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[Turn over JURONG JUNIOR COLLEGE 2015 JC 2 PRELIMINARY EXAMINATION Higher 1 CANDIDATE NAME CLASS 15S CHEMISTRY 8872/02 Paper 2 Structured Questions 28 August 2015 2 hours Candidates answer Section A on the Question Paper. Additional Materials: Answer Paper Data Booklet READ THESE INSTRUCTIONS FIRST Write your name, class and exam index number on all the work you hand in. Write in dark blue or black pen on both sides of the paper. You may use a soft pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. Section A Answer all the questions. Section B Answer two questions on separate answer paper. 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 Examiner’s Use 1 2 3 4 B5 B6 B7 Total This document consists of 14 printed pages and no blank page.

2 © Jurong Junior College 8872/02/ J2 PRELIMINARY EXAMINATION/2015 [Turn over Section A Answer all the questions. 1 Ethanoic acid, also known as acetic acid, is a colourless liquid that has a strong and distinct pungent and sour smell. Aside fr om culinary uses, as flavouring and as a preservative, ethanoic acid is used to make many polymers and fibres. It can be made by the following method: For Examiner’s Use (a) Draw the structure of compound A. [1] (b) (i) Ethanoic acid can be formed from the oxidation of ethanol. Suggest suitable reagent and conditions to perform this reaction. (ii) Write a balanced equation to represent the reaction in (b)(i). [3] (c) 2-chloroethanoic acid can be formed from ethanoic acid using suitable reagents and conditions via substitution reaction. Explain why 2-chloroethanoic acid and ethanoic acid has different acidity. [2]

3 © Jurong Junior College 8872/02/ J2 PRELIMINARY EXAMINATION/2015 [Turn over 1 (d) A gas is said to exhibit ideal gas behavior if it obeys the ideal gas equation pV = nRT where p = pressure of gas in Pa, V = volume of gas in m3, n = amount of gas (mol), R = 8.31 J K−1 mol−1 (a constant), and T = temperature in K. For Examiner’s Use Three experiments were performed where different masses of ethanoic acid were expanded into a vessel of volume 0.0150 m 3 at different pressures and at a temperature of 100 oC. Experiment Mass of ethanoic acid/ g Pressure/ Pa Relative molecular mass 1 0.002 6.346 2 0.015 31.011 3 0.050 86.128 (i) Assuming ideal behaviour, calculate the relative molecular mass of ethanoic acid for each experiment 1 to 3 and enter the values into the above table. (ii) In gaseous state just above the boiling point, the monomer and dimer forms of ethanoic acid exist together in equilibrium. 2CH3COOH  (CH3COOH)2 Draw a fully labelled diagram to illustrate the bond formed when ethanoic acid dimerises.

4 © Jurong Junior College 8872/02/ J2 PRELIMINARY EXAMINATION/2015 [Turn over 1 (d) (iii) Use Le Chatelier’s Principle to predict and explain how an increase in pressure will affect the position of equilibrium in d(ii) and the trend in relative molecular mass of ethanoic acid. For Examiner’s Use [4] (e) The salt of ethanoic acid, sodium ethanoate, may be added to food as a seasoning. It is often used to give potato chips a salt and vinegar flavor. The enthalpy change for the solution of sodium ethanoate in water, ∆H1 can be determined by using the energy cycle given below. CH 3COO–(g) + Na+(g) CH 3COONa(s) CH 3COO–(aq) + Na+(aq) ∆H2 = –780 kJ mol–1 ∆H3 = –763 kJ mol–1 (i) Name the enthalpy change that is represented by ∆H3. (ii) With reference to the energy cycle and the data given above, calculate ∆H1. [2] [Total: 12] ∆H2 ∆H3 ∆H1

5 © Jurong Junior College 8872/02/ J2 PRELIMINARY EXAMINATION/2015 [Turn over 2 (a) The element iron is a transition metal that is very common in our planet. It has many uses in different industries and even in the human body. It has four naturally occurring isotopes. isotope Relative abundance / % 54Fe 5.845 56Fe 91.754 57Fe 2.119 58Fe 0.282 For Examiner’s Use (i) Write the full electronic configuration of iron. (ii) Use the relative abundance data to calculate the relative atomic mass of iron to 3 decimal places. Show your working. [2] (b) Iron is used as a catalyst in the manufacture of ammonia in the Haber process. N2(g) + 3H2(g)  2NH3(g) (i) State the optimum industrial conditions of temperature and pressure used in the Haber process. (ii) Explain why these particular conditions are chosen.

6 © Jurong Junior College 8872/02/ J2 PRELIMINARY EXAMINATION/2015 [Turn over 2 (b) (iii) With the aid of the Boltzmann dist ribution curve, explain how the presence of a catalyst affects the rate of this process. For Examiner’s Use [7] (c) Nitrogen is one of the Period 2 elements and it forms the nitride ion, N3−. State and explain how you would expect the radius of the following ions to compare with the radius of nitride ion.  fluoride ion, F −  lithium ion, Li + [2] [Total: 11]

7 © Jurong Junior College 8872/02/ J2 PRELIMINARY EXAMINATION/2015 [Turn over 3 Halogenoalkanes are used widely in the industry to produce organic compounds commercially. Halogenoalkanes can also undergo hydrolysis with sodium hydroxide to produce alcohol commercially. For Examiner’s Use (a) Using monohalogenohexanes, C6H13X, as an example, describe and explain the relative reactivity of chloro and iodo–compounds towards aqueous sodium hydroxide. [2] (b) (i) A sequence of reactions, starting from compound M, a dihalogeno compound, is shown below. In the appropriate boxes draw the structures of compounds N, P and Q.

8 © Jurong Junior College 8872/02/ J2 PRELIMINARY EXAMINATION/2015 [Turn over 3 (b) (ii) For the reactions in the scheme shown above suggest For Examiner’s Use  the reagents and conditions for reaction I,  the type of reaction in reaction I, [5] (c) Draw the structure of a suitable alkene needed to form compound M in (b)(i). [1] [Total: 8]

9 © Jurong Junior College 8872/02/ J2 PRELIMINARY EXAMINATION/2015 [Turn over 4 Dental hygiene is big business; sales of teeth-whitening products are soaring. There are two ways that teeth may become discoloured. The antibiotic tetracycline, excess fluoride, or trauma can darken or reveal the yellow inner tooth. Coffee, tea or smoking attacks the outer surface. Common whitening methods target only outer stains. The yellow layer beneath the white enamel protects your teeth as you chew. Enamel, the hardest substance in your body, is composed primarily of calcium phosphate. When spaces between the rods fill with organic material, the stain become too deep to brush away. All teeth-whitening options, except natural method, use hydrogen peroxide (H 2O2) as the oxidising agent. Carbamide peroxide is used as the H 2O2 source in many products. The molecule decomposes in water yielding H2O2 as indicated in the equation below. carbamide peroxide  urea + H2O2 H2O2 reacts rapidly with the electron-rich molecules that discolour the teeth. The stain molecules are broken into smaller molecules with lighter colour, so the teeth appear whiter. The whiteness of the teeth and the time required depend up