2024 Prelims VJC H2 Chem P3 (QP)

© VJC 2024 9729/03/PRELIM/24 [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 16 September 2024 2 hours READ THESE INSTRUCTIONS FIRST Write your name and CT group on all the work 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. 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. A Data Booklet is provided. 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. This document consists of 27 printed pages and 1 blank page. For Examiner’s Use Section A 1 / 23 2 / 19 3 / 18 Section B 4 / 20 OR 5 / 20 Total / 80

2 © VJC 2024 9729/03/PRELIM/24 Section A Answer all the questions in this section. 1 (a) Chlorine is bubbled through 100 cm3 of hot 4.0 mol dm–3 sodium hydroxide until the reaction is complete. 6NaOH(aq) + xCl2(aq) → yNaCl(aq) + zNaClO3(aq) + 3H2O(l) (i) State the type of reaction that occurs. Explain your answer in terms of changes in oxidation numbers. [1] (ii) Determine the values of x, y and z. [1] (iii) Determine the concentration of Na+(aq), in mol dm–3, after the reaction. [1] …….…………..……………………………………………………………………………… …….…………..……………………………………………………………………………… …….…………..……………………………………………………………………………… …….…………..……………………………………………………………………………… …….…………..……………………………………………………………………………… …….…………..……………………………………………………………………………… …….…………..……………………………………………………………………………… …….…………..……………………………………………………………………………… …….…………..……………………………………………………………………………… …….…………..……………………………………………………………………………… …….…………..……………………………………………………………………………… …….…………..……………………………………………………………………………… …….…………..……………………………………………………………………………… …….…………..……………………………………………………………………………… …….…………..……………………………………………………………………………… …….…………..……………………………………………………………………………… …….…………..……………………………………………………………………………… …….…………..……………………………………………………………………………… …….…………..……………………………………………………………………………… …….…………..………………………………………………………………………………

3 © VJC 2024 9729/03/PRELIM/24 [Turn over (b) Compound A is an ether with molecular formula C 4H10O. When A is heated in a sealed container, an equilibrium mixture is produced. C4H10O(g) ⇌ C2H6(g) + CO(g) + CH4(g) H = –7.00 kJ mol–1 Table 1.1 shows the activation energy, Ea, for the reaction in the presence and absence of I2. Table 1.1 Ea (with I2) / kJ mol–1 Ea (without I2) / kJ mol–1 143 224 (i) State the role of I2 in this reaction and explain what effect it has on the value of Kc. [1] (ii) Complete the energy profile diagram for this reaction in Fig. 1.1. Include labels to show the enthalpy change and the activation energy data in Table 1.1. Fig. 1.1 [2] (iii) Suggest the effect of increasing the pressure on the position of equilibrium. [1] …….…………..……………………………………………………………………………… …….…………..……………………………………………………………………………… …….…………..……………………………………………………………………………… …….…………..……………………………………………………………………………… …….…………..……………………………………………………………………………… …….…………..……………………………………………………………………………… …….…………..……………………………………………………………………………… reaction progress energy / kJ mol–1 C4H10O(g)

4 © VJC 2024 9729/03/PRELIM/24 (c) Potassium chloride, KCl, and magnesium chloride, MgCl2, are both ionic solids. The following data can be used to answer some parts of this question. Table 1.2 standard enthalpy change value / kJ mol–1 standard enthalpy change of solution, Hosol, of KCl +15 lattice energy, Holatt, of KCl(s) –701 standard enthalpy change of hydration, Hohyd, of K+ –322 standard enthalpy change of hydration, Hohyd, of Cl– –364 standard enthalpy change of solution, Hosol, of MgCl2 –155 lattice energy, Holatt, of MgCl2(s) –2493 (i) Define the term entropy and state the effect on the entropy of the chemical system for the following reaction. Explain your answer. [2] K+(g) + Cl–(g) → KCl(s) (ii) Potassium chloride dissolves readily in water at 25°C. By considering the enthalpy change and Gibbs free energy change, state and explain the sign of the standard entropy change for the dissolution of potassium chloride. [1] (iii) Define enthalpy change of hydration. [1] (iv) Complete the energy cycle involving the enthalpy change of solution ( Hsol), lattice energy ( Hlatt) of magnesium chloride, and the enthalpy changes of hydration (Hhyd). Label the enthalpy changes in your diagram. State symbols should be used. [2] (v) Hence, calculate the enthalpy change of hydration of magnesium ions, Mg 2+. Show your working. [1] (vi) Explain why the lattice energy of MgC l2 is more exothermic than the lattice energy of KCl. [1] MgCl2(s)

5 © VJC 2024 9729/03/PRELIM/24 [Turn over (vii) Molten magnesium chloride is electrolysed for 15.0 minutes by a constant current. At the cathode, 4.75 ⨯ 1022 magnesium atoms are produced. Calculate the value of the current used. [2] …….…………..……………………………………………………………………………… …….…………..……………………………………………………………………………… …….…………..……………………………………………………………………………… …….…………..……………………………………………………………………………… …….…………..……………………………………………………………………………… …….…………..……………………………………………………………………………… …….…………..……………………………………………………………………………… …….…………..……………………………………………………………………………… …….…………..……………………………………………………………………………… …….…………..……………………………………………………………………………… …….…………..……………………………………………………………………………… …….…………..……………………………………………………………………………… …….…………..……………………………………………………………………………… …….…………..……………………………………………………………………………… …….…………..……………………………………………………………………………… …….…………..……………………………………………………………………………… …….…………..……………………………………………………………………………… …….…………..……………………………………………………………………………… …….…………..……………………………………………………………………………… …….…………..……………………………………………………………………………… …….…………..……………………………………………………………………………… …….…………..……………………………………………………………………………… …….…………..……………………………………………………………………………… …….…………..……………………………………………………………………………… …….…………..……………………………………………………………………………… …….…………..………………………………………………………………………………

6 © VJC 2024 9729/03/PRELIM/24 …….…………..……………………………………………………………………………… …….…………..……………………………………………………………………………… …….…………..……………………………………………………………………………… …….…………..……………………………………………………………………………… …….…………..……………………………………………………………………………… …….…………..……………………………………………………………………………… …….…………..……………………………………………………………………………… …….…………..……………………………………………………………………………… …….…………..………………………………………………………………………………