2024 MI PU3 H2 Chem EOY P2 student (final)

Class Adm No Candidate Name: This question paper consists of 22 printed pages and 2 blank pages. 2024 Preliminary Examination Pre-University 3 H2 CHEMISTRY 9729/02 Paper 2 Structured Questions 10 September 2024 2 hours Candidates answer on the Question paper. Additional materials: Data Booklet READ THESE INSTRUCTIONS FIRST Do not turn over this question paper until you are told to do so Write your name, class and admission number 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. The use of an approved scientific calculator is expected, where appropriate. A Data Booklet is provided. 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. Question 1 2 3 4 5 Total Marks 15 17 15 13 15 75

2 1 (a) Table salt can be fortified with iodine to supplement the diet. Common iodine chemicals used to fortify salt are sodium or potassium iodate(V). Aqueous acidified iodate(V) ions, IO3–, react with iodide ions, as shown. IO3– + 6H+ + 5I– → 3I2 + 3H2O The initial rate of this reaction is investigated. Table 1.1 shows the results obtained. Table 1.1 Expt [IO3–] / mol dm–3 [H+] / mol dm–3 [I–] / mol dm–3 initial rate / mol dm–3 min–1 1 0.0400 0.0150 0.0250 4.20 × 10–2 2 0.0200 0.0150 0.0250 2.10 × 10–2 3 0.0200 0.0150 0.0500 8.40 × 10–2 It is known that the reaction is second order with respect to hydrogen ions. (i) Determine the order of the reaction with respect to IO3– and I– ions. Explain your reasoning. …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… ………………………………………………………………………………………………… [2] (ii) Hence, write the rate equation for the reaction. ………………………………………………………………………………………………… [1]

3 [Turn over The reaction is then repeated at the same temperature but at different pH. Table 1.2 lists the concentrations of IO3–, I– and the pH at which the experiments are carried out. Table 1.2 Expt [IO3–] / mol dm–3 [I–] / mol dm–3 pH [H+] / mol dm–3 4 0.0400 0.0250 1.0 5 0.0400 0.0250 2.0 (iii) Complete Table 1.2 with the concentrations of H+ ions in experiments 4 and 5. [1] (iv) Calculate the value of rate at pH 1.0 rate at pH 2.0. rate at pH 1.0 rate at pH 2.0 = …………………….……..[1]

4 (b) In an aqueous solution, iron(III) ions react with iodide ions as shown. 2Fe3+ + 2I– → 2Fe2+ + I2 Th