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, solution. The chemical equation for the reaction is shown below. Ga2O3 (s) + 6HCl (aq) → 2GaCl3 (aq) + 3H2O (l) The excess hydrochloric acid requires 14.00 cm 3 of 0.100 mol dm −3 sodium hydroxide, NaOH, solution for complete neutralisation. (i) Calculate the amount (in moles) of sodium hydroxide required for complete neutralisation. [1] ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. (ii) Calculate the amount (in moles) of hydrochloric acid that reacted with gallium oxide. [2] ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. (iii) Calculate the mass of gallium oxide present in the impure sample. [2] ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………….

− 5 − Turn over 2. The table below shows some data on the oxides of elements in Period 3 of the Periodic Table. Oxide Na2O MgO Al2O3 SiO2 P4O6 SO2 Melting point / K 1193 3125 2345 1883 297 200 (a) Predict an approximate pH value for the solutions formed by adding Na 2O and P 4O6 separately to water. Explain your answer. [3] ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. (b) With reference to structure and bonding, explain the following. (i) The melting point of MgO is higher than Na2O. [3] ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. (This question continues on the following page)

− 6 − Turn over (Question 2 continued) (ii) The melting point of SiO2 is higher than that of P4O6. [3] ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. (c) (i) SO2 exists as two resonance structures. Draw the two Lewis structures. Label clearly the formal charge of each atom in both structures. [4] Lewis structure I Lewis structure II (ii) Using your answer from part (c)(i), explain briefly which is the more stable structure. [1] ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. (This question continues on the following page)

− 7 − Turn over (Question 2 continued) (iii) Identify the type of hybridisation found in O of SiO2. [1] ………………………………………………………………………………………………………………. (d) The Born−Haber cycle for MgO under standard conditions is shown below. Mg2+ (g) + O2− (g) D Mg2+ (g) + O (g) + 2e− C E Mg (g) + O (g) B Mg (g) + 1 2 O2 (g) A Mg (s) + 1 2 O2 (g) F MgO (s) The enthalpy change of the processes are shown in the table below. Process Enthalpy change / kJ mol−1 A + 150 B + 248 C + 2186 D + 702 F − 602 (This question continues on the following page)

− 8 − Turn over (Question 2 continued) (i) Define the enthalpy change, F. [1] ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. (ii) Identify the processes A and D in the cycle. [2] Process A : ………………………………………………………………………………………………………………. Process D : ………………………………………………………………………………………………………………. (iii) Determine the value of the enthalpy change for process E. [2] ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. (This question continues on the following page)

− 9 − Turn over (Question 2 continued) (iv) Calculate a value for the second ionisation energy of Mg , using section 8 of the data booklet. Explain why the second ionisation energy is larger than the first ionisation energy. [2] ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………….

− 10 − Turn over 3. (a) The equation for the decomposition of gaseous hydrogen iodide at 400 oC is shown.