2019 NYJC 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 17 September 2019 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 /18 2 /13 3 /14 4 /15 5 /15 Total /75 This document consists of 20 printed pages.

2 H2 Chemistry 9729/02 NYJC J2/2019 PRELIM Answer all questions in the spaces provided. 1 (a) Ammonia is one of the world’s most produced inorganic chemical due to its many uses. The current method of producing ammonia is the Haber-Bosch process. This involves reacting nitrogen and hydrogen in a recycled process as shown. Nitrogen and hydrogen are pumped into the reactor where reaction to form ammonia takes place. The output from the reactor then goes into a condenser. 3H2(g) + N2(g) 2NH3(g) H < 0 (i) An optimal temperature of 500 oC is used inside the reactor. Expla in why this temperature is used. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. ............................................................................................................................. [2] (ii) Finely divided iron is used as catalyst inside the reactor. Outline the mode of action of the iron catalyst in this reaction. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. ............................................................................................................................. [2]

3 H2 Chemistry 9729/02 NYJC J2/2019 PRELIM [Turn Over (iii) Using a Boltzmann diagram, explain why rate increases in the presence of catalyst. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. ............................................................................................................................. [3] (iv) The condenser helps to cool the gases and in doing so, maximise s the yield of ammonia. Explain in terms of structure and bonding how this is achieved. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. ............................................................................................................................. [2]

4 H2 Chemistry 9729/02 NYJC J2/2019 PRELIM (v) Hydrazoic acid, HN3, is a compound of nitrogen and hydrogen like ammonia. The plots of pV/RT against p for one mole of an ideal gas and one mole of ammonia are given below. On axes above, sketch a graph to illustrate the behaviour of one mole of hydrazoic acid. Explain your answer. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. .............................................................................................................................. [2] p pV/RT 1.0 NH3 Ideal Gas

5 H2 Chemistry 9729/02 NYJC J2/2019 PRELIM [Turn Over (b) Globally, approximately 88 % of ammonia is used as fertili sers. Research is actively carried out to seek new uses for ammonia in other areas. For example, when NH 3(aq) is added to a solution of Zn 2+(aq), a solution of [Zn(NH3)4]2+(aq) can be formed. It is then possible to design an electrochemical cell based on the following half equations. Zn2+(aq) + 2e– Zn(s) Eo = –0.76V [Zn(NH3)4]2+(aq) + 2e– Zn(s) + 4NH3(aq) Eo = –1.04V (i) Draw a fully labelled diagram of the electrochemical cell that could be set up, showing the polarity of the electrodes during discharge. [2] (ii) Write a balanced equation for the overall reaction that occurs during the discharging process. Hence calculate Go of the electrochemical cell. [2]

6 H2 Chemistry 9729/02 NYJC J2/2019 PRELIM (c) Ammonia is used in the pharmaceutical industry for synthesising of drugs. An example is acetazolamide, a drug used for treating heart failure. acetazolamide O Nb S Na N S O O N H H H (i) The molecule of acetazolamide contains both  (sigma) and  (pi) bonds. With respect to the C=Na bond circled, draw a labelled diagram to show how orbitals overlap to form  (sigma) and  (pi) bonds. [1] (ii) Suggest how the basicity of N a might compare t