OCR A Jun 2013 Paper 4 Q3

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3 Many modern textiles are created using a mixture of natural and synthetic polymers. (a) Silk is a natural fibre. It is made up of two main proteins, fibroin and sericin. A section of a fibroin strand is shown below. H O CH3 H O H O CH3 H O H O H O CH2 OH (i) Proteins are natural condensation polymers. State what is meant by a condensation polymer.[1] (ii) A student hydrolysed a sample of fibroin protein. She analysed the amino acids that were formed from the hydrolysis. She found that fibroin contained the amino acid glycine, H2NCH2COOH. Draw the structures of the two other amino acids that make up the section of fibroin shown in the diagram above. (iii) The isoelectric point of glycine is 5.8. Define the term isoelectric point and draw the structure of glycine at its isoelectric point. isoelectric point[2]OCR 2013 [2]<br />
 (b) The student then hydrolysed a section of sericin protein. She analysed the amino acids formed using Thin-Layer Chromatography (TLC). (i) Name the process by which TLC separates amino acids.[1] (ii) The chromatogram the student obtained, and a table of Rf values for amino acids, are shown below. Estimate the Rf value for the amino acid found at X. Hence identify the amino acid found at X. solvent front base line Amino acid alanine aspartic acid glycine leucine methionine threonine Rf value 0.38 0.15 0.26 0.75 0.58 0.35[2] (c) Quiana is a synthetic polymer that can be spun into a soft, silky fabric. The monomers used to make Quiana are shown below. HO (CH2)6 OH H2N NH2 Draw the repeat unit of the polymer formed from these two monomers.OCR 2013 [2] Turn over<br />
 (d) Polymer D has been developed by the textile industry. The repeat unit of polymer D is shown below. 10 polymer D (i) Polymer D is a condensation polymer. Draw the structure of each of the monomers that make up polymer D. (ii) Polymer D reacts with a third monomer to form an addition polymer. The repeat unit of this polymer is shown below. [2] Draw the structure of the third monomer. addition polymerOCR 2013 [1] [Total: 13]<br />

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