Edexcel Jun 2011 Paper 6 Q3

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PMT 3 Propyl ethanoate is an ester which has a smell similar to that of bananas or pears. It can be made in the laboratory from propan-1-ol and ethanoic acid. The equation for the reaction is CH3COOH + CH3CH2CH2OH (cid:85) CH3COOCH2CH2CH3 + H2O Procedure 1. Propan-1-ol (50 cm3) and ethanoic acid (50 cm3) are mixed thoroughly in a 250 cm3 round-bottomed flask. 2. Concentrated sulfuric acid (10 cm3) is added drop by drop to the mixture, keeping the contents of the flask well-shaken and cooled in an ice-water bath. 3. When the acid has all been added, a reflux condenser is fitted to the flask and the mixture gently boiled over an electric heating mantle for about 30 minutes. 4. The mixture is cooled, and the apparatus rearranged for distillation. The crude ester (about 60 cm3) is distilled off. 5. The distillate is placed in a separating funnel and shaken with about half its volume of 30% sodium carbonate solution, with the pressure being released at intervals. The lower aqueous layer is then discarded. 6. The crude ester is shaken in a separating funnel with about half its volume of 50% calcium chloride solution, which removes unreacted alcohol. The lower layer is discarded. 7. The ester is run into a clean, dry flask containing some anhydrous calcium chloride and swirled. 8. The ester is filtered into a clean, dry flask, with a few anti-bumping granules, and distilled. The fraction boiling between 100C and 103C is collected. (a) (i) Explain why the concentrated sulfuric acid is added slowly with cooling. (1)(ii) Explain why the mixture is heated under reflux for about 30 minutes. (2) Under refluxFor about 30 minutes*P38481A0812*<br /> PMT (iii) What is the main function of the sulfuric acid in this reaction? (1)(iv) Suggest the identity of two impurities that might be present in the crude distillate from step 4. (2)(v) What data would you need about propyl ethanoate to be sure that the instruction in step 5 to discard the lower layer is correct? (1)(vi) Step 5 requires that you release the pressure at intervals. Explain why the pressure in the funnel increases. (2)(vii) Explain why anhydrous calcium chloride is added in step 8 and state how the appearance of the liquid changes when this stage is complete. (2)(viii) What is the reason for adding anti-bumping granules in step 8? (1)*P38481A0912* Turn over<br /> (b) (i) Use the data in the table below to show, by calculating the numbers of moles, which reactant is in excess. Substance Ethanoic acid Propan-1-ol Density/g cm3 Molar mass /g mol1 1.05 0.804 60.1 60.1 (ii) The mass of the ester collected was 35.0 g. Calculate the percentage yield of the ester propyl ethanoate. Assume the molar mass of propyl ethanoate is 102 g mol1. PMT (2) (2) 10 *P38481A01012*<br /> (c) A student who carried out this experiment, according to the instructions, obtained a product that boiled at 95C. The student suspected that the alcohol originally provided was not propan-1-ol, but was 2-methylpropan-2-ol, since that would have given an ester with this boiling temperature. (i) Draw the structural formula for the ester that is formed from the reaction of ethanoic acid with 2-methylpropan-2-ol. (ii) Suggest a simple test-tube experiment that the student could carry out on the original alcohol to see if the suspicion could be correct. Give the reagents used and the expected result for both propan-1-ol and 2-methylpropan-2-ol. Explain why the results are different. PMT (1) (4)(Total for Question 3 = 21 marks) TOTAL FOR PAPER = 50 MARKS *P38481A01112* 11<br />

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