CIE Jun 2015 v1 Paper 3 Q2

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In this experiment you will measure the heat given out by the reaction of excess zinc with copper(II) sulfate solution and use this to estimate the concentration of the copper(II) sulfate. Zn(s) + CuSO4(aq)ZnSO4(aq) + Cu(s) FA 4 is zinc powder. FA 5 is aqueous copper(II) sulfate, CuSO4. (a) Method Read through the instructions carefully and prepare a table below for your results before starting any practical work.Support the plastic cup in the 250 cm3 beaker. Use the 50 cm3 measuring cylinder to transfer 40 cm3 of FA 5 into the plastic cup. Measure and record the initial temperature of the solution in the plastic cup. Start the stopwatch. Measure and record the temperature of the solution every 30 seconds up to and including the temperature at 2 minutes. Stir the solution frequently. 1 minutes, add all the powdered zinc to the solution in the plastic cup and At time t = 2 2 stir the mixture. Record the temperature every 30 seconds from t = 3 minutes up to and including t = 9 minutes. Stir the solution constantly. II III IV [4] (b) (i) On the grid opposite, plot the temperature (y-axis) against the time (x-axis). The scale for the temperature axis must allow you to plot a point with a temperature 5 C greater than the maximum temperature you recorded. (ii) (iii) Draw the following best- t straight lines on the graph.a line through the points between time t = 0 minutes and time t = 2 minutes a line through the points between time t = 5 minutes and time t = 9 minutes a vertical line at time t = 2 2 1 minutes Extrapolate therst two straight lines so that they intersect the vertical line at time t = 2 2 Use these extrapolated lines to determine the theoretical temperature change at time t = 2 2 1 minutes. 1 minutes.UCLES 2015 9701/31/M/J/15 change in temperature =C [5]<br /> UCLES 2015 9701/31/M/J/15 [Turn over<br /> (c) Calculations Show your working and appropriate signi cantgures in thenal answer to each step of your calculations. (i) Use your answer to (b)(iii) to calculate the heat energy produced in the reaction. (Assume that 4.2 J are required to increase the temperature of 1 cm3 of solution by 1 C.) heat energy produced =J (ii) The molar enthalpy change, H, for the reaction shown below is 219 kJ mol1. Zn(s) + CuSO4(aq)ZnSO4(aq) + Cu(s) Use this value and your answer to (i) to calculate the number of moles of copper(II) sulfate in your reaction. moles of CuSO4 =mol Use your answer to (ii), to calculate the concentration of copper(II) sulfate, in mol dm3, in FA 5. (iii) concentration of CuSO4 =mol dm3 [3] (d) (i) Calculate the maximum percentage error in the highest temperature that you recorded in your results table. maximum percentage error =% (ii) A student suggested that the concentration of the copper(II) sulfate could be determined more accurately if a greater mass of zinc had been used. Explain whether you agree with this student.(iii) A second student suggested that the concentration of the copper(II) sulfate could be determined more accurately if a smaller volume of copper(II) sulfate was used. Explain whether you agree with this student.[3] [Total: 15]UCLES 2015 9701/31/M/J/15<br />

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