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1.1 Cracking Hydrocarbons
Fractions from crude oil can be broken down by thermal decomposition in a
The fraction is vaporised and passed over a hot catalyst.
The cracking of fractions causes the molecules to split apart and form smaller
Some of the smaller molecules are alkanes, but some are alkenes that contain
carbon-carbon double bonds.
Alkenes are unsaturated, because they contain fewer hydrogen atoms than
alkanes with the same number of carbon atoms.
General formula: CnH2n
They burn in air.
Alkenes are more reactive than alkanes.
Alkenes react with bromine water turning the orange-yellow solution colourless.
1.2 Making Polymers from Alkenes
Polymers are v. large molecules made from many small molecules called
Lots of ethane molecules join to form poly(ethane), commonly called polythene.
This reaction is called addition polymerisation.
1.3 The properties of plastics
Polymers have v. long molecules (that tangle together) with strong bonds holding
the atoms together within the molecules.
Thermosoftening polymers have weak intermolecular forces between the
When they are heated they become soft.
When they cool down, they become soft.
This means that they can be heated to mould them into shape.
When thermosetting polymers are heated for the first time chemical bonds form
between the polymer molecules.
They link together to form a giant network.
The strong bonds make the plastic set hard and cannot be softened by
We use thermosoftening plastics where flexibility is important and where they
are not exposed to high temperatures.
Thermosetting plastics are more rigid and can withstand higher temperatures.
1.4 New and Useful Polymers
Polymers can be designed with specific properties by choosing different
monomers and by changing the conditions used to make them.
Polymers are widely used for food packaging and generally not biodegradable.
Polymers used for drinks bottles are strong, flexible, lightweight, clear and
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New polymers have been produced to replace traditional materials in many uses.
Polymers have been developed to coat fabrics that make them waterproof but are
able to let gases through,
New polymers have been developed for medicinal purposes.
Hydrogels (these are used in agriculture and food).
Smart polymers can be used to control the release of drugs.
Shape memory polymers return to their original shape after being bent and are
used for stitching wounds.
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Additives are used in foods to improve:
Additives can be natural products or synthetic chemicals.
Substances like salt, vinegar and sugar have been used as additives for ages.
There are six main types of additive:
E-numbers are given to food additives approved for use in Europe.
Additives must be included in the list of ingredients on food labels.…read more
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Tectonic plates move because of convection currents in the mantle, due to
3.3 The Earth's Past Atmosphere
The Earth's early atmosphere was formed by volcanic activity.
Consisted mainly of CO2. May have been water vapour, with traces of methane
As plants colonised the Earth, the levels of oxygen rose.
3.4 Gases in the Atmosphere
The main gases in the Earth's atmosphere are oxygen and nitrogen.…read more