Question

In a chemistry lab, Rina took some mercury and water in two test tubes A and B respectively. Then she drained off both the liquids and on observing the empty test tubes, found that test tube A is completely dry and some water droplets are stuck to test tube B. What could be the reason for this?

• A. Cohesive force between water and glass is more
• B. Adhesive force between mercury and glass is more
• C. Adhesive force between water and glass is more
• D. Cohesive force among mercury atoms are weak

Answer 1

The correct option is C Adhesive force between water and glass is more

Cohesive forces are the intermolecular forces that cause a tendency in liquids to resist separation. These attractive forces exist between molecules of the same substance.

Adhesive forces are the attractive forces between unlike molecules. They are caused by forces acting between two substances, such as mechanical forces (sticking together) and electrostatic forces (attraction due to opposing charges).

In the case of a liquid wetting agent, adhesion causes the liquid to cling to the surface on which it rests. When water is poured on clean glass, it tends to spread, forming a thin, uniform film over the glasses surface.

This is because the adhesive forces between water and glass are strong enough to pull the water molecules out of their spherical formation and hold them against the surface of the glass, thus avoiding the repulsion between like molecules.

Whereas in the case of mercury and glass, cohesive forces of mercury is more than adhesive forces between mercury and glass, so test tube A becomes completely dry.