MCQ Detailed View

The boiling point of alcohols depends mainly on molecular weight, number of hydroxyl (-OH) groups, and hydrogen bonding. More hydroxyl groups increase the strength of hydrogen bonding, which raises the boiling point because stronger intermolecular forces require more energy to overcome.

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  Methanol (CH₃OH) contains one hydroxyl group. Its boiling point is about 65 °C.

  
  


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  Ethanol (C₂H₅OH) also has one hydroxyl group but a slightly larger molecular size than methanol, so its boiling point is higher, about 78 °C.

  
  


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  Ethylene glycol (HO–CH₂–CH₂–OH) contains two hydroxyl groups. This allows stronger hydrogen bonding compared to ethanol or methanol, giving it a much higher boiling point of around 197 °C.

  
  


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  Glycerol (HO–CH₂–CHOH–CH₂–OH) contains three hydroxyl groups. With three sites for hydrogen bonding, glycerol forms extensive intermolecular interactions. This makes it the alcohol with the highest boiling point among the given options — about 290 °C.

  
  

The trend shows that as the number of hydroxyl groups increases, the ability to form hydrogen bonds increases, which directly raises the boiling point. Molecular size also plays a role, but hydrogen bonding is the dominant factor in alcohols.

In industrial and biological contexts, glycerol’s high boiling point and strong hydrogen bonding make it useful as a moisturizer, antifreeze agent, and solvent. Ethylene glycol is commonly used in antifreeze solutions because of its higher boiling and freezing point properties compared to simple alcohols. Methanol and ethanol, on the other hand, are widely used as fuels and solvents due to their lower boiling points and easier evaporation.

Thus, among the listed alcohols, glycerol has the greatest boiling point because of its three hydroxyl groups and the strongest intermolecular hydrogen bonding network.