EJC Prelim P2

© EJC [Turn Over EUNOIA JUNIOR COLLEGE JC2 Preliminary Examination 2018 General Certificate of Education Advanced Level Higher 2 CANDIDATE NAME CIVICS GROUP 1 7 – INDEX NUMBER CHEMISTRY Paper 2 Structured Questions 9729/02 13 September 2018 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name, civics group and registration number on the work you hand in. Write in dark blue or black pen. You may use an HB pencil for any diagrams or graphs. Do not use paper clips, highlighters, 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 2 3 4 5 6 Total This document consists of 21 printed pages and 1 blank page.

2 © EJC 9729/02/J2PE/18 For Examiner’s Use Answer all the questions in the spaces provided. 1 The table below shows the melting points of some oxides of Period 3 elements. compound chemical formula melting point / ºC sodium oxide Na 2O 1132 aluminium oxide Al2O3 2980 sulfur trioxide SO 3 16 (a) (i) Briefly relate the melting points of these oxides to their structure and bonding. ................................................................................................................................ ................................................................................................................................ ................................................................................................................................ ................................................................................................................................ ................................................................................................................................ ................................................................................................................................ ................................................................................................................................ ................................................................................................................................ ................................................................................................................................ ........................................................................................................................... [2] (ii) Describe the reactions, if any, of these oxides with water, stating the approximate pH of any solution formed. Write equations for all the reactions that take place. ................................................................................................................................ ................................................................................................................................ ................................................................................................................................ ................................................................................................................................ ................................................................................................................................ ................................................................................................................................ ................................................................................................................................ ........................................................................................................................... [4]

3 © EJC 9729/02/J2PE/18 [Turn over For Examiner’s Use (b) Suggest a reason for each of the following observations: (i) Effervescence is observed when aqueous sodium carbonate is added to an aqueous solution of aluminium chloride. Write equations for the reactions involved. ................................................................................................................................ ................................................................................................................................ ................................................................................................................................ ................................................................................................................................ ................................................................................................................................ ................................................................................................................................ ........................................................................................................................... [2] (ii) Silicon tetrachloride, SiC l 4, hydrolyses in water while carbon tetrachloride, CC l4, remains insoluble in water. ................................................................................................................................ ................................................................................................................................ ................................................................................................................................ ................................................................................................................................ ................................................................................................................................ ........................................................................................................................... [1] (c) Gaseous N 2O5 dissociates to form NO 2 and O 2 as shown in the following reaction equilibrium: () () ()25 2 22 N Og 4 N Og Og +ˆˆˆ †‡ˆˆ ˆ The value of the equilibrium constant, Kp, is 1.80×104 atm3 at 750 K and 3.23×103 atm3 at 700 K. (i) Write an expression for Kp for the above dissociation. [1]

4 © EJC 9729/02/J2PE/18 For Examiner’s Use (ii) Calculate the equilibrium constant in terms of pressure at 700 K for the reaction represented below: () () ()22 2 5 1 Og 2 N Og N Og2 + ˆˆˆ †‡ˆˆ ˆ [1] (iii) Will the enthalpy change for the dissociation be a positive or negative value? Justify your answer briefly. ................................................................................................................................ ................................................................................................................................ ................................................................................................................................ ................................................................................................................................ ................................................................................................................................ ................................................................................................................................ ........................................................................................................................... [2] (iv) State and justify the effect on the position of equilibrium if the total volume of the system at equil