2022 RI Prelim P2 QP

© Raffles Institution 2022 9729/02/S/22 [Turn Over RAFFLES INSTITUTION 2022 YEAR 6 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME CLASS INDEX NUMBER CHEMISTRY 9729/02 Paper 2 Structured Questions 14 September 2022 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Do not open this question booklet until you are told to do so. Write your name, class and index number in the spaces at the top of this page. Write in dark blue or black pen. You may use an HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. Answer all questions in the spaces provided on the Question Paper. The use of an approved scientific calculator is expected, where appropriate. A Data Booklet is provided. Do not write anything in it. You are reminded of the need for good English and clear presentation in your answers. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use 1 / 19 2 / 20 3 / 19 4 / 17 Total / 75 This document consists of 24 printed pages and 4 blank pages.

2 For examiner’s use Answer all questions in the space provided. 1 This question is about the compounds of iodine and their reactions. (a) Hydrogen iodide is a primary source of iodine in chemical reactions. It can be synthesised from iodine via the following two steps. step 1 3I2 + 2P ⎯→ 2PI3 step 2 PI3 + 3H2O ⎯→ 3HI + H3PO3 Given that 65 cm 3 of HI gas is collected at standard temperature and pressure, calculate the mass of iodine reacted. [2] (b) (i) Explain the trend and variation in the boiling points of the hydrogen halides shown in the table below. hydrogen halide HF HCl HBr HI boiling point / oC +20 −85 −67 −35 …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. ……………………………………………………………………………………………….…. ……………………………………………………………………………………………… [2]

3 For examiner’s use (ii) Describe and explain the trend in the thermal stability of HCl, HBr and HI. .…………………………………………………………………………………………………. .…………………………………………………………………………………………………. .…………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. ……………………………………………………………………………………………… [2] (c) Iodate(V) ion, IO3– , is commonly used as an oxidising agent in chemical reactions. (i) Draw a ‘dot-and-cross’ diagram of IO3–. [1] (ii) With reference to the Valence Shell Electron Pair Repulsion theory , s tate and explain the shape and bond angle about the iodine atom in IO3–. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. ……………………………………………………………………………………………… [2] Both iodate(V) and iodide ions can be obtained via the disproportionation of iodine under alkaline conditions. (iii) Using oxidation numbers , or otherwise, construct a balanced chemical equation for the disproportionation of iodine under alkaline conditions. ……………………………………………………………………………………………… [1]

4 For examiner’s use (d) IO3– can be converted to periodic acid, HIO4. HIO4 can be used to split alcohols with two adjacent hydroxy groups, such as glycol A. Fig. 1.1 shows t he splitting of glycol A by H IO4 to form ethanal and butanone , via an intermediate B. Fig. 1.1 (i) On intermediate B in Fig. 1.1, draw three curly arrows to indicate the movement of electron pairs for step 2. [1] (ii) By considering the hybridisation of the atoms , compare the Ca–H bond strength in glycol A and in ethanal. Explain your answer. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. ……………………………………………………………………………………………… [2]

5 For examiner’s use (iii) Draw a labelled diagram to show all the valence orbitals of C a and O in ethanal and how they overlap to form the Ca=O bond. Assume that the O atom in ethanal is sp2 hybridised. [2] (iv) Compound C reacts with HIO4 to form compound D as shown below. Draw the skeletal formula of compound C in the box provided. [1]

6 For examiner’s use (v) Butanone reacts with HCN in the presence of trace amount of KOH. Describe the mechanism for this reaction, showing all charges and relevant lone pairs and show the movement of electron pairs by using curly arrows. [3] [Total: 19]

7 For examiner’s use 2 Nitrogen dioxide, NO 2, is a highly reactive gas due to the presence of an unpaired electron on the nitrogen atom. (a) (i) State three basic assumptions of the kinetic theory as applied to an ideal gas. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. ……………………………………………………………………………………………… [2] (ii) Fig. 2.1 shows how pV T varies with pressure for 1 mol of ideal gas and 1 mol of NO2 at T1 K. On Fig. 2.1, sketch a graph to show how pV T varies with pressure for 1 mol of NO2 at a higher temperature of T2 K. Label your graph as (a)(ii) and explain your answer. Fig. 2.1 …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………….... [2] NO2 pressure pV T ideal gas

8 For examiner’s use (b) Nitrogen dioxide undergoes the following gas phase reaction with hydrogen chloride, as shown in equation 2.1. equation 2.1 2NO2(g) + HCl(g) ⎯→ NOCl(g) + HNO3(g) To study the kinetics for this reaction , t hree separate experiments were carried out in a vessel of fixed volume at a constant temperature of 500 K. The initial concentrations of NO2 and HCl are shown in Table 2.1. Table 2.1 experiment initial [NO2] / mol dm−3 initial [HCl] / mol dm−3 1 1.00 0.05 2 0.50 0.05 3 0.50 0.01 To monitor the progress of the reaction for each experiment , the total pressure in the vessel w as measured at regular time intervals and the corresponding concentration s of NOCl were calculated. Fig. 2.2 shows how the concentration of NOCl varies with time for experiments 1 and 2. time / s Fig. 2.2 0 0.01 0.02 0.03 0.04 0.05 0 50 100 150 200 250 300 experiment 1 experiment 2 [NOCl] / mol dm−3

9 For examiner’s use (i) With reference to Fig. 2.2, calculate the mole fraction of NOCl present in the vessel for experiment 1 at t = 200 s. [2] (ii) Calculate the total pressure, in Pa, in the vessel for experiment 1 at t = 200 s. You may assume that all the gases behave ideally. [2]

10 For examiner’s use (iii) Using Fig. 2.2, determine the initial rate of reaction for experiments 1 and 2. Hence, deduce the order of reaction with respect to NO2.