JJC H2 CHEM P2

JURONG JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME CLASS CHEMISTRY 9746/02 Paper 2 Structured 25 August 2009 1 hour 30 minutes Candidates answer on the Question Paper Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name and class 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. A Data Booklet is provided. Do not write anything on the Data Booklet. 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 1 2 3 4 5 6 7 Total This document consists of 15 printed pages and 2 blank pages. [Turn over Page 1 of 15

1. (a) The volume of a sample of SO 2 was monitored at various pressures while keeping temperature constant. The following results were obtained. P/ kPa V/ m 3 PV/ kPa m3 6.0 0.375 12.0 0.188 18.0 0.125 (i) Draw diagrams to illustrate the shape of SO2 and SO3 molecule. Include the name of the shape in your diagrams. (ii) For each pressure stated above, calculate the values of PV, giving each of your numerical answers to one decimal place. (iii) Using your answer (a)(ii), deduce with justification whether the sample of SO 2 is behaving ideally. ………………………………………………………………………………….. (iv) Suggest a reason for this behaviour of SO2 in the sample. [7] Page 2 of 15

1. (b) A 2:1 mixture by volume of SO 2 and O 2 at an initial pressure of 15 atm is allowed to reach equilibrium at 250 °C. 2SO2 (g) + O2 (g)  2SO3 (g) The equilibrium pressure was found to be 11 atm. (i) Calculate the partial pressure of each gas at equilibrium. (ii) Hence calculate the value of K p, stating its units. (iii) State and explain the effect of lowering pressure on the yield of SO3. ………………………………………………………………………………… ………………………………………………………………………………… ………………………………………………………………………………… ………………………………………………………………………………… ………………………………………………………………………………… [6] Page 3 of 15

1. (c) (i) 2SO2 (g) + O2 (g)  2SO3 (g) H = 197 kJ mol-1 The enthalpy change of atomisation of oxygen is +248 kJ mol-1. On the grid below, incorporate these enthalpy changes into an energy cycle for calculating the average bond energy of S=O bond. (ii) Hence calculate the average bond energy of the S=O bond. [3] [Total: 16] Energy/ kJ mol -1 Page 4 of 15

2. (a) When dissolved in water, iron( III) chloride undergoes hydrolysis and gives off heat in an exothermic reaction. The resulting brown solution is acidic. Given the charge density of Fe 3+ is very similar to that of A l3+, explain, with the aid of an equation, why iron(III) chloride solution is acidic. …………………………………………………………………………………………. [1] (b) An important application of iron(III) chloride solution is etching copper from copper-based metals in printed circuit boards. Etching of copper occurs in two steps: FeCl3 + Cu → FeCl2 + CuCl Step I FeCl3 + CuCl → FeCl2 + CuCl2 Step II (i) Write the electronic configuration of copper in CuCl. …………………………………………………… (ii) Hence predict, with explanation, the colour of CuCl solution. ………………………………………………………………………………… ………………………………………………………………………………… ………………………………………………………………………………… [3] Page 5 of 15

2. (c) Anhydrous iron( III) chloride is also used as a catalyst in the synthesis of 3-nitrophenylethanone from nitrobenzene and ethanoyl chloride, CH3COCl. The first step in the above reaction is the formation of acylium carbocation: FeCl3 + CH3COCl FeCl4 – + CH3CO+ Describe the subsequent step(s) in the mechanism for the reaction of nitrobenzene to form 3-nitrophenylethanone. In your answer, show any relevant charges, lone pairs of electrons and movement of electrons. [2] [Total: 6] + acylium ca rbocation Page 6 of 15

3. Vanillin is used widely as a flavoring, usually in sweet foods such as ice cream and chocolate. It exists as a yellow solid and dissolves readily in water to form a yellow solution. CHO OCH3 OH vanillin The kinetics of the reaction between vanillin and HCN were investigated using two different initial concentration of HCN. Both experiments were conducted at 25 oC in a pH 9.0 buffer. 0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 (a) Assuming that the reaction produces a colourless product, suggest one plausible method by which the concentration of vanillin may be followed during the course of the reaction. ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… [1] [vanillin]/ mol dm 3 [HCN] = 0.100 mol dm3 [HCN] = 5.00 mol dm3 Time/ min Page 7 of 15

3. (b) Using the graph, determine the order of the reaction with respect to vanillin. Show working on the graph. [2] (c) In the experiment using 0.100 mol dm -3 HCN, the half-life of the reaction is 4.75 min. Hence determine, with explanation, the order of reaction with respect to HCN. [2] (d) Q is a structural isomer of vanillin. When treated with an acid catalyst, it forms a compound R with the molecular formula C 8H6O2. COOH Q CH2OH State the type of reaction that occurred and draw the structure of R. Type of reaction …………………………………………………………………… Structure of R [2] [Total: 7] Page 8 of 15

4. (a) Manganese commonly occurs as the ore pyrolusite, which is mainly manganese(IV) oxide. Manganese( IV) oxide undergoes a two-step reaction under alkaline condition to produce compounds Y and Z. (i) The brown solid Y contains 63.8% by mass of manganese and 36.2% by mass oxygen. Using these information, determine the empirical formula of Y. (ii) Suggest the identity of Z and state the type of reaction that occurs at step II. Construct a balanced equation for the reaction. Identity of Z …………………………………………………………………. Type of reaction ……………………………………………………………. Equation: [4] (b) A Leclanché cell consists of a zinc anode and a carbon cathode coated with MnO 2. During discharge, MnO2 is converted to Mn2O3. (i) Write the ion-electron equations for the reaction which occurs during discharge at the anode and cathode respectively. Anode ………………………………………………………………………….. Cathode ……………………………………………………………………….. (ii) The voltage of this Leclanché cell is found to be 1.5 V. With reference to the Data Booklet, calculate E ( MnO2/Mn2O3). [3] [Total: 7] Page 9 of 15

5. (a) Elements X and W belong to Period 3 of the Periodic Table. Both elements X and W have giant lattices. When water is added to chlorides of X and W , solutions of pH 7 and 2 are formed respectively. (i) Identify the elements X and W. X is ……………………………………………………………. W is …………………………………………………………….. (ii) Write an equation to illustrate the action of water with the chloride of W. …………………………………………………………………………………. [3] (b) The oxides MgO, A l2O3 and SiO 2 are all used as refractory materials due to their high melting points If a sample of one of the oxides was provided as a white powder, describe the reactions you could carry out on the powder to determine which of the three oxides it was. In your answers, include the reagents used for each test and describe the observations. [4] [Total: 7] Page 10 of 15