2023 VJC H2 Chem Prelim P3 (QP)

1 © VJC 2023 9729/03/PRELIM/23 [Turn over CANDIDATE NAME CT GROUP VICTORIA JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION Higher 2 ……………………………………………….………….. …………………………….. CHEMISTRY 9729/03 Paper 3 Free Response Candidates answer on the Question Paper. Additional Materials: Data Booklet 19 September 2023 2 hours READ THESE INSTRUCTIONS FIRST Write your name and CT group 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. If additional space is required, you should use the pages at the end of this booklet. The question number must be clearly shown. Section A Answer all questions. Section B Answer one question. The use of an approved scientific calculator is expected, where appropriate. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use Section A 1 / 24 2 / 16 3 / 20 Section B 4 / 20 OR 5 / 20 Total / 80 This document consists of 28 printed pages.

2 © VJC 2023 9729/03/PRELIM/23 Section A Answer all the questions in this section. 1 (a) Describe and explain the trend in thermal stability of the hydrogen halides. [2] ……………………...…………………..…………………………………………………….. ……………………...…………..…………………………………………………………….. …………………………….………………………………………………………………….. ……………………..……...………………………………………………………………….. ……………..……………...………………………………………………………………….. (b) A sodium salt of the interhalogen ion, IBrx− is prepared. When heated, the salt evolves bromine vapour, leaving sodium iodide as the residue. The bromine vapour evolved requires 32.0 cm 3 of 0.100 mol dm −3 of aqueous sodium thiosulfate for complete reaction. The balanced ionic equation for the reaction between bromine and thiosulfate is as shown below. S2O32−(aq) + 4Br2(g) + 5H2O(l) → 2SO42−(aq) + 8Br−(aq) + 10H+(aq) (i) Construct a balanced equation for the thermal decomposition of NaIBrx. [1] (ii) Calculate the amount of bromine gas evolved. [1] The sodium iodide residue was completely reacted with concentrated sulfuric acid to give HI gas, which immediately further reacted with concentrated sulfuric acid to give H2S, together with black crystals of iodine. The mass of the iodine crystals formed was found to be 1.63 g. (iii) Calculate the amount of iodine formed and hence deduce the formula of the interhalogen ion. [2] ……………………...…………..…………………………………………………………….. …………………………….………………………………………………………………….. ……………………..……...………………………………………………………………….. ……………………...…………………..…………………………………………………….. ……………………...…………..…………………………………………………………….. …………………………….………………………………………………………………….. ……………………..……...………………………………………………………………….. ……………..……………...………………………………………………………………….. …………………………….………………………………………………………………….. ……………………...…………..……………………………………………………………..

3 © VJC 2023 9729/03/PRELIM/23 [Turn over …………………………….………………………………………………………………….. ……………………..……...………………………………………………………………….. ……………………...…………………..…………………………………………………….. ……………………...…………..…………………………………………………………….. (c) Chloroalkanes and bromoalkanes can be made by the reaction of the corresponding halogen with alkanes. One example is given below. CH3CH2CH3 + Cl2 → CH3CH2CH2Cl + HCl (i) State the conditions needed for this reaction. [1] (ii) Name and describe the mechanism of this reaction. [2] (iii) Suggest why it is not possible to make iodoalkanes by this method. [1] ……………………...…………..…………………………………………………………….. …………………………….………………………………………………………………….. ……………………..……...………………………………………………………………….. ……………………...…………………..…………………………………………………….. ……………………...…………..…………………………………………………………….. …………………………….………………………………………………………………….. ……………………..……...………………………………………………………………….. ……………..……………...………………………………………………………………….. …………………………….………………………………………………………………….. ……………………...…………..…………………………………………………………….. …………………………….………………………………………………………………….. ……………………..……...………………………………………………………………….. ……………………...…………………..…………………………………………………….. …………………………….………………………………………………………………….. ……………………..……...………………………………………………………………….. ……………..……………...…………………………………………………………………..

4 © VJC 2023 9729/03/PRELIM/23 (d) Suggest a structural formula for each of the compounds , A to D, in the following schemes shown in Figure 1.1. [4] Figure 1.1 ……………………...…………………..…………………………………………………….. ……………………...…………..…………………………………………………………….. …………………………….………………………………………………………………….. ……………………..……...………………………………………………………………….. ……………..……………...………………………………………………………………….. …………………………….………………………………………………………………….. ……………………..……...………………………………………………………………….. ……………………...…………………..…………………………………………………….. ……………………...…………..…………………………………………………………….. …………………………….………………………………………………………………….. ……………………..……...………………………………………………………………….. ……………..……………...………………………………………………………………….. …………………………….………………………………………………………………….. ……………………...…………………..…………………………………………………….. ……………………...…………..……………………………………………………………..

5 © VJC 2023 9729/03/PRELIM/23 [Turn over (e) Chlorofluoroalkanes, CFCs, were once used as refrigerant fluids and aerosol propellants. In many applications they have now been replaced by alkanes. This is because CFCs contribute to the destruction of the ozone layer. (i) Suggest one reason why CFCs were originally used for these purposes. [1] (ii) Explain how CFCs destroy the ozone layer. [1] (iii) Suggest one potential hazard of using alkanes instead of CFCs. [1] ……………………...…………..…………………………………………………………….. …………………………….………………………………………………………………….. ……………………..……...………………………………………………………………….. ……………………...…………………..…………………………………………………….. ……………………...…………..…………………………………………………………….. …………………………….………………………………………………………………….. ……………………..……...………………………………………………………………….. ……………………..……...………………………………………………………………….. (f) Figure 1.2 shows two reactions involving benzene and a suitable Lewis acid as a catalyst. Figure 1.2 (i) Suggest the type of reaction for reaction 1. [1] (ii) Suggest the reagents and conditions for a reaction that could be used to distinguish between Y and Z, and describe the observations. [2]