Edexcel Jan 2014 (IAL) Paper 6 Q4

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4 This question concerns the preparation of an ester, 3-methylbutyl ethanoate. The ester can be produced by the reaction of 3-methylbutan-1-ol and ethanoic anhydride: C5H11OH + (CH3CO)2O (cid:314) CH3COOC5H11 + CH3CO2H Reagents (cid:120) 3-methylbutan-1-ol [molar (cid:120) ethanoic anhydride Required product mass = 88.0 g mol1; density = 0.81 g cm3] (cid:120) 3-methylbutyl ethanoate [molar mass = 130.0 g mol1; boiling temperature = 142 C] Safety information (cid:120) 3-methylbutan-1-ol is highly flammable (cid:120) 3-methylbutyl ethanoate is highly flammable (cid:120) ethanoic anhydride is corrosive, causing skin blistering and peeling The steps of the experimental procedure are as follows: Step 1 Place 10.0 cm3 of 3-methylbutan-1-ol in a flask and add a few anti-bumping granules. Step 2 Set up the apparatus for reflux. Pour 12.5 cm3 of ethanoic anhydride (a slight excess) down the condenser. Warm the mixture until the reaction starts and then reflux gently for five minutes. Allow the mixture to cool. Step 3 Transfer the cooled mixture to a separating funnel, leaving the anti-bumping granules in the flask. Add about 25 cm3 of water and shake the mixture. Allow the two layers to separate and discard the lower aqueous layer. The addition of water converts any unreacted ethanoic anhydride into ethanoic acid. Step 4 Add about 10 cm3 of aqueous sodium hydrogencarbonate to the separating funnel and shake carefully. When the vigorous effervescence has finished, insert the stopper and shake the funnel, frequently releasing the pressure. Repeat the washing with further quantities of aqueous sodium hydrogencarbonate until no more gas is produced. Discard the lower aqueous layer each time. Step 5 Transfer the ester to a conical flask and shake the flask for five minutes with a suitable drying agent. Step 6 Filter the dried ester directly into a flask. Set up the apparatus for simple distillation, adding a few anti-bumping granules to the flask. Distil off the ester. 10 *P42975RA01016*<br /> (a) State two safety precautions, each related to a specific hazard of this experiment. You may assume that eye protection and laboratory coats are being worn and that the experiment was carried out in a fume cupboard. (2) Hazard 1Precaution 1Hazard 2Precaution 2(b) Draw a labelled diagram of the apparatus needed for heating under reflux in Step 2. You do not need to show stands or clamps. (3) *P42975RA01116* 11 Turn over<br /> (c) Why are anti-bumping granules added to the flask in Step 1? (1)(d) What is the purpose of adding aqueous sodium hydrogencarbonate in Step 4? (1)(e) In the following list of substances, only one would be a suitable drying agent to use in Step 5. Identify this drying agent, giving a reason for your choice: (2) ed phosphoric(V) acid (cid:120) concentrat (cid:120) sodium hydroxide solid (cid:120) anhydrous sodium sulfate (cid:120) concentrated sulfuric acid Drying agentReason(f) In Step 6, the ester is distilled off. Suggest a suitable temperature range over which to collect the ester. From C to C (g) (i) Calculate the maximum mass of 3-methylbutyl ethanoate that could be obtained in this experiment from 10 cm3 of 3-methylbutan-1-ol. Give your answer to three significant figures. (1) (3) 12 *P42975RA01216*<br /> (ii) A student carried out the synthesis and obtained 9.45 g of 3-methylbutyl ethanoate. Calculate the percentage yield. (2) (Total for Question 4 = 15 marks) TOTAL FOR PAPER = 50 MARKS *P42975RA01316* 13<br />

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