DHS Prelim P2_Qn

This question paper consists of 21 printed pages and 1 blank page. © DHS 2017 [Turn over Name: Index Number: Class: DUNMAN HIGH SCHOOL Preliminary Examination 2017 Year 6 H2 CHEMISTRY 9729/02 Paper 2 (Structured) 11 Sep 2017 2 hours Additional Materials: Data Booklet INSTRUCTIONS TO CANDIDATES 1 Write your name, index number and class on this cover page. 2 Write in dark blue or black pen. 3 You may use an HB pencil for any diagrams or graphs. 4 Do not use staples, paper clips, glue or correction fluid. 5 Answer all questions in the spaces provided on the Question Paper. The number of marks is given in brackets [ ] at the end of each question or part question. You are advised to show all workings in calculations. You are reminded of the need for good English and clear presentation in your answers. For Examiner’s Use Question No. Section A Marks 1 13 2 13 3 20 4 14 5 15 Total 75

2 © DHS 2017 9729/02 [Turn over Answer all questions in the spaces provided. 1 The chalcogens, or the oxygen family, are the elements in group 16 of the Periodic Table. These elements are common in both organic and inorganic compounds. (a) The graph below shows the trend in the first ionisation energies of oxygen, sulfur and selenium. (i) Explain the trend in the first ionisation energies of oxygen, sulfur and selenium. [2] (ii) On the same grid above, sketch the trend in the first ionisation energies of nitrogen, phosphorus and arsenic. [1] 1st Ionisation Energy / kJ mol-1 Oxygen Sulfur Selenium

3 © DHS 2017 9729/02 [Turn over (b) A common chalcogen -containing reagent used in both organic and inorganic synthesis is hydrogen peroxide, H 2O2. Hydrogen peroxide readily decomposes at room temperature. However, this process is slow. Iodide ions, I–, catalyse this decomposition, as shown below: Step I: H2O2 + I – → H2O + IO– (slow) Step II: H2O2 + IO– → H2O + O2 + I – The overall equation for the decomposition of hydrogen peroxide is shown below: 2H2O2 → 2H2O + O2 The enthalpy and entropy changes for the reaction above are shown in the table below: Enthalpy change / kJ mol–1 –98 Entropy change / J K–1 mol–1 +71 (i) Using the data above, complete the diagram below to show the energy profile diagram for the decomposition of hydrogen peroxide in the presence of iodide ions. [2] Energy Progress of Reaction

4 © DHS 2017 9729/02 [Turn over (ii) An unknown amount of hydrogen peroxide was allowed to decompose in a 5 dm 3 closed vessel at 120 ºC. When all the hydrogen peroxide was decomposed, a pressure of 177 kPa was measured in the vessel. Determine the amount of hydrogen peroxide that decomposed in the vessel. (Assume that H 2O and O 2 are ideal gases under