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CIE Jun 2015 v5 Paper 3 Q2
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![In this experiment you will determine the enthalpy change, H, for the reaction of zinc with iron(II) sulfate. Zn(s) + FeSO4(aq)Fe(s) + ZnSO4(aq) In order to do this, you will determine the enthalpy changes for the reactions of zinc and iron with aqueous copper(II) sulfate. Excess of the two metals will be used during the determinations. Then you will use Hess Law to calculate the enthalpy change for the reaction above. FA 4 is zinc, Zn. FA 5 is iron, Fe. FA 6 is 0.500 mol dm3 copper(II) sulfate, CuSO4. (a) Determination of the enthalpy change for the reaction of zinc, FA 4, with aqueous copper(II) sulfate, FA 6. MethodSupport a plastic cup inside the 250 cm3 beaker. Use the measuring cylinder to transfer 25 cm3 of FA 6 into the plastic cup. Measure and record the initial temperature of the solution in the space below. Add all the FA 4 from the container to the FA 6 in the plastic cup. Stir constantly until the maximum temperature is reached. Measure and record the maximum temperature. Tilt the cup if necessary to ensure the thermometer bulb is fully immersed. Calculate and record the temperature rise.UCLES 2015 9701/35/M/J/15 [3] [Turn over<br />
(b) Calculations Show your working and appropriate signi cantgures in thenal answer to each step of your calculations. (i) Calculate the energy produced during this reaction. [Assume that 4.2 J are needed to raise the temperature of 1.0 cm3 of solution by 1.0 C.] (ii) Calculate the number of moles of copper(II) sulfate in 25 cm3 of FA 6. energy produced =J (iii) Calculate the enthalpy change, in kJ mol1, for the reaction below. Zn(s) + CuSO4(aq)Cu(s) + ZnSO4(aq) moles of CuSO4 =mol enthalpy change =kJ mol1 sign value [2]UCLES 2015 9701/35/M/J/15<br />
(c) Determination of the enthalpy change for the reaction of iron, FA 5, with aqueous copper(II) sulfate, FA 6. MethodSupport the second plastic cup inside the beaker. Use the measuring cylinder to transfer 25 cm3 of FA 6 into the plastic cup. Measure and record the initial temperature of the solution in the space below. Add all the FA 5 from the container to the FA 6 in the plastic cup. Stir constantly until the maximum temperature is reached. Measure and record the maximum temperature. Tilt the cup if necessary to ensure the thermometer bulb is fully immersed. Calculate and record the temperature rise. Keep solution FA 6 for use in Question 3. (d) Calculations Show your working and appropriate signi cantgures in thenal answer to each step of your calculations. (i) Calculate the energy produced during this reaction. [Assume that 4.2 J are needed to raise the temperature of 1.0 cm3 of solution by 1.0 C.] [2] (ii) Calculate the enthalpy change, in kJ mol1, for the reaction below. Fe(s) + CuSO4(aq)Cu(s) + FeSO4(aq) energy produced =J enthalpy change =kJ mol1 sign valueUCLES 2015 9701/35/M/J/15 [2] [Turn over<br />
(e) Use your values for the enthalpy changes calculated in (b)(iii) and (d)(ii) to calculate the enthalpy change for the reaction below. Zn(s) + FeSO4(aq)Fe(s) + ZnSO4(aq) Show clearly how you obtained your answer by drawing a Hess Law energy cycle. (If you were unable to calculate the enthalpy changes, assume that the value in (b)(iii) is 210 kJ mol1 and the value in (d)(ii) is 144 kJ mol1. Note: these are not the correct values.) enthalpy change =kJ mol1 sign value [2] (f) (i) Calculate the maximum percentage error in the temperature rise in (c). percentage error =% (ii) Apart from using a more accurately calibrated thermometer, suggest one improvement that could be made to this experiment that would increase the accuracy.[2] [Total: 13]UCLES 2015 9701/35/M/J/15<br />](https://learnah.org/wp-content/uploads/2018/08/June_2015_v5_QP_-_Paper_3_CIE_Chemistry_A-level_2-0.jpg)
![PMT Page 3 Mark Scheme Syllabus Paper Cambridge International AS/A LevelMay/June 2015 9701 35 Question Indicative material Mark (c)(i)(ii) Correctly calculates Concentration = 0.10.900 = 0.09(00) and No. of moles = (i)(b) /1000 (iii)(iv) Correctly calculates No. of moles of I 2 = 0.5(ii) and Concentration of I 2 = (iii)/25 1000 (v) Equation correctly balanced 3+ 2+ 2Fe + 2I2Fe + I and use of 2:1 mole ratio: answer to (v) = 2(iv) (vi) Two steps are required:Mr = 38.56 (v)Mass of water = Mr(55.8 + 18 + [296.1]) or Mr266 Correctly calculates x from mass of water moles of water = mass 18 and answer expressed to nearest integer Final answers to (i)(v) shown to 24 sf (minimum 4 steps attempted) [6] [Total: 14] (a) Initial and highest thermometer readings shown and temperature rise correctly calculated with unambiguous headings and correctly displayed units. Examiner to calculate Supervisors and candidates T. Calculate the difference between the two values. III and IV awarded dependant on comparability between Supervisors and candidates T values. (b)(i)(ii) Correctly calculates energy produced = 254.2T(a) and moles of FA 6 = 0.525 / 1000 (= 0.0125) (iii) and both answers to a minimum of 2 sf Correct expression H = (i) / 1000(ii) (c) Precision of readings shown in (a) and (c): all four thermometer readings shown to 0.0 or 0.5 C Examiner to calculate Supervisors and candidates T. Calculate the difference between the two values.Cambridge International Examinations 2015 [3] [2]<br />
PMT Page 4 Mark Scheme Syllabus Paper Cambridge International AS/A LevelMay/June 2015 9701 35 Marks awarded dependant on comparability between Supervisors [2] and candidates T values. (d)(i)(ii) Correct expressions energy produced = 254.2T(c) and H = (d)(i) / 1000 x (b)(ii) Correct (negative) sign shown in answers to (b)(iii) and (d)(ii) [2] and both answers shown to 24 sf (e) Hess Law cycle drawn to show displacement equation across top left hand downward arrow, labelled (b)(iii) or calculated value right hand downward arrow, labelled (d)(ii) or calculated value or allow from clear use of equations: Fe equation reversed and added to Zn equation or arrows showing correct directions Correctly calculates (b)(iii)(d)(ii), with correct sign. (f)(i) Correctly calculates: max % error = ( 2 x 0.5 T(c))100 [2] (ii) One of the following: [2] use a more concentrated solution of copper(II) sulfate (and larger quantities of metals) use a lid with hole for thermometer or another specific suggestion to improve insulation plot a cooling curve use a larger volume / use a burette / pipette to reduce percentage error in volume use a pipette / burette instead of a measuring cylinder [Total: 13]Cambridge International Examinations 2015<br />](https://learnah.org/wp-content/uploads/2018/08/June_2015_v5_MS_-_Paper_3_CIE_Chemistry_A-level_2-0.jpg)
