Question

The viscosity of which liquid is highest-
1. Water
2. Glycol
3. Alcohol
4. Acetone

Answer 1

Correct Answer - Option 2 : Glycol

Concept:

Viscosity: It is the property of a fluid, by virtue of which it opposes the relative motion between its different layers is known as viscosity.

This force is known as the viscous force.

Mathematically, \(F = - η A\frac{{dv}}{{dx}}\;\)

where, η = coefficient of viscosity, A = area, dv/dx = velocity gradient.

• Hydrogen bond: The electrostatic force of attraction between a hydrogen atom which is covalently bonded to a highly electronegative atom and any other electronegative atom which is present in the same or different molecules.
• In the solid-state, it is maximum.
• In the gaseous state, it is minimum.
• There are two types of hydrogen bonds found:
  • Intermolecular H-bonding: It occurs between different molecules of a compound and results in increasing solubility in water and high boiling point.
    • e.g. HF, water [H2O] molecule
  • Intramolecular H-bonding: It occurs within different parts of the same molecule and results in decreasing solubility in water and low boiling point.
    • e.g. o -nitrophenol
• The molecules having O—H, N—H or H—F bonds in it, show abnormal properties due to H-bond formation. For example;
  • Glycerol is viscous and has a very high boiling point due to the presence of intermolecular H-bonding.
  • H-bonding also plays an important role in the biological system and stability of proteins and nucleic acids(DNA RNA etc). 

Explanation:

• Hydrogen bonding and strong intermolecular interactions increases the viscosity of the liquid. 
• Ethylene glycol HO−CH₂−CH₂−OH has two −OH  groups. The hydrogen bonding is due to these −OH groups. 
• More is the number of −OH groups, more are the hydrogen bonds and greater is the viscosity. Ethanol has only one −OH group.

Hence the correct option is Glycol.