Edexcel Jan 2013 Paper 6 Q3 (with explained solutions) |

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Edexcel Jan 2013 Paper 6 Q3

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3 The compound 2-ethanoylaminobenzoic acid can be made by reacting 2-aminobenzoic acid with ethanoic anhydride. NH2 OH + (CH3CO)2O heat under reflux OH + CH3COOH NHCOCH3 2-aminobenzoic acid ethanoic anhydride 2-ethanoylaminobenzoic acid The steps of the experimental procedure are as follows: 1. Measure out 4.00 g of 2-aminobenzoic acid into a pear-shaped flask. Add ethanoic anhydride. 2. Add anti-bumping granules to the flask, fit a reflux condenser and bring the mixture slowly to the boil. Heat under reflux for 15 minutes. 3. Allow the reaction mixture to cool and add 5 cm3 of water. Bring the contents of the flask back to the boil and then remove from the heat. 4. Let the reaction mixture cool to room temperature. A pale brown crystalline solid will form. 5. Collect the solid by suction filtration. 6. Purify the solid by recrystallization using ethanoic acid as the solvent. 7. Determine the melting temperature of the dry solid. (a) (i) Calculate the minimum volume, in cm3, of ethanoic anhydride needed for 4.00 g of 2-aminobenzoic acid to react completely. [Molar masses / g mol1: (CH3CO)2O = 102; C6H4(NH2)COOH = 137 Density (CH3CO)2O = 1.082 g cm3.] (3) *P41217A0616*<br />
(ii) A student obtained 2.97 g of 2-ethanoylaminobenzoic acid from 4.00 g of 2-aminobenzoic acid. Calculate the percentage yield obtained by this student. Give your answer to two significant figures. (b) (i) When this experiment is carried out, the actual volume of ethanoic anhydride used is greater than that calculated in (a). Suggest why this is so. (3) (1)(ii) Anti-bumping granules are added in step 2. What would be observed if bumping occurred? (1)(iii) Ethanoic anhydride is corrosive to both the skin and the respiratory system. Suggest two precautions to minimise the risks when using ethanoic anhydride, other than wearing eye protection and a lab coat. (2)*P41217A0716* Turn over<br />
(iv) Outline how you would carry out the recrystallization in step 6. (4)(v) Suggest a reason why the recrystallization will slightly reduce the yield of 2-ethanoylaminobenzoic acid.(vi) Draw a labelled diagram of the apparatus that could be used to find the melting temperature of the dry solid in step 7. (1) (2) *P41217A0816*<br />
(vii) State two ways you would use the results from (vi) to check the identity and purity of the product. (2)(Total for Question 3 = 19 marks) *P41217A0916* Turn over<br />
BLANK PAGE 10 *P41217A01016*<br />

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Reject Mark 0.03 Reject Mark (1) (1) Acceptable answers Moles of 2-aminobenzoic acid = 4137 / 0.029197 / 0.0292 Mass of ethanoic anhydride needed =0.029197 x102 = 2.9781 g allow TE from first step Volume of ethanoic anhydride = 2.9781 / 1.082 = 2.7524 cm3 Allow TE from 2nd step Allow any answer that rounds to 2.7 or 2.8 to 2 sf Correct answer alone scores 3 marks NOTE The use of 1sf in the moles of 2-aminobenzoic acid loses the first mark even though it gives an answer which rounds to 2.8 (1) (1) Acceptable answers Mr 2-aminoethanoylbenzoic acid = 179 Theoretical yield = 0.029197 mol / = 0.029197 x 179 = 5.2263 g (1) % yield = 2.975.23 x 100/ 0.0165920.029197x100 = 56.828 % = 57 (%) correct answer to 2sf (with no working) scores 3 marks ALLOW TE from 3ai of moles of 2-aminobenzoic acid (1) Question Number 3 (a)(i) Question Number 3 (a)(ii)<br />
Question Number 3 (b)(i) Acceptable answers To (try to) make sure all the 2-aminobenzoic acid reacts Comment: allow discussion of small volume measurement Question Number 3 (b)(ii) Acceptable answers large bubbles / liquid rising up condenser / shooting out of the top /uneven boiling / liquids will splash out of flask / liquid will boil up suddenly Reject To ensure ethanoic anhydride is in excess To completely dissolve the reactant Ethanoic anhydride is volatile Reject Just breaks flask Just bubbles Strong bubbling Liquid spills over Liquid sprinkles over Uneven heating Air pockets No smooth boiling Boil vigorously Question Number 3 (b)(iii) Acceptable answers Wear gloves (Measure out in) fume cupboard / hood (1) Ignore: Wear a mask Allow for second mark In a well ventilated laboratory (1) Reject Mark Mark Mark<br />
Question Number 3 (b)(iv) Acceptable answers Dissolve solid in minimum (volume) (1) Allow: Small volume Ignore: To make a saturated solution of hot / boiling ethanoic acid / solvent (1) (filter hot solution) leave to cool (and recrystallize) Filter (wash with ice cold solvent) and dry (1) (1) Mark Reject Melt instead of dissolve water Filter and dry with no solid formed in previous steps Question Number 3 (b)(v) Acceptable answers Small amount of product remains in solution (when cool) / after recrystallization) / solid remaining on filter paper / solid remaining in funnel / solution absorbed on filter paper /solid lost during washing with cold solvent. Reject Mark Just transfer errors Side reactions or incomplete reaction<br />
Mark Reject Thermometer above solid sample In water bath Question Number 3 (b)(vi) (max 1) Acceptable answers Thermometer with capillary near to bulb (1) Allow: Thermometer dipping into solid sample In a container of oil Or In a sand bath Or (Electrically) heated block Or (horizontal) test tube inside boiling tube / double skinned test tube (1) Question Number 3(b)(vii) Acceptable answers Compare experimental value to literature / data book value (1) Sharp melting temperature / narrow melting temperature range (1) Reject Mark Total for Q3 = 19 marks<br />

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