RI Prelim P3 (Qns)

© Raffles Institution 2020 9729/03/S/20 [Turn Over RAFFLES INSTITUTION 2020 YEAR 6 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME CLASS INDEX NUMBER CHEMISTRY 9729/03 Paper 3 Free Response 18 September 2020 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Do not open this question booklet until you are told to do so. Write your name, class and index number in the spaces provided at the top of this page. 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 t he Question Paper. If additional space is required, you should use the pages at the end of this booklet. The question number must be clearly shown. Section A Answer all questions. Section B Answer one question. The use of an approved scientific calculator is expected, where appropriate. A Data Booklet is provided. Do not write anything in it. You are reminded of the need for good English and clear presentation in your answers. 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 Section A Section B Total 1 / 19 (Circle the question you have answered) / 80 2 / 20 4 / 20 3 / 21 5 / 20 This document consists of 35 printed pages.

2 © Raffles Institution 2020 9729/03/S/20 For examiner’s use Section A Answer all the questions in this section. 1 In an aerosol spray , liquefied -gas propellants are sealed in a pressurised canister. Upon release into the air, the propellants instantly vaporise. Table 1.1 shows the boiling points of some aerosol propellants. Table 1.1 propellant CF2Cl2 N2O CH3OCH3 boiling point / oC −30 −89 −24 Mr 121.0 44.0 46.0 (a) (i) In N2O, the central atom is nitrogen. Draw a dot-and-cross diagram to show the bonding in N2O. Include all lone pairs in your diagram. [1] (ii) Predict and explain the shape and bond angle about the oxygen atom in CH3OCH3. [2] (iii) Explain why CH3OCH3 has a higher boiling point than CF2Cl2. [1] ……………………………………………………………………………………..….............. ……………………………………………………………………………………..….............. ……………………………………………………………………………………..….............. ……………………………………………………………………………………..….............. ……………………………………………………………………………………..….............. ……………………………………………………………………………………..….............. ……………………………………………………………………………………..….............. ……………………………………………………………………………………..….............. ……………………………………………………………………………………..….............. ……………………………………………………………………………………..….............. ……………………………………………………………………………………..….............. ……………………………………………………………………………………..….............. ……………………………………………………………………………………..…..............

© Raffles Institution 2020 9729/03/S/20 [Turn Over 3 For examiner’s use ……………………………………………………………………………………..….............. ……………………………………………………………………………………..….............. ……………………………………………………………………………………..….............. ……………………………………………………………………………………..….............. ……………………………………………………………………………………..….............. ……………………………………………………………………………………..….............. ……………………………………………………………………………………..….............. ……………………………………………………………………………………..….............. ……………………………………………………………………………………..….............. ……………………………………………………………………………………..….............. Question 1 continues on the next page.

4 © Raffles Institution 2020 9729/03/S/20 For examiner’s use (b) An important property of an aerosol propellant is that it should be a gas at room temperature and pressure. (i) State two assumptions of the kinetic theory as applied to an ideal gas. [2] (ii) Fig. 1.1 illustrates the behaviour of 1 mol of ideal gas at 293 K. Fig. 1.1 On Fig.1.1, sketch and label the graph for 1 mol of N2O at 293 K. [1] (iii) On the same axes in Fig. 1.1, sketch and label the graph for 1 mol of N2O at 500 K. Explain your answer. [2] ……………………………………………………………………………………..….............. ……………………………………………………………………………………..….............. ……………………………………………………………………………………..….............. ……………………………………………………………………………………..….............. ……………………………………………………………………………………..….............. ……………………………………………………………………………………..….............. ……………………………………………………………………………………..….............. ……………………………………………………………………………………..….............. ……………………………………………………………………………………..….............. ……………………………………………………………………………………..….............. ……………………………………………………………………………………..….............. ……………………………………………………………………………………..….............. ……………………………………………………………………………………..….............. 1 p ideal gas pV RT

© Raffles Institution 2020 9729/03/S/20 [Turn Over 5 For examiner’s use Question 1 continues on the next page.

6 © Raffles Institution 2020 9729/03/S/20 For examiner’s use (c) Dimethylether, CH 3OCH3, can be formed from the reaction between carbon monoxide , CO, and hydrogen, H2, as shown by equation 1. equation 1 3CO(g) + 3H2(g) ⇌ CH3OCH3(g) + CO2(g) ∆H = −245 kJ mol–1 A mixture of CO and H 2 was introduced into a 10 m 3 sealed vessel at 500 K. The initial total pressure was 40 atm at 500 K. After dynamic equilibrium was established, the total pressure in the vessel decreased to 28 atm at 500 K. (i) Write an expression for the equilibrium constant, Kp, for this reaction, and state its units. [2] (ii) Use of the Data Booklet is relevant to this question. The amo unt of CH3OCH3 at equilibrium was found to be 732 mol. Show that the equilibrium partial pressure of CH3OCH3 in the sealed vessel is 3 atm. [1] (iii) At equilibrium, it was found that 60% of the CO had been converted to the products. Calculate the equilibrium pressure of CO in atm. [2] (iv) Hence, calculate the equilibrium pressure of H2 in atm and determine the value of Kp for the reaction. [2] (v) After dynamic equilibrium was established, some Ar(g) was added into the same 10 m3 sealed vessel at 500 K. Explain the effect on the partial pressure of CH3OCH3. [1] (vi) Explain the effect on the value of Kp of the reaction when the temperature is increased from 500 K to 550 K. [2] ……………………………………………………………………………………..….............. ……………………………………………………………………………………..….............. ……………………………………………………………………………………..….............. ……………………………………………………………………………………..….............. ……………………………………………………………………………………..….............. ……………………………………………………………………………………..….............. ……………………………………………………………………………………..….............. ……………………………………………………………………………………..….............. ……………………………………………………………………………………..…..............

© Raffles Institution 2020 9729/03/S/20 [Turn Over 7 For examiner’s use ……………………………………………………………………………………..….............. ……………………………………………………………………………………..….............. ……………………………………………………………………………………..….............. ……………………………………………………………………………………..….............. ……………………………………………………………………………………..….............. ……………………………………………………………………………………..….............. ……………………………………………………………………………………..….............. ……………………………………………………………………………………..….............. ……………………………………………………………………………………..….............. ……………………………………………………………………………………..….............. ……………………………………………………………………………………..….............. ……………………………………………………………………………………..….............. ……………………………………………………………………………………..….............. ………………