Edexcel Jan 2010 Paper 1 Q18 (with explained solutions) |

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Edexcel Jan 2010 Paper 1 Q18

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PMT (2) 18 This question is about hexane, C6H14, and hex-1-ene, C6H12. (a) What test would you use to distinguish between hexane and hex-1-ene? Give the results of the test for each substance. Test:Result with hexane:Result with hex-1-ene:(b) Hex-1-ene has a number of isomers, including two stereoisomers of hex-2-ene. (i) Complete the formula to show the structure of E-hex-2-ene. C C * (ii) Explain why stereoisomerism can occur in alkenes, and why hex-2-ene has stereoisomers but hex-1-ene does not. (1) (2)16 *N35131A01624*<br />
PMT (c) The enthalpy change of combustion of hexane was measured using a spirit burner to heat a known mass of water in a calorimeter. The temperature rise of the water was measured. The results of the experiment are shown below. Mass of hexane burnt Mass of water in calorimeter Initial temperature of water Final temperature of water 0.32 g 50 g 22 C 68 C The specific heat capacity of water is 4.18 J g1C1. (i) Calculate the energy in joules produced by burning the hexane. Use the expression energy transferred = massspecific heat capacitytemperature change. (ii) Calculate the enthalpy change of combustion of hexane. The mass of 1 mole of hexane is 86 g. Give your answer to TWO significant figures. Include a sign and units in your answer. (iii) The value for the enthalpy change of combustion in this experiment is different from the value given in data books. Suggest TWO reasons for this difference. (1) (3) (2)*N35131A01724* 17 Turn over<br />
PMT (iv) A student suggested that the results would be more accurate if a thermometer which read to 0.1C was used. Explain why this would not improve the accuracy of the result. A calculation is not required. (1)(d) Hex-1-ene can be converted to hexane in the following reaction. (i) What catalyst is used in this reaction? C6H12(l) + H2(g)C6H14(l) (1)(ii) The enthalpy change of this reaction Hreaction can be calculated from the following enthalpy changes of combustion. Substance Hex-1-ene, C6H12 Hydrogen, H2 Hexane, C6H14 Enthalpy change of combustion /kJ mol1 4003 286 4163 Complete the Hess cycle by adding labelled arrows. Use your cycle to calculate the enthalpy change Hreaction. (3) C6H12(l) + H2(g) Hreaction C6H14(l) 6CO2(g) + 7H2O(l) 18 Hreaction =kJ mol1 *N35131A01824*<br />
PMT (iii) The enthalpy change for the reaction of some other alkenes with hydrogen is shown below. Reaction C3H6 + H2C3H8 C4H8 + H2C4H10 C5H10 + H2C5H12 Standard enthalpy change / kJ mol1 125 126 126 Explain why the values are so similar. (1)(Total for Question 18 = 17 marks) *N35131A01924* 19 Turn over<br />

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PMT Mark Smokiness of flame Bromide Iodine Goes clear Reject Mark Acceptable Answers Reject Allow formulae throughout instead of names Test : add bromine (water) /bromine solution ALLOW bromine gas /bromination (1) Result: no change with hexane / stays orange brown/ stays red brown/ stays yellow and goes colourless with hex-1-ene(1) 2nd mark cq on 1st OR Test : add (acidified) potassium manganate((VII)) (solution) (1) ALLOW potassium permanganate for potassium manganate(VII) Result: no change with hexane/stays purple and goes colourless / brown with hex-1-ene (1) OR Test : add alkaline potassium manganate((VII)) (solution) (1) ALLOW potassium permanganate for potassium manganate(VII) Result: no change with hexane/stays purple and goes green with hex-1-ene (1) Acceptable Answers CH3 H C H C3H7 ALLOW Partially or fully displayed as long as the two H are trans Allow bonds which go closer to the H than to C of alkyl groups on l.h.s. Question Number 18 (a) Question Number 18 (b) (i)<br />
PMT Acceptable Answers Reject QWC C=C restricts rotation/ C=C prevents twisting /C=C cant rotate/ lack of free rotation round C=C (so the groups cant change position relative to the bond) (1) Hex2-ene has different groups on the C at each end of C=C / hex-1-ene has 2 hydrogens on the C at one end of C=C / hex-1-ene doesnt have different groups on the C at one end of C=C / hex-1-ene has no group which takes priority on the C at one end of C=C (1) (answer can be considered from either hex 1- ene or hex-2-ene) Alkenes cant rotate Double bond is fixed Bonds cant rotate Double bond is on first carbon (unless further explanation) Acceptable Answers Reject ignore signs (50 x 46 x 4.18) = 9614(J)/ 9.614 kJ (if converted to kJ units must be stated) ALLOW 9610 / 9600 /9.61 kJ /9.6 kJ (50.32 x 46 x 4.18) = 9676(J) Mark Mark Question Number 18 (b) (ii) Question Number 18 (c) (i)<br />
PMT Reject Mark Acceptable Answers One mark each for moles of hexane energy change sign, units, 2 sig figs (for energy change calculated) Moles hexane = 0.32/86 = (3.72 x 10-3) (1) (9614/ 3.72 x 10-3) = 2584000 J/ 2584 kJ (1) H = -2600 kJ mol-1 /-2 600 000 J mol-1 / -2.6x106 J mol-1 (1) Allow TE: 0.32g in (i) (gives 61.53J), H = -17 kJ mol-1 /-17 000 J mol-1 /-1.7x104 J mol-1 50.32g in (i) (gives 9676J) H = -2600 kJ mol-1 /-2 600 000 J mol-1 /-2.6x106 J mol-1 Rounding of moles to 4x10-3 gives 2400 kJ mol-1 or-15 kJ mol-1 max 2 (loses moles mark) Answer alone (3) Max 2 if negative sign missing and/or more than 2 sf or error in units Mark Acceptable Answers Reject Any 2 from:Heat losses (from calorimeter)/ poor insulationIncomplete combustion/burningIncomplete transfer of heat/ loss by convectionEvaporation of fuel (after weighing)Heat capacity of calorimeter (notMeasurements not carried out under included)/ heat absorbed by calorimeter standard conditions /H2O is gas, not liquid, in this experiment Just energy losses Not all hexane burns Data books give average values Hexane is impure Human error Question Number 18 (c) (ii) Question Number 18 (c) (iii)<br />
PMT Mark Mark Acceptable Answers Reject Using 0.1C thermometer gives a more precise reading but does not improve accuracy Reject Zeolite Carbon Hydrogen Uv light Error in reading temperature is less than the effect of ignoring heat loss etc ALLOW Other errors are greater than error in temperature reading / Readings are within margins of error/ The accuracy with the thermometer is not significantly different from other measurement errors / 0.1C is insignificant compared to temperature change / Using 0.1C thermometer does not change significant figures in final answer / Using 0.1C thermometer does not reduce errors Acceptable Answers Nickel / Ni Finely divided nickel/ Raney nickel ALLOW Platinum /Pt Palladium/ Pd Rhodium/ Rh Accept one of the above answers combined with a comment such as at high temperature, heat also needed, under pressure, lumps of, powdered Accept combinations of above answers eg Pt and Pd Question Number 18 (c) (iv) Question Number 18 (d) (i)<br />
PMT Reject Mark Acceptable Answers Left hand arrow, pointing down, labelled Hc hex-1-ene + Hc hydrogen/ -4003-286/-4289 OR Pointing up with signs given above reversed (1) Right hand arrow pointing down labelled Hc hexane / -4163 OR Pointing up with signs given above reversed (1) Ignore oxygen on both arrows Arrows may be labelled H1 etc if key given or use of numbers in calculation makes this obvious. (Hreaction4163 = -4003286 / or words applying Hess law correctly) Hreaction = -126 however obtained(1) TE: If arrows point up and signs are not reversed Hreaction = +126 Max (1) Acceptable Answers Reject Same (number and type of) bonds are broken and made in each reaction / one C=C (and one H-H) are broken and two C-H made ALLOW reaction is CH=CH- + H2-CH2-CH2- each time (Similar energy change) as in each case H2 reacts with C=C All are alkenes going to alkanes all have the same double bond which reacts in the same way Acceptable Answers Reagent: chlorine/ Cl2 (1) Condition: uv/ sunlight (1) ALLOW light Mark independently Ignore reference to temp and pressure if given with uv light. If answers reversed/both on one line 1 out of 2 Reject Cl Just heat Acceptable Answers (free) radical (1) Substitution (1) Mark independently Reject Mark Mark Mark Question Number 18 (d) (ii) Question Number 18 (d) (iii) Question Number 19 (a) (i) Question Number 19 (a) (ii)<br />

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