MJC_2008 H2 Chem Prelim Paper 2 (Question Paper)

Reg Number Class Candidate Name _____________________________ Meridian Junior College JC2 Prelim Examination 2008 H2 Chemistry 9746 11 September 2008 1 hr 30 min Paper 2 STRUCTURED QUESTIONS Additional Materials Data Booklet INSTRUCTION TO CANDIDATES Write your name, class and register number in the spaces provided at the top of this page. Write in dark blue or black ink. You may use a soft 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. All working must be shown clearly. You are reminded on the need for good English and clear presentation of your answers. FOR EXAMINER’S USE INFORMATION FOR CANDIDATES Q1 / 12The number of marks is given in brackets [ ] at the end of each question or part of question. Q2 / 12 Q3 / 10 Q4 / 11 Q5 / 15 Total / 60 This question paper consists of 19 printed pages. 1

Answer all the questions in the space provided. 1(a) Phosgene gas, COCl 2, can be prepared by allowing gaseous chlorine and carbon monoxide to react under pressure. A sci entist needed to prepare isotopically- labeled phosgene for use in an organic synthesis. 13CO (g) + Cl2 (g) 13COCl2 (g) Some Cl 2 (g) and 5.00 atm of isotopically-labeled 13CO (g) were pumped into a steel cylinder set at 25 °C which was then sealed. The cylinder was subsequently heated to 227 °C and the partial pressure of Cl 2 (g) was found to be 5.59 atm at 227 °C. The cylinder was then maintained at 227 °C for an extended peri od of time to allow dynamic equilibrium to be reached. The new partial pressure of Cl 2 (g) was found to be 4.50 atm. (i) Calculate the partial pressure of 13CO (g) at 227 °C. [1] (ii) Write an expression for the equilibrium constant, K p. Hence, or otherwise, calculate the Kp value for the equilibrium at 227 °C, stating its units. [2] 2

(iii) Calculate the average molecular mass of the gaseous mixture at equilibrium. [Ar of 13C: 13.0, O: 16.0, Cl: 35.5] [2] (iv) Sketch on the graph below to show what the scientist should expect to observe if additional 13CO (g) was added at time t to the cylinder which was maintained at constant temperature of 227 °C. Label the graph extensions for each species till equilibrium is reached. [2] Partial Pressure 13CO Cl2 13COCl2 0 Time (b)(i) State one of the assumptions of the kinetic theory of gases. [1] 3

(ii) The plots of PV/RT against P for one mole of an ideal gas and one mole of SO 2 at 300K are given below. Show, on the same axes, how one mole of CO 2 will behave at the same temperature of 300K. Label your graph clearly. [1] PV/RT Ideal Gas (300K) SO2 (300 K)