DHS_H1_CHEM_P2_QP

This question paper consists of 15 printed pages and 1 blank page. © DHS 2015 [Turn over Name: Index Number: Class: DUNMAN HIGH SCHOOL Preliminary Examination 2015 Year 6 H1 CHEMISTRY 8872/02 Paper 2 Section A (Structured Questions) 16 September 2015 Paper 2 Section B (Free–Response Questions) 2 hours Additional Materials: Data Booklet, Writing Paper INSTRUCTIONS TO CANDIDATES 1 Answer all questions in Section A, and any two questions in Section B. 2 Write your name and class on this cover page. Section A 3 Write your answers in the spaces provided on this question paper. 4 You are advised to spend a maximum of 1 hour on Section A. Section B 5 Write your name and class on the Cover Sheet provided. 6 Write your answers on the separate writing papers provided. 7 Answer any two questions. 8 Start each question on a fresh sheet of paper . Marks will be deducted if you fail to do so. 9 At the end of the examination, fasten all your work securely together with the Cover Sheet on top. 10 You are advised to spend a maximum of 1 hour on Section B. INFORMATION FOR CANDIDATES 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 9 2 8 3 8 4 7 5 8 Total 40

2 © DHS 2015 8872/02 [Turn over Section A Answer all questions in the spaces provided. 1 (a) Calcium ethanedioate, CaC 2O4, is a white needle–like crystalline solid. When a pure sample of anhydrous CaC 2O4 was heated strongly at 400 C until no further change in mass is observed, a white solid B and 0.028 g of carbon monoxide gas were obtained as the only products. (i) Given that 1 mole of CaC 2O4 decomposes to give 1 mole of CO(g), write a balanced equation for the thermal decomposition of CaC2O4 and identify solid B. equation : solid B : (ii) Hence, determine the mass of B obtained in the reaction. [3] (b) The formula of potassium hydrogen ethanedioate can be written as K xHy(C2O4)z. In an experiment to determine the values of x, y and z, 4.50 g of this compound was dissolved in water and the solution made up to 1 dm3. 20.0 cm 3 of the solution was pipetted into a conical flask and then titrated with 0.0200 mol dm ––3 KMnO4 in an acidic medium. It was found that 16.50 cm 3 of KMnO 4(aq) was needed for the complete reaction with ethanedioate ions, C 2O4 2–, present. During the titration, effervescence of carbon dioxide is produced. Given the reaction of manganate(VII) in acidic medium as: MnO 4 – + 8H+ + 5e– Mn2+ +4H2O (i) Write a balanced half–equation for the reaction of C2O4 2 during titration. half– equation :

3 © DHS 2015 8872/02 [Turn over (ii) Calculate the mass of C2O4 2– presen