2019 TMJC H2 Chem Prelim P2 QP

Tampines Meridian Junior College 2019 JC2 Prelim H2 Chemistry CANDIDATE NAME CIVICS GROUP __________________________________________________________________________________ H2 CHEMISTRY 9729/02 Paper 2 Structured Questions 19 September 2019 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name and civics group in the spaces at the top of this page. Write in dark blue or black pen on both sides of the paper. You may use an HB pencil for any diagrams, graphs or rough working. Do not use paper clips, 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. The number of marks is given in brackets [ ] at the end of each question or part question. __________________________________________________________________________________ This document consists of 19 printed pages. Examiner’s Use Paper 1 MCQ / 30 Paper 2 Q1 / 14 Q2 / 9 Q3 / 13 Q4 / 12 Q5 / 11 Q6 / 16 / 75 Paper 3 / 80 Paper 4 / 55 Total / 100 Grade TAMPINES MERIDIAN JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATION

2 Tampines Meridian Junior College 2019 JC2 Prelim H2 Chemistry 1 (a) Carbon forms compo unds with Group 16 elements such as oxygen, sulfur and selenium. The properties of some of these compounds are given below. compound structure net dipole moment boiling point / C CO2 O=C=O 0 sublimes CS2 S=C=S 0 46 COS S=C=O 0.71 –50 COSe Se=C=O 0.73 –22 (i) Explain, in terms of structure and bonding, the difference in the boiling points of CS2 and COS. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. ……………………………………………………………………………………….[2] (ii) Explain why  CO2 has no net dipole moment.  COSe has a greater net dipole moment than COS. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. ……………………………………………………………………………………….[2]

3 Tampines Meridian Junior College 2019 JC2 Prelim H2 Chemistry Carbon forms the backbone of organic compounds. Hydrocarbons are the simplest organic compounds that contain carbon and hydrogen. (b) Compound A is an isomer of the hydrocarbon octane, C8H18. A Controlled chlorination of compound A in the presence of UV light produces different mono-chlorinated products with a molecular formula of C8H17Cl. (i) Suggest the total number of constitutional isomers which can be formed from the possible mono-chlorination of compound A. Draw the structural formulae of any two of these products. Total number of possible mono-chlorinated products = ……………………… [3] (ii) Draw the skeletal formula of the isomer of octane which could produce only one possible mono-chlorinated product if it undergoes free radical substitution. [1]

4 Tampines Meridian Junior College 2019 JC2 Prelim H2 Chemistry (c) Besides reaction of alkanes with halogens, the process of thermal cracking, in which large alkane molecules are broken down into smaller alkanes and alkenes, proceeds via free radical mechanism. The following are reactions involved when propane undergoes thermal cracking. CH3CH2CH3   ●CH3 + ●CH2CH3 -- (1) CH3CH2CH3   ●H + ●CH2CH2CH3 -- (2) ●CH3 + CH3CH2CH3   CH4 + ●CH2CH2CH3 -- (3) ●CH2CH3   ●H + CH2=CH2 -- (4) ●CH3 + CH2=CH2   ●CH2CH2CH3 -- (5) ●CH3 + ●CH3   CH3CH3 -- (6) 2 ●CH2CH3   CH3CH3 + CH2=CH2 -- (7) (i) Reactions (1) and (2) are termed initiation steps. By quoting relevant data from the Data Booklet, deduce which one is more likely to occur. …………………………………………………………………………………………. ……………………………………………………………………………………….[1] (ii) From reactions (3) to (7), identify those which may be termed propagation steps in the mechanism. ……………………………………………………………………………………….[1] (iii) Which gas, if detected in the product mixture, would support the occurrence of both reactions (2) and (4)? ……………………………………………………………………………………….[1] (iv) Suggest why reaction (7) may be termed a disproportionation reaction. …………………………………………………………………………………………. ……………………………………………………………………………………….[1]

5 Tampines Meridian Junior College 2019 JC2 Prelim H2 Chemistry (d) Methanoic acid, H2CO2, is the simplest carboxylic acid. Draw a dot -and-cross diagram of methanoic acid. Suggest the shape around the carbon atom in methanoic acid. Shape around C atom ………………………………………….. [2] [Total: 14]

6 Tampines Meridian Junior College 2019 JC2 Prelim H2 Chemistry 2 Hydrogen peroxide reacts with acidified iodide ions to liberate iodine, according to the following equation: H2O2(aq) + 2H+(aq) + 2I–(aq)  2H2O(l) + I2(aq) In investigations of this reaction, t he following results were obtained by varying the volumes of hydrogen peroxide and iodide ions. experiment volume of H2O2 / cm3 volume of I– / cm3 volume of H2O / cm3 initial rate / mol dm–3 s–1 1 20.0 20.0 20.0 1.2 x 10–2 2 20.0 30.0 10.0 1.8 x 10–2 3 50.0 10.0 0.0 1.5 x 10–2 (a) Explain why water was added to experiments 1 and 2. ………………………………………………………………………………………………….. ………………………………………………………………………………………………..[1]

7 Tampines Meridian Junior College 2019 JC2 Prelim H2 Chemistry (b) The reaction was determined to be zero order with respect to hydrogen ions. (i) Sketch the rate-concentration graph for H+ ions. [1] (ii) Determine the order of reaction with respect to the other two reactants. Hence, write down the rate equation. [3]

8 Tampines Meridian Junior College 2019 JC2 Prelim H2 Chemistry (c) In order to further investigate the kinetics of the reaction, experiments 4 and 5 were conducted. The following results were obtained by varying the concentrations of hydrogen peroxide and iodide ions. experiment initial [H2O2(aq)] / mol dm–3 initial [I–(aq)] / mol dm–3 4 0.020 0.500 5 0.050 1.000 The half-life of hydrogen peroxide was 9.6 min in ex periment 4. Explain and predict the half-life of hydrogen peroxide in experiment 5. ………………………………………………………………………………………………….... …………………………………………………………………………………………………… ………………………………………………………………………………………………….... …………………………………………………………………………………………...…….[2] (d) An alternative method of investigating the rate of the above reaction is by withdrawing aliquots at specified time intervals and titrating the iodine formed in each aliquot with sodium thiosulfate solution. Suggest how the reaction can be quenched at specified time intervals. ………………………………………………………………………………………………….. ………………………………………………………………………………………………..[1] (e) Hydrogen peroxide decomposes easily. Suggest a method whereby the shelf -life of the hydrogen peroxide solution could be increased. ………………………………………………………………………………………………….. ………………………………………………………………………………………………..[1] [Total: 9]

9 Tampines Meridian Junior College 2019 JC2 Prelim H2 Chemistry 3 Lithium forms