C2 - Material Choices (b)

C2 - Material Choices

1. Crude Oil

   • Mixture of hydrocarbons
     • Molecules that are made of a chains of carbon and hydrogen atoms only.
     • Varying chain length
   • Properties
     • As the length of the hydrocarbon changes the properties also change.
       • When supplied heat the smaller molecules receive enough energy to overcome the weak intermolecular forces
         • Low mpt and bpt
       • Longer chains need more energy
         • Higher mpt and bpt
     • Bonds in crude oil
       • Strong covalent bonds between the carbons and hydrogens of the molecule
       • Weak intermolecular molecular forces of attraction between molecules

2. Uses of Crude Oil

   • Separated by fractional distillation
     • • Most of the hydrocarbons in crude oil are used to make fuels.
       • Some are sued to make new compounds
         • Plastics, medicines, fertilisers and food
         • Chemical synthesis
   • The petrochemical industry refines crude oil to produce fuels and lubricants.
   • It also produced raw materials that can be used to make synthetic chemicals
   • Some less useful hydrocarbons can be reacted with hydrogen so that they split into more useful hydrocarbons

3. Polymers

   • Polymerisation
     • Plastics are formed when lots of small molecules (monomer) join together to make a very long molecule (polymer)
       • Carbon based
       • Formed under high pressure
   • Properties
     • Polymers made from varying monomers have different properties
       • Strong and rigid
         • HDPE
           • Used to make milk bottles
       • Light and stretchable
         • LDPE
           • Plastic bags and water bottles
       • Strong and Durable
         • PVC
           • Rigid
             • Window frames and piping
           • Stretchy
             • Synthetic leather
       • Impact resistant and soft
         • Polystyrene
           • Packaging
       • Heat resistant
         • Melamine resin and polypropene
           • Plastic Kettles
   • Replacing natural materials
     • Synthetic fibres are replacing cotton, wool and silk
       • Lighter, more durable, water-resistant and often cheaper
     • Rigid PVC has replaced wood as a material for window frames
       • Weather-resistant, strong, durable, no painting

4. Structure and Properties of Polymers

   • Properties
     • Depend on molecular arrangement
     • Density
       • Polymers packed together tightly = high density
       • Polymer chains are spread out = low density
   • Forces
     • Weak forces
       • Free to slide over each other
       • Easily stretched
       • Low mpt.
     • Strong forces
       • Inflexible
       • higher mpt.
       • Cross links prevent free movement
         • Crosslinks are chemical bonds
   • Modification
     • Increase chain length
       • Stronger
     • Cross-linking
       • Stronger, stiffer, more heat resistance
     • Plasticisers
       • Softer and easier to shape
       • Work by reducing intermolecular forces
     • Crystallinity
       • Made more crystalline
         • Strighter chains with no branches
         • Higher density
         • Stronger and have higher mpt.

5. B

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