NYJC_H2_CHEM_P3_QP Prelim

[Turn over NANYANG JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION Higher 2 CHEMISTRY 9647/03 Paper 3 Free Response 12 September 2011 2 hours Candidates answer Section A on the Question Paper Students answer on separate paper. Additional Materials: Answer Paper Graph Paper Data Booklet 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 working. 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 brackets [ ] at the end of each question or part question. At the end of the examination, fasten all your work securely together. For Examiner’s Use Section A 1 2 3 4 5 Section B Answer all questions on separate answer paper. Total This document consists of 13 printed pages and 1 blank page.

2 NYJC 2011 H2 Chemistry 9647/03 Prelim [Turn Over Answer any four questions. 1 This question is about the reactions of compounds containing the cyanide group. (a) Cyanogen, (CN) 2 is called a pseudohalo gen because several of its reactions are similar to those shown by halogens Cl 2, Br2 and I2. For example, it can be reduced to hydrogen cyanide, which is a weak acid. ½ ( C N ) 2 + H+ + e HCN E Ө = +0.37 V (i) By analogy with the reactions of halogens or halides ions and by making use of the above data and information in the Data B ooklet, predict the reactions, if any, that might occur when the following reagents are mixed. I. Cl 2 + HCN II. Na2S2O3 + (CN)2 III. K2Cr2O7 + (CN)2 (ii) Draw a dot-and-cross diagr am of the cyanogen molecule, suggesting its shape. [8] (b) (i) When chiral 2-chloroheptane, C 7H15Cl reacts with ethanolic sodium cyanide, the optical isomerism of the product is reversed. Explain, with the aid of structural formu la, why the optical isomerism is reversed. (ii) Another compound A with the same molecular formula C 7H15Cl also reacts with ethanolic sodium cyanide. A, which is optically active, eventually loses its optical activity after reaction wit h ethanolic sodium cyanide. Give the structural formula of A and describe the mechanism of its reaction with ethanolic sodium cyanide. (iii) Predict which reaction b(i) or b(ii) will proceed at a faster rate when the concentration of ethanolic sodium cyani de is increased. Explain your answer. [8]

3 NYJC 2011 H2 Chemistry 9647/03 Prelim [Turn Over (c) Suggest the reagents and condit ions required for stage I and the structural formula for B, C and D for the fo