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Question: Most viscous among the following is:...

Most viscous among the following is:

A

Propan-1-ol

B

Propan-2-ol

C

Propane-1, 2-diol

D

Propane-1,2,3-triol

Answer

Propane-1,2,3-triol

Explanation

Solution

The viscosity of a liquid is primarily determined by the strength of intermolecular forces between its molecules. Stronger intermolecular forces lead to higher viscosity. Among organic compounds, hydrogen bonding is a significant intermolecular force. The more hydroxyl (-OH) groups a molecule possesses, the greater its capacity for forming hydrogen bonds, and consequently, the higher its viscosity.

  • Propan-1-ol (CH₃CH₂CH₂OH): Contains one hydroxyl (-OH) group.
  • Propan-2-ol (CH₃CH(OH)CH₃): Contains one hydroxyl (-OH) group.
  • Propane-1,2-diol (HOCH₂CH(OH)CH₃): Contains two hydroxyl (-OH) groups. This allows for more extensive hydrogen bonding compared to propanols.
  • Propane-1,2,3-triol (HOCH₂CH(OH)CH₂OH): Also known as Glycerol. Contains three hydroxyl (-OH) groups. This compound has the highest number of hydroxyl groups among the options, enabling it to form the most extensive network of hydrogen bonds.

Due to the presence of three hydroxyl groups, Propane-1,2,3-triol (Glycerol) can form the strongest and most numerous hydrogen bonds among the given compounds. This strong intermolecular attraction results in a significantly higher resistance to flow, making it the most viscous liquid.