MJC H2 Chem 2012 Prelim P3 QP

Class Reg Number Candidate Name _____________________________ MERIDIAN JUNIOR COLLEGE Preliminary Exam Higher 2 ___________________________________________________________________ H2 Chemistry 9647/3 Paper 3 Free Response 18 Sep 2012 2 hours Additional Materials: Data Booklet Writing paper ___________________________________________________________________ INSTRUCTIONS TO CANDIDATES Write your name, class and register number in the spaces provided at the top of this page. Answer 4 out of 5 questions in this paper. Begin each question on a fresh page of writing paper. Fasten the writing papers 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 document consists of 14 printed pages (including the cover pages) copyright chem dept @ meridian jc

copyright chem dept @ meridian jc Answer any 4 out of 5 questions in this paper. Begin each question on a fresh sheet of writing paper. 1 Sugars, or saccharides, are the most abundant bio- molecules found on the planet and play many important biological roles. A simple sugar , a derivative of a straight chain polyhydroxyl alcohol and glycerol , is considered to be the parent of all sugars. (a) 2-chloropropane-1,3-diol can be synthesised from glycerol via the reaction scheme below. Suggest reagents and conditions for steps I to III, and draw the structural formula of intermediates A and B. [5] CH2-CH-CH2 OH OH OH KMnO4, dilute H2SO4 heat CH2-CH-CH2 OH OH Cl Step III H2O Step I A Step II B C-CH-C O O Cl OHHO glycerol 2-chloropropane-1,3-diol HOOC C O COOH

copyright chem dept @ meridian jc (b) Glucose, an important simple sugar or monosaccharide, is required by the cells in our body as a source of energy and metabolic intermediate. A common source of glucose is sucrose or table sugar. In humans and other mammals, sucrose is broken down into its constituent monosaccharides , glucose and fructose as shown below. sucrose glucose fructose (i) Name the functional group, other than ether (R -O-R), present in sucrose. (ii) Suggest the type of reaction undergone by sucrose. [2] (c) Glucose undergoes complete combustion to form carbon dioxide and water. (i) Write a balanced equation for the complete combustion of glucose. (ii) The standard enthalpy change of formation of CO 2, H2O and glucose is -394 kJ mol-1, -286 kJ mol-1 and -1275 kJ mol-1 respectively. Use your answer in (c)(i) and the data given to calculate the energy released when 9.0 g of glucose undergoes complete combustion. (iii) In a calometric experiment, 9 .0 g of glucose was burnt completely and the energy released raised the temperature of 650 cm 3 of water by 44oC. Calculate the energy released by the combustion of 9.0 g of glucose in the experiment. (iv) Suggest a reason for the discrepancy between the answers in (c) (ii) and (c)(iii). [5] O CH2OH OH OH HO HO O CH2OH HO HO OH CH2OHO CH2OH O OH HO HO O CH2OH HO OH CH2OH +

copyright chem dept @ meridian jc (d) Group II nitrates and sugars undergo decomposition when heated. (i) Write an equation for the thermal decomposition of Group II nitrates. (ii) Suggest why the numerical value of the entropy change is very similar for the decomposition reaction of all the Group II nitrates. (iii) Predict, with reasoning, whether magnesium nitrate or barium nitrate has a higher decomposition temperature. [4] (e) Chlorophyll is an extremely important bio- molecule which allows plants to absorb energy from light. It consists of a chlorin ring with a magnesium ion, Mg2+, at the centre of the ring. With the aid of an energy cycle, cal culate the enthalpy change of hydration of Mg2+ using the following data and appropriate data from the Data Booklet. enthalpy change of solution of MgCl2 = - 153 kJ mol-1 enthalpy change of hydration of Cl- = - 362 kJ mol-1 enthalpy change of formation of MgCl2 = - 642 kJ mol-1 enthalpy change of atomization of Mg = + 148 kJ mol-1 first electron affinity of Cl = - 364 kJ mol-1 [4] [Total: 20]

copyright chem dept @ meridian jc 2(a) H alogens react readily with hydrogen. X2(g) + H2(g) ® 2HX(g) (where X = Cl, Br or I) (i) Describe how you could carry out this reaction using chlorine. (ii) Describe two observations you would make if this reaction was carried out with bromine. (iii) Describe and explain the trend observed in the reactions of the elements chlorine, bromine and iodine with hydrogen. [6] (b) Some halogens also react readily with alkanes. Consider the following sequence of reactions. C 6H14 C6H13X C6H13OH alkane W (i) State the reagent and conditions needed for r eaction 1 when X is bromine, Br. (ii) Use bond energy data from the Data Book let to calculate the Δ Ho of reaction 1 when X is iodine, I. (iii) Hence, suggest why it is not possible to synthesise iodoalkane by reaction 1. (iv) In another separate experiment using reaction 1, alkane W, C 6H14, produced only two isomeric monobromo compounds Y and Z, with the molecular formula C6H13Br. Compound Z is chiral. Suggest the structures of W, Y and Z. [6] Reaction 1 Reaction 2

copyright chem dept @ meridian jc (c) Both isomers Y and Z with formula C 6H13Br can undergo reaction 2 with aqueous sodium hydroxide solution to form alcohols. When the reaction of one of these isomers with aqueous sodium hydroxide was investigated, the following kinetic data was obtained. Experiment Initial [C6H13Br] / mol dm-3 Initial [OH-] / mol dm-3 Initial rate of reaction / mol dm-3 min-1 1 1.30 2.60 13.0 2 2.60 1.30 26.0 3 3.90 2.60 39.0 4 7.80 5.20 78.0 (i) Use these data to deduce the order of reaction with respect to each of the reagents, showing how you arrive at your answers. Hence, write the rate equation for the above reaction. (ii) Suggest which isomer Y or Z was being investigated in the above reaction and explain your choice. (iii) Hence, using the isomer you have suggested in (c )(ii), describe a mechanism that is consistent with your rate equation, and indicate which step in the mechanism is the rate determining step. (iv) Draw a labeled energy profile diagram of the mechanism you described in (c)(iii). [8] [Total: 20]

copyright chem dept @ meridian jc 3(a) Iron metal has traditionally been extracted from its ore using a Blast furnace. The process uses coke (carbon) and haematite (Fe 2O3) in three stages, whereby · coke is first oxidised by air to form carbon dioxide; · the carbon dioxide formed further reacts with more coke to form carbon monoxide; · the haematite is reduced to obtain the iron metal New research proposes that iron could be recovered via electrolysis. This involves passing current via inert platinum electrodes into a mixture of molten Fe 2O3. This new process is thought to be more advantageous than using the current Blast furnace method. (i) Draw a diagram to illustrate the electrolysis set -up, showing clearly the polarity of the electrodes and the species attracted to and formed at each electrode. (ii) Give the equations, including state symbols, for the reactions occurring at each electrode. (iii) An initial pilot production plant using the new method yields 5 kg of iron per day. Calculate th