OCR 2023 Chemistry B H433/03: Practical skills in chemistry A Level Question Paper & Mark Scheme (Merged)

2 OCR 2023 1 Ozone, O3 , is a serious pollutant when present in the troposphere. (a) Give one polluting effect of ozone in the troposphere. ................................................................................................................................................... .............................................................................................................................................. [1] (b) Tropospheric ozone is produced by the reactions of nitrogen oxides, NOx , and hydrocarbons. These, together with carbon monoxide, CO, are pollutants produced by motor vehicles. Catalytic converters in vehicle exhausts catalyse the reaction in Equation 1.1 and also the oxidation of hydrocarbons to carbon dioxide and water. 2NO(g) + 2CO(g) N2 (g) + 2CO2 (g) Equation 1.1 (i) The bar chart below shows the reduction in the various pollutant levels when a suitable catalytic converter is fitted. Calculate the percentage reduction in NOx levels when a catalytic converter is fitted. Give your answer to 2 significant figures. parts per million (by volume) 9000 8000 7000 6000 5000 4000 3000 2000 1000 0 CxHy NOx CO pollutant Without catalytic converter With catalytic converter percentage reduction ..................................................... % [2] 3 OCR 2023 Turn over 4 OCR 2023 (ii) A student says that the reactions in a catalytic converter decrease car pollution to zero. Comment on this statement. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ...................................................................................................................................... [3] (iii) The diagram below represents an energy profile for the catalysed reaction in Equation 1.1. enthalpy progress of reaction On the diagram: • Indicate the activation enthalpy of the catalysed reactio