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Methane

 

Methane is a hydrocarbon with the formula CH4, consisting of one carbon and four hydrogen atoms. 

It is produced in the laboratory by heating a mixture of ground mixture of anhydrous sodium ethanoate (sodium acetate) and soda-lime (this is quicklime soaked with a concentrated solution of sodium hydroxide).

CH3COONa(S)   +   NaOH(S)          ®       Na2CO3(S) + CH4(g)
                                               
from soda-lime
       

Note: soda-lime is used because it does not attack glass readily and is not deliquescent. Soda-lime is therefore a non-deliquescent form of sodium hydroxide.

Properties of Methane (Physical and Chemical)

Physical properties

1. Methane is a gas which is colorless and odorless.

2. It is almost insolution in water.

3. It is much less dense than air (vapor density = 8, vapor density of air = 14.4).

4. It is neutral to litmus.

Chemical Reactions

1. Combustion: On the application of a flame or electric spark, methane burns or explodes in air with a pale, non-luminous flame. The products of combustion is steam, carbon(IV) oxide and enormous heat.

CH4(g) + 2O2(g) ® CO2(g) + 2H2O(g) DH = -890 kJ mol-1

Note: the cause of explosions in coal mines is the ignition of the mixture of methane (the important constituent of natural gas produced in coal mines) and oxygen of the air.

2. Reaction with chlorine - methane reacts slowly at ordinary temperature with chlorine in the presence of light to form a mixture of products - light acts as catalyst (the reaction is photocatalysis).

Different products are possible:

First products:

CH4(g) + Cl2(g)  ®    CH3Cl(g)         +      HCl(g)
                                
Chloromethane
       

Second products (with excess of chlorine):

CH3Cl(g)  +  Cl2(g)     ®     CH2Cl2(g)      +     HCl(g)
                                             
Dichloromethane
       

Third products (with excess of chlorine):

CH2Cl2(g)     +     Cl2         ®        CHCl3(g)     +     HCl(g)
                                              Trichloromethane
       

Fourth and final products (with excess of chlorine):

CHCl3(g)   +    Cl2(g)         ®          CCl4(g)      +       HCl(g)
                                           Tetrachloromethane
       

Note:

  • The above reactions are substitution reactions - each hydrogen atom is replaced with an atom of chlorine successively to give the products. This is so because methane (the alkanes in general) is saturated (i.e., all the valence electrons of carbon are bonded with hydrogen atoms, so, there is "no vacancy").

  • Successive substitution occurs with increasing difficulty.

  • Similar reactions as above are formed between gaseous bromine and methane - the reactions are however slower.

  • Methane and other alkanes are inert, i.e., they are unreactive. The above two reactions are the only ones shown by alkanes at ordinary temperature and pressure.

Uses of Methane

1. Used as fuel - for domestic and industrial heating. Methane is advantageous as fuel because it is nonpoisonous, has no smell and leaves no residue (i.e. it is environmentally friendly).

2. Used for the production of certain important compounds. Example, carbon black, hydrogen, alkynes, carbon disulphide, hydrochloric acid, trichloromethane (also called chloroform) and tetrachloromethane.

Uses of Halogenated Products of Methane

1. Methyl chloride (chloromethane), CH3Cl, a gas, used chiefly in the production of silicone resins and rubbers. Most of it is made from methanol and hydrogen chloride:

CH3OH(l) + HCl(aq) ® H2O(l) + CH3Cl(g)

2. Methylene chloride (dichloromethane), CH2Cl2, is a liquid, used in paint and vanish removers and as a solvent for aerosol paints.

3. Chloroform (trichloromethane), CHCl3 - the chief use of chloroform is for the production of chlorodifluoromethane (Freon-22). Also used in surgical operations as anaesthetic.

4. Tetrachlorometane or carbon tetrachloride, CCl4. This is the most important of the chlorinated methanes. The industrial usefulness of this compound is based largely on its conversion to dichlorodifluoromethane (Freon-12), trichlorofluoromethane (Freon- 11), and tetrachloroethylene. Also used as solvent and for removal of grease in the industry.

Related:

Hydrocarbon and Alkanes
Isomerism in Alkanes
IUPAC Nomenclature of Alkanes
Petroleum and Petrol

 

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