MJC_H1_CHEM_P2 ANS

No part of this paper should be repro duced for commercial use without the prior written permission of Meridian Junior College. Name : ______________________ Class: ______ Reg Number: _____ Meridian Junior College 2009 JC2 Preliminary Examination Answers H1 Chemistry 8872 14 September 2009 2 hours Paper 2 Candidates to answer Section A on the Question Paper and Section B on separate writing paper. Additional Materials: Data Booklet Writing paper INSTRUCTION TO CANDIDATES Write your name, class and regi s ter number in the spaces pr ovided at the top of this page. Section A Answer all questions. Examiner’s Use Paper 1 MCQ / 30 Q1 / 7 Q2 / 8 Q3 Section B Answer any tw o questions. Paper 2 Section A At the end of the examination, fasten your answers for Section B behind Section A. INFORMATION FOR CANDIDATES / 10 Q4 / 15 Q5 / 20 Q6 / 20 Q7 / 20 Total / 110 Paper 2 Section B The number of marks is given in brackets [ ] at the end of each question or part question. You are reminded of the need for good English and clear presentation in your answers. This question paper consists of Page 1 to 19. ©chemistry department@meridian jc

Section A 1(a) Magnesium bromide, MgBr 2, is a white solid that r eadily absorbs moisture from the atmosphere. It is often used as a mild sedative. (i) Using magnesium bromide as an exam ple, explain what is meant by the term lattice energy. Lattice energy is the energy released when one mole of MgBr 2 is formed from gaseous Mg2+ and Br- ions at standard conditions. (ii) Use the energy level diagram, t ogether with the giv en data, determine the lattice energy of magnesium bromide. ©chemistry department@meridian jc Enthalpy change of hydration of magnesium ion, ∆Hhyd(Mg2+) -1921 kJ mol-1 Enthalpy change of hydration of bromide ion, ∆Hhyd(Br-) -336 kJ mol-1 Enthalpy change of solution of magnesium bromide, Hsoln( MgBr2) -186 kJ mol-1 ∆Hlatt ө (MgBr2) = + (-1921) + 2(-336) – (-186) ∆Hlatt ө (MgBr2) = - 2407 kJ mol-1 ∆ ∆Hlatt MgBr2 (s) ∆Hsoln (MgBr2) Mg2+(aq) + 2Br-(aq) Hhyd( 2+gM ) + 2 x ∆Hhyd( -Br ) Mg2+(g) + 2Br-(g) 1

(iii) Explain how you would expect the numerical magnitude of the lattice energy of MgBr2 to compare with that of sodium fluoride, NaF. Charge of cation q+ : Na+ < Mg2+ Ionic radius of cation: Mg2+ < Na+ & Ionic radius of anion: F- < Br- Hlatt : MgBr2> NaF [4] (b) (i) With the aid of an equation, define the first ionisation energy of iodine. ©chemistry department@meridian jc 2 I (g) → I + (g) + e (ii) State and explain how you would expec t the first ionisation energy of iodine to compare with that of fluorine.