ACSI 2018 Prelim Paper 2

1 Anglo-Chinese School (Independent) Year 6 Preliminary Examination 2018 INTERNATIONAL BACCALAUREATE DIPLOMA PROGRAMME CHEMISTRY HIGHER LEVEL PAPER 2 Tuesday 11th September 2018 2 hours 15 minutes INSTRUCTIONS TO CANDIDATES • Do not open this examination paper until instructed to do so. • Write your candidate session number in the box above. • A calculator is required for this paper. • A copy of the Chemistry Data Booklet is required for this paper. • Write your answers in the boxes provided. • If you use additional sheets of paper for your answer, attach them to the booklet. Indicate the question number clearly on these sheets. 0 0 2 3 2 9 For examiner’s use Qn 1 /6 Qn 2 /11 Qn 3 /5 Qn 4 /18 Qn 5 /9 Qn 6 /11 Qn 7 /11 Qn 8 /15 Qn 9 /9 Wrong s.f. /units Total /95 Candidate Session Number ________________________________________________________________________ This question paper consists of 22 printed pages including this cover page.

2 Answer all questions. Write your answers in the boxes provided. 1. (a) The emission spectrum of hydrogen is shown in the diagram below. (i) Describe the emission spectrum of hydrogen. [2] (ii) State an electron transition that corresponds to a line in the visible emission spectrum. [1] (b) The first seven ionization energies of an atom, X, in kJ mol−1, are 1012 1903 2912 4957 6274 21 269 25 298 (i) Write the electronic configuration of element X which belongs to Period 3. [1] (This question continues on the following page) High energy Low energy

3 (Question 1 continued) (ii) Explain the general increase in the ionization energy values. [2] 2. The halogens form many interhalogen compounds and ions with other halogen atoms. Two such species are ClF5 and ICl4 −. (a) Draw the Lewis (electron dot) structures of ClF5 and ICl4 − and state their molecular geometry. [4] Molecular Geometry: Molecular Geometry: (This question continues on the following page)

4 (Question 2 continued) (b) A student proposed the two possible shapes for the C lF3 molecule were trigonal planar and T-shape. He did some research and learnt that the molecule has an overall dipole moment. Which of the two shapes is consistent with the fact that the C lF3 molecule has an overall dipole moment? Justify your answer in terms of bond polarity and molecular geometry. [2] (c) (i) The following exergonic equilibrium gives rise to triiodide ion: I2 + I− ⇌ I3− Explore if the reaction is an acid-base reaction. [2] (ii) Explain with reference to its atomic structure, why the magnitude of the electron affinity of iodine is lower than fluorine. [2] (This question continues on the following page)

5 (Question 2 continued) (iii) Use section 15 of the data booklet, state one change if all the ligands in [FeI6]3- complex are replaced with fluoride ligands. [1] 3. The oxides MgO and SiO2 are used as refractory materials due to their high melting points. (a) If a sample of one of the oxides was provided as a white powder, describe a chemical reaction that can be carried out to determine the identity of the unknown oxide sample. Hence, state the chemical equation for the reaction. [3] (b) Explain in terms of bonding, why silicon dioxide does not exist as simple molecules like carbon dioxide. [2]

6 4. At 400 K, 0.400 mole of hydrogen and 0.400 mole of iodine gas were introduced into a reaction vessel in the presence of a platinum catalyst. The reaction scheme represent ed five molecular scenes, A to E of the reaction between hydrogen and iodine over time to liberate hydrogen iodide gas. Each “diatomic” symbol represented 0.100 mole. (a) (i) State an equation for the reversible reaction between hydrogen and iodine gas. [1] (ii) State two characteristics of a system in dynamic equilibrium. [2] (b) (i) Write the expression for the reaction quotient, Qc, for the reaction between hydrogen and iodine. [1] (This question continues on the following page) A B C D E Hydrogen atom Iodine atom

7 (Question 4 continued) (ii) Calculate the value of Qc for each scene, A to E in the reaction scheme. [3] (iii) Hence, state the value of Kc for the reaction of hydrogen and iodine at 400 K. [1] (iv) State the significance of the magnitude of Kc in (b)(iii). [1] (v) The reaction mixture in scene E is heated to 600 K causing 50% of hydrogen iodide present to decompose. Calculate the value of Kc at 600 K. [3] (This question continues on the following page)

8 (Question 4 continued) (vi) State and explain the effect of platinum catalyst on the position of equilibrium and the magnitude of Kc. [2] (c) (i) Use section 1 of the data booklet and your answer in (b)(v), determine the value of G, in kJ mol-1, for the above reaction at 600 K (If you did not obtain an answer to (b)(v), use a value of 1.50 for the Kc value at 600 K, although this is not the correct answer.) [1] (ii) Using your answers in (b)(iii) and (b)(v), deduce with reason, the sign of the enthalpy change of reaction between hydrogen and iodine. [3]

9 5. The production of a colour-treating solution involves the acid buffered oxidation of iodide to iodine by hydrogen peroxide in one of the many steps in the synthesis process. 2I− + H2O2 + 2H+ → I2 + 2H2O Two experiments were carried out to determine the rate of the oxidation reaction and the results are given below. (a) Suggest how you could determine the concentration of KI with respect to time indirectly in the laboratory. [2] (This question continues on the following page) Experiment with [H2O2] = 0.1 mol dm-3 Experiment with [H2O2] = 0.2 mol dm-3 Time / s [KI] / mol dm-3 [KI] / mol dm-3 0 0.0200 0.0200 5 0.0190 0.0175 25 0.0149 0.0103 50 0.0112 0.0054 75 0.0085 0.0030 100 0.0063 0.0015 125 0.0047 0.0003

10 (Question 5 continued) (b) Plot the [KI] vs Time graphs for both experiments on the axes provided in pencil. [2] (This question continues on the following page) 0.0000 0.0010 0.0020 0.0030 0.0040 0.0050 0.0060 0.0070 0.0080 0.0090 0.0100 0.0110 0.0120 0.0130 0.0140 0.0150 0.0160 0.0170 0.0180 0.0190 0.0200 0 25 50 75 100 125 [KI] / mol dm-3 Time / s