MJC H2 CHEM P3

No part of this paper should be repro duced for commercial use without the prior written permission of Meridian Junior College. Class Reg Number Candidate Name _____________________________ Meridian Junior College 2009 JC 2 Preliminary Examination H2 Chemistry 9746 14 September 2009 2 hours Paper 3 Free Response Additional Materials Data Booklet Writing paper INSTRUCTION TO CANDIDATES Write your name, class and regi ster number in the spaces pr ovided at the top of this page. Answer any 4 out of 5 questions. Begin each question on a fresh page of writing paper. Fasten the writing pa pers behind the given Cover Page for Questions 1 & 2 and Cover Page for Questions 3, 4 & 5 respectively. Hand in Questions 1 & 2 and 3, 4 & 5 separately. You are advised to spend about 30 min per question only. INFORMATION FOR CANDIDATES The number of marks is given in brackets [ ] at the end of each question or part question. You are reminded of the need for good English and clear presentation in your answers. This question paper consists of 15 printed pages. ©chemistry department@ meridian jc 1

Answer any 4 out of 5 questions in this paper. Begin each question on a fresh page of writing paper. 1 Sulphuryl chloride, SO 2Cl2, is often used as a source of C l2 for various organic reactions. Sulphuryl chloride is also a highly reactive gaseous compound. When heated, it decomposes endothermically as follows: SO2Cl2(g) SO 2(g) + Cl2(g) A 7:2 mole ratio of SO 2Cl2 and C l2 is placed in an evacuated vessel at 375 K and 6 atm. After 10 minutes, the mixtur e reached equilibrium and the partial pressure of SO2 is found to be 0.625 atm. (a) Write an expression for the equilibrium constant, Kp, and calculate its value. [3] (b) Suggest, with a reason, how the position of equilibrium might alter when the temperature is increased at the 20th minute. Hence, draw labelled sketches on the same graph to show how the number of moles of sulphuryl chloride and sulphur dioxide gas would change from the start of the decomposition till the new equilibrium is reached. [3] (c) Sulphuryl chloride is commonly c onfused with thionyl chloride, SOC l2. Equimolar amounts of SOC l2 and SO2Cl2 are added separately to wa ter to yield an acidic solution with the evolution of some white fumes. Suggest, with the aid of suitable equat ions, which compound would yield a solution with a lower pH value. [2] (d) Sulphuryl chloride is a very good source of C l2. Propene undergoes free radical substitution with sulphuryl chloride to give 3-chloroprop-1-ene. (i) Name the type of hybridisation that is present in the carbon atom, C x, of propene as shown above. Sketch the shape of the hybrid orbitals of C x. [2] CH2=CXHCH3 +S O 2Cl2 475 K, u Trace of hyd v light rogen peroxide CH2=CHCH2Cl +S O 2 +H Cl ©chemistry department@ meridian jc 2

(ii) The initiation stage of this mechanism is unique as it consists of two steps: Step 1 Homolytic fission of hydrogen peroxide results in the formation of two hydroxyl radicals. Step 2 The hydroxyl radical will then combine with one of the C l atoms of the sulphuryl chloride to form two stable compounds and a chlorine radical. 1 Define the term homolytic fission. 2 Using the information given, deduce the equation for Step 2 of the initiation stage. [2] (iii) Compound A can be synthesised from 3-chloroprop-1-ene in a 3-step synthesis. Propose a suitable reacti on scheme, suggesting suitable reagents, conditions and intermediate products formed, in the synthesis of compound A. HOOCCH2CH(OH)CH2COOH Compound A [3] (iv) The reaction of 3-chloroprop-1-ene and bromine in trichloromethane in the dark produces an equimolar mixture of compounds B and C. 1 Outline the mechanism that occurs for the formation of either B or C. 2 Hence, account for the formation of the equimolar mixture of B and C. Include the structural formula of isomers B and C in your answer. [5] [Total: 20] ©chemistry department@ meridian jc 3

2 Chlorine was identified as an element in 1810 by Sir Humphry Davy. Bromine was discovered by Antoine Balard in 1825 when he found bromide salts in ashes of sea weeds. Iodine was accidently discovered by Bernard Courtois in 1811 while he was isolating sodium carbonat e from sea weed. The reactions of halogen-containing compounds span all fields of chemistry. (a) On an industrial site, an unfortunate accident involving a chemical leak occurred when contractors accidentally poured cold bleach, NaC lO, into a drum filled with dilute hydrochloric acid. The reaction between the two chemicals created pressure in the drum, causing the lid to rise, resulting in the release of a choking gas. Civil Defence officers were called to the scene to render assistance. (i) Name the gas released that created t he pressure in the drum and write a balanced equation for its production. (ii) The Civil Defence officers flushed the plant room with water to dilute the choking gas and bring its concentration down to safety levels. Using bonding and structure, explain why this action taken by the Civil Defence officers was not very successful. (iii) The gas identified in (a)(i) cannot be produced via the reaction between the corresponding halide and excess concentrated sulphuric acid. However, another halogen can be produc ed via a similar reaction. Explain this observation, including balanced equations in your answer. (iv) At the scene of the accident, ther e were three other sealed drums containing gaseous hydrogen astatine, hydrogen bromide and hydrogen iodide respectively. Using relevant values from the Data Booklet , explain the relative thermal stability of the three hydrogen halides. [9] (b) Aqueous chloric (III) acid, HC lO 2, is unstable and decom poses in a variety of ways, two of which are as follows : Reaction I : 3HC lO 2 2C lO3 - + Cl- + 3H+ Reaction II : 5HClO2 4C lO2 + Cl- + H+ + 2H2O ©chemistry department@ meridian jc 4

(i) Use the following data to calculate Eθ cell for each of the reactions above under acidic conditions. Hence, deduce how HC lO2 might decompose in acidic solution. Acidic solution couple Eθ / V HClO2 / Cl- + 1.57 ClO3 - / HClO2 + 1.21 ClO2 / HClO2 + 1.27 (ii) Similar decomposition reactions can al so take place in alkaline medium where chlorate (III) exists as ClO2 - instead. Alkaline solution couple Eθ / V ClO2 - / Cl- + 0.78 ClO3 - / ClO2 - + 0.33 ClO2 / ClO2 - + 1.16 Based on the above information, s uggest which ion is the weakest reducing agent in alkaline medium. [4] (c) Unlike chlorates ( VII) and bromates ( VII), which contain only the XO4 - ion (X = Cl or Br), iodates (VII) can contain the ions IO5 3- and IO6 5- as well as IO4 - . (i) Suggest a reason for this difference. (ii) Draw the dot and cross diagram for IO6 5-. (iii) Barium iodate (VII), Ba 5(IO6)2, can be obtained by h eating crystals of barium iodate (V), Ba(IO3)2. Iodine and oxygen are also produced. 1 Construct a balanced equation for thi