Viscosity
Viscosity is the friction or resistance to motion that exists between the molecules
of a liquid when they move past each other. It is logical that the stronger the
attraction between the molecules of a liquid, the greater its resistance to flow—
and thus the greater its viscosity. The viscosity of a liquid depends on its
intermolecular forces. Because hydrogen bonds are such strong intermolecular
forces, liquids with hydrogen bonds tend to have high viscosities. Water, for
example, is strongly hydrogen bonded and has a relatively high viscosity. You
may have noticed how fast liquids with low viscosity, such as alcohol and
gasoline, flow.
TIP
More viscous liquids move more slowly.Surface Tension
Molecules at the surface of a liquid experience attractive forces downward,
toward the inside of the liquid, and sideways, along the surface of the liquid. On
the other hand, molecules in the center of the liquid experience uniformly
distributed attractive forces. This imbalance of forces at the surface of a liquid
results in a property called surface tension. The uneven forces make the surface
behave as if it had a tight film stretched across it. Depending on the magnitude of
the surface tension of the liquid, the film is able to support the weight of a small
object, such as a razor blade or a needle. Surface tension also explains the
beading of raindrops on the shiny surface of a car.
Capillary Action
Capillary action, the attraction of the surface of a liquid to the surface of a solid,
is a property closely related to surface tension. A liquid will rise quite high in a
very narrow tube if a strong attraction exists between the liquid molecules and the
molecules that make up the surface of the tube. This attraction tends to pull the
liquid molecules upward along the surface against the pull of gravity. This
process continues until the weight of the liquid balances the gravitational force.
Capillary action can occur between water molecules and paper fiber, causing the
water molecules to rise up the paper. When a water soluble ink is placed on the
paper, the ink moves up the paper and separates into its various colored
components. This separation occurs because the water and the paper attract the
molecules of the ink components differently. These phenomena are used in the
separation process of paper chromatography, as shown in the paper