Edexcel Jun 2009 Paper 3 Q4 (with explained solutions) |

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Edexcel Jun 2009 Paper 3 Q4

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PMT 4 2-chloro-2-methylbutane may be prepared by reacting 2-methylbutan-2-ol with concentrated hydrochloric acid: (CH3)2C(OH)CH2CH3 + HCl(CH3)2C(Cl)CH2CH3 + H2O The steps of the experimental procedure are as follows. 1. Place 5.00 cm3 of 2-methylbutan-2-ol and about 20 cm3 of concentrated hydrochloric acid into a separating funnel. 2. Continuously shake the mixture for 10 minutes. 3. Remove the aqueous layer and slowly add about 10 cm3 of dilute sodium hydrogencarbonate solution to the separating funnel. 4. Shake the mixture gently, inverting the separating funnel and opening the tap at regular intervals. 5. Remove the aqueous layer and transfer the organic layer to a conical flask. 6. Add a few pieces of anhydrous calcium chloride to the conical flask and shake the mixture. 7. Decant the liquid into a distillation flask and distil it to collect the pure 2-chloro-2-methylbutane. Data 2-methylbutan-2-ol 2-chloro-2-methylbutane Density / g cm3 Molar mass / g mol1 Boiling temperature / C 0.805 88 102 0.866 106.5 85.5 (a) Draw a diagram of the separating funnel, clearly labelling the 2-methylbutan-2-ol and the concentrated hydrochloric acid layers (step 1). [The density of concentrated hydrochloric acid is 1.18 g cm3.] (2) 10 *N34473A01016*<br />
PMT (b) (i) Why is it necessary to continuously shake the 2-methylbutan-2-ol and the concentrated hydrochloric acid for the reaction to occur (step 2)? (1)(ii) Explain the purpose of the sodium hydrogencarbonate solution (step 3). (1)(iii) Why is the tap of the separating funnel opened at regular intervals (step 4)? (2)(iv) What is the purpose of the calcium chloride (step 6)? (1)(v) What is meant by decant the liquid (step 7)? (1)*N34473A01116* 11 Turn over<br />
PMT (c) An incomplete diagram of the distillation apparatus is shown below. Heating mantle (i) Draw a thermometer in the diagram, showing clearly where the bulb of the thermometer is placed. (ii) Draw clearly labelled arrows on the diagram to show the flow of water into and out of the condenser. (1) (1) 12 *N34473A01216*<br />
PMT (d) The typical yield from this preparation is 70 %. Calculate the mass of 2-chloro-2-methylbutane that would be formed from 5.00 cm3 of 2-methylbutan-2-ol if a 70 % yield were obtained. The equation for the reaction and the table of data are repeated below. (CH3)2C(OH)CH2CH3 + HCl(CH3)2C(Cl)CH2CH3 + H2O 2-methylbutan-2-ol 2-chloro-2-methylbutane Density / g cm3 Molar mass / g mol1 Boiling temperature /C 0.805 88 102 0.866 106.5 85.5 (2) (Total for Question 4 = 12 marks) TOTAL FOR PAPER = 50 MARKS *N34473A01316* 13<br />

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Question Number 3 (b) Correct Answer Br Br Br OR Br Accept Reject C O Mark Accept OH for OH Question Number 4 (a) Correct Answer Reject Funnel with neck & tap (1) IGNORE stopper Organic layer above aqueous layer (1) Stand alone See diagrams Conical /filter / Buchner funnel with tap Funnel too full to be stoppered Mark YES NO<br />
Correct Answer Reject (Organic & aqueous) layers are immiscible OR consequence of not shaking e.g. layers form Accept to ensure layers mix IGNORE references to rate Just to mix reagents Explanations in terms of density differences Mark Correct Answer Reject Mark Just neutralize / neutralization 1 Neutralize (excess) acid / H+ Accept remove acid / H+ React with acid IGNORE Use of HCl for hydrochloric acid release of CO2 Correct Answer Reject Carbon dioxide / CO2 /gas is formed (1) Release pressure / pressure builds up (1) Correct Answer Reject Drying agent or to remove water Dehydrating agent Correct Answer Reject Mark Mark Mark To pour off the liquid leaving the solid behind Pour / pour carefully / transfer Question Number 4 (b)(i) Question Number 4 (b)(ii) Question Number 4 (b)(iii) Question Number 4 (b)(iv) Question Number 4 (b)(v)<br />
Mark Mark Mark Correct Answer Reject Bulk of the thermometer bulb adjacent to the outlet leading to the condenser (see diagram) At least half the thermometer bulb in this region Reject Correct Answer Water in through the lower tube and out through the upper If words are used (water in & water out) ignore the direction of any arrows Correct Answer Reject Mass of alcohol = 5 x 0.805 = 4.025 (g) (1) Moles of alcohol = 4.02588 = 0.0457 = moles of 2-chloro-2-methylbutane Mass 2-chloro-2-methylbutane (100% yield) = 0.0457 x 106.5 = 4.87 70% yield = 4.87 x 70 = 3.41 g (1) 100 ignore sf except for 1 sf If the molar masses are transposed penalise once (answer = 2.32 g) Correct answer and some working (2) Question Number 4 (c)(i) Question Number 4 (c)(ii) Question Number 4 (d)<br />

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