Physical Properties of Alkanes - Practice Questions & MCQ

The various important physical properties of alkanes are discussed below:

• State: Due to weak forces, the alkanes up to four carbon atoms, i.e, methane, ethane, propane and butane are colourless, odourless gases but the next thirteen members are colourless, odourless liquids. Alkanes from C₁₈ onwards are colourless and odourless solids.
• Density: The density of alkanes increases very slowly with the rise of molecular mass until it becomes constant at about 0.8. Thus, all alkanes are lighter than water.
• Solubility: They are generally insoluble in polar solvents such as water but soluble in non-polar solvents like ether, carbon tetrachloride, benzene, etc. The solubility decreases with increase in molecular mass.
• Boiling point: The boiling points of straight-chain or n-alkanes increase regularly with the increasing number of carbon atoms. Among the isomeric alkanes, the normal isomer has a higher boiling point than the branched-chain isomers. The greater the branching of the chain, the lower will be the boiling point.
• Melting point: The melting points of alkanes do not follow a very smooth gradation with the increase of molecular size. Alkanes with even number of carbon atoms have high melting point than the next lower and next higher alkanes having odd number of carbon atoms.