Edexcel Jun 2016 (IAL) Paper 4 Q

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13 This is a question about using the Landolt Iodine Clock to study the reaction kinetics of iodate(V) ions reacting with hydrogensulfate(IV) ions. Reaction 1 IO 3 (aq) + 3HSO3 (aq) (cid:111) I(aq) + 3HSO4 (aq) One version of this clock involves the iodide ions formed reacting rapidly with the iodate(V) ions in acid solution to form iodine: Reaction 2 IO 3 (aq) + 5I(aq) + 6H+(aq) (cid:111) 3I2(aq) + 3H2O(l) The iodine is immediately reduced to iodide by the hydrogensulfate(IV) ions: Reaction 3 I 2(aq) + HSO3 (aq) + H2O(l) (cid:111) 2I(aq) + HSO4 (aq) + 2H+(aq) Once all of the hydrogensulfate(IV) ions have been used up, then the iodine reacts with starch to produce a blue-black complex. (a) What would be the problem if the amount of hydrogensulfate(IV) ions were in excess? (1)(b) Why is it important that Reaction 2 and Reaction 3 are very much faster than Reaction 1? (1)(c) A series of experiments is carried out in which different volumes of the iodate(V) ions solution are used. (i) Why is it important that the temperature is kept constant? (1)20 *P46664A02028* D O N O T W R I T E I N T H I S A R E A D O N O T W R I T E I N T H I S A R E A D O N O T W R I T E I N T H I S A R E A<br /> (ii) It is assumed that the initial rate of reaction is proportional to 1/time taken for the blue-black complex to form. The following results are obtained. Complete the table and use the results to plot a graph of 1000/time on the vertical axis, against the volume of iodate(V) ions on the horizontal axis. Volume of IO3 (aq) / cm3 Time taken, t / s 1000 t / s1 10.0 180 5.56 8.0 200 5.00 6.0 300 3.33 5.0 357 2.80 4.0 444 2.25 (5) 2.0 900 (iii) Suggest a suitable piece of apparatus for measuring the volume of the solution containing iodate(V) ions. (1)A E R A S I H T N I E T I R W T O N O D A E R A S I H T N I E T I R W T O N O D A E R A S I H T N I E T I R W T O N O D *P46664A02128* 21 Turn over<br /> (iv) If the total volume of the reaction mixture is kept constant, the volume of the iodate(V) ion solution may be used instead of the concentration to plot the graph. Explain why this is possible (1)(v) Deduce the order of the reaction with respect to iodate(V) ions. Justify your answer. (2)(vi) Reaction 1 is first order with respect to hydrogensulfate(IV) ions. Outline how you would show this. (1)(vii) Write the rate equation for Reaction 1. State the units of the rate constant. Rate equation: (2) Units of rate constant22 *P46664A02228* D O N O T W R I T E I N T H I S A R E A D O N O T W R I T E I N T H I S A R E A D O N O T W R I T E I N T H I S A R E A<br /> A E R A S I H T N I E T I R W T O N O D A E R A S I H T N I E T I R W T O N O D A E R A S I H T N I E T I R W T O N O D (d) The Landolt Iodine Clock can be used to determine the activation energy of Reaction 1 using the equation: ln rate =E a1 R T + constant (i) State the experimental measurements you would make to provide the numerical data for the calculation of the activation energy. (1)(ii) Describe how you would use your experimental measurements to obtain a value for the activation energy. You should includehow the data are processed the graph you would plot and its expected shapehow the activation energy of the reaction can be calculated from the graph produced. (6)(Total for Question 13 = 22 marks) TOTAL FOR SECTION B = 49 MARKS *P46664A02328* 23 Turn over<br />

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