TPJC H1Chem 08PrelimP2

TAMPINES JUNIOR COLLEGE Preliminary Examinations 2008 CHEMISTRY (Higher 1) 8872/2 PAPER 2 Thursday 21 August 2008 2 hours Additional materials: Writing Paper Graph Paper Data Booklet INSTRUCTIONS TO CANDIDATES Write your name and Civics Group on all the w ork you hand in. Write in dark blue or black pen. Section A Answer all questions in the space provided. Section B Answer two questions on separate answer paper. At the end of the examination, fasten the answers to Section B to Section A. The number of marks is given in brackets [ ] at the end of each question or part question. Question Marks Section A Name : _____________________ CG : ________ B4 B5 B6 TOTAL / 80 This document consists of 10 printed pages. [Turn over 8872_02 / 1

Section A Answer all questions in this section in the spaces provided. 1 (a) (i) On the grid given below, sketch the general trends of the first ionisation energy of the elements across the thir d period of the Periodic Tabl e. Your sketch is expected to be clear though qualitative only. Na Mg Al Si P S Cl Ar 1st ionisation energy / kJ mol–1 (ii) Explain the general trend of your sketch in (a)(i). ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ [3] (b) (i) In the spaces provided, draw the elec tronic configuration of phosphorous and sulphur. phosphorous 3p 2p 3s1s 2s sulphur 3p 2p 3s1s 2s (ii) Briefly explain the relative magnitudes of the first ionisation energies of phosphorous and sulphur. ___________________________________________________________________ ___________________________________________________________________ [3] 8872_02 / 2

(c) The elements in Period 3 range from metals on the left of the per iodic table to non- metals on the right. Describe a chemical property of an oxide of magnesium which shows that it is a metal and a chemical property of an ox ide of sulphur which shows that it is a non-metal. Give chemical equations where relevant. _________________________ _____________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ____________________________________________________________________ [4] (d) When diluting sulphuric acid with water, ca re must be taken because the process is highly exothermic: H 2SO4(l)  H2SO4(aq) H < 0 (i) Given that the enthalpy c hange of formation of H 2SO4(l) and H 2SO4(aq) are 814 kJ mol 1 and 908 kJ mol 1 respectively, calculate the enthalpy change of reaction for the dilution. (ii) 1.00 mol of H 2SO4(l) was diluted to a volume of 1.00 dm 3 of H 2SO4(aq) in a calorimeter. Assuming that the density of the final solution is 1.06 g cm 3 and that its specific heat capacity is 3.50 J g 1 K 1, what would be the temperature rise of the solution in the calorimeter? [4] [Total: 14] 8872_02 / 3

2 (a) (i) State what is meant by a buffer solution. ________________________________________________________________ ________________________________________________________________ (ii) Explain, using equations, how an aqueous mixture of ethanoic acid, CH3COOH, and sodium ethanoate, CH3COO–Na+, can act as a buffer solution • on the addition of acid, • on the addition of alkali. [3] (b) The diagram below shows a reaction scheme involving ethanoic acid. CH2COOH ( i ) Give the displayed formulae of compounds M and N in the spaces provided. (ii) State the reagents and conditions required for conversions I and II. I : _____________________________ II : _____________________________ (iii) Ethanoic acid is soluble in water. Explain this observation with the aid of a diagram. CH3COOH ethanoic acid │ Cl chloroethanoic acid CH3C=O │ H N I II PCl5 M Na 2CO3(aq) 8872_02 / 4

(iv) Chloroethanoic acid is a stronger acid than ethanoic acid. State which acid has the lower pKa value and explain the difference in acid strength. ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ (v) How do you think the str ength of fluoroethanoic acid, CH2FCOOH, compares with that of chloroethanoic acid? Briefly explain your answer. _________________________ _______________________________________ [10] [Total: 13] [continued on next page 8872_02 / 5

3 Hydrogen accounts for 90% of the atoms in the universe. It has three naturally occurring isotopes: ordinary hydrogen (1H or protium) which is the most abundant, deuterium (2H or D) and tritium (3H or T) which is radioactive. All three occur as diatomic molecules, examples of which are H2 and D2, who have boiling points of 20.39 K and 23.67 K respectively. Hydrogen gas (H 2) is produced on an industrial scale worldwide, with about 3 x 10 12 dm3 (at s.t.p.) being produced annually in the United States alone. All the production methods are energy intensive. Some of the methods employed include electrolytic and thermal methods. The most common thermal method of producing hydrogen gas is a two-step method using water and a simple hydrocarbon. Many modern American plants use methane as the hydrocarbon. The first step involves the following reaction which is nickel-catalysed. CH 4(g) + H2O(g)  CO(g) + 3H2(g) H = +206 kJ mol1 (1) In regions such as Scandanavia, hydr ogen gas is produced using an electrolytic method. In this method, electricity is used to dec ompose water into hydrogen and oxygen gas. Under typical operating conditions, it takes about 400 kJ of energy to produce 1 mole of hydrogen gas. One of the major uses of hydrogen is the hydrogenation of the alkene (C=C) bonds in liquid oils to form solid fats and margari ne. The equation below illustrates the complete hydrogenation of a typical “mono-unsaturated” oil. The conditions of the hydrogenati on process can be carefully c ontrolled to give “partial hydrogenation.” A concern about the hydrogenation process is that the “trans fats” produced pose health risks when consumed. The double bonds in unsaturated fats and oils tend to have the groups around them arranged in the "cis" form. However, t he relatively high temperatures used in the hydrogenation process tend to flip some of the carbon-car bon double bonds into the "trans" form. (a) In an experiment, separate beams of protium and deuterium ions were passed through an electric field. Sketch on the diagram bel ow, the expected paths taken by each beam. Your sketch should be clearly labeled and the relative magnitude of the angles of deflection clearly shown. [2] source CH3(CH2)7CH=CH(CH2)7COOCH2 CH3(CH2)7CH=CH(CH2)7COOCH CH3(CH2)7CH=CH(CH2)7COOCH2 CH3(CH2)7CH2CH2(CH2)7COOCH2 CH3(CH2)7CH2CH2(CH2)7COOCH CH3(CH2)7CH2