ASR 2020 J2Prelim H2Chem P2 QP

ASRJC JC2 PRELIM 2020 9729/02/H2 [Turn over ANDERSON SERANGOON JUNIOR COLLEGE 2020 PRELIMINARY EXAMINATION NAME:______________________________ ( ) CLASS: 20 /____ CHEMISTRY 9729/02 Paper 2 Structured Questions 15 September 2020 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name, class and register number on all the work you hand in. Write in dark blue or black pen. You may use an HB pencil for any diagrams or graphs. Do not use staples, 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. A Data Booklet is provided. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use Paper 2 1 / 13 2 / 14 3 / 12 4 / 10 5 / 14 6 / 12 Total / 75 This document consists of 23 printed pages and 1 blank page.

2 ASRJC JC2 PRELIM 2020 9729/02/H2 Answer all the questions in the spaces provided. 1 One early nineteenth century Periodic Table had copper placed in the same group as potassium because they both formed +1 ions. (a) State the full electronic configurations of potassium and copper atoms. …….……………………………………………………………………………………………………. …….…………………………………………………………………………………………………[1] (b) (i) The mass of an atom is the sum of the masses of all subatomic particles it contains. Calculate the mass, in kg, of one atom of 64 29Cu . Quote relevant values from the Data Booklet and give your answer to three significant figures. [2] (ii) During the process of ionisation, a Cu atom loses an electron. Cu(g)  Cu+(g) + e− State the electronic configuration of Cu+. Explain your answer. 1s2 .……………………………………………………………………………………………… explanation ..…………………………………………………………………………………… …………………………………………………………………………………………………[2]

3 ASRJC JC2 PRELIM 2020 9729/02/H2 [Turn over (iii) On the Cartesian axes given in Fig . 1.1, sketch the shape of the following three 3d orbitals found in copper atom. Fig. 1.1 [2] x y z x y z x y z 3dxz 3dz2 3dx2–y2

4 ASRJC JC2 PRELIM 2020 9729/02/H2 (c) (i) Define the term standard enthalpy change of formation. …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………[1] (ii) Table 1.1 enthalpy change value / kJ mol–1 standard enthalpy change for P(s) + 2O2(g) + 3e–  PO43–(aq) –1284 standard enthalpy change for K(s)  K+(aq) + e– –251 standard enthalpy change for K3PO4(s)  3K+(aq) + PO43–(aq) –2 Using a labelled energy cycle, and the enthalpy values given in Table 1.1, determine the standard enthalpy change of formation of solid potassium phosphate, K3PO4. [3] (iii) The value of GO at 298 K for K(s)  K+(aq) + e– is –284 kJ mol–1. Using data from Table 1.1, calculate SO for the reaction, and explain its sign. …………………………………………………………………………………………………… …………………………………………………………………………………………………[2] [Total: 13]

5 ASRJC JC2 PRELIM 2020 9729/02/H2 [Turn over Question 2 starts on the next page.

6 ASRJC JC2 PRELIM 2020 9729/02/H2 2 2–methylpropane, (CH 3)2CHCH3, is an important precursor for petrochemical industry. Butane, CH3(CH2)2CH3, can be converted to 2–methylpropane in the presence of a suitable heterogeneous catalyst. CH3(CH2)2CH3(g) (CH3)2CHCH3(g) equilibrium 1 (a) Explain briefly how a heterogeneous catalyst increases the rate of equilibrium 1. …………………………………………………………………………………………………………. …………………………………………………………………………………………………………. ……………………………………………………………………………………………………….[1] (b) Butane gas was added to an enclosed vessel at 373 K . The concentration of butane and 2–methylpropane was measured at regular time intervals and a graph was plotted as shown in Fig. 2.1. Fig. 2.1 (i) Using information from Fig. 2.1, calculate the partial pressures of butane and 2–methylpropane in the mixture at equilibrium. You may assume that both gases behave ideally. [2] 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00concentration (mol dm–3) time

7 ASRJC JC2 PRELIM 2020 9729/02/H2 [Turn over (ii) Write the Kp expression of equilibrium 1 and calculate its value. [2] (c) State how the partial pressure of butane will change when argon is added to the enclosed vessel at constant volume. ……………………………………………………………………………………………………….[1] (d) Bromine reacts with alkanes in the presence of light. (i) Outline the mechanism of the reaction between 2–methylpropane and bromine to form 2–bromo–2–methylpropane. [3] (ii) Suggest why it is not possible to make iodoalkanes by this method. …………………………………………………………………………………………………... …………………………………………………………………………………………………... ………………………………………………………………………………………………...[1]

8 ASRJC JC2 PRELIM 2020 9729/02/H2 (e) Iodoalkanes can be made by warming a chloroalkane with a solution of sodium iodide in propanone, in which sodium chloride is almost insoluble. CH3CH2Cl + NaI CH3CH2I + NaCl equilibrium 2 (i) By considering the equation for equilibrium 2, suggest why the reaction goes almost to completion, despite the C–I bond being weaker than the C–Cl bond. …………………………………………………………………………………………………... …………………………………………………………………………………………………... ………………………………………………………………………………………………...[1] A student performed two experiments to investigate the effect of changes in concentration on the rate of this reaction. The initial concentration and rate data obtained for each experiment is given in Table 2.1. Table 2.1 experiment initial [CH3CH2Cl] / mol dm–3 initial [NaI] / mol dm–3 initial rate / mol dm–3 s–1 1 1.0 x 10–3 2.0 x 10–3 3.0 x 10–11 2 3.0 x 10–3 4.0 x 10–3 1.8 x 10–10 (ii) Determine the order of reaction with respect to each reactant and hence deduce the rate equation for this reaction. Use data from Table 2.1 to explain your answers. [3] [Total: 14]

9 ASRJC JC2 PRELIM 2020 9729/02/H2 [Turn over 3 (a) Iron reacts with  chlorine, Cl2 to form iron(III) chloride FeCl3.  iodine, I2 to form iron(II) iodide, FeI2. Using the information provided, suggest how the reactivity of chlorine and iodine as oxidising agent varies down the group. Relate this variation to relevant EO values and the changes in oxidation numbers. .................................................................................................................................................. .................................................................................................................................................. .................................................................................................................................................. ......................................................................................