CIE Jun 2016 v2 Paper 5 Q1

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PMT A more reactive metal will displace a less reactive metal from a solution of its salt. This reaction is exothermic. If the same reaction is set up in an electrochemical cell then, instead of an enthalpy change, electrical energy is produced and a cell voltage can be measured. You are to plan an investigation of the reaction of three different metals (magnesium, iron and zinc) with aqueous copper(II) sulfate. You will plan to investigate whether there is a relationship between their cell potential values, , and their enthalpy changes of reaction, Hr. Mg(s) + Cu2+(aq)Mg2+(aq) + Cu(s) Fe(s) + Cu2+(aq)Fe2+(aq) + Cu(s) Zn(s) + Cu2+(aq)Zn2+(aq) + Cu(s) Copper(II) sulfate solution is classified as a moderate hazard. Zinc sulfate solution is classified as corrosive. Iron(II) sulfate solution is classified as a health hazard. (a) Predict how Hr may change as increases. Give a reason for your prediction.[1] (b) The first part of the investigation is to determine the enthalpy change, Hr, for the reaction of the same number of moles of three powdered metals with 0.500 mol dm3 copper(II) sulfate. When determining the Hr for the reaction of the metals listed above with aqueous copper(II) sulfate, the independent variable is,the dependent variable is.[2]UCLES 2016 9701/52/M/J/16<br /> You are provided with a sample of powdered metal and 50.0 cm3 of 0.500 mol dm3 aqueous copper(II) sulfate. (c) (i) Draw a fully labelled diagram to show how the apparatus should be set up to allow you to determine the increase in temperature of aqueous copper(II) sulfate. You should use apparatus normally found in a school or college laboratory. PMT [1] (ii) State the measurements you would make in your experiment.[2] (iii) Other than eye protection, state one precaution you would take to make sure that the experiment proceeds safely.[1]UCLES 2016 9701/52/M/J/16 [Turn over<br /> (iv) For the reaction with magnesium, calculate the mass of magnesium, in g, you would use so that it is in a small excess. You must show your working. [Ar: Mg, 24.3] PMT mass of Mg =g [2] (v) Explain why the metal used should be in powdered form rather than in strips.[1] (vi) The aqueous copper(II) sulfate and metal mixture should be stirred continuously. Explain why.[1] (d) In one experiment, the increase in temperature when excess magnesium powder is added to 50.0 cm3 of 0.500 mol dm3 aqueous copper(II) sulfate is 58.5 C. Calculate the enthalpy change for this reaction, Hr, in kJ mol1. Assume the specific heat capacity, c, of the reaction mixture is 4.18 J g1 K1. Assume 1.0 cm3 of 0.500 mol dm3 aqueous copper(II) sulfate has a mass of 1.0 g. Include a sign in your answer. Mg(s) + Cu2+(aq)Mg2+(aq) + Cu(s) Hr =kJ mol1 [2]UCLES 2016 9701/52/M/J/16<br /> (e) The second part of the investigation involves determining the cell potential, electrochemical cells. , for the three PMT cell reaction Mg(s) + Cu2+(aq)Mg2+(aq) + Cu(s) Zn(s) + Cu2+(aq)Zn2+(aq) + Cu(s) Fe(s) + Cu2+(aq)Fe2+(aq) + Cu(s) for the magnesium/copper Draw a diagram of the apparatus you would use to measure the cell. Your labels should include the names of the metals and the names and concentrations of the solutions you would use. [3] (f) Explain why the enthalpy change determination and cell potential determination should be carried out at the same temperature as each other.[1]UCLES 2016 9701/52/M/J/16 [Turn over<br /> PMT (g) Accepted values are shown for the cell reactions. cell reaction 1 2 3 Mg(s) + Cu2+(aq)Mg2+(aq) + Cu(s) Zn(s) + Cu2+(aq)Zn2+(aq) + Cu(s) Fe(s) + Cu2+(aq)Fe2+(aq) + Cu(s) Hr / V +2.72 +1.10 +0.78 Use your prediction in (a), your answer to (d) and data from the table to predict Hr values for reactions 2 and 3. Complete the table with these values. [1] [Total: 18]UCLES 2016 9701/52/M/J/16<br />

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