record the initial temperature of FA 3. 4. Calculate and record the average initial temperature. 5. Add FA 3 quickly from the second measuring cylinder into the cup. Cover the cup with lid provided and stir the mixture immediately. Measure the maximum temperature obtained. Record this temperature. 6. Calculate and record the change in temperature, T. 7. Wash and carefully dry the styrofoam cup. Experiment 2 Repeat experiment 1 above using 45 cm3 of water and 30 cm3 of FA 3 instead. Experiments 3, 4, 5 and 6 35 cm3 of FA 3 is a rough value of z. You are to perform four more experiments, each with a different volume of FA 3 added to 25 cm 3 FA 4 in order to plot a graph of the form shown on page 5 and to obtain an exact value for z.

7 H2 Chemistry 9729/04 NYJC J2/20 PX [Turn over Remember  You should not use more than 60 cm3 of FA 3 for any experiments.  You already have data for 10 cm3 of FA 3 a