Edexcel Jun 2015 (IAL) Paper 3 Q4 (with explained solutions) |

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Edexcel Jun 2015 (IAL) Paper 3 Q4

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4 Cyclohexene, C6H10, can be prepared by dehydrating cyclohexanol, C6H11OH, with phosphoric acid. H3PO4 C6H11OH C6H10 + H2O Procedure Step 1 12.0 cm3 of cyclohexanol was put into a small flask. 5 cm3 of concentrated phosphoric acid, an excess, was added slowly to the cyclohexanol using a dropping pipette. Some anti-bumping granules were added to the mixture and the flask was set up for distillation. Step 2 The portion of the distillate collected between 80(cid:113)C and 90(cid:113)C contained only cyclohexene and water. Step 3 The distillate of cyclohexene and water was transferred to a separating funnel and a saturated solution of sodium chloride was added. Most of the water which was in the distillate went into the saturated sodium chloride layer. Step 4 The crude cyclohexene was run out of the separating funnel and dried with anhydrous calcium chloride. Step 5 The calcium chloride was removed by filtration through glass wool, and the liquid was redistilled to collect pure cyclohexene. Cyclohexene has an unpleasant smell and irritates the eyes, so the entire experiment was carried out in a fume cupboard. In Step 1, tubing was connected to carry any uncondensed cyclohexene to a drain. (a) The chemicals involved in this reaction are all hazardous if they make contact with the eyes, or if swallowed or inhaled. Other than their effect on the eyes or their toxicity, state two different hazards of the chemicals involved in this reaction. Name the chemical associated with each hazard. (2) Chemical Hazard *P44883A01116* 11 Turn over<br />
(b) Calculate the number of moles of cyclohexanol used in this experiment. The density of cyclohexanol is 0.962 g cm3. (c) Draw a labelled diagram showing how to distil the reaction mixture in Step 1 and collect the distillate boiling between 80(cid:113)C and 90(cid:113)C. (2) (4) 12 *P44883A01216*<br />
(d) Explain the difference between a dehydrating agent, such as the phosphoric acid used in Step 1, and a drying agent, such as the anhydrous calcium chloride used in Step 4. (2)(e) Suggest one advantage of using glass wool, rather than filter paper, when removing the calcium chloride in Step 5. (1)(f) Calculate the mass of cyclohexanol needed to obtain 10.0 g cyclohexene if the yield is 75%. (3) *P44883A01316* 13 Turn over<br />
(g) The cyclohexene was tested by mixing it with bromine dissolved in an organic solvent. (i) What colour change would be observed? (1)(ii) Give the displayed formula for the organic product of this reaction. (1) (Total for Question 4 = 16 marks) TOTAL FOR PAPER = 50 MARKS 14 *P44883A01416*<br />

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$Acceptable Answers Two different hazards must be given to score 2 marks. Phosphoric acid corrosive ALLOW burns skin/ damages skin (1) Cyclohexanol / cyclohexene (in)flammable ALLOW Irritant (1) IGNORE Comments on glass wool, calcium chloride Cyclohexene / cyclohexanol is volatile Acceptable Answers Correct final answer scores (2) Mass of 12 cm3 C6H11OH = 12 x 0.962 (1) = 11.544 / 11.54 / 11.5 (g) Number of moles = (11.544 / 100 = 0.11544) = 0.115 / 0.12 (mol) ALLOW TE from incorrect mass (1) Ignore sf except 1 sf Reject Additional hazards e.g. irritant harms skin carcinogenic Additional hazards e.g. explosive carcinogenic Reject 0.11 Mark Mark Question Number 4(a) Question Number 4(b)<br /> Question Number 4(c) Reject Conical flask Sealed receiver, beaker Acceptable Answers Flask with heat source AND stillhead AND a closed system to the left hand side of the outlet to the condenser. Heat source can be electrical heater, water bath ALLOW bunsen or just arrow ALLOW appropriate tubing or flask with long neck as alternative to stillhead (1) Bulb of thermometer opposite opening to condenser (1) Water condenser sloping downwards AND direction of water (1) Connected to receiver with a vent OR delivery tube to an open narrow necked flask (1) Ignore fractionating column if included. Drawing showing reflux distillation scores max 1 for water direction in condenser. Mark<br /> Mark Acceptable Answers Reject Reference to removal of solvents other than water Dehydrating agent removes water in a (chemical) reaction OR causes two H and one O atoms to be lost (in a reaction) OR removes the elements of water (from reactant molecules) OR removes water from molecules of a compound ALLOW answers indicating a reaction occurs eg H+ protonates OH in alcohol forming water removes water causing bonds to break reference to elimination reactions (1) Drying agent removes water mixed with other materials OR removes water from a mixture OR removes water in a physical change ALLOW Absorbs water (1) A dehydrating agent removes water in a reaction but there is no reaction when a drying agent removes water scores 1 Question Number 4(d)<br /> Reject Mark Acceptable Answers Glass wool less absorbent OR No cyclohexene left on wool OR filtration is faster through glass wool OR filter paper absorbs liquids/ product/ mixture IGNORE yield is higher with glass wool/ lower with filter paper more efficient filtration Question Number 4(e)<br /> Mark Acceptable Answers Reject Theoretical yield = (10.0 x 75/100) = 7.5g (0.12195 x 75/100) = 0.09146 Look at final answer. If correct award 3 marks. There are several correct methods. All involve calculating a number of moles of cyclohexene, a mass of cyclohexanol and the use of the 75% but these stages can be done in different orders. EITHER Need theoretical yield of (10.0 x 100/75) = 13.3333 / 13.33 / 13.3 g (1) 13.3333g= (13.3333/82) = 0.1626 / 0.163 mol cyclohexene (1) 0.1626 mol cyclohexanol = 16.26 / 16.3 / 16 g (1) OR Mol of cyclohexene = (10/82) = 0.12195 (1) Mol of cyclohexanol = (0.12195 x 100/75) = 0.1626 (1) Mass of cyclohexanol = (0.1626 x 100) = 16.26 / 16.3 / 16 g (1) OR Mol of cyclohexene = (10/82) = 0.12195 (1) Theoretical mass of cyclohexanol = (0.12195 x 100) = 12.195/12.2g (1) Mass of cyclohexanol = (12.2 x 100/75) = 16.26 / 16.3 / 16 g (1) ALLOW 16.2 (g) in all methods from rounding 9.146 (g) from incorrect use of 75% scores (2) Ignore SF in final answer except 1 SF Question Number 4(f)<br /> Acceptable Answers Reject Mark Red to colourless 1 Brown / red-brown / orange / yellow/ yellow-brown to colourless ALLOW Brown / red-brown / orange / yellow is decolorised. IGNORE Clear for colourless Acceptable Answers Reject Mark Benzene ring Just skeletal formula/ molecular formula Bromoalcohols Non-adjacent Br atoms ALLOW Rings with CH2 and/or CHBr IGNORE Angles in ring Placing of H and Br inside or outside ring Total for Question 4 = 16 marks Question Number 4(g)(i) Question Number 4(g)(ii)<br />$

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