Properties of alkane

Physical Properties:

First four alkanes methane, ethane, propane and butane are gases. Next thirteen members (C₅-C₁₇) are colourless liquids. Higher alkanes are wax-like solids. Alkanes are non-polar compounds. They are soluble in non-polar solvent such as CCl₄, CHCl₃, benzene. However, alkanes are insoluble in polar solvent like water. Alkanes generally have low boiling point as they are non-polar. Boiling point increase with increasing molar mass. Boiling point decreases with increased branching.

Chemical Properties:

Alkanes are saturated compounds and the C—C and C—H bonds are non-polar. Therefore, they are less reactive and inert towards acids, bases, oxidizing and reducing agent. However, they undergo substitution reaction.

1) Halogenation:

Alkane reacts with chlorine in the presence of UV light, yield a mixture of products.

CH₄  +  Cl₂  —–>  CH₃Cl   +  HCl

CH₃Cl  +  Cl₂  ——>  CH₂Cl₂   +  HCl

CH₂Cl₂ +  Cl₂  ——>  CHCl₃   +  HCl

CHCl₃ +  Cl₂   ——-> CCl₄  +  HCl

2) Combustion:

Alkanes are highly combustible in nature. They burn in air or oxygen giving carbon dioxide and water.

CH₄  +  O₂ —–>  CO₂   +  H₂O

3) Pyrolysis:

Pyrolysis is the conversion of a compound into smaller fragments in the absence of air through the application of heat. e.g.

C₃H₈  ——-> CH₄ + C₂H₄ + C₃H₆ + H₂