(A410U10-1) 28 Examiner only 12. The oxidation of carbon monoxide to carbon dioxide in the presence of suitable catalysts is an important method of removing this toxic gas from gas mixtures produced during incomplete combustion. © WJEC CBAC Ltd. 2CO O2 2CO2 + Some catalysts for this reaction are produced by soaking aluminium oxide pellets in a solution of a transition metal chloride followed by drying. Two suitable transition metal chlorides are palladium chloride and ruthenium chloride. (a) These catalysts are examples of heterogeneous catalysts. (i) State what is meant by heterogeneous in this context. [1] (ii) Give another example of a heterogeneous catalyst, clearly identifying the reaction that it catalyses. [1] (b) Some information regarding these catalysed reactions is given below. (A410U10-1) Turn over. 29 Examiner only © WJEC CBAC Ltd. Activation energy / kJ mol–1 Frequency factor, A / mol dm–3 s–1 palladium catalyst 61.7 6.1 × 109 ruthenium catalyst 79.4 14.1 × 109 (i) At a temperature of 600 K, the value of the rate constant for the reaction catalysed by palladium is 2.58 × 104. I. Give the unit for this rate constant. [1] ............................................................................................................... II. Find the value of the rate constant for the ruthenium catalyst under the same conditions and hence identify which of these two catalysts is the more effective. [4] (ii) Under certain conditions the oxidation of carbon monoxide can occur without a catalyst. The rate equation for this process is rate = k[CO][O2] Suggest a two-step mechanism for the uncatalysed oxidation of carbon monoxide. Label the rate determining step clearly. [3] 30 (A410U10-1) Examiner only (c) Carbon monoxide is classed as a reducing agent. (i) State what is meant by a reducing agent. [1] (ii) Explain why carbon monoxide is a reducing agent whilst the corresponding oxide of lead, PbO, is not. [2] © WJEC CBAC Ltd. 13 BLANK PAGE TURN OVER TO PAGE 32 FOR QUESTION 13 (A410U10-1) Turn over. 31 © WJEC CBAC Ltd.