Edexcel Jun 2013 Paper 6 Q4

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4 The procedure outlined below can be used to extract caffeine from tea. 1. Add 25 g of tea, 10 g of calcium carbonate and 250 cm3 of water to a large beaker. 2. Gently boil the mixture for 15 minutes. 3. While the mixture is still warm, filter using suction filtration. 4. Transfer the filtrate to a separating funnel and separate the caffeine from the aqueous mixture using solvent extraction, with dichloromethane as the solvent. 5. Dry the extract. 6. Remove the solvent. [Density of dichloromethane = 1.32 g cm3] (a) (i) Outline how to carry out the solvent extraction in step 4, to obtain a solution of caffeine dissolved in dichloromethane. (3)*P41653A01316* 13 Turn over<br /> (ii) How would you dry the extract in step 5? Include the name of a suitable drying agent in your answer. (2)(b) (i) The solvent dichloromethane is harmful and can enter the body through inhalation and skin absorption. Suggest a possible way to minimise each of these risks when using dichloromethane. (2) InhalationSkin absorption(ii) Suggest a suitable way to remove the solvent in step 6. (1)(c) The extraction can also be carried out using liquid carbon dioxide. Suggest an advantage of using this rather than dichloromethane. (1)14 *P41653A01416*<br /> (d) A student carrying out this extraction obtained 85 mg of caffeine. Calculate the percentage by mass of caffeine obtained from the sample of tea used. (e) Caffeine obtained in this way is often a pale green solid, due to impurities. State the name of another technique you could use to further purify the caffeine. (2) (1)(Total for Question 4 = 12 marks) TOTAL FOR PAPER = 50 MARKS *P41653A01516* 15<br />

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