Explain why the angle of contact of mercury with glass is obtuse , while that of water with glass is acute.
The cohesive force between the molecules of mercury is more than the adhesive force between the molecules of mercury and those of glass.This results in the formation of a convex meniscus for the surface of mercury. Actually,cohesive force and Adhesive forces are the phenomenon due to the surface tension of a liquid. The angle made by the mercury from the glass surface is always obtuse.
The adhesive force between the molecules of glass and water is more than the cohesive force between the molecules of water.This results in the formation of a concave meniscus for the surface of water. The angle made by the water from the glass surface is always acute.