Other useful substances from crude oil

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  • Other useful substances from crude oil
    • Cracking
      • Thermal de-composition
        • Breaking long hydrocarbon chains into shorter ones
      • Shorter chains are more useful, more flammable
    • Alkenes
      • Cracking produces shorter chains a mixture of alkenes and alkanes
      • Unsaturated- at least one C-C double bond
      • CnH2n
      • Ethene, propene, butene
      • Used to make plastics
      • More reactive
      • Test- add bromine water and shake gently
        • Alkane- no change, orange --> orange
        • Alkene- orange --> colourless
    • Polymers
      • Large molecule made of hundreds of small molecules (monomers)
      • Addition poly-merisation, monomers added together to form a long chain
      • Often alkenes
      • Low- density polythene- plastic bags
        • Branched polymer chain- cannot pack closely together
          • Soft, easy to melt
      • High density polyethene- plastic containers, pipes
        • Straight polymer chains- can pack closely together
          • Rigid, harder to melt
      • Thermo-softening polymers
        • Consist of individual, tangled polymer chains
          • Weak inter-molecular forces between chains
          • Slide past each other, low mp, flexible & stretchy
      • Thermo-setting polymers
        • Form cross links when melted so set permanently
          • Rigid, can't be stretched, high mp
          • Cross links are very strong
    • Problems with plastic
      • Recycle, burry it (land fill), burn it
      • Polymers are non-biodegradble
        • Can't be broken down by micro-organisms
      • Take hundreds of years to decompose
      • Take up a lot of space
      • Wildlife can get trapped in waste
      • Solution:
        • Use cornstarch to build up the plastic
        • The micro-organisms in the soil feed on the cornstarch, helping break it down
        • Needs a lot of space to grow


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