Consider the following statements about the physical properties of amines.
(A) Lower aliphatic amines are soluble in water because they can form hydrogen bonds with water molecules.
(B) The solubility of amines in water increases with increase in molar mass due to increase in size of the alkyl part.
(C) Alcohols are more polar than amines and form stronger intermolecular hydrogen bonds than amines.
(D) Intermolecular association is more in secondary amines than in primary amines.
(E) Aniline and other arylamines get coloured on storage due to atmospheric oxidation.
Which of the statements given above are correct? Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (A), (C) and (E) only
The N–H bonds of primary and secondary amines take part in hydrogen bonding, with water and with one another. This decides their solubility and their boiling points.
(A) Lower aliphatic amines are soluble in water because they can form hydrogen bonds with water molecules. — True.
(B) The solubility of amines in water increases with increase in molar mass due to increase in size of the alkyl part. — False. The alkyl part is hydrophobic, so as it grows the solubility decreases; higher amines are essentially insoluble in water.
(C) Alcohols are more polar than amines and form stronger intermolecular hydrogen bonds than amines. — True. Oxygen (3.5) is more electronegative than nitrogen (3.0), so the O–H bond is more polar than the N–H bond.
(D) Intermolecular association is more in secondary amines than in primary amines. — False. A primary amine has two hydrogen atoms on nitrogen for hydrogen bonding and a secondary amine only one, so association is more in primary amines.
(E) Aniline and other arylamines get coloured on storage due to atmospheric oxidation. — True. They are usually colourless when pure.
NCERT (2026-27 edition):
9.5 Physical Properties – “…Aniline and other arylamines are usually colourless but get coloured on storage due to atmospheric oxidation.”
“Lower aliphatic amines are soluble in water because they can form hydrogen bonds with water molecules. However, solubility decreases with increase in molar mass of amines due to increase in size of the hydrophobic alkyl part.” … “…alcohols are more polar than amines and form stronger intermolecular hydrogen bonds than amines.”
“This intermolecular association is more in primary amines than in secondary amines as there are two hydrogen atoms available for hydrogen bond formation in it.”