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C1b. oils, Earth and Atmosphere
4. Products of oil
C1b 4.1 Cracking hydrocarbons
We can split large hydrocarbons molecules up into smaller
molecules by heating them up and passing the gas through a
It is called catalytic cracking and takes place in a cat cracker.
Cracking produces unsaturated hydrocarbons which we call
The reaction is an example of thermal decomposition.
An alkene is an unsaturated hydrocarbon, because it contains a
double bond between two of their carbon atoms.
To test if a hydrocarbon is unsaturated or saturated (an alkene
or alkane) we use bromine water. If there is double bond the
bromine water turns colourless (alkene) and if there are no
double bonds the bromine water will stay orange-yellow
C1b 4.2 Making polymers from alkenes
Crude oil is used for fuels, electricity in oil-fired power stations.
The chemicals we make from crude oil are used in our everyday
lives. For example margarines, medicines, dyes and explosives
Plastics are made up of polymers.
Polymers are large molecules made when monomers join
Poly(ethane) or polythene is very useful. It is made from
ethene. Plastic bags, plastic drink bottles, dustbins and cling
film are made out of these.
Poly(propane) or polypropylene is made from the hydrocarbon
propene. Poly(propane) is very strong, tough plastic. It is used
t make milk crates, ropes etc.
When alkene molecules join together, the double bond between
the carbon atoms in each molecule `opens up'. It is replaced by
single bonds as thousands of molecules join together. This is
an example of an addition reaction. Because a polymer is
made, we call it addition polymerisation.
C1b 4.3 The Properties of Plastic
The intermolecular forces between the polymers depend on the
monomers used and the condition we choose to carry out
Thermo softening plastics are plastics that soften when heated.
For example poly(ethene), poly(chloroethene), poly(propene).
There are two types of poly(ethene): high density and low
density. They are both made from poly(ethene) but under
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HDPE can stronger intermolecular forces
than LDPE because there is no oxygen inside them, therefore
they can pack tightly together.
A thermosetting plastic is a polymer which sets permanently
when it is formed by heating the monomers of which it is made.
This makes chemical bonds in between the polymers.
C1b 4.4 New and useful polymers
New polymers are being developed all the time. They are
designed to have properties that make them specially suited
for certain uses.…read more