2016 C1 Promotional Exam Paper 2

This document consists of 11 printed pages. HWA CHONG INSTITUTION C1 Promotional Examination Higher 2 NAME CT GROUP 16S CHEMISTRY Paper 2 Structured questions Candidates answer on the Question Paper. Additional Materials: Data Booklet. 9729/02 30 September 2016 1 hour 10 minutes READ THESE INSTRUCTIONS FIRST Write your name and CT group on all the work you hand in. Write in dark blue or black pen. You may use an HB pencil for any diagrams or graphs. Do not use staples, paper clips, highlighters, glue or correction fluid. Answer all questions in the spaces provided on the Question Paper. The use of an approved scientific calculator is expected, where appropriate. A Data Booklet is provided. 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. FOR EXAMINERS’ USE ONLY Paper 1 Paper 2 Paper 3 Percentage Multiple Choice Structured Free Response 100 Q1 / 12 Q1 / 15 Q2 / 13 Q2 / 15 Q3 / 15 Q3 / 4 / 20 Deductions Deductions / 20 Subtotal: / 40 Subtotal: / 50

2 2016 HCI C1 H2 Chemistry Promotional Exam / Paper 2 Answer all the questions in this section. 1 Fatty acids are carboxylic acids with a long hydrocarbon chain. The hydrocarbon chain can either be saturated or unsaturated. (a) Caprylic acid is an example of a saturated fatty acid. When caprylic acid dissolves in a solvent, the hydrocarbon chain and the carboxylic acid functional group interact differently with the solvent. Caprylic acid has minimal solubility in water, but is soluble in tetrachloromethane, CCl4. (i) State the intermolecular forces of attraction acting between water molecules and between CCl4 molecules. Water: …………………………………… CCl4: …………….………………………… [1] (ii) In the table below, state the interaction that will occur between the relevant part of caprylic acid and water and CCl4 respectively. Interaction with: Water CCl4 Hydrocarbon chain of caprylic acid Carboxylic acid functional group of caprylic acid [2] (iii) Using your answers in (a)(i) and (a)(ii), explain why caprylic acid has minimal solubility in water, but is soluble in CCl4. …………………………………………………….……………………………………............ …………………………………………………….……………………………………............ …………………………………………………….……………………………………............ [1]

3 2016 HCI C1 H2 Chemistry Promotional Exam / Paper 2 (b) In order to determine the degree of unsaturation of the hydrocarbon chains in fatty acids, the fatty acid is dissolved in CCl4. A known excess of Br2 or ICl is added in the dark, and further analysis is done to determine how much Br2 or ICl reacted with the fatty acid. (i) Br2 and ICl react with the fatty acids in an electrophilic addition reaction. Explain why Br2 and ICl are electrophiles. Br2: ……………………………………………….……………………………………............ …………………………………………………….……………………………………............ ICl: ……………………………………………….……………………………………............ …………………………………………………….……………………………………............ [2] (ii) Explain why the reaction needs to be carried out in the dark. …………………………………………………….……………………………………............ …………………………………………………….……………………………………............ [1] (iii) Describe the electrophilic addition mechanism of the reaction that occurs between Br2 and an unsaturated fatty acid represented by the generic structure below. [2]

4 2016 HCI C1 H2 Chemistry Promotional Exam / Paper 2 (c) ICl can react with benzene in the presence of a suitable catalyst to form iodobenzene. Explain why benzene undergoes a substitution reaction as compared to an alkene which undergoes an addition reaction. …………………………………………………….……………………………………..................... …………………………………………………….……………………………………..................... [1] (d) Iodobenzene undergoes a sequence of reactions as shown below. State the reagents and conditions required for the transformations to take place. Reagents and conditions for Step 1: …………………………………………………………… Reagents and conditions for Step 2: …………………………………………………………… [2] [Total: 12]

5 2016 HCI C1 H2 Chemistry Promotional Exam / Paper 2 2 Ribose, xylulose, glucose and fructose are members of a family of compounds known as monosaccharides, or simple sugars. Monosaccharides with 5 carbon atoms: ribose xylulose Monosaccharides with 6 carbon atoms: glucose fructose (a) (i) On the diagram of xylulose below, identify all chiral carbons by labelling them with an asterisk. [1] (ii) Every carbon atom in a monosaccharide is bonded to one oxygen atom. However, monosaccharides differ from each other in the total number of carbon atoms, the position of their carbonyl (C=O) group and/or their stereochemistry. Suggest the structure of a three-carbon monosaccharide that does not exhibit enantiomerism. [1] (iii) Suggest the general molecular formula for a monosaccharide with n carbon atoms. …………………………………………………….……………………………………............ [1] (iv) Two glucose molecules may undergo a condensation reaction to form the disaccharide maltose, in the process eliminating a molecule of water. Suggest the molecular formula of maltose. …………………………………………..……………………………………………………… [1]

6 2016 HCI C1 H2 Chemistry Promotional Exam / Paper 2 The disaccharide sucrose may be hydrolysed to give glucose and fructose. The reaction is slow but its rate may be increased with the addition of some H+ ions. sucrose + H2O --------------> glucose + fructose Sucrose, glucose and fructose are optically active, thus the kinetics of the hydrolysis reaction may be studied using a polarimeter. Optically active compounds may be termed dextrorotatory or laevorotatory as follows. Type of optically active compound Effect on plane-polarised light Angle of rotation observed using polarimeter dextrorotatory clockwise rotation positive (+) laevorotatory anticlockwise rotation negative (−) The rate equation may be written as: Rate = k[sucrose]x[H2O]y[H+]z The value of z is known to be 1. As [H 2O] and [H+] are constant, the rate equation may be reduced to Rate = keff[sucrose]x 25.0 cm3 of 0.580 mol dm–3 sucrose was mixed with 25.0 cm3 of 1.00 mol dm–3 HCl at 30 °C. A jacketed polarimeter tube, also kept at a constant temperature of 30 °C, was filled with a portion of the resulting solution and the stopwatch was started. At various suitable time t, the angle of rotation At was observed and recorded in the table below. Time t / min 0 11 25 45 73 112 More than 2 days Observed angle of rotation At / ° +16.1 +14.3 +12.2 +9.6 +6.7 +3.6 −4.4 (=Afinal) (At – Afinal) / ° 20.5 18.7 16.6 14.0 11.1 8.0 The reaction is assumed to have gone to completion after more than two days, when the angle of rotation was recorded for the last time. (b) (i) Sucrose and glucose are dextrorotatory. Is fructose dextrorotatory or laevorotatory? Circle the correct term and support your choice using relevant experimental data. Fructose is dextrorotatory laevorotatory ………………………………………………………………………………………………….. ………………………………………………………………………………………..………… [1] (ii) Explain why [H+] is taken as constant in the experiment. …………………………………………………………………………………………………. ……………..................................................................................................................... [1] H+

7 2016 HCI C1 H2 Chemistry Promotional Exam / Paper 2 (iii) The differen