TJC H2 Chem 2013 Prelim P3 QP

9647/03/TJC Prelim 2013 [Turn Over 1 CHEMISTRY (H2) 9647/03 Paper 3 Free Response Friday 20th September 2013 2 hours Candidates answer on separate paper. Additional materials: Answer paper Data Booklet READ THESE INSTRUCTIONS FIRST Write your name, Civics Group and Index number in the spaces provided on the cover page and on all the work you hand in. Write in dark blue or black pen on both sides of the paper. You may use a soft pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. Answer any four questions. A Data Booklet is provided. You are reminded of the need for good English and clear presentation in your answers. The number of marks is given in bracke ts [ ] at the end of each question or part question. At the end of the examination, fasten all your work securely together. This question paper consists of 11 printed pages. 1370

9647/03/TJC Prelim 2013 [Turn Over 2 Answer any four questions. 1 (a) Describe and explain the trend observed in the ease of thermal decomposition of the nitrates of the Group II elements magnesium to barium. Write an equation for any reaction that occurs. [3] (b) An alloy of aluminium and magnesium is used in boat-building. A 1.75 g sample of the alloy was dissolved in the minimum volume of 4 mol dm -3 hydrochloric acid and the solution was then made alkaline by the addition of aqueous sodium hydroxide until no further reaction occurred. The resultant mixture was filtered and the residue, A, rinsed with distilled water, all washings being added to the filtrate, B. After drying, 0.18 g of A was obtained. Carbon dioxide was passed into B and a white solid, C, which contained aluminium, was collected. Heating C to constant mass gave a residue of mass 3.16 g. (i) Write ionic equations for the reactions that occur when sodium hydroxide is added to the solution as described above. (ii) Explain, using relevant equation(s), the formation of C when carbon dioxide is passed into B. (iii) Determine the percentage composition by mass of the alloy. [7] (c) Ozone mixed with oxygen is fairly stable but rapidly decomposes in the presence of a silver catalyst as shown in the equation below. 2O 3 3O 2 Silver was added to a 800 cm 3 sample of a mixture of oxygen and ozone. Below is a table showing the increase in volume of the mixture and volume of ozone at the respective time intervals. Time/s 0 200 440 900 1500 1800 Volume of mixture/cm3 800 805 810 815 818 819 Volume of ozone/cm 3 38 28 18 8 0 (i) Given that the bond angle of ozone is 116.8 0, draw the dot and cross diagram of the ozone molecule. (ii) Calculate the volume of ozone in the mixture at t = 1500 s. (iii) By mean