TJC H2 CHEM P1 Prelim

1 2016 TJC H2 Chemistry Preliminary Examination [Turn Over CHEMISTRY 9647/01 Paper 1 Multiple Choice 19th September 2016 1 hour Additional materials: Multiple Choice Answer Sheet Data Booklet READ THESE INSTRUCTIONS FIRST Write in soft pencil. Do not use staples, paper clips, glue or correction fluid. There are forty questions on 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 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. The use of an approved scientific calculator is expected, where appropriate. This document consists of 18 printed pages. Write your name and Civics Group Write and shade your CG number followed by last 3 digits of NRIC

2 2016 TJC H2 Chemistry Preliminary Examination [Turn Over Section A Part 1 For each question there are four possible answers, A, B, C and D. Choose the one you consider to be correct. 1 During the bacterial leaching of low grade copper ores, acidified water is sprayed onto the ore chalcopyrite, CuFeS2. Bacteria then convert the insoluble ore into a solution according to the equation shown below: 4CuFeS2 + 17O2 + 4H+ 4Cu2+ + 4Fe3+ + 8SO42- + 2H2O No change occurs in the oxidation state of copper. What changes in oxidation state occur for the iron and the sulfur in this reaction? Change in oxidation state Fe S A +1 +8 B +1 -8 C -1 +6 D -1 -6 2 When cobalt metal is reacted with a solution containing cobalt(III) ions, only cobalt(II) ions are formed. How many moles of Co and Co3+(aq) would result in a mixture containing both cobalt(II) and cobalt(III) ions in the mole ratio of 3:1 after the reaction had taken place? Moles of Co Moles of Co3+ A 1 2 B 1 3 C 1 5 D 2 3 3 Sodium hydrogen carbonate, NaHCO 3, can be prepared from sodium sulfate by a three -step process. Na2SO4(s) + 4C(s)  Na2S(s) + 4CO(g) Na2S(s) + CaCO3(s)  CaS(s) + Na2CO3(s) Na2CO3(s) + H2O(l) + CO2(g)  2NaHCO3(s) What is the mass of sodium hydrogen carbonate (M r = 84.0), to the nearest k g, that could be formed from 100 kg of the sodium sulfate (Mr = 142.1), assuming a 90 % yield in each step? A 43 B 86 C 106 D 118 kg

3 2016 TJC H2 Chemistry Preliminary Examination [Turn Over + – R S T 4 The following are flight paths of charged particles when accelerated in an electric field. Which of the following correctly identifies S, T and U? S T U A 15O+ 14C+ 14N+ B 15O‾ 14C+ 28Si+ C 14N‾ 16O2+ 28Si2+ D 14N‾ 14C+ 28Si4+ 5 Lecithin is used as an emulsifying and stabilising agent in the food, pharmaceutical and cosmetic industries. Which of the following statements about lecithin is correct? A It can form van der Waals’ forces with other non-polar molecules. B It has a low boiling point. C It cannot rotate plane of polarised light. D It can form hydrogen bonds between its own molecules. 6 Mixtures of argon and another gas are commonly used during welding. One such gaseous mixture has a density of 1.82 g dm−3 at s.t.p. What could be the other gas in this mixture? [Density of argon = 1.78 g dm−3 at s.t.p.] A neon B oxygen C fluorine D carbon dioxide S T U

4 2016 TJC H2 Chemistry Preliminary Examination [Turn Over 7 Which line in the table gives the signs of H, S and G for the melting of ice at room temperature and pressure? H S G A – + – B – – + C + + + D + + – 8 Which reaction represents standard enthalpy change at 298 K? A P4(l)  4P(g) B H2(g) + Br2(g)  2HBr(g) C HF(aq) + NaOH(aq)  NaF(aq) + H2O(l) D CH4(g) + 2O2(g)  CO2(g) + 2H2O(g) 9 In the construction of heart ‘pacemakers’, it is possible to use a tiny magnesium electrode which creates an electrical cell with the inhaled oxygen. The relevant half-cells are as follows: Mg2+ + 2e- Mg EӨ = -2.38 V ½ O2 + 2H+ + 2e- H2O EӨ = +1.23 V Under standard conditions, the cell e.m.f. would be +3.61 V, but in the body a potential of +3.25 V is more usual. What is the best explanation for this lower e.m.f.? A the low concentration of Mg2+ ions surrounding the magnesium electrode B the pH of between 7 and 8 of the body fluid surrounding the electrodes C the high resistance of the body fluids surrounding the electrodes D the small size of the magnesium electrode 10 Consider the following equilibrium system: 2AlCl3(g) Al2Cl6(g) Which of the following statements will cause the position of the above equilibrium to shift to the left? A decreasing the volume of the vessel B increasing the temperature C pumping inert gas into the vessel at constant volume D pumping AlCl3 gas into the vessel

5 2016 TJC H2 Chemistry Preliminary Examination [Turn Over 11 Which of the following statements is true about the following energy profile for a catalysed reaction? A F is the intermediate formed. B The enthalpy change of the reaction is E2 – E3. C The reaction is catalysed by a heterogenous catalyst. D The second step of the reaction is the rate determining step. 12 Ethyl ethanoate undergoes a slow acid-catalysed hydrolysis in water where the concentration of acid in the solution remains constant. H+ CH3CO2CH2CH3 + H2O  CH3CO2H + CH3CH2OH The rate equation is found to be rate = k[CH3CO2CH2CH3][H+] In an experiment, when 1.0 mol dm-3 HCl was reacted with 0.10 mol dm-3 ethyl ethanoate, the half-life was found to be 42 min. In a second experiment, 2.0 mol dm -3 HCl was reacted with 0.20 mol dm -3 ethyl ethanoate. What is the half-life of the second experiment? A 10.5 min B 21 min C 42 min D 63 min 13 Ethanol has a pKa of 15.5 at room temperature. Sodium ethoxide can be produced by reacting ethanol with sodium metal, and Solution P is 0.1 mol dm-3 sodium ethoxide. Which of the following statements is incorrect? A Ethanol is a weak acid. B Ethoxide is a strong base. C The pH of Solution P is 13. D The type of reaction between ethanol and sodium is acid-base Energy Extent of reaction E1 E3 F E2

6 2016 TJC H2 Chemistry Preliminary Examination [Turn Over 14 Which of the following graphs shows the correct trend in the physical property of the period 3 elements? A B C D 15 Which of the following elements has an oxide with a giant structure and a chloride which is readily hydrolysed? A sodium B carbon C silicon D phosphorus 16 Two experiments are carried out with anhydrous potassium chloride and observations 1 and 2 are made at the end of each experiment. Experiment 1: Concentrated sulfuric acid is added to potassium chloride and the fumes produced are bubbled into aqueous potassium bromide solution – observation 1. Experiment 2: Potassium chloride is dissolved in concentrated aqu