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 [4] [Total: 12 marks]   1160

6   [Turn Over 2. Isopentyl acetate is also widely referred to as banana oil for its odour. Isopentyl alcohol Ethanoic acid Isopentyl acetate (a) Banana oil can be synthesized through a simple esterification method. The laboratory synthesis of banana oil is carried out as follows. Step 1 15 cm 3 of isopentyl alcohol and 20 cm 3 of ethanoic acid are added to a 100 cm3 round bottomed flask. Step 2 4 cm 3 of 1.5 mol dm -3 sulfuric acid is added dropwise to the flask with constant swirling. The mixture was heated under reflux for 1 hour. During reflux, the top of the reflux condenser was left open to the atmosphere. The mixture was then allowed to cool to room temperature. Step 3 The cooled mixture was poured into a separating funnel and 55 cm 3 of cold water was added. The separating funnel was shaken several times and the mixture was allowed to stand before discarding the aqueous layer. Step 4 Solid Na2CO3 was added to the organic layer and the mixture was swirled with the top of the separating funnel opened. Pure isopentyl acetate was finally obtained through distillation (i) Explain why isopentyl acetate can be separated from water using a separating funnel. 1161

7   [Turn Over 2. (a) (ii) Isopentyl acetate has a higher boiling point than isopentyl alcohol. Explain. (iii) With reference to Step 2, suggest why the reflux condenser was left open during the refluxing process to increase the yield of the ester. (iv) Suggest why Na2CO3 was added to the organic layer. (v) Why was it necessary to ensure that the top of the separating funnel was opened while swirling in Step 4? [9] 1162

8   [Turn Over 2. (b) The following ester can be formed using isopentyl alcohol as the only organic starting material.   The synthesis of the ester is as shown in the reaction sequence below. OH QR T U V S V O O + S NaCl, concentrated H2SO4Step I Step II Thionyl chloride Step III H2O/H + heat Step IV isopentyl alcohol 2. (b) (i) State the reagents and conditions needed for Step I Step II Step III Step IV 1163

9   [Turn Over 2. (b) (ii) Draw the structural formulae of Q, R, S, T, U and V. Q R S T U V (b) (iii) Compound W is an isomer of the isopentyl alcohol. W has a chiral centre and gives no yellow precipitate with alkaline aqueous iodine. Suggest the structural formula of W and indicate the chiral centre on W with an asterisk (*). [7] 1164

10   [Turn Over 2. (c) Isopentyl alcohol is one of the main ingredients for Kovac’s reagent. Kovac’s reagent is used to determine the ability of an organism to split the bicylic structure from the amino acid tryptophan.                                                                Tryptophan (i) Explain why tryptophan is a crystalline solid at room temperature. (ii) With the aid of a diagram, explain why tryptophan is soluble in water. 1165