Question

When the salt is added to water, what happens to the surface tension of the liquid?

Answer 1

The surface tension of the liquid increases after we add salt to the water.

Reason:

1. Surface tension arises due to the cohesive nature of a liquid which resists an external force on the liquid surface.
2. In the case of solute mixing in water then the surface tension depends upon the degree of contamination.
3. When salt is added to water, the surface tension of the liquid rises.
4. Although some hydrogen bonds between water molecules are broken by the strong interactions between sodium cations and partial negative oxygen and chloride anions and partial positive hydrogens, they actually increase the surface tension of water.
5. A molecule near the surface has half as many intermolecular bonds as a molecule in the bulk solution because it only has neighbors on one side.
6. As a result, the energy of molecules close to the surface increases, acting as an effective force to 'pull' water molecules inside and decrease the surface area.
7. Stronger intermolecular connections lead to increased surface tension because intermolecular bonds are what determine surface tension.
8. Molecules that disrupt and weaken the network of intermolecular connections diminish surface tension (such as detergent).