An aldehyde, an alkane and a carboxylic acid, all of similar volatility, are mixed together. The mixture is then analysed in a gas chromatograph. The gas chromatogram produced is shown. [Figure showing gas chromatogram with peaks X, Y, Z] The separation of the compounds depends on their relative solubilities in the stationary phase. The stationary phase is a liquid alcohol.

1. (a)(i)Complete the table to suggest which compound in the mixture is responsible for each peak X, Y and Z. Explain your answer by reference to the intermolecular forces of the compounds. peak | organic compound | explanation -----|------------------|------------- X | | Y | | Z | | [2][2]
2. (a)(ii)A student calculates the areas underneath the three peaks in the chromatogram. peak | X | Y | Z -----|---|---|--- area/mm² | 19 | 32 | 47 The area underneath each peak is proportional to the mass of the respective compound. Calculate the percentage by mass in the original mixture of the compound responsible for peak Z. % of mixture responsible for peak Z = ...................................... [1][1]
3. (b)(i)The mass spectrum of a halogenoalkane containing one chlorine atom or bromine atom will show an additional peak at M+2. State the isotopes of chlorine and bromine responsible for M+2 peaks. chlorine .............................................................. bromine .............................................................. [1][1]
4. (b)(ii)The mass spectrum of bromochloromethane, CH2BrCl, has a molecular ion peak, M, at an m/e value of 128. It also has M+2 and M+4 peaks. Suggest the identity of the molecular ions that give rise to these peaks. M peak ..................................................................................................................................... M+2 peak ................................................................................................................................... M+4 peak ................................................................................................................................... [2][2]
5. (c)(i)Halogenoalkanes can be formed from the reaction of an alkene with a hydrogen halide. Methylpropene reacts with hydrogen bromide to form 2-bromo-2-methylpropane. CH3 | H2C=C + HBr | CH3 methylpropene CH3 | H3C-C-CH3 | Br 2-bromo-2-methylpropane Draw the mechanism of this reaction. Include all relevant curly arrows, dipoles and charges. [3][3]
6. (c)(ii)1-bromo-2-methylpropane is also formed in this reaction. Explain why 2-bromo-2-methylpropane will be the major product in this reaction. [1][1]
7. (d)(i)Explain what is meant by the term partition coefficient, Kpartition. [2][2]
8. (d)(ii)The partition coefficient of organic compound H between dichloromethane and water is 4.75. • 2.50 g of compound H was dissolved in water and made up to 100 cm³ in a volumetric flask. • 50 cm³ of this aqueous solution were shaken with 10cm³ of dichloromethane. Calculate the mass of compound H that was extracted into the dichloromethane. mass of compound H extracted = .............................................. g [2][2]

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