CJC H2 Chem 2012 Prelim P1 QP

CATHOLIC JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATIONS Higher 2 CHEMISTRY 9647/01 Paper 1 Multiple Choice Wednesday 29 August 2012 Additional Materials: Multiple Choice Answer Sheet 1 hour Data Booklet READ THESE INSTRUCTIONS FIRST Write in soft pencil. Do not use staples, paper clips, highlighters, glue or correction fluid. Write and/or shade your name, NRIC / FIN number and HT group on the Multiple Choice Answer Sheet in the spaces provided. There are forty questions in this paper. Answer all questions. For each question, there are four possible answers, A, B, C and D. Choose the one you consider correct and record your choice in soft pencil on the separate Answer Sheet. Read the instructions on the Multiple Choice Answer Sheet very carefully. Each correct answer will score one mark. A mark will not be deducted for a wrong answer. Any rough working should be done in this booklet. Calculators may be used. This document consists of 18 printed pages and 0 blank page.

2 9647/01/CJC JC2 Preliminary Exam 2012 Section A For each question there are four possible answers, A , B , C and D. Choose the one you consider to be correct. 1 Gallium ( Ar = 69.7) occurs naturally as two isotopes, 69 31 Ga and 71 31 Ga. What is the percentage of 71 31 Ga atoms in a sample of naturally occurring gallium? A 33 % B 35 % C 60 % D 65 % 2 The mineral tellurite, TeO2 (Mr = 160.0) is often used in the manufacture of optic fibres. It was found that 1.01 g of TeO 2 in an ore sample required exactly 60 cm 3 of 0.035 mol dm –3 acidified K 2Cr2O7 for complete reaction. In this reaction, Cr 2O72– is converted into Cr3+. What is the oxidation state of Te in the final product? A +2 B +3 C +5 D +6 3 Use of the Data Booklet is relevant to this question. What do the ions 35Cl– and 40Ca2+ have in common? A Both ions have 18 neutrons. B Both ions have more protons than neutrons. C Both ions contain the same number of nucleons. D Both ions have an outer electronic configuration 3s2 3p6. 4 Carbodiimides are often used in organic synthesis as dehydrating agent to activate carboxylic acids towards amide or ester formation. Carbodiimides consist of the general structure, RN=C=NR where R is an alkyl group. What is the most likely bond angle at each nitrogen atom in carbodiimides? A 107° B 118° C 120° D 180° 5 Myoglobin, Mb, is an oxygen-carrier protein that exists in the muscle fibres of most mammals. Each Mb molecule will bind to one O 2 molecule, according to the following equation. Mb(aq) + O2(aq) MbO2(aq) Kc = 1×106 mol–1 dm3 Given that the concentration of O 2 is 6.5 × 10 –6 mol dm –3, what is the percentage of MbO2 in a Mb-MbO2 mixture? A 50.5 % B 65.0 % C 86.7 % D 88.4 %

3 9647/01/CJC JC2 Preliminary Exam 2012 [Turn over 6 The enthalpy changes involving some oxides of nitrogen are given below: N2(g) + O2(g) → 2NO(g) ∆H = +180 kJ mol–1 2NO2(g) + 1 2O2(g) → N2O5(g) ∆H = –55 kJ mol–1 N2(g) + 5 2O2(g) → N2O5(g) ∆H = +11 kJ mol–1 What is the enthalpy change, in kJ mol–1, of the following reaction? 2NO(g) + O2(g) → 2NO2(g) A –235 B –125 C –114 D –57 7 The Thermit Reaction involves mixing iron(III) oxide with aluminium powder in a crucible, with a suitable fuse to start the reaction. The reaction is as follows: Fe2O3(s) + 2Al(s) → Al2O3(s) + 2Fe(l) The fuse is first ignited, where it will burn in oxygen, forming the oxide with a large release of heat required for the Thermit reaction to take place. The commonly used material for the fuse is a clean magnesium strip. Which of the following does not help to explain why a strip of magnesium is suitable to be used as a fuse? A The large amount of heat energy released on igniting the fuse enables the reactants to overcome the high activation energy involved. B Magnesium removes the thin layer of oxide on aluminium, thus allowing aluminium to react with the iron(III) oxide. C The numerical value of the enthalpy change of formation of magnesium oxide is very large. D The strip increases the surface area for magnesium to react with the oxygen at a faster rate. 8 When a precipitate is formed, ∆Gppto, in J mol–1, is given by the following expression ∆Gppto = 2.303RTlog Ksp Data about AgBr is as follows: Ksp(AgBr) = 5.0×10–13 mol2 dm–6, ∆Hppto = –84.4 kJ mol–1 What is the ∆Sppto, in J mol–1 K–1, for the formation of AgBr(s) at 298 K? A – 47.8 B – 0.0478 C +0.0478 D +47.8

4 9647/01/CJC JC2 Preliminary Exam 2012 9 The secondary structure of DNA is the double helix. The formation of the double helix involves two DNA chains, where one has the bases Adenine (A) and Guanine (G), interacting with the bases Thymine (T) and Cytosine (C) on the other chain as shown below: The two chains coil together in a helical fashion, and this process is an example of self-assembly. What are the correct signs of ∆H and ∆S for the formation of the double helix? ∆H ∆S A – – B – + C + – D + + N HN O O sugar CH3 T N N O sugar H2N C N N N N NH2 NH N N N O NH2 sugar sugar A G Base pairs Adenine Thymine Guanine Cytosine Sugar phosphate backbone

5 9647/01/CJC JC2 Preliminary Exam 2012 [Turn over 10 The cell below is set up under standard conditions: Pt(s) / Sn2+(aq), Sn4+(aq) // HNO2(aq), H+(aq) / NO(g) / Pt(s) Ecello = +0.84 V Which of the following changes will cause the cell e.m.f. to be less than +0.84 V immediately after the cell is being set up? A adding NaOH(aq) to the HNO2(aq) / NO(g) half-cell B adjusting the partial pressure of NO(g) to be 0.5 atm C adding water to the Sn4+(aq)/Sn2+(aq) half-cell D adding SnCl2 to the Sn4+(aq)/Sn2+(aq) half-cell 11 Use of the Data Booklet is relevant to this question. The cell shown in the diagram is set up under standard conditions where X and Y are platinum electrodes. Half-cell A Half-cell B Which of the following statements is correct? A Changing X to Fe in half-cell A will not affect E cello. B The voltmeter will show a reading of about 1.80 V. C The electrons will flow from Y to X through the voltmeter. D Y will be the positive electrode. 12 Ethyl ethanoate is a common ester formed during production of wines. It gives the aroma found in younger wines and contributes towards the “fruitiness” perception in wine. The formation of ester in wine can be illustrated by the following equation. CH 3CH2OH + CH3CO2H CH3CO2CH2CH3 + H2O Kc = 4.0, ΔH = –20 kJ mol–1 Which of the following statement is correct about the above equilibrium? A As water is removed from wine, [CH3CO2CH2CH3] and Kc increases. B As temperature of the wine decreases, [CH3CO2CH2CH3] and Kc increases. C As water is added to the wine, [ CH3CO2CH2CH3] increases. D As CH3CO2H is removed from the wine, [CH3CO2CH2CH3] increases. Cl2(g) Cl–(aq) Fe2+(aq) and Fe3+(aq) X Y

6 9647/01/CJC JC2 Preliminary Exam 2012 13 HA is a weak acid and can have different degree of acidity in aqueous solution and in liquid ammonia. The respective equations that represent their dissociations are as follow. HA + H2O A– + H3O+ HA + NH3 A – + NH4+ Which of the following statement is correct? A Ammonia is more polar than water, resulting in greater dissociation of HA. B Degree of dissociation of HA is identical in aqueous solution and liquid ammonia. C p Ka of NH 3 is larger than that of H 2O, hence HA is a stronger acid in liquid ammonia. D Kb of NH3 is larger than that of H2O, hence HA is a stronger acid in liquid ammonia. 14 Amylase is the first enzyme discovered and isolated. It acts as a catalyst in the hydrolysis of starch. In a single experiment, the rate of hydrolysis of starch was mo nitored as the reaction proceeded and the following graph was obtained. Which of t