2024 Prelims VJC H2 Chem P3 (Ans)

© 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. For Examiner’s Use Section A 1 / 23 2 / 19 3 / 18 Section B 4 / 20 OR 5 / 20 Total / 80 This document consists of 30 printed pages and 0 blank page.

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] • Disproportionation reaction as Cl2 is reduced and oxidised simultaneously. Cl2 is reduced to Cl–, oxidation number of Cl decreases from 0 to –1. Cl2 is oxidised to ClO3–, oxidation number of Cl increases from 0 to +5. (ii) Determine the values of x, y and z. [1] • x = 3 y = 5 z = 1 (iii) Determine the concentration of Na+(aq), in mol dm–3, after the reaction. [1] • Concentration of Na+(aq) after the reaction = 4.0 mol dm–3 (Na+ does not participate in the reaction thus its concentration remains the same. ) (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] • I2 is a catalyst in the reaction and it has no ef