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Edexcel Chemistry for A2

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					Polymers Extension questions
1 Look closely at the structures of glycine and glutamic acid shown below.




  a) Using glycine as an example, explain what you understand by the isoelectric point of
     an amino acid.

  b) The isoelectric point of glycine is at pH = 6.0. Why is the isoelectric point of glycine not
     at pH = 7?

  c) How do you think the isoelectric point of glutamic acid will compare with that of
     glycine? Explain your answer.

2 a) Poly(ethenol) is made from ethenyl ethanoate,

     Ethenyl ethanoate is first polymerised to produce poly(ethenyl ethanoate). This is then
     converted to poly(ethenol) by replacing about 90% of the CH3COO groups in
     poly(ethenyl ethanoate) with OH groups.

     i) Draw the structure of ethenol and the repeat unit in pure poly(ethenol).

     ii) Draw the repeat unit in poly(ethenyl ethanoate).

     iii) Calculate the relative molecular mass of a sample of poly(ethenol) containing
          2000 monomer units in which 10% of the monomer units contain CH3COO groups
          which have not been replaced by OH groups.

     iv) Why is poly(ethenol) soluble in water?

  b) The solubility in water of poly(ethenol) depends on the percentage of CH3COO
     groups replaced. Maximum solubility in water occurs when about 88% of the
     CH3COO groups are replaced by OH groups. If fewer groups are replaced, the
     poly(ethenol) becomes less soluble.
     When more CH3COO groups are replaced, the solubility decreases and when all
     the groups are replaced, the poly(ethenol) is insoluble in water.

     i) Why does poly(ethenol) become less soluble if fewer CH3COO groups are
        replaced by OH groups?

     ii) Why do you think the solubility decreases when more than 88% of the CH3COO
         groups are replaced by OH groups?

     iii) When all the CH3COO groups are replaced by OH groups, the poly(ethenol)
          crystallises and becomes insoluble in water. Suggest what may have happened
          to make the poly(ethenol) insoluble?
3 This question is concerned with the molecular interactions between the polymer chains
  in various plastics.

  a) Tables of data show that the melting temperatures of low density polythene and high
     density polythene differ by 23 C.

    i) What type of molecular interactions occur between polythene molecules?

    ii) Why are the densities of the two polythenes different?

    iii) Suggest which type of polythene has the higher melting temperature and explain
         why.

  b) The same tables of data show no melting temperature for Bakelite. Why is this?

  c) The polymer Kevlar is a polyamide with a much higher melting temperature than
        polythene.

    i) Explain the term polyamide.

    ii) Kevlar is manufactured from the monomers benzene 1,4-dicarboxylic acid and
        benzene 1,4-diamine. Draw the structure of one repeat unit in a molecule of
        Kevlar.

    iii) What is the strongest type of intermolecular force in Kevlar?

    iv) Which atoms and groups are involved in the strongest type of intermolecular
        force in Kevlar?

  d) Kevlar is a very strong polymer as it contains crystalline regions.

    i) How does the arrangement of Kevlar molecules differ in crystalline regions and
       non-crystalline regions?

    ii) Why do the crystalline regions help to make Kevlar strong?

				
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