NYJC_H2_Chemistry_P3_Answers Prelim

H2 Chemistry 9647/03 NYJC J2/14 PX [Turn over NANYANG JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION Higher 2 CHEMISTRY 9647/03 Paper 3 Free Response 24 September 2014 2 hours Candidates answer Section A on the Question Paper Additional Materials: Answer 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. 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. Section B Answer all questions on separate answer paper. For Examiner’s Use Section A 1 2 3 4 5 Total This document consists of 20 printed pages and 0 blank page.

2 H2 Chemistry 9647/03 NYJC J2/14 PX Answer any four questions. 1 In 1939 the German chemist Gerhard Dom agk was awarded the Nobel Prize in Physiology or Medicine for the discovery of the antibacterial effects of Prontosil. It was found that sulfanilamide was the active component of Prontosil. (a) Benzene can be used as the starting reagent for the synthesis of sulfanilamide by the following route. (i) Suggest reagents and conditions for steps I and II, and the structure of compounds A and B. Step I: Reagents: Concentrated HNO 3, Concentrated H2SO4 Condition: 55 – 60 °C [1 mark for complete answer; no marks for partial answer] Step II: i) Reagents: Sn, HCl Condition: Heat under reflux ii) Reagent: NaOH(aq) Condition: Room temperature [1 mark for complete answer; no marks for partial answer] A B [2 x 1 mark] (ii) Step III involves the reaction of concentrated H 2SO4 together with SO 3 to generate the required electrophile. Write a balanced equation for the generation of the electrophile in Step III. SO3 + H2SO4 → SO3H+ + HSO4 - [1 mark] (iii) State the types of reaction in steps II and V.   Step II: Reduction Step V: Nucleophilic substitution [1 mark each]  sulfanilamide

3 H2 Chemistry 9647/03 NYJC J2/14 PX (iv) Explain why sulfanilamide is soluble in water. Sulfanilamide is soluble in water as they can form favourable hydrogen bonds with water. [1 mark] A derivative of sulfanilamide, compound C, is shown below. (v) The amino group of sulfanilamide has a p K b value of 12.0. Suggest a p Kb value for the amino group of compound C. Explain your answer. 9 < pKb < 12.0 (pKb of aniline = 9) [1 mark] Compound C has an electron-donating ethyl substituent on the amine substituent of the benzene. Hence, the elect