SRJC H1 CHEM P2

SRJC 2009 8872/02/PRELIM/2009 [Turn Over SERANGOON JUNIOR COLLEGE General Certificate of Education Advanced Level Higher 1 CANDIDATE NAME C L A S S CHEMISTRY 8872/02 Preliminary Examination 26 Aug 2009 Paper 2 2 hr Additional Materials: Data Booklet Answer Paper READ THESE INSTRUCTIONS FIRST Write your name and class 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 work. SECTION A : Answer all questions in the space provided. SECTION B: Answer any two questions on separate answer paper. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use MCQ P1 /30 A1 /10 A2 /10 A3 /10 A4 /10 B5 /20 B6 /20 B7 /20 Total /110 Percentage Grade This document consists of 16 printed pages and 0 blank page

2 SRJC 2009 8872/02/PRELIM/2009 [Turn Over For Examiner’s Use 1 The industrial preparation of the polymer, poly(tetrafl uoroethene), is based on the synthesis of its monom er, tetrafluoroethene (C 2F4). Tetrafluoroethene is produced from the thermal cracking of chlorodifluoromethane (CHC lF2), as shown by the following equation: 2CHClF2(g)  C2F4(g) + 2HCl(g) (a) Use relevant data from the Data Booklet to calculate the enthalpy change of the reaction. State any assumptions that you have made. [3] (b) By using your answer to (a) and the following information, H f (CHClF2(g)) = –485 kJ mol –1 Hf (HCl(g)) = –92 kJ mol –1 calculate the enthalpy change of formation of C2F4(g). [2]

3 SRJC 2009 8872/02/PRELIM/2009 ly. (c) (i) Explain the following phenomenon: Chlorine can react w ith oxygen to form C lO─, C lO2 ─, C lO3 ─ and C l2O7 but fluorine can react with oxygen to form OF2 on (ii) Predict, with reasoning, the shape of OF 2. (iii) Predict, with reasoning, the solubility of OF2 in CCl4. [5] [Total: 10] For Examiner’s Use [Turn Over

4 SRJC 2009 8872/02/PRELIM/2009 For Examiner’s Use 2 (a) 2-bromopropane can react with sodium hy droxide in two different ways depending on conditions to give two different products A and B. CH3CHBrCH3 C3H6 C3H8O C D A B I II NaCN H+/heat (i) Draw the ‘dot-and-cross’ diagram of NaOH. (ii) Suggest and explain the polarity of 2-bromopropane. (iii) Describe the condition(s) necessary for each one of the reactions I and II. In each case, state the type of reaction undergone. [Turn Over conc H2SO4, heat E C6H12O 2

5 SRJC 2009 8872/02/PRELIM/2009 (iv) Using the above reaction scheme, dr aw the structural formulae of compounds C, D and E. [7] (b) Suggest a chemical test to distinguis h 2-chloropropane, 2-bromopropane and 2-iodopropane, stating clearly the observations made. [3] [Total: 10] For Examiner’s Use [Turn Over

6 SRJC 2009 8872/02/PRELIM/2009 [Turn Over 3(a) Propanol can be converted to propanoic acid under appropriate condition. Suggest the type(s) of hybridisation of all the carbon atoms in propanoic acid. HC 1 H H C2 H H C3 O OH C1: _______ C2: _______ C3: _______ [1] (b) Propyl propanoate is synthesised indus trially mainly via the classic Fischer esterification reaction of propanol and propanoic acid which is exothermic in nature. This mixture will reach dynamic equilibrium and the ester will be produced at a yield of 65%. (i) With the aid of an appropriate rate-time graph, explain what is meant by dynamic equilibrium. For Examiner’s Use

7 SRJC 2009 8872/02/PRELIM/2009 [Turn Over (ii) Given that the equilibrium mixture at 298 K contains the following: Propanol 0.33 mol Propanoic acid 0.33 mol Propyl Propanoate 0.66 mol Water 0.66 mol Calculate the value of Kc at 298 K for the reaction. (iii) Predict, with reasoning, the effect on the value of Kc (if any) when more propanol is added to the equilibrium mixture. For Examiner’s Use

8 SRJC 2009 8872/02/PRELIM/2009 [Turn Over For Examiner’s Use (iv) Predict, with reasoning, the composition of the equilibrium mixture when the system in (b)(ii) is subjected to an increase in temperature? [5] (c) The esters responsible for the arom a of pineapple and apple are illustrated below: C H H HC H H C H H C O OC H H C H H H C H H HC H H C H H C O OC H H H Pineapple aroma Apple aroma Describe appropriate chemical test(s) to distinguish the two esters. In your description, state clearly the reagents and conditions used, and the observations made in each case. [2]

9 SRJC 2009 8872/02/PRELIM/2009 [Turn Over For Examiner’s (d) O O Wine lactone An ester with a sweet coconut scent was recently found to be responsible for the smell of white wine. It is identical to lactone found in wine and it can also be found in orange juice and black pepper. Draw the structural formulae of the organic product(s) formed when wine lactone reacts with: (i) Cl2 in CCl4, in the absence of catalyst and light . (ii) Cold alkaline KMnO4 (iii) Hot acidified KMnO4 [2] [Total: 10] Use

10 SRJC 2009 8872/02/PRELIM/2009 [Turn Over 4 (a) Many new cars have air bags which rapidly inflate during an accident to protect the front passengers. The air ba g contains sodium azide (NaN 3), silicon dioxide and potassium nitrate. To determine the amount of so dium azide in an impure sample, the azide present is first reacted with excess iodine: 2 N 3 - + I2 → 3N2 + 2I- The amount of unreacted iodine is t hen titrated with standard sodium thiosulphate solution: I 2 + 2S2O3 2- → 2I- + S4O6 2- 0.120 g of an impure sample of sodium azide was dissolved in water. The mixture was reac ted with 25.0 cm 3 of 0.050 mol dm -3 of aqueous iodine. The excess iodine was found to require 23.10 cm 3 of 0.040 mol dm -3 aqueous sodium thiosulphate for reaction. Calculate the percentage purity of sodium azide in the sample. [3] (b) A compound F of sulphur has the formula SO xCl2. 23.8 g of compound F is made to react with water (in excess) and the chloride ion is completely precipitated as 57.4 g of silver chloride. Calculate the relative molecular mass of F and determine the value of x. [2] For Examiner’s Use