Question:

Given below are two statements:
Statement-I: Pure Aniline and other arylamines are usually colourless.
Statement-II: Arylamines get coloured on storage due to atmospheric reduction
In the light of the above statements, choose the most appropriate answer from the options given below:

Updated On: Oct 10, 2024
  • Both Statement-I and Statement-II are correct.

  • Both Statement-I and Statement-II are incorrect.

  • Statement-I is correct but Statement-II is incorrect.

  • Statement-I is incorrect but Statement-II is correct.

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The Correct Option is C

Solution and Explanation

The correct answer is (C) : Statement-I is correct but Statement-II is incorrect
Pure Aniline and other arylamines are usually colourless. 
But they become coloured on storage due to atmospheric oxygen. Aniline develops a yellow to brown colour due to this reason.

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Concepts Used:

Amines - Physical Properties

  • The lower aliphatic amines have a fishy smell and are gaseous in nature.
  • Primary amines with 3 or 4 carbon atoms are fluids at room temperature though higher ones are solids.
  • Aniline and other arylamines are generally colorless. However, when we store them in the open because of atmospheric oxidation they get colored.
  • Lower aliphatic amines can form hydrogen bonds with water molecules. These amines are soluble in water.
  • A surge in the size of the hydrophobic alkyl part escalates the molar mass of amines. This normally reduces its solubility in water.
  • Higher amines are unsolvable in water. Organic solvents such as alcohol, benzene, and ether simply dissolve amines in it. Aromatic amines are unsolvable in water because the large hydrocarbon part (hydrophobic part) of aromatic amines slow down the formation of H-bonding.
  • Alcohols have higher polarity as compared to amines due to which they form more grounded intermolecular hydrogen bonds.
  • Primary and Secondary amines commonly form intermolecular associations because of hydrogen bonding between the nitrogen of one amine and hydrogen of the other amine.
  • Because of the availability of two hydrogen particles in primary amines, this type of intermolecular bonding is more noticeable in primary amines as compared to secondary amines.
  • In tertiary amines, there is no intermolecular association due to the absence of free hydrogen atoms for bonding.
  • The order of boiling point of amines is represented in the following manner:

           Primary > Secondary > Tertiary. 

Read More: Physical Properties of Amines