PJC H1 CHEM P2

PIONEER JUNIOR COLLEGE, SINGAPORE JC2 PRELIMINARY EXAMINATIONS HIGHER 1 CANDIDATE NAME CT INDEX GROUP NUMBER 8 0 CHEMISTRY 8872/02 Paper 2 Structured and Free-Response 24 September 2009 2 hours Additional Materials: Answer Paper Data Booklet READ THESE INSTRUCTONS FIRST Write your Centre number, index number and name on all 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 workings. Do not use staples, paper clips, highlighters, glue or correction fluid. Section A Answer all questions. Section B Answer two questions on separate answer paper. 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 1 Section B B4 / 20 Marks / 30 B5 / 20 Section A B6 / 20 A1 / 17 Total A2 / 16 / 100 A3 / 7 Grade This document consists of 12 printed pages. © PJC 2009 8872/02/Prelim/S/09 [Turn over

2 Section A Answer all the questions in this section in the spaces provided. 1 This question is about aluminium, an elem ent in the third peri od of the Periodic Table. (a) (i) On the grid below, sketch the trend of the first ionisation energies of elements of Period 3 from sodium to argon. (ii) Write an equation for the first ionisation energy of aluminium. (iii) Explain why the first ionisation ener gy of aluminium is lower than magnesium. [3] (b) A beam of particles of 27Al+ and 9Be+ is passed through an electric field. If the angle of deflection of the 27Al+ particle is 3o, state the angle of deflection for the 9Be+ particle. [1] For Examiner’s Use first ionisation energy / kJ mol -1 element Na Mg Al Si P S Cl Ar © PJC 2009 8872/02/Prelim/S/09 [Turn over

3 A lCl3 is a covalent compound that exists as a white solid at room temperature and pressure. When A lCl3 is heated to a sufficiently high temperature, it sublimes to gives the Al2Cl6 dimer. (c) Draw a dot-and-cross diagram for the A l2Cl6 dimer. Name the type of bond responsible for the formation of the dimer. Type of bond: ______ _______________________________ [2] (d) 2.0 mol of gaseous A lCl 3 is heated at 800 K in a 750 cm 3 vessel. When dynamic equilibrium is achieved, 0.971 mol of gaseous Al 2Cl6 is formed in the vessel. (i) Define the term dynamic equilibrium. (ii) Write a balanced equati on for the equilibrium. (iii) Calculate the value and state the units of the equilibrium constant, K c, for this reaction at 800 K. [5] For Examiner’s Use © PJC 2009 8872/02/Prelim/S/09 [Turn over

4 (e) AlCl3 dissolves in water to give an acidic solution, as shown by the following equation. [Al(H2O)6]3+(aq) + H2O(l) ⇌ [Al(H2O)5(OH)]2+(aq) + H3O+(aq) (i) Define the term Bronsted base . Hence, identify the two Bronsted bases and state one conjugate acid-base pair in the equation above. Definition of Bronsted base: __________________________________. The two Bronsted bases are _______________ and _______________. One conjugate acid-base pair: _______________ and _______________. (ii) Write an expression for the acid dissociation constant, K a, of [Al(H2O)6]3+. (iii) When 0.1 mol of A lCl 3 is dissolved in 1 dm 3 of solution, the resulting solution is found to have a pH of 3. Using your equation in (ii), calculate the Ka of [Al(H2O)6]3+. [6] [Total: 17] For Examiner’s Use © PJC 2009 8872/02/Prelim/S/09 [Turn over

5 2 Cyanohydrins can be made by reacting ketones with an acidified solution of sodium cyanide. When propanone is reacted as described, compound T is formed. (CH3)2CO + H+ + CN- → T (a) Draw the displayed formula of compound T. On your diagram, state the type of hybridisation of all the carbon atoms in T. [2] For Examiner’s Use An experiment is performed in which 2.00 mol dm -3 of propanone is reacted with an excess of an acid and sodium cyanide. The following results are obtained. time / s [(CH3)2CO] / mol dm-3 0 2.00 15 1.30 30 0.84 45 0.55 60 0.35 75 0.23 (b) (i) On the grid provided below, plot a graph of these values on suitable axes. © PJC 2009 8872/02/Prelim/S/09 [Turn over

6 (ii) Using your graph, deduce the order of reaction with respect to propanone. (iii) Why are the concentration of the acid and the concentration of sodium cyanide used in excess? [5] (c) When the experiment is repeated using 1.00 mol dm -3 of the acid and an excess of propanone and sodi um cyanide, the following Graph 1 of concentration of the acid against time is obtained. Graph 1 Graph 2 O n Graph 2 above, sketch a graph for the rate of reaction of the acid against the concentration of the acid . Hence, state the order of reaction with respect to the acid. Order of reaction with res pect to the acid: _______________________ [2] (d) The order of reaction with respect to sodium cyanide is one. Together with your answers in (b)(ii) and (c), write the rate law for this reaction. [1] For Examiner’s Use [acid] / mol dm-3 rate [acid] / mol dm-3 time / s © PJC 2009 8872/02/Prelim/S/09 [Turn over

7 (e) (i) Propanal is a functional group isomer of propanone. Suggest a simple chemical test to distinguish be tween propanal and propanone. State any observations seen. (ii) Propanal can be converted to propanone in the laboratory as follows. CH 3CH2CHO X C H 3CH=CH2 C H 3COCH3 CH 3CH(OH)CH3 Identify compound X. State the reagent and conditions for Step I and III. Compound X: Step I: Step III: (iii) Draw the structural formula of t he compound formed when propanal reacts with 2,4-dinitrophenylhydrazine. [6] [Total: 16] For Examiner’s Use I II III IV © PJC 2009 8872/02/Prelim/S/09 [Turn over

8 3 Olive oil is a popular flavouring us ed in Mediterranean cuisine. The main constituent of olive oil is oleic acid, CH3(CH2)7CH=CH(CH2)7CO2H. (a) Name the functional groups that are present in oleic acid. [1] (b) State the reagent and condition to synthesise oleic acid from CH 3(CH2)7CH=CH(CH2)7CH2OH. [1] (c) State the reagents and conditions needed to convert oleic acid into each of the following. compounds reagents and conditions CH 3(CH2)7CH(OH)CHBr(CH2)7CO2H CH 3(CH2)7CH(OH)CH(OH)(CH2)7CO2H CH 3(CH2)7CHCl(CH2)8CO2H [3] (d) Another constituent of o live oil is linoleic acid. Linoleic acid has the same functional groups as oleic acid. When linoleic acid is oxidised, the following compounds are obtained in equimolar quantities. CH3(CH2)4CO2H, HO2CCH2CO2H, HO2C(CH2)7CO2H Write the two possible structural formula of linoleic acid. [2] [Total: 7] For Examiner’s Use © PJC 2009 8872/02/Prelim/S/09 [Turn over