MI_H2_CHEM_P2 Prelim

Class Adm No Candidate Name: This question paper consists of 18 printed pages. [Turn over 2011 Preliminary Examination II Pre-university 3 CHEMISTRY 9647/02 Paper 2 Structured Questions 16 September 2011 Candidates answer on the Question Paper. 2 hours Additional Materials: Data Booklet 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 or graphs. Do not use paper clips, highlighters, glue or correction fluid. Answer all questions. A Data Booklet is provided. 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. You are reminded of the need for good English and clear presentation in your answers. For Examiners Q 1 2 3 4 5 Total Score 12 4 8 41 7 72

Page 2 of 18 1 Planning (P) Biodiesel, which could be obtained from natural products such as soybean, is a renewable and generally cleaner-burning fuel than petroleum diesel. However, it was claimed that biodiesel is less efficient as the heat content of biodiesel is less than that of petroleum diesel. The enthalpy change of combustion of straight chain alkanes can be estimated by finding the enthalpy change of combustion of a –CH 2– unit. This data could be obtained from the standard enthalpy change of combustion of straight chain alkanes. The enthalpy change of combustion of straight chain alkanes with 1 to 5 carbons are as shown: No. of carbon atoms Alkane H o combustion / kJ mol-1 1 CH 4 -890 2 C 2H6 -1560 3 C 3H8 -2219 4 C 4H10 -2877 5 C 5H12 -3509 In this question, it is assumed that petroleum diesel contained only hydrocarbon C20H42 (l), and that soybean oil used as a biodiesel. a) i) Plan a series of experiments to find out the enthalpy change of combustion of successive alkanes shown in the table above. Illustrate by means of a well labelled diagram how the experiment will be set up.

Page 3 of 18 [Turn over ii) Show how you will use your da ta to estimate a value of the enthalpy change of combustion of C20H42 (l). Use c to represent specific heat capacity of water and C to represent the heat capacity of the calorimeter. [6] b) A student calculated a value of enthalpy change of combustion of C 20H42 (l) using the bond energy data from the Data Booklet. Explain if the value would be a reliable estimate of the actual value. [1] …………………………………………………………………………………..………… ……………………………………………………………………………………………..

Page 4 of 18 c) Soybean oil used as a biodiesel contained primarily the methyl ester of linoleic acid (C19H34O2). The enthalpy change of formation are given as follows: Substance H o formation / kJ mol-1 CO2 (g) -394 H2O (l) -286 C19H34O2 (g) -6