Wettability and interfacial forces: Which fluid property explains why mercury forms a convex meniscus and does not wet glass?

Introduction / Context:
Wetting behavior in capillaries and containers depends on the balance between cohesive forces within a liquid and adhesive forces between the liquid and a solid surface. Mercury–glass interaction provides a classic counterexample to water, which wets glass.

Given Data / Assumptions:

• Room temperature behavior in clean glass and pure mercury.
• No contamination or oxide layers altering surface chemistry.
• Qualitative comparison of forces.

Concept / Approach:
When cohesion (liquid–liquid attraction) exceeds adhesion (liquid–solid attraction), the liquid minimizes contact area with the solid, producing a convex meniscus and non-wetting behavior. Mercury’s strong metallic bonding leads to high cohesion relative to adhesion to silica glass; thus, it does not wet the glass surface.

Step-by-Step Solution:

Verification / Alternative check:
Capillary action reverses: mercury is depressed in capillary tubes (negative capillarity), consistent with non-wetting and high contact angle observations.

Why Other Options Are Wrong:

• Surface tension: a related property, but the key explanation is the balance of cohesion vs adhesion; surface tension alone does not specify wetting without considering adhesion.
• Viscosity: flow resistance, not directly responsible for wetting.
• Adhesion: If adhesion dominated, mercury would wet glass (concave meniscus), which is not observed.

Common Pitfalls:
Equating high surface tension with non-wetting universally; water has high surface tension yet wets glass because adhesion exceeds cohesion at that interface.

Final Answer:
cohesion