NJC H2 CHEM P2 Prelim

NATIONAL JUNIOR COLLEGE PRELIMINARY EXAMINATIONS Higher 2 CANDIDATE NAME SUBJECT CLASS REGISTRATION NUMBER CHEMISTRY Paper 2 Structured Answer on the Question Paper. Additional Materials: Data Booklet 9647/02 Fri 16 Sept 2011 2 hours READ THE INSTRUCTIONS FIRST Write your subject class, registration number and name 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 paper clips, highlighters, glue or correction fluid. Answers all questions. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use 1 /12 2 /13 3 /13 4 /16 5 /18 Total /72 This document consists of 18 printed pages and 0 blank page.

NJC/H2 Chem/02/2011 [Turn over 2 1 Planning (P) You are to design an experiment to determine the enthalpy change of solution of Mg(OH) 2 in water. Mg(OH) 2 (s) + aq  Mg(OH)2 (aq) ∆Hsoln You are provided with the following data and a list of apparatus and reagents: Data: H+ (aq) + OH (aq)  H2O(l) ∆H1 = – 57 kJmol1 Reagents: o 2.0 mol dm 3 of HCl o Mg(OH) 2 solid Apparatus: o A thermometer with 0.2 oC division o A 100 cm 3 Styrofoam cup with a lid o Two 50 ml measuring cylinders (a) Suggest a reason why ∆Hsoln of solid Mg(OH) 2 cannot be determined by measuring temperature change when a certain amount of solid Mg(OH)2 is dissolved in water. …………………………………………………………………………………….…………...… ……………………………………………………………………………………….….……….. [1] (b) Given that the enthalpy change of reaction between solid Mg(OH) 2 and hydrochloric acid is approximately – 30.0 kJmol1, (i) give the thermochemical equation of the reaction between solid Mg(OH) 2 and hydrochloric acid. ……………………………………………………………………………..……………… [1] (ii) prove with calculations whether 50.0 cm 3 of 2.0 mol dm –3 HCl and 1.17g of Mg(OH)2 are suitable quantities to work with. For Examiner’s Use

NJC/H2 Chem/02/2011 [Turn over 3 [1] 1 (b) (iii) Hence give a detailed procedure to determine the enthalpy change of reaction between solid Mg(OH) 2 and HCl solution accurately. …………………………………………………………………………………….…….… ……………………………………………………………………………………….….… ………………………………………………………………………………………..…… …………………………………………………………………………………….…….… ……………………………………………………………………………………….….… ………………………………………………………………………………………..…… …………………………………………………………………………………….…….… ……………………………………………………………………………………….….… ………………………………………………………………………………………..…… …………………………………………………………………………………….…….… ……………………………………………………………………………………….….… ………………………………………………………………………………………..…… …………………………………………………………………………………….…….… ……………………………………………………………………………………….….… ………………………………………………………………………………………..…… …………………………………………………………………………………….…….… …………………………………………………………………………………….…….… For Examiner’s Use

NJC/H2 Chem/02/2011 [Turn over 4 ……………………………………………………………………………………….….… ………………………………………………………………………………………….…. …………………………………………………………………………………….…….… ……………………………………………………………………………………….….… ………………………………………………………………………………………….…. …………………………………………………………………………………….…….… ……………………………………………………………………………………….….… ………………………………………………………………………………………….…. …………………………………………………………………………………….…….… [5] 1 (c) Given the following data, show how the en thalpy change of reaction between solid Mg(OH) 2 and hydrochloric acid can be determined accurately. Expt Mass of weighing bottle and solid sample / g a Mass of weighing bottle and residual solid / g b Initial temp of 50.0 cm3 of hydrochloric acid / oC T 1 Final constant temp of hydrochloric acid / oC T2 where T2> T1 [1] For Examiner’s Use

NJC/H2 Chem/02/2011 [Turn over 5 1 (d) By considering the data given and your answer to part (c), construct a suitable energy cycle that will enable you to determine the enthalpy change of solution of Mg(OH)2. [2] (e) Suggest and explain a safety precaution for this experiment. ………………..………………………………………………………………………….…….… …………………….……………………………………………….………………………….…. [1] [Total: 12] For Examiner’s Use

NJC/H2 Chem/02/2011 [Turn over 6 2 A student was given a sample of 3-oxo-3-phenylpropanal. O O 3-oxo-3-phenylpropanal (a) Describe what the student might observe when 3-oxo-3-phenylpropanal is warmed gently with Fehling’s solution. Write an equation for this reaction. [2] For Examiner’s Use

NJC/H2 Chem/02/2011 [Turn over 7 O O O O 3-oxo-3-phenylpropanal NaBH4 in methanol O O OH B C D FeBr3 E I II IIIIV O O Br Heated Al2O3V F cold alkaline KMnO4VI G O OH H+/ K2Cr2O7 heat N N + 2 H2O 2 (b) The student carried a series of tests on 3-oxo-3-phenylpropanal as follows: (i) State the reagents and conditions needed for Reaction I : …………………………………………………………………..……… Reaction II : …………………………………………………………………….…… For Examiner’s Use

NJC/H2 Chem/02/2011 [Turn over 8 2 (b) (ii) Suggest the structures for E and G. E G (iii) Suggest a mechanism for reaction III . In your answer, show any relevant charges, lone pairs of electrons or movement of electrons you consider to be important in this mechanism. [7] For Examiner’s Use

NJC/H2 Chem/02/2011 [Turn over 9 2 (c) When C was added to an aqueous solution of silver nitrate, a cream precipitate was observed immediately. (i) Write equations to show the formation of the cream precipitate. (ii) However, no precipitate was observed when compound H was heated with an aqueous solution of silver nitrate. O OH Br H Suggest an explanation for the unreactivity of H. ………………………………………………………………….………………….…… …………………………………………………………………….……………….…… ……………………………………………………………………………….…….…… ………………………………………………………………………………………..… ………………………………………………………………………………………..… [4] [Total: 13] For Examiner’s Use

NJC/H2 Chem/02/2011 [Turn over 10 3 The diagram below represents part of the structure of a haemoglobin molecule. (a) (i) Write the names for each of the secondary structures in the boxes in the above diagram. (ii) With reference to the haemoglobin molecule, explain what is meant by the term quanternary structure of proteins. …………………………………………………………………….………….……….… ……………………………………………………………………….……….……….… …………………………………………………………………………………..…….… (iii) With the aid