OCR A Jun 2010 Paper 2 Q4

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Infrared spectroscopy and mass spectrometry are used to identify substances. 15 (a) Police use breathalysers to detect ethanol in the breath of drivers. (i) Some modern breathalysers use infrared spectroscopy. Suggest two characteristic infrared absorptions that could be used to identify the presence of ethanol vapour. 1 . cm1 2 . cm1 [2] (ii) Some older breathalysers used the redox reaction between acidified dichromate(VI) ions and ethanol. A colour change was seen which indicated the presence of ethanol in the breath. What is the colour change that would be seen in this breathalyser if ethanol was present in the breath? [1]to(iii) Give an equation to show the reaction between acidified dichromate(VI) ions and ethanol. Use [O] to represent the acidified dichromate(VI) ions, the oxidising agent.[2]OCR 2010 Turn over<br /> (b) Infrared spectroscopy and mass spectrometry are used in the search for organic molecules in outer space. Compound A has been analysed by infrared spectroscopy. 16 transmittance (%) 100 80 60 40 20 4000 3500 3000 2000 2500 wavenumber / cm1 1500 1000 500 The mass spectrum of compound A is shown below. relative abundance (%) 100 80 60 40 20 0.0 10 20 30 m / z 40 50 60OCR 2010<br /> (i) A research chemist concludes that compound A is a hydrocarbon. What evidence is there to support this conclusion? 17[2] (ii) How does the mass spectrum confirm that compound A has a molecular formula of C4H10?[1] (iii) Draw the structural isomers of C4H10. (iv) Identify the fragment ions that give rise to the following peaks in the mass spectrum. m/z 15 is . m/z 29 is . m/z 43 is . [1] [3] (v) Use your answer to part (iv) to identify which of the isomers in part (iii) is compound A. Explain your reasoning. [1] [Total: 13] Turn overOCR 2010<br />

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