2019 MI Prelim H2 Chem P3 QP

Class Adm No Candidate Name: This question paper consists of 9 printed pages and 1 blank page. 2019 Preliminary Exams Pre-University 3 H2 CHEMISTRY 9729/03 Paper 3 Free Response 20 Sept 2019 2 hours Candidates answer on separate paper. Additional materials: Answer Paper Data Booklet Graph Paper READ THESE INSTRUCTIONS FIRST Do not turn over this question paper until you are told to do so Write your name, class and admission number 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, glue or correction fluid. Section A Answer all questions. Section B Answer one question. A Data Booklet is provided. The use of an approved scientific calculator is expected, where appropriate. 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. Question Section A Section B Total 1 2 3 4 5 Marks 19 19 22 20 20 80

2 Section A Answer all the questions in this section. 1 (a) 3–chloropropanoic acid, CH2ClCH2CO2H, is a weak Brønsted acid. A 0.100 mol dm3 solution of CH2ClCH2CO2H has a pH of 2.49. (i) Calculate the pKa of 3–chloropropanoic acid. [3] (ii) State and explain the differences in the relative acid strength between 3–chloropropanoic acid and propanoic acid. [2] (iii) 3-chloropropanoyl bromide is the acid derivative of 3–chloropropanoic acid . Propose a 3 -step synthetic route for the formation of 3 -chloropropanoyl bromide, using 3-hydroxypropanal as the starting reagent. State clearly the reagents and conditions used for each step. [5] (b) A student investigated th e rate of reaction between 3–chloropropanoic acid and aqueous sodium carbonate. The rate of the reaction may be determined by measuring how long it takes for the gas to be completely released. A series of experiments were carried out to study the order of reaction with respect to 3–chloropropanoic acid and sodium carbonate. The following results were obtained. Experiment Number Volume / cm3 Time / s 3–chloropropanoic acid Na2CO3 H2O 1 20.0 40.0 40.0 78 2 20.0 30.0 50.0 100 3 5.0 20.0 25.0 75 (i) Write an equation, including state symbols, for the reaction between sodium carbonate and 3–chloropropanoic acid. [1] (ii) State the relationship between time and rate. [1] (iii) Determine the order of the reaction with respect to 3 –chloropropanoic acid and sodium carbonate. [2] (iv) Hence, write the rate equation, stating the units of k. [2] (v) With the aid of an appropriate diagram, explain how the addition of a catalyst can increase the rate of a reaction between 3–chloropropanoic acid and sodium carbonate. [3] [Total: 19]

3 [Turn over 2 (a) Using only the elements C, H and O, draw the structural formulae of two different organic compounds, each containing a single carbon atom , with an oxidation state of 0 and +2 respectively. [2] (b) A symmetrical organic compound A, C 2H4N2O2, upon reacting with hot d ilute NaOH(aq) produces a colourless, pungent gas that turns moist red litmus paper blue. (i) Draw the structure of compound A and state the functional group present. [2] (ii) The functional group present in compound A can be reduced by lithium aluminium hydride, LiAlH4. Draw the dot-and-cross diagram for LiAlH4. [1] (iii) Other than LiAlH4, NaBH4 can also be used for the reduction of certain functional groups. LiAlH4 is able to produce hydride ion, H - more readily than NaBH 4. Suggest why LiAlH4 is a more powerful reducing agent than NaBH4. [1] (c) Quinones are used in photography as a reducing agent. Quinone compounds are multifunctional as they exhibit properties of both ketones and alkenes. The following scheme involves 1, 2-benzoquinone, where step I involves the use of LiAlH4. O O OH OH C Step I Step II HOOCCH2COOH conc H2SO4, reflux D alkaline KMnO4(aq), cold Step III C9H8O4 1,2-benzoquinone (i) Draw the structures of C and D. [2] (ii) Identify the chiral centres on B. Hence, explain why it does not display optical activity.[2] (iii) Using a simple chemical test, suggest how 1,2-benzoquinone can be distinguished from compound B. In your answer, state all reagents and conditions used and the expected observations. [2] B

4 (iv) When compound B undergoes partial hydrogenation, it forms compound E. E Describe the mechanism of the reaction when compound E reacts with Br2 in CCl4 in the dark. In your answer, show all relevant charges and movement of electrons clearly. [3] (d) K2Cr2O7 and KMnO4 are common oxidising agents used in organic synthesis where KMnO4 is the more powerful of the two . Compound F, C 4H8O, reacted with K2Cr2O7 and KMnO4 separately to yield different products as shown in the reactions below. C4H8O C4H6O2 C4H8O C2H4O2 Given the following information,  All three compounds, F, G and H react with sodium metal.  G and H react with Na2CO3, but F does not.  F and G decolourise aqueous bromine. Suggest the structures of compounds F, G and H, explaining the chemistry involved. [4] [Total: 19] F K2Cr2O7/H2SO4 G F KMnO4/H2SO4 H

5 [Turn over 3 (a) Phenylethanoic acid is used as a treatment for hyperammonemia, a condition where there is an accumulation of ammonia in the human body. O OH phenylethanoic acid (i) In an experiment, 60 cm 3 of 0.10 mol dm −3 of sodium hydroxide was added to 20 cm3 of 0.20 mol dm−3 of phenylethanoic acid in a conical flask. Calculate the pH of the final solution when all 60 cm3 of sodium hydroxide was added to the flask. [3] (ii) 2-amino-2-phenylethanoic acid can be synthesised from phenyl ethanoic acid through a series of substitution reactions. Draw the displayed formula of 2-amino-2-phenylethanoic acid. [1] (iii) Write two equations to show how an aqueous solution of 2-amino-2-phenylethanoic acid is able to resist the change in pH upon addition of small amounts of acid and base. [2] (iv) Draw the structure of the predominant form when 2-amino-2-phenylethanoic acid is in an aqueous solution of pH 10. [1] (b) (i) Predict and explain whether phenylethanoyl chloride or phenylethanoic acid has a higher reactivity towards nucleophilic reagents. [2] (ii) Given that phenylethanoyl chloride has a boiling point of 95 °C and phenylethanoic acid has a boiling point of 266 °C, explain th is difference in terms of struct