VJC 2020 H2 Chem Prelim P2 QP

 VJC 2020 9729/02/PRELIM/20 [Turn over CANDIDATE NAME CT GROUP VICTORIA JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION Higher 2 ……………………………………………….………….. …………………………….. CHEMISTRY 9729/02 Paper 2 Structured Candidates answer on the Question Paper. 15 September 2020 2 hours Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name and CT group on all the work you hand in. Write in dark blue or black pen on both sides of the paper. You may use a soft pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. Answer all questions. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use 1 / 20 2 / 11 3 / 8 4 / 19 5 / 17 Total / 75 This document consists of 17 printed pages and 1 blank page..

 VJC 2020 9729/02/PRELIM/20 2 Answer all the questions in the spaces provided. 1 (a) (i) Complete the diagram to show the relative energies of all the electrons in an iron atom. [1] (ii) Write an equation for the second ionisation energy of iron. …………………………………………………………………………………………….….... [1] (iii) Explain why the second ionisation energy of iron is lower than that of chromium. ……………………………………………………………………………………………………... ……………………………………………………………………………………………………... ………………………………………………………………………………………………..... [1] (b) A piece of rusted iron was analysed to find out how much of the iron had been oxidised to rust (also known as hydrated iron(III) oxide). A small sample of the rusted iron was dissolved in excess dilute sulfuric acid to give 250 cm3 of solution. The resultant solution contains Fe2+ and Fe3+ from iron and rust respectively. (i) 25.0 cm 3 of this solution required 16.90 cm 3 of 0.0200 mol dm 3 KMnO4 for complete oxidation of Fe2+. Calculate the amount of Fe2+ in 25.0 cm3 of the solution. 5Fe2+ + MnO4 + 8H+  5Fe3+ + Mn2+ + 4H2O [1] energy 1s 

3  VJC 2020 9729/02/PRELIM/20 [Turn over (ii) To another 25.0 cm3 of the solution, an oxidising agent was added to convert all the Fe2+ ions present to Fe3+ ions. The Fe3+ ions were then titrated with 0.100 mol dm 3 EDTA4 solution and 17.60 cm3 was required. Assuming 1 mol of EDTA4 reacts with 1 mol of Fe3+, calculate the amount of Fe3+ in 25.0 cm3 of the solution. [1] (iii) From your answers in (b)(i) and (b)(ii), calculate the amount of original Fe3+ in 250 cm3 of the rusted iron solution. [1] (iv) Determine the percentage of iron that had been oxidised to rust in the sample. [1] (c) (i) Explain if a real gas, such as N2O3, behaves more or less ideally at:  high pressures ……………………………………………………………………………………………………... ……………………………………………………………………………………………………... ……………………………………………………………………………………………………...  high temperatures ……………………………………………………………………………………………………... ……………………………………………………………………………………………………... ……………………………………………………………………………………………….......... [2]

 VJC 2020 9729/02/PRELIM/20 4 (ii) At room temperature, N2O3 dissociates as shown. N2O3(g) ⇌ NO(g) + NO2(g) This dissociation involves homolytic fission of N–N bond. Draw a ‘dot-and-cross’ diagram for the N2O3 molecule. [1] (iii) Hence, state the shape around each N atom in the N2O3 molecule. ………………………………………………………………………………………………..... [1] (iv) Suggest the common feature of NO and NO 2 that allows each of them to undergo dimerisation to form N2O2 and N2O4 respectively. ………………………………………………………………………………………………..... [1] (d) (i) With an appropriate sketch of Boltzmann distribution, explain how a catalyst is able to increase the rate of a chemical reaction for a given temperature T. ……………………………………………………………………………………………………... ……………………………………………………………………………………………………... ……………………………………………………………………………………………………... ………………………………………………………………………………………………….. [2] (ii) On the sketch in d(i), draw a new distribution curve at a higher temperature T’, clearly labelled T’. [1]

5  VJC 2020 9729/02/PRELIM/20 [Turn over (e) X is an organic liquid that is found as a contaminant in crude oil. It contains only C, H and S. When 0.841 g of X was subjected to complete combustion, 1.76 g of CO 2, 0.360 g of H 2O and a gas which can decolourise acidified potassium manganate (VII) were formed. (i) What is the empirical formula of X? [2] (ii) X is unsaturated and has a structure in which all the carbon and sulfur atoms are connected together in a five-membered ring. Draw the structure of X. [1] (iii) Hence, construct the equation for the complete combustion of X. ……………………………………………………………………………………………….... [1] (iv) X behaves similarly like benzene in its reaction s with electrophile. Suggest a possible structure when X is reacted with CH3COCl in the presence of a Lewis acid catalyst. [1] [Total: 20]

 VJC 2020 9729/02/PRELIM/20 6 2 (a) Water is a very stable molecule and was thought to be a chemical element. In 1800, one of the earliest form of electrochemical cells was invented and scientists, Nicholson and Carlyle, caused a big stir by decomposing water into hydrogen and oxygen by electrolysis. In one experiment to electrolyse water , copper was used at both electrodes. A gas was generated only at one electrode during the electrolysis. Write half-equations for the reaction that took place during the electrolysis. anode: …………………………………………………………………………………………………. cathode: ……………………………………………………………………………………………..[1] (b) In another electrolysis experiment with copper electrodes, the electrolyte was replaced with an acidified solution of copper(II) sulfate, CuSO4. During this electrolysis, the mass of cathode increased and H2 gas was evolved. (i) When a constant current of 2.0 A was applied for 30 min, the mass of cathode increased by 0.635 g. Calculate the volume of H2 evolved, measured at r.t.p. [3] (ii) When the concentration of Cu2+ in the electrolyte was 0.100 mol dm−3, Cu(OH)2(s) started to precipitate at pH 4.84. Write the expression for the solubility product, Ksp, of Cu(OH)2(s). ……………………………………………………………………………………………….... [1] (iii) Calculate the Ksp of Cu(OH)2(s), stating the units. [2]

7  VJC 2020 9729/02/PRELIM/20 [Turn over (c) For a reversible reaction, M3+(aq) + ne– ⇌ M(3 – n)+(aq), the Nernst equation below shows the dependence of its reduction potential, EM3+/M(3n)+, to the concentration of M3+ and M(3 – n)+ as expressed in Q, at 298 K. EM3+/M(3n)+ = EꝊM3+/M(3n)+ – .0 0252 n ln Q where EꝊM3+/M(3n)+ i