Edexcel Jun 2010 Paper 3 Q4 (with explained solutions) |

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Edexcel Jun 2010 Paper 3 Q4

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PMT 4 An experiment to prepare 0.100 mol of 1-bromobutane uses the reaction of butan-1-ol with hydrogen bromide. Hydrogen bromide is formed in the reaction mixture from potassium bromide and moderately concentrated sulfuric acid. The process has an 80 % yield after purification of the 1-bromobutane. KBr + H2SO4KHSO4 + HBr CH3CH2CH2CH2OH + HBrCH3CH2CH2CH2Br + H2O The steps of the experimental procedure are as follows. 1. Add measured amounts of potassium bromide and butan-1-ol to 10 cm3 of water into a 50 cm3 two-necked flask. 2. Fit the two-necked flask with a reflux condenser and a tap funnel. 3. Immerse the flask in a beaker of cold water and add 10 cm3 of concentrated sulfuric acid from the tap funnel, a few drops at a time. 4. Remove the flask from the cold water and close the tap on the tap funnel. Heat the mixture under reflux for 30 minutes. 5. Allow the mixture to cool. Then set up the apparatus for distillation. Boil the mixture and collect the distillate in a measuring cylinder. 6. Transfer the distillate to a separating funnel. The distillate consists of two layers, an aqueous layer and impure 1-bromobutane. Separate the two layers. 7. Wash the impure 1-bromobutane with concentrated hydrochloric acid and separate the two layers. 8. Wash the 1-bromobutane layer with sodium hydrogencarbonate solution, releasing any gas formed. 9. Collect the 1-bromobutane layer in a conical flask and add anhydrous sodium sulfate. 10. Decant the 1-bromobutane into a 50 cm3 flask. Data Property Density /g cm3 Molar mass /g mol1 Boiling temperature / C Butan-1-ol 0.81 74 117.3 1-bromobutane 1.3 137 101.7 Water 1.0 18 100.0 10 *N35693A01016*<br />
PMT (a) (i) Show, by calculation, that 0.125 mol of butan-1-ol is needed to make 0.100 mol of 1-bromobutane. (ii) Calculate the volume of 0.125 mol of butan-1-ol, in cm3. (iii) Calculate the minimum mass of potassium bromide required in step 1. [The molar mass of potassium bromide is 119 g mol1] (2) (2) (1) *N35693A01116* 11 Turn over<br />
PMT (b) Complete and label the diagram below of the apparatus assembled in steps 1, 2 and 3. [You may assume that the apparatus is suitably clamped.] (4) tap funnel concentrated sulfuric acid two-neckedask reactants 12 *N35693A01216*<br />
PMT (c) (i) State, with a reason, whether the upper or lower layer contains 1-bromobutane in step 6. (1)(ii) The product is washed with concentrated hydrochloric acid in step 7 to remove unreacted butan-1-ol. In step 8, why is the product then washed with sodium hydrogencarbonate solution and what causes a build up of gas? (2)(d) (i) What further step is necessary to purify the 1-bromobutane obtained in step 10? (1)(ii) How does the step in (d)(i) give information about the purity of the product? (1)(Total for Question 4 = 14 marks) TOTAL FOR PAPER = 50 MARKS *N35693A01316* 13<br />

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$Qu ties on Number 4 (a)(i Question Number 4 (a)(ii) Acceptable Answers Re t jec Mark t any clear indication that they appreciate / 0.1 80 0.8 (= 0.125) From the equation 1 mol butan-1-ol gives 1 mol of 1-bromobutane / ratio 1:1 OWTTE (1) As 80% yield, 0.125 mol of butan-1-ol gives 0.125 x 0.8 mol = 0.1 mol of 1-brombutane (1) Accep the proportion calculation and the mole ratio Examples: Number of moles of butan-1-ol = 0.1 x 100 OR butane Nu = 80 100 (= 0.1) In both these examples butan-1-ol/ 1-bromobutane as appropriate, must be present to g The numerical expression alone would gain (1) OR As above examples but additionally using molar masses to calculate masses e mb r of moles of 1-bromo x 0.125 ain (2) Acceptable Answers Reject Mark 25 = 1.4 /11.42/11.420/11.419753 cm (1) 74 x 0.125 (1) = 9.25 g) 9. 0.81 ie Accept 11.4 /11.42/11.420/11.419753 cm3 (2) (with no working) ign re sf unless only one 1sf 6CH0701 1006<br /> Question Number 4 (a)(iii) Question Number 4 (b) Acceptable Answers Reject Mark 0.125 x 119 = 14.875 /14.87/14.88/14.9/15 (g) 1 s Acceptable Answers Reject Mark heated beaker (of cold water) stopper in the top/tap funnel in the top of the condenser unless clearly open Flask in beaker of labelled cold water (1) Water need not be drawn in but Condenser with jacket (1) Need not be labelled, can be at any angle so long as it goes upwards Condenser inlet and outlet with correct water direction (1) This mark can be given if no jacket is present open at top and no leaks(1) This mark is conditional on a condenser Do not penalise accidental closures in drawing or attempts to draw out perimeter of apparatus making the condenser appear closed If distillation set up is drawn the beaker of cold water mark can be awarded 6CH0701 1006<br /> Qu ties on Number 4 (c)(i Question Number 4 (c)(ii) Question Number 4 (d )(i) Question Number 4 (d)(ii) Acceptable Answers Re t jec Mark Lower layer as more dense Lower layer is 1-bromobutane because it is denser Lower layer as denser than wate r / butan-1-ol Acceptable Answers Reject Mark e ove / neutralize / react with remaining acid/H2SO4 oric acid/HCl/acid/sulfuric To r m hydrochl (1) by re cting to form carbon dioxide (gas) (1) Acceptable Answers Reject Mark Dry/filter/ an or yth ng else /distil isti late illation /redistil Distillation /fractional dist /d Accept any recognisable spelling Ignore further description Allow a description which includes the words he ati g / boiling followed by condensing Acceptable Answers Reject Mark re if it agrees)} asure boiling temperature of liquid {and Me compare with Data Book value (101.7 oC) (Pu OR Boils at boiling temperature of liquid/ 101.7 o range/ boils at one part OR Collect the product at 101.7 oC/ between 100 and 103 oC C / boils over a very icular temperature small temperature 6CH0701 1006<br />$

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