Hydrocarbons part-1

Hydrocarbons are the organic compounds which contains only C and H.

Methods of preparation:

a) Methane is Prepared in the laboratory by heating a mixture of fused anhydrous sodium acetate and soda lime in a hard glass test tube, The methane liberated is collected over water.
 CH3COONa +NaOH - - -) Na2CO3 +CH4

 b) Pure methane is obtained in the laboratory by the action of zinc- copper couple and alcohol on methyl iodide. Reduction takes place and methane is liberated.

CH3I+ 2[H]---)  CH4 + HI

 Zinc - copper couple is placed in a flask fitted with a stopper carrying a dropping funnel and a delivery tube.
A mixture of methyl iodide and 95% ethyl alcohol is dropped on the zinc copper couple. Methane is liberated. This gas contains methyl iodide vapours as impurity.
So the gas is passed through a U - tube containing zinc - copper couple which converts any methyl iodide in to methane. The methane is collected over water.

Physical Properties:
1.At room temperature and standard pressure, methane is a colorless, odorless gas.
2.Methane is lighter than air, 
3.having a specific gravity of 0.554. 
4.It is only slightly soluble in water.

Chemical properties:

Uses:
 Domestic and industrial fuel.
 Shoe polish.
 Printing ink.
 Tyre manufacturing. 
 Manufacture of methyl alcohol.

Ethene or ethylene 

1)It is the first member of the unsaturated aliphatic hydrocarbon series, and has a double bond.
2)Its molecular weight is 28.
3)Ethene occurs in nature in free state in small quantities in plants.
4)ethene is found in various sources such as natural gas and coal gas.

Preparation of ethene:
In the laboratory ethene is prepared by dehydration of ethanol. On heating ethyl alcohol with sulphuric acid at a temperature of 170 ° C temperature forms ethene.

Cracking or Dehydrogenation:

When alkanes of high molecular weight are heated at high temperature, the molecules breaks into alkane and alkenes of low molecular weight. This process is called cracking.
Ethane when heated upto 500°C forms ethene.

Physical properties:

Ethene is a colourless gas.
Ethene posses pleasant odour at STP.
Ethene is completely soluble in organic solvents and slightly soluble in water.
It is lighter than air.
Boiling point of ethene is -102 ° C and melting point is: –169° C.

Chemical properties :
   

Uses
It has anaesthetic effect on inhalation.
To ripen green fruits

An essential ingredient in manufacture of synthetic chemicals such as ethylene glycol, diethyl ether, ethylene oxide and mustard gas

To manufacture polymers like poly ethylene and poly vinyl chloride

It is also useful in the synthesis of important chemicals useful in industries.


Ethyne (acetylene)

It is generally prepared in a laboratory by the action of water on calcium carbide.

Procedure:

A thin layer of sand is spread atomic the bottom of a conical flask.

A few small pieces of calcium carbide (CaC2) are placed over the sand.
The whole apparatus is set upon.

Water is added to the flask drop wise with the help of a thistle funnel.

Ethyne (acetylene) gas so produced is collected in a gas jar by the downward displacement of water.

Physical properties:

Ethyne is a colourless gas with a characteristic smell. 
It is significantly soluble in water. However readily soluble in organic solvents. 
It is used in welding to produce oxy-acetylene flame of temperature about 3000°C

Chemical properties:

Contiued in part - 2