SRJC H2 Chem 2013 Prelim P3 QP

1   Turn Over] SERANGOON JUNIOR COLLEGE General Certificate of Education Advanced Level Higher 2 CANDIDATE NAME CLASS CHEMISTRY 9647/03 Preliminary Examination 27 Aug 2013 Paper 3 Free Response Questions 2 hours Additional Materials: Data Booklet, Cover Page Writing Papers READ THESE INSTRUCTIONS FIRST Write your name and class on all the work you hand in. 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 work. Do not use staples, paper clips, highlighters, glue or correction fluid. Answer any four questions. A Data Booklet is provided. You are reminded of the need for good English and clear presentation in your answers The number of marks is given in the brackets [ ] at the end of each question or part question. Start each question on a fresh piece of paper. At the end of the examination, fasten all your work securely together with the cover page provided and ensure your script is arranged in an orderly manner. This document consists of 11 printed pages 1281

2   Turn Over] 1 Phosphorus is the thirteenth element in the world to be discovered and due to this is sometimes referred to as the Devil’s element. The reference is also made due to its versatility in forming chemical species with explosive and toxic nature. (a) One example of a highly reactive phosphorus-containing ion is phosphonium, PH 4 +. (i) Write a balanced chemical equation for the reaction between phosphonium iodide and potassium hydroxide to form phosphine, PH3. (ii) Hence, suggest a suitable method of measuring the rate of reaction. (iii) Draw a ‘dot-and-cross’ diagram showing the electrons (outer shells only) in the phosphonium ion, and use the VSEPR (valence shell electron pair repulsion) theory to predict its shape. You may find both a written description and a 3-dimensional sketch useful in your answer. (iv) The bond angle in ammonia is 107.8 o. Predict the H – P – H bond angle in phosphine and justify your answer. [7] (b) Although phosphorus is present in numerous harmful chemicals, it is a useful feature in organophosphorus compounds. Ylides are a class of organophosphorus compounds that are well-known for their role in the Wittig reaction. The synthesis of methylpropene via the Wittig reaction is shown below. P                     PC H 3                      PC H 2 (i) Name the type of reaction that occurs in step I and outline the mechanism for the reaction. (ii) Suggest why 2-bromo-2-methylpropane is not preferred in step I. (iii) State the role of butyl lithium, C4H9Li, in step II. [5] C4H9Li II CH3Br I