Edexcel Jun 2009 Paper 2 Q23

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PMT Answer ALL the questions. Write your answers in the spaces provided. SECTION C As levels of fossil fuel resources are getting lower, society is increasingly looking at the use of biofuels as alternatives to coal, oil and gas. Biofuels are derived from plants and examples include bioethanol, biodiesel and Miscanthus, a plant more commonly known as elephant grass. These fuels have the advantage of being renewable and the plants take in carbon dioxide as they grow. Bioethanol is produced from crops such as sugar cane or corn. The raw plant material is treated to produce a sugary solution which is then fermented to produce ethanol, water and carbon dioxide gas. The ethanol is removed by distillation. The resulting solution contains about 96 % ethanol. The remaining water has to be removed by absorption using a suitable drying agent so that the ethanol can burn efficiently. The bioethanol can then be burnt alone or mixed with petrol in vehicle engines. Biodiesel is formed by the hydrolysis of vegetable oils using sodium hydroxide solution, followed by esterification with methanol and a sodium hydroxide catalyst. Biodiesel can then be used on its own in diesel-engined vehicles or mixed with diesel derived from crude oil. Plants which are used to produce the vegetable oils include rapeseed in the UK, soya bean in the USA and palm oil in Asia. Miscanthus, or elephant grass, is a quick growing, high-yield plant that grows up to four metres in height. After harvesting, the grass is left to dry and then burnt in power stations designed to run on solid fuels such as coal. In the United Kingdom, farms that produce elephant grass are normally situated within 50 miles of such a power station. In an experiment to simulate the production of bioethanol, a student produced a water/ ethanol mixture by fermentation of sucrose solution using yeast. It was then proposed to separate the ethanol from water by carrying out a distillation on the mixture. The mixture would then be dried using a suitable drying agent. 23 (a) Draw a diagram to show the most significant intermolecular force between an ethanol molecule and a water molecule. Label the bond angle between the molecules and state its value. (2) *h34472A01924* 19 Turn over<br /> PMT (b) The student proposed to set up the apparatus as shown below to carry out the distillation to try to separate the ethanol from water. There are three errors with the set-up. Draw a circle around each error. Describe what effect these errors would have if the student attempted to carry out the separation as shown. [Clamps are not shown in the diagram but you can assume the apparatus is supported adequately.] (6) Anti-bumping beads Heating mantle20 *h34472A02024*<br /> PMT (c) If a balance accurate to two decimal places was used to record the mass of ethanol collected, what would be the percentage error due to the balance readings if the total mass of ethanol collected was 20.10 g? (d) Suggest a suitable drying agent to absorb the water remaining with the ethanol after distillation. Describe how you would use it to produce a dry sample of ethanol. (1) (2)*h34472A02124* 21 Turn over<br /> PMT (e) Describe a chemical test you could carry out to confirm the presence of the OH group in ethanol. What result would you expect to see? (2) TestResult(f) *(i) Explain what is meant by a carbon neutral fuel. (2)*(ii) Suggest TWO reasons why these biofuels may not be carbon neutral and describe TWO effects that large scale production of biofuels may have on society. Which of the three biofuels do you think is the most sustainable? Justify your choice. (5)22 *h34472A02224*<br /> PMT(Total for Question 23 = 20 marks) TOTAL FOR SECTION C = 20 MARKS TOTAL FOR PAPER = 80 MARKS *h34472A02324* 23<br />

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