Edexcel Jan 2012 Paper 6 Q4 (with explained solutions) |

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Edexcel Jan 2012 Paper 6 Q4

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4 2-ethanoylaminobenzoic acid, C9H9NO3, is a compound which emits flashes of light when its crystals are crushed or scraped. It is prepared under strictly supervised conditions. PMT The steps of the experimental procedure are as follows. 1. Place 3.5 g of 2-aminobenzoic acid, C7H7NO2, in a dry 50 cm3 flask fitted with a reflux condenser. 2. Add 7.0 cm3 of ethanoyl chloride (an excess) by pouring it carefully down the condenser. 3. Heat slowly to boiling and reflux for 15 minutes. 4. Allow to cool and then add 5 cm3 of water. 5. Bring the solution back to boiling by heating slowly. 6. Allow the solution to cool slowly at room temperature. 7. Collect the crystals of 2-ethanoylaminobenzoic acid by suction filtration. 8. Recrystallize the 2-ethanoylaminobenzoic acid from a 50% ethanoic acid/water mixture. (a) Explain how the process of heating under reflux works and why it is often necessary to heat under reflux, as in step 3. (3)12 *P35988A01216*<br />
(b) (i) Suggest why water was added (step 4). PMT (1)(ii) Suggest why the mixture was cooled before the water was added (step 4). (1)(c) (i) Draw a fully labelled diagram of the apparatus used for suction filtration (step 7). (ii) Suggest two advantages of suction filtration over normal filtration. (3) (2) First advantageSecond advantage*P35988A01316* 13 Turn over<br />
(d) (i) Draw a fully labelled diagram of the apparatus you would use to determine the melting temperature of the 2-ethanoylaminobenzoic acid crystals. (2) PMT (ii) Give two aspects of the melting temperature determination that would indicate the crystals were pure. (2)14 *P35988A01416*<br />
PMT (e) In the equation for this reaction, the mole ratio of 2-aminobenzoic acid, C7H7NO2, and 2-ethanoylaminobenzoic acid, C9H9NO3, is 1:1. In an experiment, 3.5 g of 2-aminobenzoic acid produced 2.35 g of recrystallized 2-ethanoylaminobenzoic acid. Calculate the percentage yield of the product for this reaction. (3) (Total for Question 4 = 17 marks) TOTAL FOR PAPER = 50 MARKS *P35988A01516* 15<br />

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Question Number 4 (a) Acceptable Answers Reject Mark Overcomes activation energy (1) (1) As liquid(s) vaporise/boil they are cooled and condense back to liquid(s) Any two from: Used to heat volatile liquids Prevents escape of flammable vapours (1) Prevents escape of reactants/ products/solvents (1) Allows time to react/Allows complete reaction/Allows faster reaction/ increases yield (1) Question Number 4 (b)(i) Question Number 4 (b)(ii) Acceptable Answers Reject Mark To react with/remove (excess) ethanoyl chloride IGNORE references to product(s) dissolving Dissolve unreacted reagents/excess acid/HCl Acceptable Answers Reject Reaction (with water) is exothermic /gives out heat/violent/vigorous Note that the answer may be given in b(i) Reaction explosive Prevent flask cracking Mark 6CH0801 1201<br />
Question Number 4 (c)(i) Question Number 4 (c)(ii) Acceptable Answers Reject Mark Large gap between funnel and flask Blocked outlet to pump (1) (1) Buchner/side armed flask Side arm connected to pump Buchner funnel with flat filter paper The filter paper must be labelled or clearly shown above the pores of the funnel (1) Acceptable Answers Reject Reduces transfer losses Less product lost /higher yield Mark (1) Faster Dries solid/precipitate/crystals OR removes maximum amount of solution (1) 6CH0801 1201<br />
Question Number 4 (d)(i) Acceptable Answers Reject Mark (1) A variety of methods may be used. Either Crystals in (sealed) capillary tube Thermometer and capillary in (heated) oil/water bath or in melting temperature apparatus heater (1) Or Crystals balanced on thermometer (1) Clamped horizontally in horizontal double glass skinned test tube (1) Notecrystals in a test or boiling tube with a thermometer in the tube (1) Acceptable Answers Question Number 4 (d)(ii) Melting temperature should be Reject Mark sharp/over a 1-2 oC range/narrow temperature range (1) And at correct value/consistent with literature (1) 6CH0801 1201<br />
Question Number 4 (e) Mark Acceptable Answers Reject Answers to 1 sf Number of moles of reactant = 3.5 (1) = 0.02555 137 Either Number of moles of product = 2.35 (1) = 0.01313 179 Percentage yield = 0.01313 x 100 0.02555 =51.4/51 % (1) ACCEPT 51.5% Or Mass of product = 0.02555 x 179(1) = 4.573 g Percentage yield = 2.35 x 100 4.573 = 51.4%/51% (1) ACCEPT answers to 4 or more sf provided they round to 51.4 or 51.5 Correct answer with no working scores (3) ALLOW internal TE ACCEPT 51.5% TOTAL FOR PAPER = 50 MARKS 6CH0801 1201<br />

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