Chemistry UTME Question Analysis: Alcohol Comparison

Chemistry UTME Question Analysis

Comparison of Alcohols: Pentane-2-ol vs. Pentane-2,3-diol

This section deals with a question regarding the physical properties of two alcohols: pentane-2-ol and pentane-2,3-diol. To provide a thorough understanding, we will analyze the structure, boiling points, hydrogen bonding, volatility, and solubility characteristics of both compounds.

Alcohol Structures

1. Pentane-2-ol:
      - Structure: This is a secondary alcohol with the hydroxyl (-OH) group positioned on the second carbon of the pentane chain.
      - Formula: $C_5H_{12}O$
      - Symmetry: Features a symmetrical structure that influences its physical properties.
   
2. Pentane-2,3-diol:
      - Structure: This compound has both hydroxyl groups located on the second and third carbons of the pentane chain, making it a diol.
      - Formula: $C_5H_{12}O_2$
      - Symmetry: Less symmetrical compared to pentane-2-ol due to the presence of two -OH groups.
   

Boiling Point

• Boiling Point of Alcohols:
     - The boiling point of alcohols is influenced by molecular weight, symmetry, and the ability to form hydrogen bonds.
• Pentane-2-ol:
     - Lower boiling point due to less hydrogen bonding capacity.
• Pentane-2,3-diol:
     - Higher boiling point due to increased hydrogen bonding from two hydroxyl groups, which can form more extensive intermolecular hydrogen bonds compared to pentane-2-ol.
• Conclusion on Choice B:
     - Therefore, the statement indicating that pentane-2,3-diol has a higher boiling point due to increased hydrogen bonding is correct.
  

Volatility

• Volatility:
     - Volatility refers to a substance's tendency to evaporate. A lower boiling point typically correlates with higher volatility.
• Pentane-2,3-diol:
     - Its higher boiling point suggests it has lower volatility compared to pentane-2-ol. This indicates that choice C (higher volatility) is incorrect.
  

Solubility in Water

• Solubility:
     - Alcohols with more hydroxyl (-OH) groups are generally more soluble in water due to the ability to form hydrogen bonds with water molecules.
• Pentane-2,3-diol:
     - Should have higher solubility in water compared to pentane-2-ol because of an additional -OH group that enhances interactions with water.
• Conclusion:
     - Thus, choice D claiming lower solubility in water is also incorrect.
  

Summary of Answer Options

• A: A lower boiling point due to less symmetry
    - This is misleading as boiling point mainly depends on hydrogen bonding rather than symmetry alone.
• B: A higher boiling point due to increased hydrogen bonding
    - This is correct and highlights the strong intermolecular forces in pentane-2,3-diol.
• C: Higher volatility
    - Incorrect due to the higher boiling point of pentane-2,3-diol.
• D: Lower solubility in water
    - Incorrect as it has more -OH groups, hence more soluble.
  

Conclusion

The most accurate answer to the question is B: A higher boiling point due to increased hydrogen bonding.

The discussion highlights the importance of molecular structure in determining boiling points, volatility, and solubility of alcohols, which is crucial for understanding their properties in both chemical research and practical applications.