1 C1.5.1 Obtaining Useful Substances From Crude Oil
1.1 Hydrocarbons can be cracked to produce smaller, more useful
molecules: the hydrocarbons are heated, the vapours are either
passed over a hot catalyst or mixed with steam and heated to a very
high temperature so that thermal decomposition reactions then occur.
1.1.1 The products of cracking include alkanes and unsaturated hydrocarbons
called alkenes. Alkenes have the general formula CnH2n.
22.214.171.124 Alkenes are unsaturated hydrocarbons; they contain a double covalent
bond. The presence of this double bond allows alkenes to react in ways that
alkanes cannot. They can react with oxygen in the air, so they could be used
as fuels. They can be used to make ethanol and polymers.
126.96.36.199.1 Alkenes react with bromine water,
turning it from orange to colourless.
2 C1.5.2 Polymers
2.1 Alkenes can be used to make polymers
such as poly(ethene) and poly(propene). In
these reactions, many small molecules
(monomers) join together to form very large
2.1.1 Polymers have many useful applications and
new uses are being developed: new packaging
materials, waterproof coatings for fabrics, dental
polymers, wound dressings, hydrogels, smart
materials (including shape memory polymers).
188.8.131.52 Many polymers are not biodegradable, so
they are not broken down by microbes
leading to problems with waste disposal.
184.108.40.206.1 Plastic bags are being made
from polymers and cornstarch so
that they break down more easily.
Biodegradable plastics made
from cornstarch have been
220.127.116.11.1.1 Many polymers can be recycled reducing the disposal problems and the amount of crude oil
used but the different polymers must be separated from each other first, which can be difficult
and expensive to do.
3 C1.5.3 Ethanol
3.1 Ethanol can be produced by hydration of ethene with steam in the presence of a catalyst;
ethene + steam → ethanol
3.1.1 Ethanol can also be produced by fermentation with yeast, using renewable resources;
sugar → carbon dioxide + ethanol