Question

The magnitude of surface tension of liquid depends on the attractive forces between the molecules.

Arrange the following in increasing order of surface tension: water , alcohol $\left(C_2{H}_{5}OH\right)$ and hexane $\left[C{H}_3\right(C{H}_2{)}_{4}C{H}_3]$

Answer 1

$\text{Surface tension and intermolecular attractive forces}:$

The magnitude of surface tension of a liquid depends on the attractive forces between the molecules. When the attractive forces are large, the surface tension becomes higher.

Hexane $\left[C{H}_3\right(C{H}_2{)}_{4}C{H}_3]$ is a nonpolar molecule. It has weak London dispersion forces only.

But water and alcohol are polar molecules. Both water and alcohol molecules exhibit $H$- bonding and dipole- dipole interactions.

These forces are stronger than London forces. Due to this water and alcohol has stronger interaction between the molecules than hexane.

Therefore, hexane has lower surface tension than the other two.

$H$-bonding is stronger in water than alcohol, so water has stronger intermolecular forces of attraction than alcohol.

Hence, the increasing order of surface tension is: Hexane < Alcohol < Water.