HCI H2 CHEM P3 Prelim

This document consists of 14 printed pages. HWA CHONG INSTITUTION JC2 Preliminary Examinations Higher 2 CANDIDATE NAME CT GROUP 10S CENTRE NUMBER INDEX NUMBER CHEMISTRY Paper 3 Free Response Candidates answer on separate paper Additional Materials: Answer Paper Data Booklet 9647/03 13 September 2011 2 hours INSTRUCTIONS TO CANDIDATES Write your name and class 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 any four questions. Begin each question on a new piece of paper. 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. Write down the question numbers for the questions that you have attempted on the cover page provided.

2 © Hwa Chong Institution 2011 9647 / 03 / JC2 Prelim 2011 Answer any four questions. 1 (a) The primary ingredient of a shampoo is a surfactant. A surfactant is an amphiphilic molecule, that is, it contains both a discrete polar portion and a well-defined non-polar fragment. A common surfactant used in shampoos is sodium lauryl sulfate. S O O O Na sodium lauryl sulfate simplified representation When a surfactant is added to water, the molecules orientate themselves on the water’s surface as shown in the diagram below. When even more surfactants are added, the surfactant molecules will group together in th ree-dimensional spherical clusters, with the hydrocarbon chains filling the interior of the cluster and the ionic ends composing the outer surface. These molecular conglomerations are known as micelles. (i) By identifying all favorable interactions, explain the molecular orientation of the surfactant molecules at the surface of the water. (ii) Explain how micelles help to remove grease from hair. [3]

3 © Hwa Chong Institution 2011 9647 / 03 / JC2 Prelim 2011 (b) Many shampoos, particularly those targeted fo r babies and children, claim to cause no eye irritation or sting. Compound A has been shown to be slightly effective as a “no- tears” formulation. The reaction scheme below outlines the synthesis of compound A. C11H23CO2H C11H23COCl H2NCH2CH2OH C11H23CONHCH2CH2OH SO3 C11H23CONHCH2CH2O S O O OH C11H23CONHCH2CH2O S O O O- + N OH HO HON OH HO HO Z II I III IV H N O H N O H H O lauramidopropyl betaine (i) State the reagent and condition needed for step I. (ii) State the type of reaction in step IV. (iii) Step II in the above reaction scheme is not satisfactory. Identify the problem arising from the use of the reagent H 2NCH2CH2OH in the attempt to synthesize C11H23CONHCH2CH2OH. (iv) The reagent in step II, H2NCH2CH2OH, can be synthesized from chloroethane in 3 steps. Give the reagents and conditions for each step, as well as the structures of the intermediates formed. [6] (c) The bicyclic product B is a precursor for the synthesis of certain types of novel non-ionic surfactants that help to improve the solubility, foaming action and conditioning action of a shampoo formulation. Describe the mechanism for the formation of the bicyclic product B formed in the following reaction. 2 NH Br N Br B [4] A

4 © Hwa Chong Institution 2011 9647 / 03 / JC2 Prelim 2011 (d) SO3 in step III is manufactured from the reaction between SO 2 and O 2, in the presence of V2O5 , in the Contact Process as shown below: 2SO2 (g) + O2 (g) 2SO3 (g) (i) When a 2:1 mixture of SO 2 and O 2 was allowed to reach equilibrium at 800 K and a total equilibrium pressure of 8 atm, the partial pressure of SO 2 was found to be 0.150 atm. Write an expression for Kp and calculate its value at 800 K. (ii) State the role of V2O5 and describe its mode of action in the above reaction. [7] [Total: 20]

5 © Hwa Chong Institution 2011 9647 / 03 / JC2 Prelim 2011 2 (a) The most common fuel used in engines today is gasoline, which is made up of hydrocarbons containing between 4 to 10 carbon atoms. Another common petroleum- derived fuel is diesel oil, which is made up of hydrocarbons containing 12 or more carbon atoms. The fuel ignition process in a gasoline and diesel engine are very different for the following reasons. Gasoline is highly flammable and exposure to a spark will cause an explosion. However, diesel oil cannot be ignited even if a lighted match is thrown into a container of the fuel. Using your knowledge of chemical bonding, explain why gasoline and diesel oil have such different combustion characteristics. [2] (b) The problems associated with the internal combustion engine led to a quest to produce ‘cleaner’ fuels. Hydrogen gas is touted as the cleanest fuel since the only product is water. One of the methods of producing hydrogen fuel is to convert an ethanol-water-oxygen mixture to hydrogen at the surface of a suitable catalyst. Carbon dioxide is the only other product. The efficiency of this process is measured by the number of hydrogen molecules that may be produced per molecule of ethanol. (i) Write an equation, including state symbols, for the conversion of the ethanol- water-oxygen mixture to hydrogen gas. (ii) Predict and explain the sign of the entropy change for this reaction. (iii) State and explain two advantages of using ethanol in preference to methanol in the production of hydrogen by this process. [5] (c) The efficiency of a fuel is dependent on the heat produced on combustion of the fuel as well as its expansion ratio. The heat produced in the combustion causes r apid expansion of the gaseous products which then moves the pistons in the engine and does useful work. The expansion ratio of a fuel is the volume increase that accompanies the combustion of that fuel. (i) Write equations, including state symbols, for the combustion of hydrogen and ethanol in the engine respectively to give gaseous products. (ii) Using relevant data from the Data Booklet , calculate the enthalpy change of combustion for hydrogen and ethanol respectively. (iii) Hence deduce whether hydrogen gas or ethanol is the more efficient fuel. [5]

6 © Hwa Chong Institution 2011 9647 / 03 / JC2 Prelim 2011 (d) The distinctive scent of rose oil comes mainly from a family of closely related chemicals called the rose ketones. Compounds C, D and E belong to this family. C and D have the same molecular formula, C 13H20O, while E has molecular formula, C13H18O. C can exist as a pair of enantiomers, but D and E do not show any optical activity. 1 mol of C and D each reacts with 2 mol of liquid bromine at room temperature. 1 mol of E, however, reacts with 3 mol of liquid bromine. C, D and E react with hydrogen in the presence of nickel to give the same compound, C 13H26O: OH C and D each undergo oxidative cleavage with acidified KMnO 4 to give ethanoic acid as one of the two organic products. In addition, C also gives compound C 10H14