Edexcel Jun 2011 Paper 3 Q5 (with explained solutions) |

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Edexcel Jun 2011 Paper 3 Q5

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PMT 5 An experiment was carried out to prepare iodoethane, CH3CH2I. Procedure 1. Put some solid, moist red phosphorus into a flask. 2. Add ethanol to the flask. 3. Set up the apparatus as shown in diagram 1. Diagram 1 water out water in water bath heat 4. Add 25.4 g of powdered iodine, in small portions, to the flask. 5. Before each addition, remove the condenser. Add the iodine and then immediately replace the condenser. 6. When all the iodine has been added, allow the flask to stand for 10 minutes and then heat the flask for one hour as shown in diagram 1. 7. Separate the iodoethane from the reaction mixture and dry it. 8. Finally, purify the iodoethane using the apparatus shown in diagram 2. Collect the iodoethane over a suitably narrow temperature range. 12 *P37682A01216*<br />
PMT water out water in water bath Appearance Flammability Boiling temperature / C Diagram 2 heat Data Name ethanol colourless liquid flammable flammable 78 72 iodoethane colourless liquid Equations 2P + 3I2 (cid:111) 2PI3 3CH3CH2OH + PI3 (cid:111) 3CH3CH2I + H3PO3 *P37682A01316* 13 Turn over<br />
(a) (i) Identify the technique shown in each diagram. PMT (2) Diagram 1Diagram 2(ii) Explain why a stopper should not be placed in the top of the condenser shown in diagram 1. (1)(b) (i) Give one reason why the iodine was added over a period of time and in small amounts. (1)(ii) Explain why water baths were used in both step 6 and step 8 rather than heating the flasks directly with a Bunsen flame. (1)(iii) Suggest the temperature range suitable for the collection of iodoethane shown in diagram 2. (1) FromtoC 14 *P37682A01416*<br />
(c) (i) Calculate the number of moles of iodine, I2, in 25.4 g of iodine. Use the relative atomic mass of I = 127 (ii) In this reaction, 1 mol I2 forms 2 mol CH3CH2I. Calculate the maximum mass of iodoethane, in g, that could be formed from 25.4 g of iodine. Use the following relative atomic masses: C = 12, H = 1, I = 127 (iii) In a preparation, the mass of iodoethane collected was 23.4 g. Calculate the percentage yield in this preparation. PMT (1) (3) (1) (Total for Question 5 = 11 marks) TOTAL FOR PAPER = 50 MARKS *P37682A01516* 15<br />

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$Question Number 5 (a) (i) Diagram 1: (heating under) Acceptable Answers reflux Diagram 2: distillation (1) (1) IGNORE simple before distillation Acceptable Answers Question Number 5 (a) (ii) (Expansion of vapour will) build up pressure / prevent explosion Question Number 5 (b) (i) The reaction is vigorous Acceptable Answers OR the reaction is exothermic OR the reaction is (very) fast or violent ALLOW To stop a reactant or product escaping ALLOW To prevent too much heat being produced IGNORE any reference to accidents Mark Mark Mark Reject fractional distillation /condensation Reject Just dangerous OR to prevent vapour escaping OR so that heat is not able to escape Reject So that all the iodine reacts/so that iodine is not in excess OR It is very reactive OR Increase the time for which the solids are in contact OR To compensate for heat loss OR Iodine/I2 is toxic 6CH0701 1106<br /> Mark Reject Any mention that iodine/I2 is flammable OR Just gentle heating OR To prevent the reaction going (any) faster Question Number 5 (b) (ii) (One or both of) the liquids Acceptable Answers flammable / the mixture is flammable/ the organic compounds are flammable OR ethanol and iodoethane are flammable OR ethanol is flammable OR iodoethane is flammable OR to keep the temperature below 100C OR to control the temperature throughout the heating OR for uniform heating OR to prevent uneven heating Mark Question Number 5 (b) (iii) Acceptable Answers Reject Any lower temperature: 69 to 71 (oC) Any upper temperature: 73 to 75 (oC) NOTE: Award the mark if the correct numbers are written the other way round (e.g. from 74 (oC) to 70 (oC)) 6CH0701 1106<br /> Acceptable Answers Question Number 5 (c) (i) 0.1(00) (mol) Question Number 5 (c) (ii) 1st mark Acceptable Answers Reject 0.2(00) (mol) Reject Mark Mark Mr (CH3CH2I) = 156 (1) 0.2(00) mol of iodoethane (1) 2nd mark CQ on (c)(i) 0.2(00) x 156 = 31.2 g (1) 3rd mark is cq on moles of iodoethane NOTE If 0.2(00) mol of iodine given in Q5 (c)(i), by CQ marking can score all 3 marks here with: Mr (CH3CH2I) = 156 (1) 0.4(00) mol of iodoethane 0.4(00) x 156 = 62.4 g (1) (1) 6CH0701 1106<br /> Question Number 5 (c) (iii) Mark Acceptable Answers Reject 23.4 x 100 % = 92.1% 25.4 23.4 x 100 % = 75% ans to (c)(ii) IGNORE s.f. except 1 s.f. NOTE If 0.2(00) mol of iodine given in 5 (c)(i), by CQ marking can score the mark here with: 23.4 x 100 % = 37.5% 62.4 TOTAL FOR PAPER = 50 MARKS 6CH0701 1106<br />$

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