HCI Prelim H2 CHEM P3

This document consists of 11 printed pages. HWA CHONG INSTITUTION C2 Preliminary Examinations Higher 2 CANDIDATE NAME CT GROUP 15S CENTRE NUMBER INDEX NUMBER CHEMISTRY Paper 3 Free Response Candidates answer on separate paper. Additional Materials: Answer Paper Data Booklet 9647/03 19 September 2016 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 attempted on the cover page provided.

2 © Hwa Chong Institution 2016 9647 / 03 / C2 Prelim 2016 Answer any four questions. 1 (a) Suggest and explain how the boiling points of 1-chlorobutane and 1-bromobutane differ from each other. [2] (b) (i) Define the term standard enthalpy change of combustion. [1] (ii) Use of the Data Booklet is relevant to this question. In an experiment to determine the enthalpy change of combustion of bromobutane, a quantity of the fuel was burnt underneath a copper can containing 200 g of water. It was found that the temperature rose by 45.0 C after 2.35 g of bromobutane had been burnt. The heat transfer was known to be only 80% efficient. Calculate the enthalpy change of combustion of the bromobutane. Ignore the heat capacity of the copper can. [2] (c) An experiment was set up to study the reaction between 2 -bromo-3-methylbutane and sodium hydroxide. The reagents used were FA1, containing 0.0100 mol dm –3 of 2-bromo-3-methylbutane and FA2, containing 0.0100 mol dm –3 NaOH. In each experiment, the reagents were dissolved in a suitable solvent to ensure good mixing. The results are recorded in the table below. Expt Volume of FA1 / cm3 Volume of FA2 / cm3 Volume of solvent / cm3 Rate / mol dm–3 s–1 1 10.0 30.0 60.0 7.40 x 10-7 2 5.0 20.0 25.0 9.86 x 10-7 3 10.0 5.0 35.0 4.93 x 10-7 (i) Use the data in the table to deduce the order of reaction with respect to 2-bromo-3-methylbutane and sodium hydroxide. Hence, write a rate equation for this reaction. [3] (ii) With reference to your answer to (c)(i), describe the mechanism for the reaction between 2-bromo-3-methylbutane and sodium hydroxide. [3] (iii) Calculate the rate constant for the reaction, stating the units. [2]

3 © Hwa Chong Institution 2016 9647 / 03 / C2 Prelim 2016 (d) In a separate experiment, a student performed the following qualitative analysis tests on three different bromoalkanes: 1 -bromobutane, 2 -bromobutane and 2 -bromo-2- methylpropane. Different solvents were used for Test 1 and Test 2 and it was observed that th e choice of solvents did have an effect on the type of reaction mechanisms undergone by the bromoalkanes. Test 1: When silver nitrate was added to the bromoalkanes using ethanol as the solvent, silver bromide was precipitated for all three bromoalkanes at different rates. AgNO3 + RBr + C2H5OH  ROC2H5 + HNO3 + AgBr Test 2: When sodium iodide in propanone solvent wa s added to the bromoalkanes, sodium bromide was precipitated for 1-bromobutane and 2 -bromobutane at different rates, but not 2-bromo-2-methylpropane. NaI + RBr  RI + NaBr The observations for each test were recorded in the following table. Time taken for precipitate to appear Test 1 Test 2 1-bromobutane 5 min Almost immediately 2-bromobutane 3 min 5 min 2-bromo-2-methylpropane Almost immediately No precipitate (i) Different nucleophilic substitution mechanisms have been proposed for the reactions in the two tests. Considering the information provided, suggest the predominant mechanism undergone in each test. [1] (ii) Considering the structure of the bromoalkane, explain why the test results support your answer in (d)(i). [2] (iii) Considering the interactions involved with the solvent, explain why the suggested mechanism for Test 1 occurs predominantly. [1] (e) 2-methylbenzonitrile can be used as a starting reagent to form compound A. Propose a synthesis route for the formation of compound A in no more than 3 steps, showing clearly the reagents, conditions and structures of the intermediates formed. 2-methylbenzonitrile Compound A [3] [Total: 20]

4 © Hwa Chong Institution 2016 9647 / 03 / C2 Prelim 2016 2 Ethanoic acid behaves as a weak acid in water, with Ka = 1.8 x 10–5 mol dm–3. In contrast, ethanoate ion behaves as a weak base in water, with Kb = 5.6 x 10–10 mol dm–3. (a) (i) Write the expressions for Ka and Kb of ethanoic acid and ethanoate ion respectively, and use these expressions to show that the product Ka  Kb has a constant value at a fixed temperature. [2] (ii) Compare the relative strength of ethanoate ion and water as bases, and explain with the aid of an equation , whether a solution of sodium ethanoate is a cidic, alkaline, or neutral. [2] (iii) Calculate the pH of a solution which contains 0.50 mol dm –3 ethanoic acid and 0.50 mol dm–3 sodium ethanoate. [1] (b) The Strecker synthesis is a route to prepare amino acids. Glycine (2-aminoethanoic acid ) can be prepared from methanal as shown in the reaction scheme below. C H H O A elimination of H2O C H H NHNH3 HCN H C NH2 H C N H C NH2 H C O OH reaction I reaction II reaction III reaction IV glycine (i) Suggest a structure for compound A. [1] (ii) The product of reaction II is an imine, which has a C=N bond. Methanal undergoes reaction with another compound B to form an orange solid C which also has a C=N bond. Name compound B and draw the structure of the orange solid C. [2] (iii) What type of reaction is occurring during reaction III? [1] (iv) State the reagents and conditions for reaction IV. [1] (v) Compound D is an isomer of glycine. Upon warming D with dilute sodium hydroxide, a gas which turns litmus blue is evolved. Draw the structure of D. [1] (vi) A carbonyl compound E can be used as