Question

When a sparingly soluble substance like alcohol is dissolved in water, surface tension of water?
A. Increases
B. Decreases
C. Remains constant
D. Becomes infinite

Answer 1

Hint: Surface tension depends on the force of attraction between the particles within the solid and also upon the gas, liquid or solid in contact with it. Greater the force of attraction between the molecules, more is the surface tension. So, find the force of attraction between the molecules in water and find what happens to the force of attraction when a sparingly soluble substance like alcohol is added to the water. Characteristics of the surface tension changes when chemicals or any other solid, liquid or gas is added to it.

Complete answer:
The intermolecular attraction or the force of attraction between the molecules of water is high. When we dissolve a sparingly soluble substance like alcohol in water, the force of attraction between the molecules decreases. But, the force of attraction is proportional to the surface tension of the liquid. Thus, the surface tension of the water also decreases.
Hence, when a sparingly soluble substance like alcohol is dissolved in water, the surface tension of the water decreases.

So, the correct answer is “Option B”.

Note:
When the temperature of the liquid increases, the net force of attraction between the molecules decreases. Hence, the surface tension of the liquid also decreases. The surface tension also depends on the density of the liquid. Higher the density, more is the surface tension of the liquid. The liquid with highest density is liquid and thus it has highest surface tension. While the liquid with lowest density is alcohol. Hence, it has the lowest surface tension.