Organic Chemistry
Specification Points
Year 10 – Organic Chemistry
Crude oil, hydrocarbons and alkanes
Crude oil is a finite resource found in rocks made from the remains of an ancient biomass,
mainly plankton that was buried in mud. Crude oil is a mixture of a very large number of
compounds, mainly hydrocarbons (molecules made of hydrogen and carbon only).
Most of the hydrocarbons in crude oil are hydrocarbons called alkanes.
Alkanes are a homologous series with a general formula of CnH2n+2
The first four members of the alkanes are methane, ethane, propane and butane.
Alkane molecules can be represented in the following forms: C2H6 or structural formula.
Fractional distillation and petrochemicals
Hydrocarbons in crude oil can be separated into fractions by fractional distillation by
evaporating the oil and allowing it to condense at different temperatures. Fractions
contain molecules with a similar number of carbon atoms.
The fractions are processed to produce fuels and feedstock for the petrochemical
industry.
Many of the fuels on which we depend for our modern lifestyle, such as petrol, diesel oil,
kerosene, heavy fuel oil and liquefied petroleum gases, are produced from crude oil.
Many useful materials on which modern life depends are produced by the petrochemical
industry, such as solvents, lubricants, polymers, detergents.
Properties of hydrocarbons
Some properties of hydrocarbons depend on the size of their molecules, including boiling
point and viscosity which increase with increasing molecular size and flammability which
decreases with increasing molecular size. These properties influence how hydrocarbons
are used as fuels.
During combustion, the carbon and hydrogen in the fuels are oxidised. The complete
combustion of a hydrocarbon produces carbon dioxide and water and energy.
Students should be able to write balanced equations for the complete combustion of
hydrocarbons with a given formula.
Knowledge of trends in properties of hydrocarbons is limited to boiling points, viscosity
and flammability.
Cracking and alkenes
Hydrocarbons can be broken down (cracked) to produce smaller, more useful molecules.
This process involves heating the hydrocarbons to vaporise them. 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. Be able to balance cracking equations.
The products of cracking include alkanes and another type of hydrocarbon called alkenes.
Alkenes are more reactive than alkanes and react with bromine water, turning it from
orange to colourless.
Cracking produces small molecules which have high demand for use in fuels.
Alkenes are used to make polymers and as starting material to make many other
chemicals.
Structure and formulae of alkenes
Alkenes are hydrocarbons with a double carbon to carbon bond. The general formula for
the homologous series of alkenes is CnH2n
Alkenes are unsaturated, they have two fewer hydrogen atoms than the comparable
alkane
The first 4 members of the homologous series are ethene, propene, butene and pentene.
Alkene molecules can be represented in the following forms: C3H6 or structural formulae.
Reactions of alkenes
Alkenes are hydrocarbons with the functional group C=C.
Alkenes react with oxygen in combustion reactions in the same way as other
hydrocarbons, but they tend to burn in air with smoky flames because of incomplete
combustion.
Alkenes react with hydrogen, water and the halogens, by the addition of atoms across the
carbon-carbon double bond so that the double bond becomes a single carbon-carbon
bond. The addition of hydrogen to an alkene (unsaturated) takes place in the presence of
a catalyst to produce the corresponding alkane (saturated).
The addition of water to an alkene takes place by reaction with steam in the presence of a
catalyst to produce an alcohol.
Addition of a halogen to an alkene produces a saturated compound with two halogen
atoms in the molecule, eg: ethene reacts with bromine to produce dibromoethane.
Students should be able to draw fully displayed structural formulae of the first four
members of the alkenes and the products of their addition reactions with hydrogen,
water, chlorine, bromine and iodine.
Polymers
Polymers have very large molecules. The atoms in the polymer molecules are linked to
other atoms by strong covalent bonds.
The intermolecular forces between polymer molecules are relatively strong and so these
substances are solids at room temperature.
Addition polymerisation
Alkenes can be used to make polymers such as poly(ethene) and poly(propene) by
addition polymerisation.
In addition polymerisation reactions, many small molecules (monomers) join together to
form very large molecules (polymers).
Students should be able to:
• recognise addition polymers and monomers from diagrams in the forms shown and
from the presence of the functional group C=C in the monomers
• draw diagrams to represent the formation of a polymer from a given alkene monomer
• relate the repeating unit to the monomer.
Ceramics, polymers and composites
Most of the glass we use is soda-lime glass, made by heating a mixture of sand, sodium
carbonate and limestone. Borosilicate glass, made from sand and boron trioxide, melts at
higher temperatures than soda-lime glass.
Clay ceramics (pottery and bricks) are made by shaping wet clay and then heating in a
furnace.
The properties of polymers depend on what monomers they are made from and the
conditions under which they are made. For example, low density (LD) and high density
(HD) poly(ethene) are produced from ethene using different catalysts and reaction
conditions.
Thermosoftening polymers consist of individual, tangled polymer chains and melt when
they are heated. Thermosetting polymers consist of polymer chains with cross-links
between them and so they do not melt when they are heated.
Most composites are made of two materials, a matrix or binder surrounding and binding
together fibres or fragments of the other material, which is called the reinforcement.
Examples of composites include wood, concrete and fibreglass. Some advanced
composites are made using carbon fibres or carbon nanotubes instead of glass fibres.
Students should be able to, given appropriate information:
• compare quantitatively the physical properties of glass and clay ceramics, polymers,
composites and metals
• explain how the properties of materials are related to their uses and select
appropriate materials.
Independent Study suggestions
1. Look at the specification points above – use the textbook pages (244-277) or the revision guide pages
(150-151) to make a few notes/spider diagram/revision cards
2. Have a go at the questions in the revision guide on pages 153-156
3.
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Watch the Fuse School short 3-4 minute explanation videos on any area you need extra help with:
Coal, oil and gas: https://www.fuseschool.org/topics/59/contents/828
Fractional distillation: https://www.fuseschool.org/topics/59/contents/269
Uses of crude oil fractions: https://www.fuseschool.org/topics/59/contents/830
Functional groups: https://www.fuseschool.org/topics/59/contents/270
Formulae of organic compounds: https://www.fuseschool.org/topics/59/contents/268
Alkanes and Alkenes: https://www.fuseschool.org/topics/59/contents/233
Complete and incomplete combustion: https://www.fuseschool.org/topics/65/contents/330
Isomers: https://www.fuseschool.org/topics/59/contents/1198
Cracking: https://www.fuseschool.org/topics/59/contents/273
Alkenes and bromine water: https://www.fuseschool.org/topics/59/contents/829
Halogenation: https://www.fuseschool.org/topics/59/contents/883
Polymers: https://www.fuseschool.org/topics/59/contents/1000
Making polyethene: https://www.fuseschool.org/topics/59/contents/943
Polymers from chloroethene an propene https://www.fuseschool.org/topics/59/contents/279
Thermosetting polymers: https://www.fuseschool.org/topics/59/contents/972