Edexcel Jun 2010 Paper 6 Q4

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PMT (2) 4 N-phenylethanamide may be prepared in the laboratory by reacting ethanoic anhydride with phenylamine; both the reactants and the products are flammable. The equation for the reaction is shown below. NH2 H3C H3C HN CH3 H3C C OH N-phenylethanamide A student is asked to prepare pure N-phenylethanamide starting from 9.00g of phenylamine. (a) Calculate the minimum mass, in grams, of ethanoic anhydride required to react completely with 9.00g of phenylamine. [Molar masses /gmol1: C6H5NH2 = 93.0; CH3COOCOCH3 = 102] *N36508A01116* 11 Turn over<br /> PMT (b) The steps of the experimental procedure are as follows. 1. Mix the amount of ethanoic anhydride calculated in (a) with 10g of glacial (pure) ethanoic acid in a round-bottom flask and add a further 1g of the ethanoic anhydride. 2. Cool the flask from step 1 in a beaker of cold water and add 9.00g of phenylamine, drop by drop, with gentle shaking. 3. Add anti-bumping granules and reflux the mixture from step 2 for 30 minutes. 4. Pour the liquid from the reflux flask into a beaker containing 100cm3 of distilled water and allow the mixture to stand until no more crystals are formed. 5. Filter the crystals under reduced pressure using a Buchner funnel and flask, washing the crystals with cold water. 6. Transfer the crystals to a boiling tube and dissolve them in the minimum volume of boiling water. Filter the hot solution using a glass filter funnel, cool the filtrate in a beaker of ice-cold water and filter the crystals formed using a Buchner funnel and flask. 7. Dry the crystals between filter papers and then by storing them in a desiccator. 8. Weigh the dry crystals and calculate the yield. (i) Explain why, in step 1, the student is told to add a further 1g of the ethanoic anhydride to the calculated mass so that it is in excess. (1)(ii) Explain why, in step 2, the phenylamine is added drop by drop and the mixture immersed in cold water. (1)12 *N36508A01216*<br /> PMT (iii) The student set up the apparatus for the reflux (step 3) as shown in the diagram below. Water in Water out The apparatus has been incorrectly set up in TWO ways. State and explain these mistakes and how they should be corrected. You may assume that the apparatus is suitably clamped and that the reaction mixture contains anti-bumping granules. (4)*N36508A01316* 13 Turn over<br /> PMT (iv) Draw a labelled diagram of a Buchner funnel and flask (step 5). State how the reduced pressure is achieved (an explanation of this is not required). Diagram (3) Reduced pressure is achieved by(c) A student obtained 7.49g of N-phenylethanamide from 9.00g of phenylamine. Calculate the percentage yield. [Molar masses /gmol1: C6H5NH2 = 93.0; C6H5NHCOCH3 = 135] (2) 14 *N36508A01416*<br /> PMT (d) Yields of less than 100% are often explained as being due to transfer losses. Explain this term by referring to the recrystallization of N-phenylethanamide in steps 6 and 7. (1)(e) Another student reported a yield of greater than 100%. Assuming that the student used the correct amounts of reagents and carried out the calculation correctly, suggest a reason for this result. (1)(Total for Question 4 = 15 marks) TOTAL FOR PAPER = 50 MARKS *N36508A01516* 15<br />

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