Question

Which compound will have the highest boiling point?
(a) $C{{H}_{4}}$
(b) $C{{H}_{3}}OH$
(c) ${{C}_{2}}{{H}_{5}}OH$
(d) $HCHO$

Answer 1

Hint: The boiling point of the organic compound depends on the interactions between their molecules. The compounds that can form hydrogen bonding will have the highest boiling point and the compounds that will have van der Waal forces will have the lowest boiling point.

Complete answer:
In an organic compound, the boiling point can be calculated by the interactions between the molecules. There are many types of interactions between the molecules like hydrogen bonding, dipole-dipole interaction, and van der Waal forces. The compounds that can form hydrogen bonding will have the highest boiling point, the compounds that will have dipole-dipole interactions will have a moderate boiling point, and the compounds that will have van der Waal forces will have the lowest boiling point.
Among the chains in the carbon compounds, the number of carbon atoms in the chain increases, the boiling point also increases. But with the branching of the chain, the boiling point will decrease.
$C{{H}_{4}}$ is a hydrocarbon and will have van der Waal forces. In $C{{H}_{3}}OH$, the hydrogen atom is attached to an electronegative atom, so it will form hydrogen bonding. In ${{C}_{2}}{{H}_{5}}OH$, the hydrogen atom is attached to an electronegative atom, so it will form hydrogen bonding. In $HCHO$, there is a polar carbonyl group and it will form dipole-dipole interaction.
So, the highest boiling point will be of ${{C}_{2}}{{H}_{5}}OH$ because the molecular mass of ${{C}_{2}}{{H}_{5}}OH$ is more than the molecular mass of $C{{H}_{3}}OH$.

Therefore, the correct answer is an option (c).

Note:
The boiling point of the organic compounds having comparable masses will be in the order of: Carboxylic acid > Alcohols > Ketones > Aldehydes > Ethers > Hydrocarbons.