DHS_2008 Prelim - H2 Chemistry Paper 3

This question paper consists of 8 printed pages and 0 blank page. [Turn over CANDIDATE NAME ____________________________ CLASS________ DUNMAN HIGH SCHOOL (SENIOR HIGH) YEAR 6 PRELIMINARY EXAMINATION 2008 H2 CHEMISTRY Paper 3 Free–Response 9746/03 15 September 2008 2 hours Additional materials: Data Booklet Cover Sheet Answer Paper INSTRUCTIONS TO CANDIDATES 1 Write your name and class on this question paper, the Cover Sheet and on all the work you hand in. 2 Answer ANY FOUR questions. 3 Write your answers on the separate answer paper provided. 4 Start each question on a fresh sheet of paper. 5 A Data Booklet is provided. 6 You are reminded of the need for good English and clear presentation in your answers. 7 The number of marks is given in brackets [ ] at the end of each question or part question. 8 You are advised to show all workings in calculations. 9 You may use a calculator. 10 At the end of the examination, fasten all your work securely together with the Cover Sheet on top.

2 © DHS 2008 9746/03 [Turn over Answer any four questions. 1(a) When under attack, the bombardier beetle uses ‘chemical warfare’. It defends itself from attack by mixing together solutions of hydrogen peroxide and hydroquinone (C 6H4(OH)2) in the presence of enzymes. This reaction releases free oxygen that produce enough energy to bring the mixture to boiling point. An audible ex plosion occurs as the beetle fires a hot spray at its attacker from its abdomen. Quinone, C 6H4O2 is one the products formed. + H2O2 (aq) hydroquinone OHHO OO + 2H2O (l) quinone (aq) (aq) (i) State Hess’ Law. (ii) Construct an energy cycle and use the following data to calculate the enthalpy change of reaction inside the beetle. C6H4(OH)2 (aq) Æ C6H4O2 (aq) + H2 (g) ΔHθ= +177 kJ mol–1 H2O2 (aq) Æ H2O (l) + ½O2 (g) ΔHθ= –95 kJ mol–1 H2 (g) + ½O2 (g) Æ H2O (l) ΔHθ= –286 kJ mol–1 (iii) Draw a labelled energy profile for the reaction above and indicate clearly the activation energy and enthalpy change of reaction. [7] (b) When developing exposed film from a came ra, aqueous alkaline hydroquinone reacts with silver ions in a light–activated reaction in I. + 2Ag+ (aq) hydroquinone OHHO OO + X quinone (aq) (aq) OH- II Y NaOH (aq), followed by CH3I I (i) Identify X and state the role of hydroquinone in reaction I. (ii) Draw the structural formula of Y and name the type(s) of reaction involved in II. (iii) Write a balanced equation for the reaction between quinone and each of the following reagents: (1) LiAlH4 in dry ether (2) HBr (iv) State what would be observed when 2,4–dinitrophenylhydrazine is added a solution of quinone. Draw the structural formula of the organic product formed. (v) One student attempts to synthesise hydroquinone from 1,4–dichlorobenzene using hot aqueous sodium hydroxide. State with reasons whether the student would be successfu