Question

What happens when oil is added to water ?

1. Surface tension of water decreases

2. Surface tension of water increases

3. Oil will float

1. Both 1 & 3
2. Both 2 & 3
3. 3 only
4. None

Answer 1

Correct Answer - Option 1 : Both 1 & 3

Explanation:

Surface Tension: It is a kind of force that exists on the surface of a liquid caused by the attraction of the particles on the surface of a liquid by other phases of liquid or liquid itself.

• It tends to minimize surface area​
• The water droplet is spherical due to this phenomenon.

• It is measured as the force acting per unit length of an imaginary line drawn on the liquid surface.
  \(Surface\;tension = \frac{{Force}}{{length}}\)

Two factors that can affect the surface tension of a liquid are:

• Temperature: If temperature increases then the surface tension of a liquid decreases.
• Soluble Impurities: In the case of less soluble impurities, the surface tension decreases. But, for highly soluble impurities in the liquid the surface tension increases

When oil is added to water:

• Oil has less density as compared to water. Therefore, it will float on water.
• When Oil or any other non-polar liquid float over water, it decreases the number of hydrogen bonds to form with other surfaces.
• Hence, the force per unit length decreases.

Therefore surface tension of water will decrease.