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The surface tension of which of the following liquids is maximum :-
A
$C_6H_6$
B
$H_2O$
C
$C_2H_5OH$
D
$CH_3OH$
Detailed Solution
Surface tension is the force acting per unit length perpendicular to a line drawn on the surface of a liquid; it arises from the inward pull of intermolecular attractions on the surface molecules.
The stronger the intermolecular forces, the higher the surface tension.
Water has extensive three-dimensional hydrogen bonding, with each molecule able to form up to four hydrogen bonds.
Methanol and ethanol also form hydrogen bonds, but fewer per molecule because of the alkyl group; benzene has only weak dispersion forces.
Approximate surface tensions at $20^\circ C$ (mN/m): water 72.8, benzene 28.9, methanol 22.6, ethanol 22.3.
So the surface tension is maximum for $H_2O$.
The stronger the intermolecular forces, the higher the surface tension.
Water has extensive three-dimensional hydrogen bonding, with each molecule able to form up to four hydrogen bonds.
Methanol and ethanol also form hydrogen bonds, but fewer per molecule because of the alkyl group; benzene has only weak dispersion forces.
Approximate surface tensions at $20^\circ C$ (mN/m): water 72.8, benzene 28.9, methanol 22.6, ethanol 22.3.
So the surface tension is maximum for $H_2O$.