2021 TJC H2Chemistry P1 Prelim

1 9729 / TJC Prelim / 2021 [Turn Over TEMASEK JUNIOR COLLEGE 2021 JC2 PRELIMINARY EXAMINATION Higher 2 CHEMISTRY 9729/01 15 September 2021 1 hour Additional Materials: Multiple Choice Answer Sheet (OMS) Data Booklet READ THESE INSTRUCTIONS FIRST Write in soft pencil. Do not use staples, paper clips, glue or correction fluid. Write your name, Class and index number on the Answer Sheet in the spaces provided. There are thirty 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 15 printed pages and 1 blank page. Write your name and Civics Group Write and shade your index number

2 9729 / TJC Prelim / 2021 [Turn Over 1 One diatomic molecule of an element E has an average mass of 1.18 x 10–22 g. E reacts with ethene to form C2H4E2. How many E atoms are there in 49.5 g of C2H4E2? A 1.75 x 1023 B 3.01 x 1023 C 3.50 x 1023 D 6.02 x 1023 2 The radioactive isotope decays to give an element Q and emits a high energy α-particle (which is a helium nucleus,). No other particle is produced. Q + How many neutrons are present in element Q? A 219 B 135 C 133 D 86 3 Lecithin is an emulsifier added to chocolate to help bind the cocoa solids, sugar and milk so they stick to the cocoa butter. Its structure is shown below. R: long hydrophobic carbon chains Which of the following statements about lecithin is correct? A It can form instantaneous dipole-induced dipole interactions with non-polar molecules present in chocolate. B It can form hydrogen bonds between its own molecules. C All bond angles surrounding each carbon atom are 109.5°. D It does not contain delocalised electrons. Ra22 3 88 He4 2 Ra22 3 88 He4 2

3 9729 / TJC Prelim / 2021 [Turn Over 4 Cholesterol is a waxy substance that is present in blood plasma and in all animal tissues. Cholesterol Which of the following statements about cholesterol are incorrect? 1 All the seventeen carbon atoms in the four rings lie in the same plane. 2 It can exhibit cis–trans isomerism at the C=C double bond. 3 It is acidic. A 1 only B 1 and 2 only C 2 and 3 only D 1, 2 and 3 5 A sample of an organic compound of molar mass M is vapourised in a gas syringe and occupies V cm3 at T K and p Pa. What is the density of the compound? A p×M×273T×10!×22700 B p×M×293T×10!×24000 C p×M×10!×22700T×273 D p×M×273T×22700

4 9729 / TJC Prelim / 2021 [Turn Over 6 Which graphs correctly describe the behaviour of a fixed mass of an ideal gas (where T is measured in K)? 1 2 3 A 1 only B 1 and 2 only C 2 and 3 only D 1, 2 and 3 7 X is a Period 3 chloride. When a few drops of water are added to X, steamy white fumes are evolved and a colourless liquid is produced. Which compound is X? A MgCl2 B AlCl3 C SiCl4 D PCl5 8 X and Y are two elements in Period 3 of the Periodic Table. They combine to form compound Z. Both X and Y form oxides that react with aqueous sodium hydroxide. The oxidation number of X in its oxide is +4. What is the formula of compound Z? A AlP B Al2S3 C Si3P4 D SiS2 T pV constant V T p constant V 1T concentration constant p

5 9729 / TJC Prelim / 2021 [Turn Over 9 The solids, sodium chloride and sodium iodide, both react with concentrated sulfuric acid at room temperature. With NaCl, the products are NaHSO4 and HCl. With NaI, the products are NaHSO4, HI, I2, SO2, H2O, S and H2S. Which of the following is the best explanation for this difference in products? A Chloride will displace iodine from solution. B Iodine is a better oxidising agent than chlorine. C Iodide is a better reducing agent than chloride. D Sulfuric acid is able to act as a dehydrating agent with NaI. 10 The graph below shows how the percentage of N2(g) in the equilibrium mixture of the Haber process varies with temperature at different pressures, P1 and P2. N2(g) + 3H2(g) ⇌ 2NH3(g) ΔHr Which row in the table is correct? ΔHr Pressure A positive P1 > P2 B positive P1 < P2 C negative P1 > P2 D negative P1 < P2 P1 P2 % N2 temperature

6 9729 / TJC Prelim / 2021 [Turn Over 11 The position of equilibrium lies to the right in each of these reactions. Reaction 1: N2H4 + HClO N2H5+ + ClO– Reaction 2: N2H5+ + NH3 NH4+ + N2H4 Based on this information, which statements are correct? 1 ClO– is the conjugate base of HClO. 2 N2H5+ is the Bronsted base in Reaction 2. 3 The order of acid strength is HClO > N2H5+ > NH4+. 4 N2H4 is the Lewis acid in Reaction 1. A 1 and 3 only B 1 and 4 only C 2 and 3 only D 2 and 4 only 12 Which of the following solutions does not change its pH significantly when a small amount of base is added? A 20 cm3 of 0.10 mol dm־3 ethanoic acid mixed with 20 cm3 of 0.20 mol dm-3 aqueous sodium hydroxide. B 20 cm3 of 0.10 mol dm־3 aqueous ammonia mixed with 30 cm3 of 0.10 mol dm-3 hydrochloric acid. C 20 cm3 of 0.10 mol dm-3 sodium hydroxide mixed with 20 cm3 of 0.20 mol dm-3 phenylammonium chloride. D 20 cm3 0.10 mol dm-3 hydrochloric acid mixed with 10 cm3 0.1 mol dm-3 sodium ethanoate solution. 13 A student dissolved 8.4 g of sodium fluoride in 250 g of water. Given the following thermodynamic data, Lattice energy of NaF −918 kJ mol−1 Enthalpy change of hydration of F− −457 kJ mol−1 Enthalpy change of hydration of Na+ −390 kJ mol−1 What would be the initial temperature of the water if the final temperature of the solution is 20.00 oC? Assume that the specific heat capacity of sodium fluoride solution is 4.2 J g−1 K−1. A 6.48 oC B 20.01 oC C 33.08 oC D 33.52 oC

7 9729 / TJC Prelim / 2021 [Turn Over 14 In oil refineries, an important process is the recovery of any sulfur from petroleum. 2H2S(g) + O2(g) 2H2O(g) + 2S(s) The enthalpy change of formation of H2S(g) is -20.5 kJ mol─1 and that of H2O(g) is -243.0 kJ mol─1. Which of the following describes how the yield of sulfur at equilibrium varies as temperature increases? A B C D 15 Which of the following is true about the value of rate constant of a pseudo first order reaction? A It depends on the concentration of reactants present in limited amount. B It depends on the concentration of reactants present in excess amount. C It is independent of the concentration of reactants. D It depends only on temperature and presence of catalyst. Yield temperature Yield temperature Yield temperature Yield temperature

8 9729 / TJC Prelim / 2021 [Turn Over 16 Consider the following reaction involving aqueous reactants S and T, and catalysed by U: S + T → V + W The solution is originally coloured due to reactant T. The kinetics of the above reaction is studied by measuring the time taken for the solution to decolourise. The results are obtained below. Experiment Volume of S / cm3 Volume of T / cm3 Volume of U / cm3 Volume of water added / cm3 Time taken / s 1 10 5 5 5 20 2 5 5 5 10 40 3 10 5 2.5 7.5 40 4 10 2.5 5 7.5 10 What is the rate law for the reaction above? A Rate = k[S][T][U] B Rate = k[S][T] C Rate = k[T][U] D Rate = k[S][U]

9 9729 / TJC Prelim / 2021 [Turn Over 17 Diborane, B2H6, is a colorless gas with a sweet odour. The structure is unique as it comprises of two bridging hydrogens shared between two boron atoms. The B2H2 ring contains two B-H-B bonds, each held together by two electrons. Diborane Which of the following statements are correct about diborane? 1 The boron atom is sp2-hybridised. 2 Only boron is electron deficient. 3 Al