Factors affecting Surface Tension

• The presence of impurities either on the surface or dissolved in it, affect surface tension of the liquid. Highly soluble substances increase the surface tension of water, whereas sparingly soluble substances reduce the surface tension of water.

• The surface tension of a liquid decreases with increase in temperature. The surface tension of a liquid becomes zero at its boiling point and vanishes at critical temperature.

Impurities present in a liquid appreciably affect surface tension. A highly soluble substance like salt increases the surface tension whereas sparingly soluble substances like soap decreases the surface tension.
The surface tension decreases with rise in temperature. The temperature at which the surface tension of a liquid becomes zero is called critical temperature of the liquid. Oxygen in the atmosphere is known to decrease the surface tension of various substances.
Key points of Factors affecting surface tension:

• Temperature ↑ surface tension ↓
• Critical temperature Surface tension: Zero
• Critical temperature of water 3744K
• Increase with impurity.