ANDC DU/Module on Surface Tension determination
Work in progress, expect frequent changes. Help and feedback is welcome. See discussion page. |
Contents
DETERMINATION OF SURFACE TENSION
To determine the surface tension of the given liquid, by using a stalagmometer by drop number method.
Learning Objectives
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REQUIREMENTS
A. CHEMICALS/SOLUTIONS
- Distilled water
- Given liquid
B APPARATUS
Stalagmometer, a piece of rubber tubing, pinch cock, pyknometer or specific gravity bottle, stand with a clamp, a water thermostat, and thermometer.
A molecule within the bulk of a liquid is surrounded by many molecules. It is equally attracted from all sides by these molecules so that the resultant force is zero. On the other hand, the surface molecules of the liquid are in a different condition with respect to the molecules in the interior of the liquid. These molecules are subjected to two kinds of pull:
It may be defined as the force acting per centimeter along the surface of the liquid at right angles to any line taken in the surface of the liquid in any direction.
If two immiscible or partially miscible liquids are taken in a vessel, then the surface tension acting along their surface of separation i.e. along the interface is called INTERFACIAL TENSION. Its value is generally intermediate between the surface tension of the two liquids but sometimes it is less than both. This is due to the fact that at the interface, the molecules of one liquid are attracted by the molecules of the other. Surface tension is a type of interfacial tension; the two phases involved being the liquid and the vapour above it. SURFACE TENSION AND TEMPERATUREThe surface tension of liquids is greatly affected by the change in temperature of the liquids. It generally decreases with the increase in temperature and becomes zero at the critical temperature. This is because of the reason that rise in temperature raises the kinetic energy of the molecules. This results in the decrease of intermolecular attraction and consequently the surface tension decreases. |
Work in progress, expect frequent changes. Help and feedback is welcome. See discussion page. |