Question

Why does vinegar/acetic acid have a higher boiling point but lower surface tension than water? Which has the stronger intermolecular force then?

Acetic acid's boiling point is 118 degrees Celsius and water's boiling point is 100 degrees Celsius. That must mean the intermolecular forces in acetic acid is stronger than water.

But according to wikipedia (https://en.wikipedia.org/wiki/Surface_tension), acetic acid's surface tensions is lower than water. That suggests water's intermolecular forces are stronger.

Answer 1

Acetic acid has a higher boiling point based on molecular weight and lower Surface tension due to its higher polarity related to the water; since its higher intermolecular force.

Explanation:

BOILING POINT (`T_B`)
In general `T_B` increases with compound molecular weight

SURFACE TENSION
Surface tension is function of the molecule polarity and hydrophilic lipophilic balance

Acetic acid OH-group behaves similar to the primary alcohols such methanol, ethanol, and propanol:

Relative polarity
Water 1.000
Methanol .762
Ethanol .654
Propanol .617
Acetic acid .648

Surface Tension (dyn/cm)
Water 72.7
Methanol 22.1
Ethanol 22.0
Propanol 23.8
Acetic acid 27.0

So, acetic acid has a higher boiling point based on molecular weight and lower Surface tension due to its higher polarity related to the water; since its higher intermolecular force.