TJC Prelim P2

TEMASEK JUNIOR COLLEGE Preliminary Examinations Higher 2 CANDIDAT E NAME CIVICS GROUP / CHEMISTRY 9746/02 Paper 2 Structured Questions 28 September 2009 1 hour 30 minutes Candidates answer on the Question Paper. Additional Materials: Data Booklet READ T HESE INSTRUCTIONS FIRST Write your Civics Group and candidate name on all the work you hand in. Write in dark blue or black pen. 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 all questions. You are reminded of the need for good English and clear presentation in your answers. You may lose marks if you do not use appropriate units. A Data Booklet is provided. 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 Total This paper consists of 16 printed pages.

Answer all questions in the spaces provided. 1 This question is about chlorine and its compounds. (a) A teacher instructed a student to r eact some chlorine gas with 250 cm 3 of 0.100 mol dm -3 aqueous sodium hydroxide, an d left the lab. After he returned, he realized that he had not s pecified the reaction temperature. The teacher found that the pH of the solution had become 12.0. After acidifying the solution and adding excess silver ni trate, 2.69 g of silver chloride was obtained. He then concluded that the student had heated the sodium hydroxide. For this question, you may assume that all of the chloride ions are precipitated by the addition of silver ions. For Examiner’s Use (i) Determine how the teacher arrived at his conclusion. (ii) If the student had not heated the aqueous sodium hydroxide and the same amount of chlorine gas was us ed, what would be the resulting mass of silver chloride obtained when excess silver nitrate is added after acidifying the solution? [5] [Turn over] 2

(b) The melting point of POCl 3 is 1.25 oC whereas the melting point of PC l5 is 166.8 oC. (i) Name and draw diagrams to illustrate the shapes of POCl 3 and PCl5. (ii) Explain, in terms of st ructure and bonding, why PC l5 has a higher melting point. For Examiner’s Use [4] [Turn over] 3

(c) Phosphorous pentachloride is commonly used in organic reactio ns such as the following: CH3OH(l) + PCl5(s) CH 3Cl(g) + POCl3(l) + HCl(g) For Examiner’s Use (i) With reference to the Data Booklet and the following bond enthalpies, calculate the enthalpy change of the above reaction.