DHS Prelim P3_Qn

This question paper consists of 11 printed pages and 1 blank page. © DHS 2015 [Turn over Name: Index Number: Class: DUNMAN HIGH SCHOOL Preliminary Examination 2015 Year 6 H2 CHEMISTRY 9647/03 Paper 3 Free Response 25 September 2015 2 hours Additional Materials: Data Booklet Writing Paper Cover Sheet INSTRUCTIONS TO CANDIDATES Write your name, register number and class on this question paper and on the Cover Sheet provided. Write in dark blue or black pen on both sides of the paper. You may use a soft pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. Answer any four questions. Start each question on a fresh sheet of paper. You are reminded of the need for good English and clear presentation in your answers. The number of marks is given in brackets [ ] at the end of each question or part question. At the end of the examination:  Fasten all work securely together with the Cover Sheet on top.  Hand in the question paper separately. The total marks for this paper is 80 marks.

2 © DHS 2015 9647/03 [Turn over Answer any four questions on writing paper. 1 (a) Non–aqueous ionic liquids, or simply ionic liquids, generally have high boiling point and low melting point. They are becoming popular solvents in organic synthesis. Ionic liquids mainly consist of ions, and at least one of them is a bulky organic ion. 1–ethyl–3–methylimidazolium tetrafluoroborate, [emim]BF 4, is an example of ionic liquid. (i) Some ionic liquids, including [emim]BF 4, are liquid at room temperature. They are called ‘room temperature ionic liquids’. Account for the low melting point of [emim]BF4. (ii) Explain why [emim]BF4 has high boiling point. (iii) Suggest an advantage of using ionic liquids over using organic solvents such as acetaldehyde (CH3COCH3) in organic synthesis. Explain your answer. [4] The two most abundant atmospheric gases react to a small extent to achieve dynamic equilibrium as shown: N2 (g) + O2 (g) 2NO (g) Kp = 0.40 (b) Atmospheric oxygen and nitrogen, each at a partial pressure of 0.80 atm, are put into a 1 dm 3 evacuated flask and equilibrium is established after 30 minutes. Calculate the equilibrium partial pressure for each of the three components at 298 K. [3] (c) On the grid provided at the back of the Cover Sheet, sketch pressure versus time curves for N 2 and NO under the conditions described in (b) at 298K from 0 to 40 minutes. Label the axes, curves and indicate significant values on the axes. [2] (d) State how the pressure verses time curves for N 2 and NO from 0 to 40 minutes will be different from that in (c), when a catalyst is used in the reaction. [1] (e) The temperature of the system was raised to 350 K at 40 min. Given the average bond energy of N=O bond is