2021 SAJC Prelim P3 Question

ST ANDREW’S JUNIOR COLLEGE JC2 Preliminary Examinations Higher 2 CANDIDATE NAME CLASS 2 0 S CHEMISTRY Paper 3 Free Response Candidate answer on the Question Paper. Additional Materials: Data Booklet 9729/03 15 September 2021 2 hours READ THESE INSTRUCTIONS FIRST Write your name and class on all the work you hand in. Write in dark blue or black pen. You may use a 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 the questions. Section B Answer one question. 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. This document consists of 39 printed pages. For Examiner’s Use Q1 24 Q2 17 Q3 19 Q4/5 20 Total 80

2 Section A Answer all the questions in this section. 1 (a) Iodates are compounds that contain the IO3 anion. (i) Draw the dot-and-cross diagram of IO3. [1] (ii) Use your knowledge of VSEPR theory to name the shape of and state the bond angle for IO3. Explain your reasoning. [3] (iii) Explain why BrO3 has a larger bond angle than IO3. [1] ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. …………………………………………………………………………………………………………………….

3 ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. (b) The decomposition of hydrogen peroxide, H2O2, can be catalysed by acidified IO3. 2H2O2 → 2 H2O + O2 With the aid of relevant data from the Data Booklet and the information below, show that IO3 is a suitable catalyst for the decomposition of H2O2 under standard conditions. IO3 + 6H+ + 5e⇌  1 2I2 + 3H2O Eo = +1.19 V In your answer, give relevant equations for the reactions that occur. [3] ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. …………………………………………………………………………………………………………………….

4 (c) The kinetics of the catalytic decomposition of H2O2 by IO3 can be investigated. 2H2O2(aq)   2H2O(l) + O2(g)  The concentration of H 2O2 remaining can be determined by titrating with standard acidified KMnO4. Briefly outline how you would determine the rate of the catalysed decomposition of H2O2 using acidified KMnO4. [3] ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. …………………………………………………………………………………………………………………….

5 (d) (i) A student collects some data for the reaction of H2O2 with acidified IO3, as shown in Table 1.2. Experiment [H2O2]/ mol dm3 [IO3]/ mol dm3 [H+]/ mol dm3 Initial rate/ mol dm3 s1 1 0.050 0.070 0.025 1.47 x 105 2 0.100 0.070 0.050 2.94 x 105 3 0.100 0.140 0.025 5.88 x 105 4 0.150 0.140 0.025 8.82 x 105 Table 1.2 Determine the order of reaction with respect to [H2O2], [IO3] and [H+]. Show your reasoning. [3] (ii) Hence, write the rate equation for the reaction, and calculate a value for the rate constant using experiment 1. Include units in your answer. [2] ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. …………………………………………………………………………………………………………………….

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7 (e) (i) NH4IO3 is an unstable compound that readily decomposes when warmed as shown: NH4IO3(s) → 1 2N2(g) + 1 2O2(g) + 1 2I2(s) + 2H2O(l) ΔHr o Using the information given below in Table 1.1, calculate the standard enthalpy change ΔHr o for the above reaction. [1] Substance Standard enthalpy change of formation / kJ mol1 NH4IO3 (s)  417.4 H2O (l)  286 Table 1.1 (ii) Explain how the value and sign of ΔGr o would compare to the value and sign of ΔHo for the decomposition of NH4IO3. [2] ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. ……………………………………………………………………………………………………………………. …………………………………………………