Assertion (A): Alcohols have higher boiling points than hydrocarbons, ethers and haloalkanes of comparable molecular masses.
Reason (R): Lower alcohols are soluble in water because they can form hydrogen bonds with water molecules.
In the light of the above statements, choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Both (A) and (R) are true but (R) is not the correct explanation of (A).
The –OH group of an alcohol can take part in hydrogen bonding, both with other alcohol molecules and with water molecules. The two kinds of hydrogen bond explain two different properties.
Assertion (A): Alcohols have higher boiling points than hydrocarbons, ethers and haloalkanes of comparable molecular masses. — True. For example, ethanol and propane have comparable molecular masses, but ethanol boils at a much higher temperature; methoxymethane boils in between.
Reason (R): Lower alcohols are soluble in water because they can form hydrogen bonds with water molecules. — True. Several lower alcohols are miscible with water in all proportions; the solubility falls as the hydrophobic alkyl group gets larger.
Why R does not explain A?
Boiling concerns the pure alcohol, where no water is present, so hydrogen bonds with water cannot decide it; R explains solubility.
The correct reason for A is intermolecular hydrogen bonding between the alcohol molecules themselves, which is lacking in ethers and hydrocarbons.
NCERT (2026-27 edition):
7.4.3 Physical Properties – “It is interesting to note that boiling points of alcohols and phenols are higher in comparison to other classes of compounds, namely hydrocarbons, ethers, haloalkanes and haloarenes of comparable molecular masses. For example, ethanol and propane have comparable molecular masses but their boiling points differ widely. The boiling point of methoxymethane is intermediate of the two boiling points.”
“The high boiling points of alcohols are mainly due to the presence of intermolecular hydrogen bonding in them which is lacking in ethers and hydrocarbons.”
“Solubility of alcohols and phenols in water is due to their ability to form hydrogen bonds with water molecules as shown. The solubility decreases with increase in size of alkyl/aryl (hydrophobic) groups. Several of the lower molecular mass alcohols are miscible with water in all proportions.”