Hydrocarbons
Hydrocarbons are compounds that contain carbon and hydrogen as
elements. It is divided into two classes namely aliphatic and aromatic
hydrocarbons.
Aliphatic saturated hydrocarbon
These are
otherwise called alkanes. Alkanes are often referred to as paraffins. Alkanes
are chemically inert in most reagents. For example, methane, ethanes, and propane.
Sources of alkanes
The major
sources of alkanes are natural gas and petroleum deposits, which are derived
from the decomposition of marine organic compounds.
Petroleum
Petroleum is
a highly complex mixture of hydrocarbons that must be refined into different
fractions to get various lower-member hydrocarbons.
Combustion
Reaction
with oxygen occurs during combustion in an engine or furnace when the alkane
is used as a fuel. Co2 and H2 O are formed as products
and a large amount of heat is released.
Liquid petroleum gas
The propane-butane fractions are separated from the more volatile components by
liquefaction. These fractions are filled in cylinders as cooking gas.
Natural gas
It contains
80% methane, 10% ethane and 10% a mixture of higher gaseous hydrocarbons.
Crude oil
Crude oil is
a mixture of gaseous, liquid and solid hydrocarbons. The hydrocarbons present
in the crude oil are paraffin, naphthalene, olefin and aromatic compounds in
verifying percentage. It is separated by a process known as the refining of
petroleum.
Refining petroleum involves the separation of crude oil into various fractions with
different boiling points.
The various
fractions coming out of the increasing temperature are described in
ascending order below:
Gaseous hydrocarbon
Petroleum ether
Gasoline
Kerosene
Diesel oil fuel for
diesel engine
Lubricating oil and
grease
Paraffin wax
Tetra ethyl lead
The anti-knocking property of the petrol samples is
increased by adding tetra ethyl lead. The anti-knocking property is due to the
increase in the octane number of petroleum samples. Now the mixing of TEL is
considered to be air pollution.
Aliphatic unsaturated compounds
Alkenes and
alkynes are aliphatic unsaturated compounds. Alkenes are hydrocarbons that
contain a carbon-carbon double bond as a function group. They are also known as
olefins. For example C2 H4.
Butylenes
Ethylene is
used for the ripening of fruits.
Ethylene and propylene are important industrial organic
chemicals. They are used in the synthesis of polymers like polythene, PVC,
Polystyrene, Teflon, Polyvinyl acetate, polyvinyl alcohol, and acrilan.
Polymerization
A polymer is
simply a large molecule built up by many smaller units called monomers.
Conversion of a large number of monomers into a single polymer is known as
polymerization.
When
ethylene is heated under pressure in the presence of oxygen, a compound
of high molar mass known as polythene is formed.
Plastics
It is the
cross-linked polymers
For example
Bakelite (phenol and formaldehyde)
Vinyl plastic
(PVC or PVA)
Polymers are
stable, cheap, hard materials.
Natural rubber
Natural rubber
is a linear polymer of isoprene. Natural rubber is extracted from the latex of
Hevea brasilienni.
Synthetic rubber
Synthetic rubber
is obtained by polymerization of chloroprene, isobutylene and styrene–butadene
mixture.
Alkynes
Alkynes are
hydrocarbons that contain a carbon-carbon triple bond. Alkynes are also called
acetylenes.
Polymerization of alkynes
When alkynes
are passed through a red-hot iron tube under pressure, they polymerise into
aromatic compounds. For example, acetylene polymerises to benzene.
Use of alkynes
Acetylene is
used in oxy acetylene torch for welding and cutting metals.
Acetylene is used as a starting material for the manufacture of PVC, synthetic rubber PVA, benzene
etc.
Aromatic hydrocarbons
We use the
term aromatic to refer to benzene and its structural homologous. Many compounds
isolated from natural sources are aromatic in part. For example Benzens. Tolunes,
benzaldehyde, estrone, morphine etc.
Coal
Coal is a
complex substance made of primarily a large array of highly unsaturated benzene-like rings linked together.
Coal Tar
When coal is
heated to 10000 C in the absence of air, thermal breakdown of coal
molecules occurs and a mixture of volatile products called coal tar distils off.
The coal tar forms the source of many organic compounds namely, benzene,
toluene, naphthalene etc.
Uses of Benzene and Tolune
Benzene is a
good solvent for resins and fats.
Benzene is
used in dry cleaning.
Toluene is
used for blending petrol.
Toluene is
used as a solvent for paints, rubber and resins.
Toluene is
used to prepare 2, 4, and 6 trinitrotoluene which is an explosive.
Rocket fuels
The fuels used
in the rockets are called rocket propellent.
Fuel when
ignited undergoes combustion to release great quantities of hot gases.
The passage
of gases through the nozzle of the motor provides the necessary thrust to move
forward, according to Newton’s third law of motion.
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