SAJC H2 Chem 2013 Prelim P2 QP

1   [Turn Over Name: Class: ST ANDREW’S JUNIOR COLLEGE JC2 Preliminary Examinations Chemistry Higher 2 9647 / 02 Paper 2 02 September 2013 2 hours Candidates answer in the spaces provided on the question paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write in dark blue or black pen. 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. You are reminded of the need for good English and clear presentation in your answers. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use: Question Marks Question Marks 1 3 2 4 TOTAL 72 This document consists of 18 printed pages including this page.    1156

2   [Turn Over 1. Planning (P)   The solubility of solid lead iodate ( V), Pb(IO3)2, in water is low. When a sample of this salt is mixed with water, a small amount dissolves and an equilibrium between the solid salt and its aqueous ions is established. Pb(IO3)2(s) Pb2+(aq) + 2IO3 -(aq) Ksp = [Pb2+][IO3 -]2 mol3 dm-9 The concentration of iodate (V) ions present in the saturated solution is described as follows:  Iodine is liberated when excess potassium iodide, K I, is added to an acidified solution containing iodate (V) ions. IO3 -(aq) + 5I-(aq) + 6H+(aq) → 3I2(aq) + 3H2O(l)  The liberated iodine can then be reacted with a standard solution of sodium thiosulfate. 2S2O3 2-(aq) + I2(aq) → 2I-(aq) + S4O6 2-(aq) You are to design a titrimetric experiment to determine the solubility product of lead iodate (V).                           1157

3   [Turn Over 1. (a) You are provided the following:  Solid lead iodate (V)  Solid potassium iodide  1 mol dm -3 hydrochloric acid  0.0200 mol dm -3 sodium thiosulfate  Starch indicator  Distilled water  And any other standard laboratory apparatus. Describe, step-by-step (including quantities of reagents used), the procedure involved in your experiment. [4] (b) Suggest one possible error that may occur during the experiment. [1] 1158

4   [Turn Over 1. (c) Calculate the solubility product of lead iodate ( V) given that 25.0 cm 3 of the saturated solution requires v cm3 of Na2S2O3. [3] 1159

5   [Turn Over 1. (d) A solution contains a mixture of chloride ions and iodide ions. You are provided with the reagents HCl (aq), NH3 (aq), AgNO3 (aq), HNO3 (aq) and distilled water together with test tubes, a filter funnel and filter papers. Devise a sequence of steps by which, using only the above materials, the two anions could be separately obtained as precipitates. Test Expected Observations Deduction