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Chemistry




Unit 6

There are several types of hydrocarbon. This unit deals with naming
hydrocarbons and their structure. Alkanes and Alkenes undergo a
variety of important reactions, many of which are important
processes in the chemical industry.

Hydrocarbons

A hydrocarbon is a substance which contains only hydrogen and
carbon. The…

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Chemistry




and a prefix which indicates the number of carbon atoms in the
molecule.

Prefix: meth, No. of Carbon Atoms in the Molecule: 1, i.e. CH4
(Methane).
Prefix: eth, No. of Carbon Atoms in the Molecule: 2, i.e. C2H6
(Ethane).
Prefix: prop, No. of Carbon Atoms in the Molecule: 3,…

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Chemistry




Ethane

Hydrocarbons exist where the carbon atoms are joined by a
covalent double bond c=c. The simplest one is called ethane.
CH2=CH2 --> C2H4.
In the shortened structural formula it is useful to show the double
bond.

Alkenes

Ethane is the first member of a series of hydrocarbons called…

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Chemistry




However, it is possible to put atoms together in a different
arrangement.

What we have formed are two isomers of butane. Both have the
same molecular formula but different structural formula.

Pentane has three isomers. All have the same formula C5H12 but all
have different structures. Butane and Cyclobutane…

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Chemistry




C3H8 + Br2 ---> C3H7Br +HBr.

When a bromine solution is added to an alkene it de-colourises the
bromine solution very quickly.

Saturated or Unsaturated

Saturated hydrocarbons have only simple bonds. Unsaturated
hydrocarbons contain at least one double (or triple) C to C bond.

We can use the bromine…

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Chemistry




Safety Note: Watch for suck-back. Do not stop heating the test-tube
before removing the delivery tube from the water.

Products of Cracking

For the following examples octane -C8H18- will be used but the
same principle applies to all alkanes. When octane is cracked the
molecule can break up in…

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Chemistry




Isomers 0 compounds having the same molecular formula but
different structural formula.


Addition reaction 0 a reaction in which an alkene breaks open its
double bond and adds atoms (Br2) to adjacent carbon atoms.


Cracking 0 the splitting of large saturated molecules to give a
mixture of small molecules,…

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Chemistry




Each homologous series has a general formula. For alkanes it is
CnH2n+2, for alkenes it's CnH2n.

Butane and Cyclobutene are isomers since they have the same
molecular formula (C4H8) but different structural formula.

Alkenes are named after the equivalent alkanes with the ending
'-ene' to '-ane'.

All hydrocarbons burn…

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Chemistry




The general formula for the alkane series is CnH2n+2.

The alkanes are members of a homologous series with the same
general formula, similar chemical reactions i.e. substitution and as
the molecular weight increases the boiling point increases.

Cycloalkanes are Carbon and Hydrogen atoms joined in rings. The
simplest is…

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Chemistry




A mixture of compounds is produced by cracking larger molecules
into smaller and more useful molecules. One of this mixture
however is unsaturated and can be used to make plastics.

A main use of the cracking of hydrocarbons is to increase the
volume of petrol required to meet demand.

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