Question

Given below are two statements: Statement (I): The boiling points of alcohols and phenols increase with increase in the number of C-atoms.
Statement (II): The boiling points of alcohols and phenols are higher in comparison to other classes of compounds such as ethers and haloalkanes. In the light of the above statements, choose the correct answer from the options given below:

• A. Both Statement I and Statement II are false
• B. Statement I is false but Statement II is true
• C. Statement I is true but Statement II is false
• D. Both Statement I and Statement II are true

Hint:

The boiling points of compounds with hydrogen bonding, such as alcohols and phenols, are generally higher compared to compounds like ethers and haloalkanes, which lack hydrogen bonding.

Answer 1

The Correct Option is D

To determine the accuracy of each statement, let's examine them individually: 

1. Statement (I): The boiling points of alcohols and phenols increase with an increase in the number of C-atoms.
   • Alcohols and phenols are both characterized by the presence of hydroxyl groups (\(-OH\)).
   • The boiling point of these compounds is generally influenced by two main factors:
     • Hydrogen bonding: The hydroxyl group can form hydrogen bonds, which significantly increases boiling points.
     • Molecular weight: As the number of carbon atoms increases, the molecular weight of the alcohol or phenol increases, leading to higher boiling points due to greater van der Waals forces (London Dispersion Forces).
   • Thus, it is true that the boiling points increase with an increase in the number of carbon atoms.
2. Statement (II): The boiling points of alcohols and phenols are higher in comparison to other classes of compounds such as ethers and haloalkanes.
   • This is primarily due to hydrogen bonding, which is much stronger than the van der Waals forces acting in ethers and haloalkanes.
   • Ethers and haloalkanes have weaker intermolecular forces as they lack the hydrogen bonding present in alcohols and phenols.
   • Therefore, alcohols and phenols generally have higher boiling points compared to ethers and haloalkanes of comparable molecular weight.

Based on the above analysis, we can conclude that both Statement (I) and Statement (II) are true. Therefore, the correct answer is:

• Both Statement I and Statement II are true

Answer 2

Statement (I): The boiling points of alcohols and phenols increase with an increase in the number of carbon atoms due to the increase in van der Waals forces (intermolecular forces) as the molecular size increases. This is a correct statement.
- Statement (II): Alcohols and phenols have higher boiling points compared to ethers and haloalkanes due to the presence of hydrogen bonding between molecules, which requires more energy to break. This is also true.
Therefore, both statements are true.