Edexcel Jun 2011 Paper 4 Q19 (with explained solutions) |

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Edexcel Jun 2011 Paper 4 Q19

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PMT SECTION C Answer ALL the questions. Write your answers in the spaces provided. 19 The chemical X is an ester with formula CH3COOC(CH3)3 which occurs in raspberries and pears. It can be prepared in the laboratory by refluxing ethanoic acid with an alcohol in the presence of a catalyst. (a) Name the alcohol and catalyst which would be used to make X. (2) AlcoholCatalyst(b) After refluxing, the resulting mixture is distilled to give an impure product containing X. The impure product is washed several times with sodium carbonate solution and then dried. (i) Name the piece of equipment in which the impure product would be washed. (1)(ii) What is the purpose of washing the impure product with sodium carbonate solution? (1)(iii) Name a suitable drying agent. (1)*P38482A01924* 19 Turn over<br />
(iv) The impure product is then redistilled and X, which has a boiling temperature of 97C, is collected. Draw a labelled diagram of the apparatus you would use. (3) PMT *(c) Spectrum 1 is the high resolution proton nmr spectrum of X, CH3COOC(CH3)3. Spectrum 1 Signal strength 4 Chemical shift, (cid:303) / ppm 20 *P38482A02024*<br />
PMT Explain how spectrum 1 is consistent with the structure of X. You should refer to the number and height of the peaks, the atoms which produce them and their splitting patterns. (4)*P38482A02124* 21 Turn over<br />
(d) X has an isomer, Y. Y is an ester which can be made from ethanoic acid and 2-methylpropan-1-ol. (i) Draw the structural formula of Y. (ii) Spectrum 2 is the high resolution proton nmr spectrum of Y. On your structural formula in (i), circle the atom or atoms causing the peak labelled Q on spectrum 2. PMT (1) (1) Spectrum 2 Signal strength 4 2 Chemical shift, (cid:303) / ppm 22 *P38482A02224*<br />
(e) X has several other structural isomers which have a broad peak at approximately 2960 cm1 in their infrared spectra. Some of the isomers have a chiral carbon atom and all have a higher boiling temperature than X. None of them reacts with 2,4-dinitrophenylhydrazine. *(i) Draw the structure of one of the isomers which is optically active, explaining how you use all the information in the question. PMT (5)(ii) Could the compound you have drawn in (e)(i) be distinguished by infrared spectroscopy from its other isomers with the properties listed above? Explain your answer. (1)(Total for Question 19 = 20 marks) TOTAL FOR SECTION C = 20 MARKS TOTAL FOR PAPER = 90 MARKS *P38482A02324* 23<br />

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$Section C Question Number 19 (a) Question Number 19 (b)(i) Question Number 19 (b)(ii) Question Number 19 (b)(iii) Acceptable Answers Reject Alcohol; (2)-methylpropan-2-ol (1) Catalyst: sulfuric acid OR any named strong acid Ignore concentration of acid (1) Accept formula for acid Formula of alcohol Just acid/H+ for catalyst Acceptable Answers Tap funnel / separating funnel Acceptable Answers To neutralize / remove/ react with (excess) acid Allow To neutralize / remove / react with (excess) H+ To remove acidic impurities To remove ethanoic acid To remove the acid (used as a) catalyst Ignore additional comments on quenching or reaction stopping Reject Buchner funnel Filter funnel Reject To purify it To remove excess acid and alcohol Just to quench acid catalyst/stop reaction Acceptable Answers Reject Add (anhydrous) calcium chloride/ sodium sulfate/ magnesium sulfate/ Allow silica gel Allow formulae of drying agents Conc. sulfuric acid Anhydrous copper sulphate Just silica Mark Mark Mark Mark 6CH04/01 1106<br /> Question Number 19 (b)(iv) Mark Acceptable Answers Reject Round bottomed or pear-shaped flask + still head with stopper or thermometer + heat source (1) This mark cannot be given if apparatus is completely sealed /large gaps between components Downwards sloping condenser (with correct water flow) + collection vessel (1) Thermometer in correct position with bulb opposite condenser opening (1) Ignore fractionating column if included between flask and condenser Conical flask Flat bottomed flask 6CH04/01 1106<br /> Question Number *19 (c) Question Number 19 (d)(i) Mark Just the peaks are due to (CH3)3 and CH3 Acceptable Answers Reject First mark (Two signals so) two hydrogen environments (1) This mark may be gained by a description of the only two environments, but reference to hydrogen must be made. Second mark (Numbers of hydrogen in each environment are/ are predicted to be) in ratio 3:9 or 1:3 OR Peak due to (CH3)3 is 3x higher than peak due to CH3 (1) Third mark Environments are CH3COO and (CH3)3 (H may have been specified in first marking point) These may be shown on a diagram of the formula of the molecule OR H-C-C=O (peak at 2.1) and H-C-C (peak at 1.3) (1) Fourth mark Singlets/ no splitting as no H on adjacent C OR Singlets as the hydrogen environments are not adjacent to other H environments Allow only one peak for no splitting (1) Acceptable Answers CH3COOCH2CH(CH3)2 Or correctly displayed Allow CH3COOCH2CH(CH3) CH3 Reject Mark 6CH04/01 1106<br /> Question Number 19 (d)(ii) Question Number 19 (e)(i) Mark Mark Acceptable Answers Reject The H on the CH3COO Accept circle round all of first methyl group Accept a hydrogen in this environment if rest of molecule is incorrect Circle round C of first methyl group Acceptable Answers Reject Any acid with 6C (5C + COOH) which is chiral, so will have a branched chain C3 H7 CH(CH3) COOH OR C2H5 CH(CH3) CH2 COOH OR (CH3)2 CHCH(CH3) COOH (1) Infrared indicates (O-H present in a) carboxylic acid (1) High boiling temperature due to hydrogen bonding (between atoms in OH groups so not an ester.) Hydrogen bonds must be possible for structure shown Allow acids can form dimers. Allow TE from formula of straight chain molecule with explanation that London forces are higher in a linear molecule (1) (Optically active so) contains chiral C/ C bonded to four different groups The formula suggested must contain a chiral carbon to score this mark This may be shown by a chiral carbon being labelled in the formula (1) Carbonyl compound/ Carbonyl group/ Aldehyde and ketone absent (as no reaction with 2,4-dinitrophenylhydrazine)/ Allow carboxylic acids do not react with 2,4- dinitrophenylhydrazine/ (1) Infrared indicates O-H Infrared indicates alkyl group Just does not contain C=O (group) 6CH04/01 1106<br /> Question Number 19 (e)(ii) Acceptable Answers Reject No because the isomers (which are carboxylic acids) contain same bonds / groups (C=O, C-O, C-H etc) (1) OR Yes because could be distinguished by infrared fingerprint (1) Yes because spectrum is unique Mark TOTAL FOR SECTION C = 20 MARKS 6CH04/01 1106<br />$

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