VJC_H2_CHEM_P2_QN Prelim

 VJC 2014 9647/02/PRELIM/14 [Turn over CANDIDATE NAME CT GROUP VICTORIA JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATIONS Higher 2 ……………………………………………….………….. …………………………….. CHEMISTRY 9647/02 Paper 2 Structured Candidates answer on the Question Paper. 16 September 2014 2 hours Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name and CT group 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 all questions. A Data Booklet is provided. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use 1 2 3 4 5 Total This document consists of 17 printed pages and 1 blank page.

 VJC 2014 9647/02/PRELIM/14 2 Answer all the questions in the space provided. 1 Planning (P) Aqueous chlorine, Cl2, displaces iodine, I2, from aqueous potassium iodide. If a solution of chlorine is mixed with an excess of aqueous potassium iodide, iodine is displaced in a 1:1 molar ratio with chlorine. The concentration of chlorine in the original solution can therefore be calculated from the concentration of the displaced iodine. I2(aq) + 2Na2S2O3(aq)  2NaI(aq) + Na2S4O6(aq) (a) Write an equation for the reaction between aqueous chl orine, and an excess of aqueous potassium iodide. ………………………………………………………………………………………………….. [1] (b) You are to plan an experiment to determine as accura tely as possible the concentration of a saturated aqueous solution of chlorine by titration. The approximate solubility of chlorine is 5 g dm–3 at 25 oC. You are provided with the following materials:  saturated aqueous chlorine;  solid sodium thiosulfate Na2S2O3.5H2O;  concentrated aqueous potassium iodide. This will be used in excess.  the apparatus and chemicals normally found in a school or college laboratory. Your plan should include details of:  a calculation of the approximate concentration of sat urated aqueous chlorine in mol dm–3 at 25 oC; [Ar: Cl, 35.5]  a detailed description of the method for preparing a solution of aqueous sodium thiosulfate that can be used in the titration. In a titration, it is usual for the titre volume to be approximate ly equal to that of the volume of solution pipetted. Calculate the mass of sodium thiosulfate, Na 2S2O3.5H2O, which will produce a solution suitable for use in this titration. The relevant calculations and reasoning must be shown in full; [Ar: H, 1.0; O, 16.0; Na, 23.0; S, 32.1]  a step–by–step description o