Question

If the soluble impurity is added to a solvent, then the angle of contact

• A. decreases
• B. increases
• C. depends on the nature of soluble impurity
• D. angle of contact is independent of the presence of impurity

Hint:

Impurities change surface tension, and the angle of contact changes accordingly, in a direction that depends on the impurity.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept
The angle of contact depends on the surface tensions at the liquid, solid and gas interfaces. A soluble impurity changes the surface tension of the liquid.

Step 2: Two kinds of impurities
A highly soluble substance such as common salt raises surface tension, so the angle of contact increases.
A surface-active substance such as soap or detergent lowers surface tension, so the angle decreases.

Step 3: Conclusion
The effect can go either way, so it depends on the nature of the soluble impurity.

Final Answer:
The angle of contact depends on the nature of the soluble impurity. \[ \boxed{\text{(C) }\text{depends on the nature of soluble impurity}} \]