NYJC H2 Chem Prelim P2 QP

[Turn Over NANYANG JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME CLASS TUTOR’S NAME CHEMISTRY 9729/02 Paper 2 Structured Questions 11 SEP 2017 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name and class on all the work you hand in. Write in dark blue or black pen. You may use an HB pencil for any diagrams, 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. A Data Booklet is provided. 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 /23 3 /14 4 /11 5 /14 Total /75 This document consists of 22 printed pages. KiasuExamPaper.com

2 NYJC 2017 H2 Chemistry 9729/02 PRELIM For Examiner's Use 1 A mmonium salts are commonly used in instant cold packs. The cold pack contains water and an inner pouch containing an ammonium salt. When the pack is squeezed, this inner pouch breaks and releases the salt, which quickly dissolves and lowers the pack’s temperature. To determine whether ammonium chloride or ammonium nitrate is more effective as the ingredient in the cold pack, a student decided to conduct an experiment to find out the enthalpy change of solution of the two salts, starting with ammonium chloride. He added ammonium chloride to water and found the temperature change by plotting a suitable graph to correct for heat transfer. In a preliminary investigation, the enthalpy change of solution of ammonium chloride was found to be approximately +15 kJ mol –1 . (a) (i) Draw dot-and-cross diagram to illustrate the bonding in ammonium nitrate. Hence state the shape with respect to each nitrogen atom. [3] (ii) The student predicted that enthalpy change of solution of ammonium nitrate is more endothermic compared to ammonium chloride. Explain why his prediction is correct. ……………………………………………………………………………………...…. …………………………………………………………………………………….…... ……………………………………………………………………………………...…. …………………………………………………………………………………….…... ………………………………………………………………………….……………… ………………………………………………………………………………………[2] KiasuExamPaper.com

3 NYJC 2017 H2 Chemistry 9729/02 PRELIM [Turn Over For Examiner's Use (b) (i) The student was told to use 100 cm 3 of water for conducting the experiment. Suggest a minimum mass of ammonium chloride that could be used. Given that 4.3 J is required to raise the temperature of 1.0 cm 3 of any solution by 1°C. Justify your choice with relevant calculations, stating any othe r assumptions you made. [1] The student carried out the following procedure to find the enthalpy change o f solution of ammonium chloride. 1. Weigh accurately 8.00 g of ammonium chloride in a weighing bottle using a weighing balance. 2. Using a 100 cm 3 measuring cylinder, add 100 cm 3 of water into a polystyrene cup. 3. Stir the water gently using the thermometer. 4. Start the stopwatch. 5. Record the temperature of the water in the container, using a 0.1 o C thermometer, at 1 min interval. 6. At the 4th min, tip the ammonium chloride into the water. Do not read the temperature at this time. 7. Stir the solution gently and record the temperature of the solution at 4.5 min. Continue to stir and record the temperature at 30 s intervals until 8th min. 8. Reweigh the weighing bottle. KiasuExamPaper.com

4 NYJC 2017 H2 Chemistry 9729/02 PRELIM For Examiner's Use (ii) Draw a sketch of the graph that you expect to obtain from the experiment. Indicate clearly on the graph how the temperature change, ǻ T , can be found. [2] (iii) Predict and explain the sign of ǻ S when ammonium nitrate is dissolved in water. ……………………………………………………………………………………...…. …………………………………………………………………………………….…... ………………………………………………………………………….……………… ………………………………………………………………………………………[1] KiasuExamPaper.com

5 NYJC 2017 H2 Chemistry 9729/02 PRELIM [Turn Over For Examiner's Use ( c ) Ammonium chloride is also used as electrolyte in zinc–carbon batteries, where the outer zinc container is the negatively charged terminal and is oxidised during discharge. The following reaction also takes place in the cell. 2MnO 2 (s) + 2e í + 2NH 4 C l (aq) ĺ Mn 2 O 3 (s) + 2NH 3 (aq) + H 2 O(l) + 2C l í (aq) E ڧ 0.5 V Use the table of standard redox potentials given in the Data Booklet to answer the questions below. (i) Write the overall equation for the reaction that occurs in the cell when electrons are discharged. ………………………………………………………………………………………[1] (ii) Calculate the voltage that is generated by this cell. ………………………………………………………………………………………[1] (iii) Calculate a value of ǻ G ڧ for the cell reaction, and explain the significance o f its sign. …………………………………………………………………………………….…... ………………………………………………………………………….……………… ………………………………………………………………………………………[2] [Total: 13] KiasuExamPaper.com

6 NYJC 2017 H2 Chemistry 9729/02 PRELIM For Examiner's Use 2 2-iodobutane can be readily converted into 2-aminobutane using ethanolic ammonia. CH 3 CH I CH 2 CH 3 + 2NH 3 ĺ CH 3 CH(NH 2 )CH 2 CH 3 + NH 4 I In order to determine the rate equation for this reaction, an investigation was carried out at a constant temperature. 4.00 mol dm í 3 ethanolic ammonia was first prepared by bubbling ammonia gas into ethanol. Equal volume of 0.20 mol dm í 3 2-iodobutane and 4.00 mol dm í 3 ethanolic ammonia were mixed. At suitable time intervals, 10 cm 3 of the reaction mixture was pipetted into a conical flask and quenched. Chlorine gas was bubbled into the reaction mixture and excess chlorine gas was subsequently removed. The reaction mixture was then titrated with 0.0250 mol dm í 3 sodium thiosulfate in the presence of an indicator. ( a ) Draw a labelled diagram to illustrate the bonding between ammonia and ethanol. [2] (b) (i) Suggest why the reaction must be quenched and describe how this can be done. ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………[2] (ii) Write an ionic equation for the reaction when chlorine was bubbled through the reaction mixture. ………………………………………………………………………………………[1] (iii) Hence, write an ionic equation for the reaction between the reaction mixture and sodium thiosulfate. ………………………………………………………………………………………[1] KiasuExamPaper.com

7 NYJC 2017 H2 Chemistry 9729/02 PRELIM [Turn Over For Examiner's Use (iv) Suggest a suitable indicator for the titration and describe how you would recognise