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Explain why the meniscus of water is concave and that of mercury is convex.

Cohesion vs Adhesion



  • Cohesion: Cohesion is the attractive force between "like" molecules. Many properties of water such as surface tension occur because of cohesive forces between water molecules.


  • Adhesion: Adhesion is the attractive force between the molecules in a liquid and a solid surface.

Water


When water is placed in a graduated cylinder, the adhesive forces between the water and the glass are stronger than the cohesive forces between the water molecules. The strong adhesive forces between the water and the glass, pull the sides of the water upwards along the glass forming a concave shaped meniscus.


Mercury


When mercury is placed in a graduated cylinder, the cohesive forces in the mercury are stronger than the adhesive forces between the mercury and the glass. The strong cohesive forces within the mercury pull it together forming a convex shaped meniscus. 

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