ACJC H2 CHEM P2 Ans Prelim

1 © ACJC 2017 9729/02/Prelim/2017 [Turn over Index No. Name Form Class Tutorial Class Subject Tutor ANGLO-CHINESE JUNIOR COLLEGE DEPARTMENT OF CHEMISTRY Preliminary Examination CHEMISTRY 9729/02 Higher 2 Paper 2 Structured Questions 15 August 2017 2 hours Candidates answer on the Question Paper Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name, index number, form class, tutorial class and subject tutor’s 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, glue or correction fluid. Answer all questions. A Data Booklet is provided. 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 Question no. Marks 1 / 7 2 / 13 3 / 9 4 / 11 5 / 5 6 / 9 7 / 14 8 / 7 TOTAL / 75 This document consists of 21 printed pages, including this cover page. 9729/02/Prelim/17 ANGLO-CHINESE JUNIOR COLLEGE © ACJC 2017 Department of Chemistry [Turn over

2 © ACJC 2017 9729/02/Prelim/2017 [Turn over For more than two millenia human ingenuity has turned natural and synthetic poisons into weapons of war. World War I was especially hailed by historians as the “Chemists’ War” because it was the first war in which chemical weapons were used on such an enormous scale, even on civilians. Chemicals were used to bring widespread destruction and death. It set the precedence for World War II. On the bright side, chemicals were used to save millions of soldiers’ lives in World War II. Question 1 examines how chemical weapons were used to kill in World War I, while Question 2 examines the use of chemicals as medicine in the battlefields of World War II. 1 A range of different chemicals - chlorine, phosgene and mustard “gas” - were used as weapons throughout World War I. Their melting and boiling points are tabulated below. Gas Melting point / 0C Boiling point / 0C chlorine -101.5 -34.0 phosgene -118 8.3 mustard “gas” 14.4 217.0 Chlorine was first used on a large scale by the German forces at Ypres in April 1915. It reacts with water in the lungs to form hydrochloric acid, which can quickly lead to death. At lower concentrations, it can cause coughing, vomiting, and irritation to the eyes. (a) Phosgene is a colourless gas, with an odour likened to that of ‘musty hay’. O C ClCl phosgene Phosgene is known to react violently with water to give hydrochloric acid and carbonic acid. Give the equation of the reaction between phosgene and water. COCl2 + 2H2O  H2CO3 + 2HCl [1] (b) The Germans introduced another chemical weapon – mustard “gas”. It was fired into enemy positions by cannons. (i) How is the name mustard “gas” misleading? It is actually a liquid at room temperature because its melting point is lower than room temperature and its boiling point is higher than room temperature. [1]

3 © ACJC 2017 9729/02/Prelim/2017 [Turn over 1 (b) The structural formula of mustard “gas” is ClCH2CH2SCH2CH2Cl. Unlike alkyl halides, mustard “gas” reacts instantly with water to form hemi -mustard, ClCH2CH2SCH2CH2OH. (ii) The following intermediate is thought to be formed by mustard “gas” itself via an intramolecular nucleophilic substitution before the attack of water. How does this intermediate make the hydrolysis of mustard “gas” easier than that of alkyl halides? The presence of angle/ring strain in this intermediate makes it more susceptible to nucleophilic attack than the mustard gas molecule itself. [1] (iii) The conversion of the intermediate in b(ii) to hemi-mustard involves two steps, the first involving the attack by water and the second involving deprotonation. Use electron arrows to show how the intermediate in b(ii) is converted into hemi-mustard. [2]

4 © ACJC 2017 9729/02/Prelim/2017 [Turn over 1 (b) (iv) Hemi-mustard can be further attacked by water to form J, C4H10SO2. Draw the structure of J. [1] (v) On reaction with concentrated sulfuric acid at 140 oC, hemi-mustard can be converted into K, C4H8SO, which does not decolourise bromine. Draw the structure of K. [1] [Total: 7 marks]

5 © ACJC 2017 9729/02/Prelim/2017 [Turn over 2 (a) Prontosil and sulfanilamide are anti-bacterial drugs. These two drugs saved many soldiers in World War II. The photo below is that of a sulfanilamide kit issued by the United States Army to its soldiers during World War II. One source states that the maximum daily dosage of sulfanilamide is 6.5 g per kg of patient. An average US army soldier may be assumed to weigh about 70 kg. Sulfanilamide has many side -effects – itching, h eadache, diarrhoe a, pale skin, vomiting, dizziness, fatigue. Is it safe for a wounded US army soldier to consume as many as 30 kits worth of tablets in a single day? Justify with calculations. Yes. Mass of drug in 30 kits = 30(12)0.5 g < 6.5(70) g [1]

6 © ACJC 2017 9729/02/Prelim/2017 [Turn over 2 (b) Prontosil was found to be active in vivo (in human bodies) while sulfanilamide was found to be active both in vivo and in vitro (in bacterial cultures grown in petri dishes). It was later proven that intestinal enzymes break down prontosil to sulfanilamide in the human intestine – in this reaction, the oxidation states of certain nitrogen atoms are altered. There are a few classes of enzymes as listed below. Transferases catalyse group transfer reactions. Hydrolases catalyse reactions that involve hydrolysis. Ligases are used in catalysis where two substrates are litigated and the formation of carbon-carbon, carbon-sulfide, carbon-nitrogen, and carbon-oxygen bonds due to condensation reactions. Reductases catalyse reduction reactions. Oxidases catalyse oxidation reactions. (i) Suggest the type of intestinal enzyme which catalyses the conversion of prontosil to sulfanilamide. Reductase [1] (ii) Name the side-product in the conversion of prontosil to sulfanilamide. 1,2,4-triaminobenzene or benzene-1,2,4-triamine [1] To analyse the sulfanilamide content in a pill, it was dissolved in HCl (aq). (c) Sulfanilamide is not very soluble in water. Explain why sulfanilamide is not soluble in water but is soluble in HCl (aq). Sulfanilamide is not very soluble in water due to limited hydrogen bonding due to the presence of benzene / hydrophobic nature of benzene. However, in acid, sulfanilamide is a base / will be protonated by acid / becomes ionic, so interactions with water change from hyd rogen bonding to the more favorable / stronger ion-dipole interactions. [2]

7 © ACJC 2017 9729/02/Prelim/2017 [Turn over 2 A 0.350 g sample of an antibiotic powder containing sulfanilamide was dissolved to form an aqueous solution. The solution was diluted and made up to the mark in a 100 cm3 graduated flask. A 25.0 cm3 aliquot was transferred into a conical flask, in which 25.0 c