Edexcel Jan 2011 Paper 1 Q19 (with explained solutions) |

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Edexcel Jan 2011 Paper 1 Q19

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19 The enthalpy change of combustion of ethanol was determined using the apparatus shown in the diagram below. In the experiment, the temperature increase of the water in the beaker is measured when a known mass of the ethanol is burned. PMT beaker water (a) The results of the experiment are summarised in the table below. spirit burner Mass of water in the beaker Mass of spirit burner + contents (initial) Mass of spirit burner + contents (final) Temperature of water (initial) Temperature of water (final) 250.00 g 63.21 g 62.47 g 21.0 C 31.5 C (i) Calculate the heat energy produced by the combustion of the alcohol using the equation heat energy produced (J) = mass of water4.18temperature change (1) *N37962A02124* 21 Turn over<br />
(ii) Calculate the number of moles of ethanol burned in this experiment (the formula of ethanol is C2H5OH). PMT (iii) Use the equation below to calculate the enthalpy change of combustion of ethanol in kJ mol1. Give the value an appropriate sign. (cid:168)H = heat energy producednumber of moles (b) The data book value for the enthalpy change of combustion of ethanol is 1370 kJ mol1. (i) Calculate the percentage error in the value calculated in (a)(iii) in comparison with the data book value. (3) (2) (1) 22 *N37962A02224*<br />
PMT (ii) List three ways in which the design of the experiment causes the results to be so different from the data book value. (You should be specific but detailed explanations are not required.) (3) 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (iii) Use the data book values for enthalpy changes of combustion given in the table below to calculate the enthalpy change of formation of ethanol. (3) Substance C(s, graphite) H2(g) C2H5OH(l) Enthalpy change of combustion / kJ mol1 394 286 1370 (Total for Question 19 = 13 marks) TOTAL FOR SECTION B = 60 MARKS TOTAL FOR PAPER = 80 MARKS *N37962A02324* 23<br />

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Question Number 19 (a) (i) Question Number 19 (a) (ii) Question Number 19 (a) (iii) Mark Mark Mark Reject 10000 (J) Reject 0.02 (mol) ethanol Acceptable Answers (q = 250 x (31.521.0) x 4.18 =) 10972.5 (J) IGNORE sf except 1 sf IGNORE units even if incorrect IGNORE any sign at this stage ALLOW 10.97 (kJ) Acceptable Answers (Mr ethanol) = 46 (1) (Mass ethanol burned = 63.2162.47 =) 0.74 (g) ALLOW 63.2162.47 as alternative to 0.74 (1) (Amount of ethanol = 0.7446 =) 0.0161 (mol) (1) NOTE: Moles of ethanol are CQ on molar mass and /or mass of ethanol burned IGNORE sf except 1 sf NOTE: Correct answer with no working /limited working scores (3) Mark the three points independently Acceptable Answers Reject Answer (i)(1000 x answer (ii)) (1) NOTE: Be aware of numbers held in calculator not corresponding to what is written in answer Value and negative sign (1) IGNORE sf except 1 sf NOTE: Answer consistent with (a)(i) and (a)(ii) with no working scores (2) E.g. 10.9725(0.7446) =682 (kJ mol1) ALLOW Just kJ as the units NOTE: If correct answer is given in J mol1, the units of J mol1 must be clearly given for the second mark to be awarded. Correct answer in J instead of J mol1 6CH01/01 1101<br />
Question Number 19 (b) (i) Question Number 19 (b) (ii) Mark Mark Acceptable Answers Reject 100 x (1370Answer to (iii))1370 = value e.g. 100 x (1370682)1370 = 50.2 % Incorrect rounding of final answer (0) Acceptable Answers Reject More accurate thermometer Just experimental /human error Experiment carried out at a different (laboratory) temperature Any three from: Heat loss (from the beaker)/beaker not insulated/heat loss as no lid on beaker (containing the water) /no stirring (1) Incomplete combustion (of the alcohol)/formation of soot (on beaker) (1) Not all of the energy from the flame is used to heat the beaker and/or the water OR Too large a distance between flame and beaker / no draught excluder (1) Heat capacity of the beaker is neglected/beaker absorbs heat/glass absorbs heat (1) Evaporation of the (hot) alcohol (1) Evaporation of the (hot) water (1) 6CH01/01 1101<br />
Question Number 19 (b) (iii) Reject Mark Acceptable Answers c [C] and trebling c [H2] (1) 2 C(s) + 3H2(g) +O2(g) (cid:138) C2H5OH(l) (cid:200) (cid:200) 2CO2 + 3H2O (cid:85)Hf = 2 x (394) + 3 x (286)(1370) =276 (kJ mol1) Correct expression or cycle (1) Evidence for both doubling H H Correct sign and answer (1) Correct answer with no working scores (3) Correct answer with an incorrect cycle (3) IGNORE units even if incorrect Alternatively the following answers score as shown even with incorrect cycle or incorrect units NOTE: (+)276 with or without working scores (2) (+)690 with or without working scores (2) 690 with or without working scores (1) 552 with or without working scores (2) 1134 with or without working scores (2) (+)1134 with or without working scores (1) (+)10 with or without working scores (2) REMINDER IF ANY OTHER ANSWER IS GIVEN: ALL WORKING MUST BE CHECKED TO SEE IF ANY MARKS CAN BE AWARDED TOTAL FOR SECTION B = 60 MARKS 6CH01/01 1101<br />

Question 15 16 17 18 19

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