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. …………………………………………………………………………………….…….… ……………………………………………………………………………………….….… ………………………………………………………………………………………..…… …………………………………………………………………………………….…….… ……………………………………………………………………………………….….… ………………………………………………………………………………………..…… …………………………………………………………………………………….…….… ……………………………………………………………………………………….….… ………………………………………………………………………………………..…… …………………………………………………………………………………….…….…