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5 marksPhase Separations

CAPE Chemistry Unit 2 · May/June 2022 · Paper 2 · Question 2(d)(iv)

At the end of an organic reaction, a TLC of the reaction mixture indicates the presence of unreacted starting material benzoic acid as well as the impurity 1,4-dimethoxybenzene.

The aqueous layer is separated and shaken with 50 cm³ of the pure organic solvent. Determine the concentration of iodine in the organic solvent at equilibrium in mol dm⁻³? Show ALL working.

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  1. 2(a)Explain how a mass spectrometer works to obtain a mass spectrum of a molecule.[4 marks]
  2. 2(b)(i)State the m/z ratio of the M⁺ and M+2 peak?[2 marks]
  3. 2(b)(ii)Deduce the formula of the fragments at m/z ratio of 43, 107 and 109.[3 marks]
  4. 2(b)(iii)Determine the formula of the M⁺ and M+2 molecular ion species and name the haloalkane.[3 marks]
  5. 2(c)(i)Name the process by which TLC separates α-amino acids.[1 mark]
  6. 2(c)(ii)The chromatogram was treated to show the positions of the separated α-amino acids. Explain how the student could analyse the chromatogram to identify the three…[2 marks]
  7. 2(c)(iii)Several α-amino acids have structures that are very similar. Suggest why this could cause problems when using TLC to analyse mixtures of α-amino acids.[2 marks]
  8. 2(d)(i)Outline a series of steps indicating how this mixture can be separated, and the two components recovered, by the process of solvent extraction.[5 marks]
  9. 2(d)(ii)State what is meant by the term 'partition coefficient'.[1 mark]
  10. 2(d)(iii)If iodine is shaken with 100 cm³ of water and 100 cm³ of an organic solvent, the concentration of iodine in the water layer is 4.0 × 10⁻³ mol dm⁻³ and in the…[2 marks]

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