The force between the molecules of a liquid in contact with that of a solid is?

Analysis

The question asks for the specific term used to describe the force of attraction between molecules of different substances—specifically, a liquid and a solid surface.

Concept Explanation

To understand this, we must distinguish between two types of intermolecular forces:

1. Cohesive Forces: These are the forces of attraction between molecules of the same substance (e.g., water molecules sticking to other water molecules). This is what causes surface tension and allows water to form droplets.
2. Adhesive Forces: These are the forces of attraction between molecules of different substances (e.g., water molecules sticking to the surface of a glass container or a leaf).

When a liquid comes into contact with a solid, the interaction between the liquid molecules and the solid surface molecules is governed by adhesive forces. If the adhesive forces are stronger than the cohesive forces, the liquid will "wet" the surface (like water on glass). If the cohesive forces are stronger, the liquid will bead up (like water on a waxed surface).

Step-by-Step Solution

• Step 1: Identify the interaction. The question specifies the force between molecules of a liquid and a solid.
• Step 2: Apply the definition. Since the molecules are of different types (liquid vs. solid), the force is defined as adhesive.
• Step 3: Evaluate the options. • A (Adhesive): Correct, as it describes attraction between different substances. • B (Cohesive): Incorrect, as it describes attraction between identical substances. • C (Magnetic): Incorrect, as this relates to magnetic fields, not molecular surface forces. • D (Repulsive): Incorrect, as this is a general term for forces that push apart, whereas the question refers to the interaction force between liquid and solid surfaces.

Conclusion

The force between molecules of a liquid and a solid is known as an adhesive force.

Exam Tip: Use the mnemonic "A for Adhesive, A for Apart"—Adhesive forces act between molecules that are "apart" (different substances), while "C for Cohesive, C for Clones"—Cohesive forces act between "clones" (identical molecules).