MI H2 Chem 2013 Prelim P2 Soln

Class Adm No Candidate Name: This document consists of XX printed pages and X blank page. [Turn over 2013 Preliminary Examination II Pre-university 3 H2 CHEMISTRY 9647/02 Paper 2 Structured Questions Wednesday, 18 Sep 2013 2 hours Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name, class and index number in the spaces provided at the top of this page. Write in dark blue or black pen in the spaces provided. You may use a soft pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. Answer all 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 brackets [ ] at the end of each question or part question. For Examiner’s Use 1 /12 2 /10 3 /13 4 /12 5 /13 6 /12 Total /72 822

2 1 Planning (P) For Examiner’s Use You are to design an experiment to determine the enthalpy change of reaction between solid Mg(OH)2 and hydrochloric acid. You are provided with the following list of apparatus and reagents. [You may assume that all other common laboratory apparatus not listed below are also available.] Reagents:  FA1: 2.50 mol dm-3 of HCl  FA2: Mg(OH)2 solid Apparatus:  A thermometer with 0.2 °C interval  A 100 cm 3 styrofoam cup with a lid  50 m l measuring cylinder (a) Write a balanced equation (including state symbols) for the reaction between solid Mg(OH)2 and hydrochloric acid. [1] Mg(OH)2(s) + 2HCl(aq) → MgCl2(aq) + 2H2O(l) 1m for balanced equation with state symbols (b) Given that the enthalpy change of reaction between solid Mg(OH) 2 and hydrochloric acid is approximately – 30.0 kJ mol1, prove with calculations whether 50.0 cm3 of 2.5 mol dm–3 HCl and 1.50 g of Mg(OH)2 are suitable quantities to use at the start of the experiment. Justify your answer. [Assuming the specific heat capacity of the solution is 4.2 J g-1 K-1] [4] Amount of HCl = 50/1000 x 2.5 = 0.125 mol Amount of Mg(OH)2 = 1.50 ÷ (24.3 + 17.0 x 2) = 0.02573 mol (L.R.) Heat released by reaction = heat absorbed by solution 30000 x 0.02573 = 50 x 4.2 x ∆T ∆T = 3.68 °C Amount of solid Mg(OH)2 is not suitable as ∆T is not within 5-10 °C. A very small ∆T will give rise to a large experimental error. 1m for calculating amount of both reagents 1m for determining L.R. 1m for determining ∆T 1m for justification 823

[Turn over 3 (c) Hence give a detailed procedure to determine the enthalpy change of reaction between solid Mg(OH)2 and HCl. [4] F