CIE Nov 2015 v3 Paper 4 Q8

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18 (a) A mixture of volatile organic compounds X, Y and Z can be separated in a gas chromatograph. Their identities can be confirmed by measuring their different retention times and comparing to known values. A gas chromatogram is shown. PMT absorption 10 15 20 time / mins (i) Suggest what is meant by the term retention time.[1] (ii) Give an example of a carrier gas used in gas chromatography.[1] (iii) Z spends the longest time in the chromatography column. Suggest why this might be the case.[1] (iv) Explain a possible limitation of gas / liquid chromatography in separating two esters such as ethyl methanoate, HCO2CH2CH3, and methyl ethanoate, CH3CO2CH3.[1] (v) A student works out the areas underneath the three peaks in the chromatogram. peak area / mm2 X 22 Y 38 Z 16 Assuming the areas underneath the peaks are proportional to the masses of the respective components, what percentage of the original mixture was made up of the organic compound, X?UCLES 2015 9701/43/O/N/15 % of X =[1]<br /> (b) The NMR spectrum of Y given below shows four absorptions. 19 PMT absorption/ ppm (i) What compound is responsible for the absorption at= 0?[1] (ii) Compound Y is an ester with the molecular formula C4H8O2. Complete the table for the NMR spectrum of Y. The actual chemical shifts for three absorptions in Y and the splitting pattern for the resonance at= 3.7 ppm have been given for you. Use of the Data Booklet may be helpful.UCLES 2015 9701/43/O/N/15 type of proton(s) number of protons splitting pattern chemical shift/ ppm 1.0 2.3 3.7 (iii) Use your conclusions to suggest a structure for the ester Y. singlet [4] [1] [Total: 11] [Turn over<br />

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