Question

Which of the following alcohols is the least soluble in water?
A.Ethanol
B.1- propanol
C.1- butanol
D.1- pentanol

Answer 1

Alcohols are polar organic compounds having hydroxyl groups attached to the parent hydrocarbon. The solubility of an alcohol in water depends on various factors like the position of the hydroxyl group, size of the carbon chain, etc.

Complete answer:
Alcohols are polar compounds due to differences in the electronegativities of carbon and oxygen. As a result, alcohols interact with each other as well as other polar compounds by hydrogen bonding and dipole- dipole interactions. Dipole- dipole interaction is the attractive force between the ends of two bonds due to polarity in the bonds. Hydrogen bonding too is a type of dipole- dipole interaction.
Alcohols can be either primary, secondary or tertiary depending on the carbon chain and the position of the hydroxyl group. Lower alcohols are readily soluble in water because the hydroxyl group of alcohol and water molecules form hydrogen bonds. Since the interactions are strong, they are readily miscible. But as we move to higher alcohols, the solubility decreases as these alcohols act almost like alkanes. The large hydrocarbon part is hydrophobic and thus there are low chances of solubility.
Of the given options, the largest alcohol of all is 1- pentanol and will thus have the least solubility in water.

Thus, the correct answer is D.

Note:
Due to their polar nature, alcohols also have high boiling points. The hydroxyl groups of two different alcohol molecules form intermolecular hydrogen bonds with each other. Also the boiling point increases with increase in the number of carbon atoms. So all alcohols have high boiling points.