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Physical Properties of Alkanes

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Alkanes contain only carbon and hydrogen atoms. Since there is very little difference between the electronegativities of carbon and hydrogen, alkanes are almost non-polar.

Physical State and Odour of Alkanes

The first four members of straight chain alkanes — methane, ethane, propane and butane are gases. The next thirteen are liquids (C5−C17). Those containing eighteen carbons or more are waxy solids. They are colourless and odourless.

Boiling points of Alkanes

Amongst isomeric alkanes, the boiling point of branched chain alkanes is lower than that of corresponding straight chain alkanes because the surface area of alkanes decreases with branching, and consequently the Van dar waals forces of attraction become weaker.

Question : Out of 2,2-dimethylbutane, 2-methylpentane and 2,3-dimethylbutane, which one has the highest boiling point?

Solubility of Alkanes

Since alkanes are non-polar in nature, they are insoluble in polar solvents such as water, alcohol etc. They are, however, highly soluble in non-polar solvents such as benzene, ether, carbon tetrachloride etc.

Density of Alkanes

Alkanes are lighter than water.

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