VJC Prelim P2_QP and Ans

© VJC 2018 9729/02/PRELIM/18 [Turn over CANDIDATE NAME CT GROUP VICTORIA JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION Higher 2 ……………………………………………….………….. …………………………….. CHEMISTRY 9729/02 Paper 2 Structured Candidates answer on the Question Paper. 11 September 2018 2 hours Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name and CT group 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 staples, paper clips, highlighters, glue or correction fluid. Answer all questions. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use 1 / 20 2 / 20 3 / 20 4 / 15 Total / 75 This document consists of 20 printed pages.

© VJC 2018 9729/02/PRELIM/18 2 Answer all the questions in the spaces provided. 1 (a) Bromine exists naturally as a mixture of two stable isotopes, 79Br and 81Br, in a 1:1 ratio. (i) Write down the full electronic configuration of 79Br2+. 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p3 [1] (ii) Define the term relative isotopic mass. Mass of an atom of isotope relative to 1 12 the mass of an atom of carbon– 12 isotope. [1] (b) Chlorine atom exists naturally as two isotopes, 35Cl and 37Cl, in a 3:1 ratio. When equimolar amounts of bromine and chlorine were mixed together, an interhalogen compound, BrC l, is formed. The product mixture contains four species with three different mass numbers 114, 116 and 118. 79Br35Cl is one of the four species. (i) With the help of the information given in (a), state the species that corresponds to each mass number. Hence, calculate the relative abundance for each mass number. mass number species relative abundance 114 79Br35Cl ½ × ¾ = 3 8 116 79Br37Cl and 81Br35Cl (½ × ¼) + (½ × ¾) = 1 2 118 81Br37Cl ½ × ¼ = 1 8 [3] (ii) Explain whether BrCl or Cl2 has a greater enthalpy change of vaporisation. BrC l has a greater enthalpy change of vaporisation as it has stronger instantaneous dipole–induced dipole interactions due to the greater number of electrons in the larger BrCl molecule. OR BrC l has a greater enthalpy change of vaporisation as it is polar with stronger permanent dipole–permanent dipole interactions than the instantaneous dipole–induced dipole interactions in Cl2. [1] (iii) Suggest with a reason how the first ionisation energy of 79Br is compared to 81Br. First ionisation energy of 79Br is the same as that of 81Br because they have the same number of protons. [1]

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