Amino acids can be separated by thin-layer chromatography. A mixture of amino acids is analysed using this technique. The chromatogram obtained is shown, drawn to scale. The table shows some R_f values for different amino acids in the solvent used. [Figure X.X]

1. (a)(i)Use the chromatogram and the R_f values to deduce the amino acid responsible for spot A and spot B. amino acid responsible for spot A amino acid responsible for spot B[1]
2. (a)(ii)A second chromatogram of the same mixture is taken using a more polar solvent. Predict the effect on the R_f values of the amino acids. Explain your reasoning.[1]
3. (b)(i)Glycine, H₂NCH₂CO₂H, is the simplest amino acid. Complete the equations to show the acid-base properties of glycine. H₂NCH₂CO₂H(aq) + HCl(aq) → H₂NCH₂CO₂H(aq) + NaOH(aq) →[2]
4. (b)(ii)In aqueous solution, amino acids exist as zwitterions. Draw the zwitterionic structure of glycine. Explain how the zwitterion for glycine is formed.[2]
5. (c)Apart from glycine, all naturally occurring amino acids have a chiral centre and exhibit stereoisomerism. Draw the two stereoisomers of alanine, CH₃CH(NH₂)CO₂H. [Figure X.X][1]
6. (d)(i)The amino acid alanine can be synthesised from 2-chloropropanoic acid, CH₃CHClCO₂H. State the reagents and conditions and name the mechanism for this reaction. reagents and conditions name of mechanism[2]
7. (d)(ii)State and explain the relative acidities of trichloroethanoic acid, chloroethanoic acid and ethanoic acid.[3]
8. (e)Serine, HOCH₂CH(NH₂)CO₂H, can react with alanine, CH₃CH(NH₂)CO₂H, to form three different structural isomers, each with the molecular formula C₆H₁₂N₂O₄. Draw the structures of these three structural isomers. [Figure X.X][3]

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