Question

It is easier to spray water to which soap is added because addition of soap to water}

• A. decreases surface tension of water
• B. increases surface tension of water.
• C. makes surface tension of water zero.
• D. increases its density.

Hint:

Surfactants like soap always reduce surface tension by disrupting intermolecular cohesive forces.

Answer 1

The Correct Option is D

Step 1: Surface tension is a property of liquids caused by cohesive forces between molecules at the surface, which creates a net inward force making the surface behave like a stretched membrane. \[ T = \frac{F}{l} \]
Step 2: Soap acts as a surfactant. When soap is added to water, its hydrophobic tails disrupt the hydrogen bonding and cohesive forces between water molecules at the surface. \[ T_{\text{soap solution<T_{\text{pure water \]
Step 3: Spraying water involves creating many tiny droplets, which significantly increases the total surface area of the liquid. The work required to increase the surface area is given by: \[ W = T \times \Delta A \]
Step 4: By decreasing the surface tension ($T$), the amount of energy or work ($W$) required to create those droplets is reduced, making the process of spraying much easier.