RI 2020 Y5 Promo QP

1 © Raffles Institution 2020 9729/S/20 [Turn Over Name: ( ) Class: 21S0____ RAFFLES INSTITUTION 2020 Year 5 Promotional Examination HIGHER 2 CHEMISTRY 9729 30 September 2020 2 hours 30 minutes Additional Materials: Multiple Choice Answer Sheet Data Booklet READ THESE INSTRUCTIONS FIRST DO NOT open this booklet until you are told to do so. Write your name and civics tutorial group in the spaces provided on the OMR sheet, cover sheets on pages 1 and 17. This paper consists of three sections A, B and C. Section A (15 marks) consists of 15 multiple-choice questions. Answer this section first. The OMR sheet will be collected after the first 35 minutes. Record your answers to this section in soft pencil on the separate OMR Answer Sheet. Section B (35 marks) consists of 3 structured questions. Section C (40 marks) consists of 3 free-response questions. Answers to Sections B and C are to be written in the spaces provided in the question paper. You are reminded of the need for good English and clear presentation in your answers. This document consists of 26 printed pages The number of marks is given in brackets [ ] at the end of each question or part question. Write in dark blue or black pen. You may be subject ed to penalty for writing answers in pencil. For Examiner’s Use Only C1 / 16 C2 / 12 C3 / 12

2 © Raffles Institution 2020 9729/S/20 [Turn Over Section A (15 marks) For each question there are four possible answers, A, B, C, and D. Choose the one you consider to be correct. 1 What is the order of the following compounds in increasing melting point? MgO MgCl2 AlCl3 A AlCl3 < MgCl2 < MgO B AlCl3 < MgO < MgCl2 C MgO < MgCl2 < AlCl3 D MgCl2 < MgO < AlCl3 2 Water has a much higher boiling point than methane but a lower boiling point than silicon tetrabromide. compound H2O CH4 SiBr4 boiling point / °C 100 –162 153 Which statements correctly explain the observed trend? 1 The O–H bonds in water are stronger than the C–H bonds in methane but weaker than the Si–Br bonds in silicon tetrabromide. 2 Hydrogen bonds between water molecules are stronger than the instantaneous dipole-induced dipole interactions in methane but weaker than the instantaneous dipole -induced dipole interactions in silicon tetrabromide. 3 Water is a simple molecule while silicon tetrabromide is a giant molecule. A 1 and 3 only B 2 only C 2 and 3 only D 1, 2 and 3 3 When lanthanum iodate(V), La(IO3)3, is heated to 560 °C, it decomposes as shown below. lanthanum iodate(V) ⎯⎯→ lanthanum periodate(VII) + iodine + oxygen In this reaction, lanthanum does not change oxidation state. If the IO3–:I2 molar ratio in this reaction is 5:2, what is the formula of the periodate(VII) ion? A IO4– B IO53– C IO65– D IO77–

3 © Raffles Institution 2020 9729/S/20 [Turn Over 4 Use of the Data Booklet is relevant to this question. The second, third and fourth ionisation energies, IE, of four different elements are shown in the table. The elements are antimony, arsenic, selenium and tellurium (though not necessarily in that order) from Groups 15 and 16. Which element is antimony? second IE / kJ mol–1 third IE / kJ mol–1 fourth IE / kJ mol–1 A 1590 2440 4270 B 1800 3010 3680 C 1950 2730 4850 D 2080 3090 4140 5 W, X, Y and Z are four elements with consecutive atomic numbers in Period 4. The table shows the number of unpaired electrons in each atom in its ground state. element W X Y Z number of unpaired electrons 0 1 2 3 Which statement is not correct? A W can be zinc. B X can be scandium. C Y can be germanium. D Z can be cobalt. 6 An equimolar mixture of H 2 and O 2 was placed in a sealed, rigid container at room temperature. The total pressure inside the container is P Pa. The mixture was sparked, and H2 and O2 reacted until H2 was completely consumed. What is the partial pressure, in Pa, of O 2 in the container after the reaction at room temperature? A 2P B P C 0.5P D 0.25P

4 © Raffles Institution 2020 9729/S/20 [Turn Over 7 Which reaction represents the standard enthalpy change of atomisation of the reactant? A O2(g) → 2O(g) B Hg(l) → Hg(g) C CO2(g) → C(g) + O2(g) D C2H4(g) → 2C(s) + 4H(g) 8 Use of the Data Booklet is relevant to this question. A self-heating coffee can uses the reaction between calcium oxide and water to heat up the coffee in the can with the press of a button. CaO(s) + H2O(l) → Ca(OH)2(aq) H = −64.5 kJ mol−1 When the button is pressed, water reacts with CaO and the heat released from the reaction is transferred to the coffee in the can. The volume of coffee in the can is 205 cm3. Assuming that the reaction is 80% efficient in transferring the heat to the coffee, what is the mass of CaO required to increase the temperature of the coffee by 42 °C? You may assume that the specific heat capacity of coffee is the same as that of water. A 25.0 g B 31.3 g C 33.1 g D 39.1 g coffee foil separator CaO water button CaO

5 © Raffles Institution 2020 9729/S/20 [Turn Over 9 The diagram represents the energy profile of a chemical reaction. Which statements about the chemical reaction are correct? 1 During the reaction, the change in temperature is positive. 2 The products are energetically less stable than the reactants. 3 For the reaction to be spontaneous, S must be positive. A 1 and 3 B 1 only C 2 only D 2 and 3 10 During the titration of ethanedioic acid against potassium manganate( VII), the following reaction takes place. 5H2C2O4 + 2MnO4− + 6H+ → 2Mn2+ + 2CO2 + 8H2O Early in the titration, it takes a while for the purple colour to be decolourised. Later in the titration, it was found that decolourisation took place more quickly. What is the correct reason for the observations? A With more MnO 4− titrated, the MnO 4− concentration increases, increasing the rate of reaction. B With more MnO 4− titrated, the MnO 4− concentration increases, shifting the position of equilibrium more to the right. C With more MnO4− titrated, the Mn2+ concentration increases, increasing the rate of reaction. D With more MnO 4− titrated, the CO 2 gas escapes, shifting the position of equilibrium more to the right. progress of reaction energy reactants products

6 © Raffles Institution 2020 9729/S/20 [Turn Over 11 H2O2 decomposes in the presence of Mn2+(aq) catalyst with the following equation: 2H2O2(aq) → 2H2O(l) + O2(g) The reaction is first order with respect to H2O2 and Mn2+. In experiment 1, 1 cm 3 of 0.1 mol dm–3 Mn2+(aq) solution was placed in a flask containing 25 cm3 of 0.1 mol dm–3 H2O2(aq). The flask was immediately stoppered with a delivery tube leading to a measuring cylinder, and a stopwatch was started at the same time. The volume of O2 gas collected was recorded at regular time intervals, and graph 1 was plotted. Which of the following sets of experimental conditions will result in graph 2? volume of Mn2+(aq) / cm3 volume of H2O2(aq) / cm3 [H2O2] / mol dm–3 W 1 25 0.2 X 1 50 0.1 Y 2 25 0.2 Z 2 50 0.1 A W and X B X and Y C W and Z D Y and Z 0 10 20 30 40 50 60 0 5 10 15 20 25 volume of O2 / cm3 time / min graph 1 graph 2

7 © Raffles Institution 2020 9729/S/20 [Turn Over 12 The graphs below show how the percentage of a gaseous product Y present at equilibrium varies with temperature at pressures of 3  106 Pa and 6  106 Pa respectively, for a reaction. Which reaction could the graphs represent? A N2O4(g) ⇌ 2NO2(g) H = +57 kJ mol−1 B N2(g) + O2(g) ⇌ 2NO(g) H = +90 kJ mol–1 C N2(g) + 3H2(g) ⇌ 2NH3(g) H = −92 kJ mol−1 D 2C(s) + O2(g) ⇌ 2CO(g