SRJC H2 CHEM P3

SERANGOON JUNIOR COLLEGE General Certificate of Education Advanced Level Higher 2 CHEMISTRY 9746/03 Preliminary Examination Paper 3 Free Response 20 August 2009 2 hours Candidates answer on separate paper. Additional Materials: Answer Paper 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 work. Do not use staples, paper clips, highlighters, glue or correction fluid. Answer any four questions. A Data Booklet is provided. You are reminded of the need for good English and clear presentation in your answers The number of marks is given in the brackets [ ] at the end of each question or part question. At the end of the examination, fasten all your work securely together. This document consists of 9 printed pages and 1 blank page SRJC 2009 9746/03/Prelim/2009 [Turn over

2 SRJC 2009 9746/03/Prelim/2009 [Turn over Answer any four questions. 1 (a) A student dissolved 8.4 g of sodium fluoride in 250 g of water. Given the following data, calculate the initial temperature of water if the final temperature of the solution is 20.0 °C. Assume that the specific heat capacity of sodium fluoride solution is 4.2 J g–1 K–1. 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 [3] (b) In the manufacture of fuel for industries, liquid MTBE is added as a solvent to petroleum to reduce pollution. C CH3 CH3 CH3 O CH3 Methyl t-butyl ether (MTBE) (i) What is meant by the term standard enthalpy change of formation of MTBE ? Support your answer with the aid of an appropriate equation with state symbols. (ii) Use the following data and by means of an appropriate energy cycle, prove that the bond energy for the C–H bond in MTBE is +418 kJ mol-1. Enthalpy change of atomisation of C(s) +715 kJ mol–1 Enthalpy change of formation of MTBE –383 kJ mol–1 Enthalpy change of vapourisation of MTBE +30.4 kJ mol–1 Bond Energy of H-H +436 kJ mol–1 Bond Energy of O=O +496 kJ mol–1 Bond Energy of C-O +360 kJ mol–1 Bond Energy of C-C +350 kJ mol–1 (iii) Suggest a reason for the difference in the C–H bond energy in (b)(ii) from the value given in the Data Booklet. [7]

3 SRJC 2009 9746/03/Prelim/2009 [Turn over (c) Magnesium chloride, MgC l2, is an important coagulant used in the preparation of soy products. The lattice energy of magnesium chloride is given to be –2490 kJ mol–1. (i) How would you expect the numerical magni tude of the lattice energy of barium chloride, BaCl2 (s) to compare with that of MgC l2 (s)? Hence predict a likely value for the lattice energy of barium chloride. (ii) The enthalpy change of reaction, for the reaction below is given to be –391 kJ mol–1. 2MgCl (s) → MgCl2 (s) + Mg (s) Comment on the stability of MgCl (s) relative to that of MgCl2 (s). [4] (d) Part of the research on Supramolecular Chemistry focuses on Host-Guest Chemistry, in which cationic transition metal complexes are involved in second-sphere coordination which is provided by ligands with an organised set of donors. For example, a transition metal rhodium complex that contains hydrogen bond donor groups (ammonia or water ligands) in its primary coordination sphere can be considered as a guest capable of binding to a hydrogen bond acceptor host via second sphere coordination. (i) State the bonding formed between rhodium and ammonia. (ii) Describe the chemical structure and bonding in solid rhodium. (iii) Show, with aid of a diagram, the intermolecular bonding in ammonia. (iv) Predict and account for the boiling point of ammonia relative to water. (v) Predict and account for the solubility of ammonia in water. [6] [Total: 20]

4 SRJC 2009 9746/03/Prelim/2009 [Turn over 2 (a) The table below gives some data on some oxides of elements in Period 3 of the Periodic Table. Oxide Na2O MgO Al2O3 SiO2 P4O6 SO2 Boiling point / K 1548 3873 3253 2503 448 263 (i) Explain, in terms of chemical bonding and structure, why the boiling point of MgO is higher than P4O6. (ii) Write an equation for the reaction of Al2O3 with dilute hydrochloric acid. (iii) Write an equation for the reaction of SO 2 and Al2O3 separately with dilute sodium hydroxide. (iv) Comment on the role of Al2O3 in reactions (a)(ii) and (iii) above. [8] (b) (i) Write a balanced equation for the action of heat on magnesium nitrate. (ii) Magnesium nitrate decomposes at a lower temperature than strontium nitrate. Explain why the two nitrates decompose at different temperatures. Predict if barium nitrate would decompose at a higher or lower temperature compared to strontium nitrate. [4] (c) For each of the following pairs of structural isomers, describe one chemical test which would enable you to distinguish them. You should state the reagents and conditions for each test, and describe the observations. (i) CH2(NH2)COCl and CH 2ClCONH2 (ii) Cl CH2I and I CH2Cl (iii) OO and OO [8] [Total: 20]

5 SRJC 2009 9746/03/Prelim/2009 [Turn over 3 (a) (i) In Singapore, chlorine is added to the drinking water. Explain briefly the importance of the addition of chlorine to drinking water. (ii) Explain, with the aid of an equation, why the addition of a base at room temperature will result in the elimination of chlorine smell from drinking water. State the type of reaction that chlorine undergoes. [3] (b) The oxyacids of chlorine are: Chemical formula HOCl HOClO HOClO2 HOClO3 Chemical Name chloric (I) acid chloric (III) acid chloric (V) acid chloric (VII) acid Ka 10–7.50 10–1.96 101 1010 (i) Describe and explain how an increase in oxygen content of the acids affects Ka. (ii) Draw the dot-and-cross diagram of C lO2 –. Suggest the shape and state the bond angle of the ion. [4] (c) (i) A sample of sodium hypochlorite, NaOC l, was dissolved in 100 cm 3 of 0.123 mol dm–3 HOCl solution forming a buffer of pH 6.20. Determine the ratio of the concentration of OCl – to HOCl in the solution. (ii) The buffer is then used to absorb HC l gas. By using the above ratio or otherwise,