Chemical Sciences Colloid and Surface Chemistry Lab  Experiments

Demonstration of the Surface Tension Lowering of Water by Soaps/Detergents

We have seen how insects like the water striders or the marsh treaders walk comfortably on the surface of water without sinking. The surfaces of water and other liquids behave like elastic membranes. The intermolecular forces of attraction in the surface liquid molecules give rise to this property, surface tension, of liquid. The water striders or the marsh treaders exploit the surface tension property of water to walk comfortably on the water surface. The surface tension of liquids is responsible for behaviours of liquids like round shapes of droplets and bubbles. Surface tension phenomenon becomes clearly visible when surfactants are used to decrease it. Surfactants can reduce the surface tension of water by a factor of three or more. The experiments here will demonstrate this effect.

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Figure 1. A water strider on water.