2018 HCIS IB2 HL Prelim Paper 2

− 1 − Turn over PRELIMINARY EXAMINATION International Baccalaureate 2 Chemistry Higher level Paper 2 Tuesday 28 August 2018 (afternoon) 2 hour 15 minutes Candidate name Candidate session number Class Instructions to candidates • Write your candidate name and session number in the boxes above. • Do not open this examination paper until instructed to do so. • Answer all the questions. • Write your answers in the boxes provided. • A calculator is required for this paper. • A clean copy of the Chemistry data booklet is required for this paper. • The maximum mark for this examination paper is [95 marks]. For Examiner’s Use Q1 / 15 Q2 / 22 Q3 / 16 Q4 / 20 Q5 / 8 Q6 / 14 Total / 95 23 pages © Hwa Chong International School 2018

− 2 − Turn over Answer all questions. Write your answers in the boxes provided. 1. (a) Gallium exists as two isotopes 69Ga (65%) and 71Ga (35%). (i) Define the term relative atomic mass. [1] ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. (ii) Calculate the relative atomic mass of gallium. [1] ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. (b) Gallium reacts with nitrogen gas to form gallium nitride, GaN. 2Ga (s) + N2 (g) → 2GaN (s) ∆Hθ = −156.8 kJ mol−1 (i) State the full electron configuration of the gallium ion in GaN. [1] ………………………………………………………………………………………………………………. (ii) Deduce, giving your reason, whether the sign of ∆Sθ for the reaction would be positive or negative. [2] ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. (This question continues on the following page)

− 3 − Turn over (Question 1 continued) (iii) Outline how the spontaneity of the reaction varies with temperatures. Explain your answer. [2] ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. (iv) Calculate the volume of nitrogen, at standard temperature and pressure, needed to react completely with 10.0 ± 0.2 g of gallium, and its absolute uncertainty. [3] ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. (This question continues on the following page)

− 4 − Turn over (Question 1 continued) (c) 2.00 g of an impure sample of gallium oxide, Ga 2O3, was dissolved in 200 cm 3 of 0.300 mol dm −3 hydrochloric acid, HC l,