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Chemistry LibreTexts

Forces of Cohesion/ Adhesion

 

Chemical Concepts Demonstrated

  • Existence of and differences between the forces of adhesion and cohesion
  • Surface tension

Demonstration

A 50:50 mixture of absolute ethanol and DI water is poured into a VERY clean glass and projected on the overhead. wine.gif

Observations

The alcohol/water vapor collects above the liquid in the goblet forming a ring where the liquid and vapor intersect.

Explanation

The force of cohesion is defined as the force of attraction between molecules of the same substance.  The force of adhesion is defined as the force of attraction between different substances, such as glass and water.

The ring is formed by the alcohol/water mixture climbing the walls of the wine goblet. When the force of adhesion between a liquid and the walls of its container is a significant fraction of the force of cohesion between the particles in the liquid, the liquid will "wet" the walls of the container.

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