MI_H2_CHEM_P2_MS Prelim

Class Adm No Candidate Name: This question paper consists of 21 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 7 41 5 72

Page 2 of 21 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. 1 m for set-up

Page 3 of 21 [Turn over 1. Weigh 30 g of CH4 into a burner set up. Ensure that the wick is soaked in the fuel. Adjust the wick such that it is about 2 cm above the cap of the burner. 2. Using a measuring cylinder, add 200 cm3 of water into the empty tin can. 3. Using the stirrer, gently stir the water for 5 seconds. Measure the initial temperature of the water with the thermometer until the temperature becomes steady. Record the initial temperature, T i. 4. Light the lamp, quickly place it in position and stir the water in the beaker gently with the thermometer. 5. As soon as a temperature rise of about 5°C has been obtained, blow out the flame. Record the final temperature , Tf. 6. Reweigh the burner and the unburnt fuel. Find the mass of alkane burnt. 7