MI Prelim 9647 P3

Class Adm No Candidate Name: This question paper consists of 11 printed pages and 1 blank page. 2017 Preliminary Examination II Pre-University 3 H2 CHEMISTRY 9647/03 Paper 3 Free Response 15th Sept 2017 2 hours Candidates answer on separate paper. Additional materials: Answer Paper Data Booklet READ THESE INSTRUCTIONS FIRST Do not turn over this question paper until you are told to do so Write your name, class and admission number on all the work you hand in. Write in dark blue or black pen. You may use an HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. Answer any four questions. A Data Booklet is provided. The use of an approved scientific calculator is expected, where appropriate. You are reminded of the need for good English and clear presentation in your answers. 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. Question 1 2 3 4 5 Total Marks 20 20 20 20 20 80

2 1 (a) Graphite is a naturally-occurring form of crystalline carbon and is found in metamorphic and igneous rocks. Graphite is extremely soft and cleaves with very light pressure yet it is extremely resistant to heat and nearly inert in contact with almost any other material. These extreme properties give it a wide range of uses in metallurgy and manufacturing. (i) With reference to the structure, account for the following properties of graphite.  Soft  Heat resistant and inert [3] (ii) The following table shows some thermochemistry data. Reaction H / kJ mol-1 Standard enthalpy change of atomisation of carbon +715 Enthalpy change of 4H(g) + O(g) + C(g) → CH3OH(l) -2069 With the use of relevant data from the Data Booklet and the above information, calculate the enthalpy change of formation of methanol. [3] (b) A butane burner is used to heat the air in a hot air balloon. The hot air balloon has a volume of 2.1 m3 and its volume does not change when the enclosed air is heated. (i) Using the ideal gas equation, calculate the amount of gas molecules the bal loon contains at temperature 800 K and a pressure of 1.0 x106 Pa. [1] (ii) Hence calculate the mass of air it contains, assuming an average relative molecular mass of 29. [1] (iii) The standard enthalpy change of combustion of butane is -2877.5 kJ mol-1. It requires 1.0 J of energy to raise the temperature of 1.0 g of air by 1.0 K. Using your answer in (b)(ii), calculate the mass of butane that needs to be burnt to raise the temperature of the air in the balloon by 20 K. Assume that the hot air balloon is a closed system. [2] (iv) The actual mass of butane that needs to be burnt to raise the temperature of the air in the balloon by 20 K was found to be 3.81 g. Suggest why this differs from your answer in (b)(iii). [1]

3 [Turn over (c) Paracetamol and aspirin are effective at pain and fever relief due to their ability to dissolve quickly in the blood stream and are soluble in fatty compounds found in cell membrane. Paracetamol Aspirin (i) Account for these properties based on the structure and bonding of aspirin. [2] (ii) One of the pain relievers cause more stomach irritation than the other. With reference to the functional groups present, s uggest and explain the pain reliever that you will recommend to someone who suffers from gastric bleeding. [2] (iii) Write the structural formula of the organic product(s) formed when paracetamol tablet is refluxed with sodium hydroxide. [2] (iv) Extensive research has been made to improve the effectiveness of the pain-relievers. Two proposals were made to modify aspirin. Drug A Drug B Given that the melting points of drugs A and B are 179 °C and 154 °C respectively, account for the melting point in terms of structure and bonding. [2] (v) State the relative solubility of drugs A and B in water. [1] [Total: 20]

4 2 Halogens a nd their compounds can be toxic but some are essential for the human body's functioning and are used in daily products. The oxidising power of chlorine allows it to act as a good disinfectant. (a) With the use of Data Booklet, explain why FeCl3 exists but FeI3 does not. [4] (b) Grignard reaction is an important reaction which helps in lengthening the carbon chain. A Grignard reagent has a general formula of R-MgX where R is an alkyl or aryl group and is formed via the reaction of an alkyl or alkyl halide with magnesium powder. R−X + Mg → R−MgX Grignard reagent Carbonyl compounds react with Grignard reagent to increase the carbon chain. (i) In the formation of Grignard reagent, it is important to carry out the reaction in a dry environment. Suggest a reason. [1] (ii) It was observed that the reaction to form the Grignard reagent is very slow at the start when magnesium powder is added to the alkyl halide in diethyl ether solvent. Suggest a reason. [1] (iii) The addition of the Grignard reagent to the carbonyl typically proceeds through a six-membered ring transition state. For the reaction of each molecule of carbonyl compound, two molecules of Grignard reagents are involved in the formation of th e transition state. Suggest the transition state of Step 1 for the reaction between propanone and CH3MgBr shown above. [1]

5 [Turn over (iv) Suggest a four-step synthesis of compound Q from a carbonyl compound. State the reagents and conditions for each stage and draw structures of the intermediate organic products. The first two steps should involve the use of Grignard reaction between CH3MgBr and a relevant carbonyl compound. Compound Q [5] (c) (i) Describe what is observed when NaCl and NaBr reacts with concentrated sulf uric acid respectively. In each case, suggest the products of the reaction and write equations where appropriate. [2] (ii) Explain any difference in their reactions with concentrated sulfuric acid. [1] (d) When cold aqueous sodium hydroxide is added to a yellow ish-green solution of chlorine in trichloromethane and shaken together, two immiscible colourless layers (aqueous layer and organic layer) were observed. (i) State the type of reaction and give an equation, including state symbols, for this reaction. [2] (ii) Assuming that the starting reagents were added in stoichiometric ratio, s uggest the chemical species found in the two immiscible colourless layers respectively. [2] (e) One of the compounds that may be formed between chlorine and iodine is iodine tetrachloride, ICl4-. Construct a ‘dot-and-cross diagram ’ to show the arrangement of electrons in ICl4-. [1] [Total: 20]

6 3 (a) Hunsdiecker reaction is the organic reaction of silver salts of carboxylic acids with halogens to give organic halides. The overall reaction is: RCO2Ag + Br2 → R-Br