RVHS 2023 J2 H2 CM Prelim P3 QP

River Valley High School 9729/03/PRELIMS/23 2023 Preliminary Examination [Turn over RIVER VALLEY HIGH SCHOOL JC 2 PRELIMINARY EXAMINATION CANDIDATE NAME CLASS 2 2 J CENTRE NUMBER S INDEX NUMBER H2 CHEMISTRY 9729/03 Paper 3 Free Response 20 September 2023 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your Centre number, index number, class and name on all the work that you hand in. 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. DO NOT WRITE IN ANY BARCODES. 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 the questions. Section B Answer one question. Circle the question number of the question you attempted. The use of an approved scientific calculator is expected, where appropriate. A Data Booklet is provided. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use Question Number 1 2 3 4 5 units s.f. Total Marks 19 24 17 20 20 80 This document consists of 28 printed pages.

2 River Valley High School 9729/03/PRELIMS/23 2023 Preliminary Examination Section A Answer all the questions in this section. 1 (a) Ethanedioyl dibromide, BrCOCOBr, is a useful reagent in organic synthesis. ethanedioyl dibromide Ethanedioyl dibromide is used in the following synthesis of compound D. It reacted in a 1:1 stoichiometric ratio with C6H5Br in step 3. (i) Suggest the identities of A, B and C. [3] (ii) State the reagents and conditions for steps 2, 4 and 6. [3] (iii) If the amount of ethanedioyl dibromide used in step 3 is decreased, another compound is formed . The compound has the molecular formula C14H8O2Br2. Suggest the structure of this compound. [1]

3 River Valley High School 9729/03/PRELIMS/23 2023 Preliminary Examination [Turn over (iv) A student has 3 unlabelled bottles, each containing a chemical found in the above synthesis pathway. These chemicals are as shown: C6H5Br Suggest 2 simple chemical tests that will allow the student to identify the chemical in each bottle, stating clearly the observations in each test. [4] ………………………………………………………………………………......… ………………………………………………………………………………......… ………………………………………………………………………………......… ………………………………………………………………………………......… ………………………………………………………………………………......… ………………………………………………………………………………......… ………………………………………………………………………………......… ………………………………………………………………………………......… ………………………………………………………………………………......… ………………………………………………………………………………......… ………………………………………………………………………………......… ………………………………………………………………………………......… ………………………………………………………………………………......… ………………………………………………………………………………......… ………………………………………………………………………………......… ………………………………………………………………………………......… ………………………………………………………………………………......… ………………………………………………………………………………......… ………………………………………………………………………………......… ………………………………………………………………………………......…

4 River Valley High School 9729/03/PRELIMS/23 2023 Preliminary Examination (b) Like ethanedioyl dibromide, Period 3 chlorides such as MgCl2 and PCl5 are halogencontaining compounds. Write equations for the reactions of these two chlorides with water. In each case, state the pH of the resulting solution. [4] ………………………………………………………………………………......………… ………………………………………………………………………………......………… ………………………………………………………………………………......……….... ……………………………………………………………………………………........….. ……………………………………………………………………………..………......….. ……………………………………………………………………..………………......….. ……………………………………………………………..………………………......….. …………………………………………………..…………………………………......….. (c) Phenylamine, C6H5NH2, is a product in step 4. Another nitrogencontaining compound, (CH3)2N2H2, known as UDMH, is used in Aerozine 50. Aerozine 50 is a 50/50 mix of hydrazine, N2H4, and UDMH. It is used as a rocket fuel, typically mixed with dinitrogen tetroxide, N 2O4, as the oxidising agent. The equation for the reaction of the UDMH with dinitrogen tetroxide is given in equation 1 and relevant thermodynamic data under standard conditions is in Table 1.1. Equation 1 (CH3)2N2H2(l) + 2N2O4(l)  2CO2(g) + 4H2O(g)+ 3N2(g) Table 1.1 Substance Hf  / kJ mol–1 S / J K–1 mol–1 (CH3)2N2H2(l) +83.3 304.7 N2O4(l) +9.1 304.4 CO2(g) 393.5 213.8 H2O(g) 241.8 188.8 N2(g) 0.0 191.6

5 River Valley High School 9729/03/PRELIMS/23 2023 Preliminary Examination [Turn over (i) Calculate the enthalpy change, Hr , for the reaction i n equation 1. [1] (ii) The entropy change, Sr , for the reaction in equation 1 is a large and positive value. Explain, without calculation, why this entropy change has such a large, positive value. [1] (iii) Calculate the free energy change, Gr , in kJ mol –1, at 298 K for the reaction in equation 1. Sr  can be used in the same manner as Hr  in a Hess’ law cycle. [2] ………………………………………………………………………………......… ………………………………………………………………………………......… ………………………………………………………………………………......… ………………………………………………………………………………......… ………………………………………………………………………………......… ………………………………………………………………………………......… ………………………………………………………………………………......… ………………………………………………………………………………......… ………………………………………………………………………………......… ………………………………………………………………………………......… ………………………………………………………………………………......… ………………………………………………………………………………......… ………………………………………………………………………………......… ………………………………………………………………………………......… ………………………………………………………………………………......… ………………………………………………………………………………......… ………………………………………………………………………………......… ………………………………………………………………………………......… ………………………………………………………………………………......… [Total: 19]

6 River Valley High School 9729/03/PRELIMS/23 2023 Preliminary Examination 2 (a) The solubility product, Ksp of a sparingly soluble salt can be determined by measuring the cell potential. An electrochemical cell comprising of the standard Ni 2+/Ni half-cell and a Ag +/Ag half-cell where a saturated solution of silver dichromate( VI) is used as the electrolyte is set up. The silver ions oxidise nickel metal to nickel(II) ions. The electrochemical cell is not under standard conditions, as the [Ag +] in a saturated solution of Ag2Cr2O7 is significantly less than 1.0 mol dm3. The Ecell was measured at +0.924 V. The Eelectrode in the Ag+/Ag half-cell is related to the [Ag+] by the following equation. Eelectrode = E electrode + 0.0592 log [Ag+] (i) Write an ionic equation for the reaction in the electrochemical cell. [1] (ii) Calculate the Gibbs free energy, G, for the reaction, per mole of nickel(II) ions formed. [1] (iii) Write an expression for the solubility product, Ksp, of silver dichromate(VI), Ag2Cr2O7. [1] (iv) Calculate the Eelectrode for the Ag+/Ag electrode in this experiment. [1] (v) Use your answer to (iv) to calculate the concentration of silver ions in the saturated solution, and hence, the Ksp of Ag2Cr2O7. If you were unable to obtain an answer in (iv), use Eelectrode = +0.50 V. [2] (vi) Determine the concentration of silver ions when a silver electrode is immersed in 0.5 mol dm 3 of K 2Cr2O7 containing some Ag 2Cr2O7 precipitate. [1] (vii) Given that NiCO 3 is sparingly soluble, p redict and explain how the Ecell in (a) would change, if at all, when a few cm 3 of concentrated Na2CO3(aq) were added to the beaker containing Ni2+/ Ni half-cell. [2] ………………………………………………………………………………......… ………………………………………………………………………………......… ………………………………………………………………………………......… ………………………………………………………………………………......… ………………………………………………………………………………......… ………………………………………………………………………………......… ……………………………………………