SYNTHESIS PART ONE HYDROCARBONS What is organic chemistry • In chemistry chemicals which contain carbon are classed as organic • Carbon is a non metal and can form four bonds with o

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SYNTHESIS PART ONE HYDROCARBONS What is organic chemistry • In chemistry chemicals which contain carbon are classed as organic • Carbon is a non metal and can form four bonds with o Powered By Docstoc
					SYNTHESIS

  PART ONE
HYDROCARBONS
  What is organic chemistry?
• In chemistry chemicals which contain
  carbon are classed as organic.
• Carbon is a non metal and can form four
  bonds with other non metals.
• This means it can form many, many
  different substances in many different
  shapes.
• Some organic substances are simple like
  methane and others are very complex
  like sugars , proteins and DNA.
       Hydrocarbons
• Organic compounds that
  contain only hydrogen and
  carbon are called
  hydrocarbons.
• There are two main groups
  you have to know about –
  alkanes and alkenes.
              Alkanes
• The simplest
  alkane is called                  Carbon atom

  methane.
• It consists of
  one carbon atom
  joined to four
  hydrogen atoms
• We write its
  formula as CH4        Hydrogen atom
• The next alkanes in the series are
• Ethane C2H6
• Propane C3H8
• Butane C4H10
• As we add another carbon atom in the
  chain we need more hydrogen atoms.
• Can you see how these two are related?
• If we double the number of carbon
  atoms and add two we get the number
  of hydrogen atoms.
• CLICK HERE TO COMPLETE THE ALKANES WORKSHEET.
            The alkenes
• In these hydrocarbons one of the
  carbons has a double bond.
• This means that there are two bonds
  holding two of the carbons together
  instead of only one
                                         Carbon atom




             Double carbon carbon bond
  Saturated & Unsaturated

• The alkanes have only single C-C
  bonds. We say they are
  saturated.
• The alkenes have a double C=C
  bond. We say they are
  unsaturated.
• The simplest alkene
  is called ethene
• It has the formula
  C2H4
• There are always
  twice as many
  hydrogen atoms as
  carbon atoms in the
  alkenes.
• The other two
  alkanes you need to
  know are propene      CLICK HERE TO COMPLETE
  and butene            ALKENE WORKSHEET
• We can test to see if a
  hydrocarbon is an alkene.
• Alkenes turn bromine water from
  orange/brown to colourless.
      H H                       H H
       I I                       I I
      C=C + Br2              Br-C-C-Br
      I I                        I I
      H H                       H H
• Alkanes will not do this
              CRACKING
• When crude oil is separated by
  fractional distillation there are always a
  higher % of the longer chained
  fractions.
• The shorter chained hydrocarbons are
  more useful so the long chained
  molecules are cracked to give more
  shorter chain hydrocarbons.
      Cracking in the School Laboratory
  • Paraffin is soaked into ceramic wool and placed at the
    end of a boiling tube (see diagram)
  • The aluminium oxide is heated strongly first. This is
    the catalyst which speeds the reaction up.
  • The paraffin is heated to vaporise it and then the
    ethene gas is collected in the test tubes.
                              Catalyst             Ethene gas
                                                   collecting
        Paraffin
        soaked into
        mineral wool
                       heat

Click here to
complete the
cracking exercise
What can we do with the ethene?
• The ethene can be used as a fuel but because
  it contains a double bond but it is much more
  useful as a raw material in the chemical
  industry.
• If it is reacted with water(steam) ethanol
  (alcohol) can be made.
•        H H                   H H
•        I I                    I I
•        C=C + H-O-H          H-C-C-O-H
•        I I                     I I
•        H H                    H H
•       ethene + steam         ethanol
                       Polymers
• Ethene and other alkenes are most useful
  for making polymers.
• Plastics are polymers.
• Given the right conditions small alkenes
  can join together to form very large
  molecules.
• The small molecules are called monomers
  and the large molecules are called
  polymers .
• The process is called polymerisation
     Click here to complete the crossword
             How are they made?
• Alkenes have a double C=C bond
• The double bond breaks and the smaller
  alkenes join together.
    ETHENE   ETHENE       ETHENE                    POLYETHENE

•


                                         Alkenes join to form polymer
     Double bond breaks
                               Click here to complete the polymer worksheet
         There are two main types of polymer.
 They are thermosetting and thermoplastic polymers.

     Thermoplastic                       Thermosetting
• They can stretch or             • Are rigid, they break
  bend                              when bent
• They soften & melt              • They char or decompose
  when heated                       when heated
• Then can be remoulded           • They cannot be moulded
  into new shapes                   into new shapes
• They have no cross links        • They have cross links
  between the polymer               between the polymer
  molecules                         molecules

          Click here to complete the matching exercise
       Properties of polymers
• Polyethene & polypropene are made
  from unsaturated monomers.
• These monomers ADD on to each other
  so we call them addition polymers.
• Other polymers are formed by
  condensation. This means another
  molecule – water is made as well as the
  polymer.
• Some polymers have branched chains.
• This affects the strength of the
  polymer.
• HDPE (high density polyethene) has few
  branches and is not as strong as LDPE
  (low density polyethene) which has
  many branches.
• Some times plasticisers have to be
  added to alter the properties.
• These allow the polymer chains to slide
  over each other which makes the
  polymer softer & more flexible.
• uPVC is the hard polymer used to make
  window frames. If plasticiser is added
  to this the polymer it produces a soft ,
  flexible substance that can be used for
  floor covering.
    Getting rid of polymers
• Some polymers are hard to dispose of.
• Thermoplastic polymers can be recycled
• Many polymers are not biodegradeable
  (will not rot) and are not affected by
  acids and other chemicals.
• There are however some new polymers
  around that have additives which allow
  them to decompose.
      Click to complete the cloze exercise

				
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