Question

What is the effect of impurities on surface tension of a liquid?

Answer 1

1. The surface tension of a liquid increases when it contains dissolved impurities, such as common salt. The angle of contact (or surface tension) for dissolved impurities increases linearly with the concentration of the dissolved materials.
2. With sparingly soluble substances such as alcohol or phenol, it decreases. Detergents are surfactants that possess hydrophobic and hydrophilic extremities. The hydrophobic ends reduce the surface tension of water. By reducing surface tension, water can penetrate the fibres of a cloth and effectively eradicate stubborn stains.
3. Decreases in the presence of insoluble surface contaminants, such as oil, grease, or dust. For instance, flawless spherical droplets do not form on mercury surfaces contaminated with dust until the dust is removed.