Question

What are the factors affecting the surface tension of a liquid?

Answer 1

Hint: Surface tension is the property of liquid caused by the imbalance of molecular forces at the surface of the liquid. Factors causing the change in molecular forces also affect the surface tension. The value of surface tension depends on the nature of the liquid, surrounding environment and purity of the liquid.

Complete step by step solution:
Factors affecting the surface tension are
1. Impurities:
Soluble impurities: If the impurities are soluble then the surface tension may increase or decrease. The surface tension of liquid will decrease when the impurities are less soluble. For example, camphor is less soluble in water, hence it decreases the surface tension of water. On the other hand, the surface tension of liquid will increase when the impurities are more soluble. For example, the salt is more soluble in water, hence it increases the surface tension of water.
Insoluble impurities: Insoluble impurities such as dirt, oil, grease, etc. will decrease the surface tension of a liquid.

2. Temperature:
The molecular attraction between liquid molecules becomes weak when we increase temperature. Hence, the surface tension of liquid decreases as we increase the temperature of the liquid. The temperature at which the surface tension of the liquid becomes zero is called the ‘Critical temperature’ of that liquid.

Note: In many applications wish to decrease or increase the surface tension. This can be done by changing factors that affect surface tension. For example, surfactants are added in water so that dirt can be easily removed from clothes.