info based on hydrocarbon

1. Hydrocarbons
Hydrocarbons are substances that contain
Hydrogen and Carbon only.
Hydrocarbons are divided into a series of
families or groups called Homologous
Series.
A Homologous Series is a group of
compound which have a General Formula
and are chemically similar.
Examples of Homologous Series are the:
Alkanes, Alkenes and Cycloalkanes.

2. The Alkanes
The Alkanes have a general formula of CnH2n+2
They run from C1 –C60 approx.
C1-C4 are gases
C5-C17 are liquids
C17-C60 are Waxy Solids
As we progress between successive members of the
series we find that there is a difference of CH2 in
their formulae. As a direct result there is a regular
increase in their Boiling Points since more
energy is required to break up the longer chains.
All Alkanes are flammable, have a pH of 7 and are
insoluble in water.

3. The Alkane members
Name Molecular Formula Common Uses
Methane CH4
Nat.Gas.Household heating &
cooking
Ethane C2H4
Propane C3H6
Portable cooking and Heating
gas
Butane C4H10
Lighter fuel/Calor Gas
Pentane C5H12
Hexane C6H14
Octane * C8H18
Petrol derivative
Diesel *C17H36
Transport
Bitumen *>C60
Road/Playgrounds

4. The Alkenes
The Alkenes are another Homologues
Series with General Formula CnH2n
All Alkenes must have a C=C double bond.
As a result the first member of the series is
Ethene ie. Methene does not exist.
Ethene C2H4
Propene C3H4
Butene C4H8
Pentene C5H10
Hexene C6H12
Only the
first three
are gases
Ethene &
propene are
important
starting
materials in
making other
chemicals

5. The Cycloalkanes
The Cycloalkanes are another
Homologous series with General Formula
CnH2n
The Cycloalkanes are Ring compounds
which means that the first member of the
series is cyclopropane.
It should be noted that the Cycloalkanes
have the same general formula as the
alkenes i.e. CnH2n but that the Cyloalkanes
are Saturated whereas the Alkenes are
Unsaturated

6. Isomers
Isomers are molecules with the same
Molecular formula but different structural
formula.
Note: There must be the same number of
carbon and hydrogen atoms but there also
must be a completely different arrangement
of Carbon atoms.

7. Cracking of Crude Oil
Crude Oil is a mixture of Hydrocarbons called
Fractions
To Separate the oil into its component fractions
we first boil it. This process is called Fractional
Distillation.
After Fractional Distillation there are a large
number of Long-Chain Hydrocarbons left.
To meet market demand these long-chain
Hydrocarbons are broken up into smaller more
desirable Hydrocarbon Chains ie they are said to
be Cracked

8. Cracking of Crude Oil (contd).representation
Steel Wool acts as a Catalyst
The hot
Paraffin vapour
is passed over
the heated steel
wool
The gas collected
is tested with
Bromine water
Safety:Beware of
Suck-back
When an Alkane is cracked one of the products is
always Unsaturated
C16H34 C13H28 + C3H6

9. The Test for Saturation/Unsaturation
An Unsaturated compound is one that contains a C=C
double bond.
A Saturated compound is one that contains C-C single
bonds only.
Alkanes are Saturated and Alkenes Unsaturated.
Alkene and
Bromine water
shaken together
Alkane and
Bromine water
shaken together
The Test: Add Br2(aq) to both an alkane and alkene.
Alkenes quickly decolourise the Br2(from brown to
clear) whereas alkanes only slowly decolourise the Br2
in the presence of UV light.