That is, Cohesion is the force of attraction between identical substance.
b] Adhesion : is the force of attraction between molecules of different substance.
That is, Adhesion is the force of attraction between non-identical substance.top↑
E.g mercury and glass.
Why Does Water Wet Glass And Why Is It That Mercury Does Not Wet Glass?
MUST READ : They ask this question a lot that, why does water wet glass and why is it that mercury does not wet glass.
Here is the answer, please master it especially if you are sitting for any O’level exam (Weac, Neco, Gce etc)
a] Water wet glass because, The adhesion of water to glass is greater or stronger than the Cohesion of water.
b] Mercury does not wet glass because, The Cohesion of mercury is greater than its adhesion to glass.
Please master those two points.top↑
Now let go to Capillarity
Capillarity : is the tendency of a liquid to rise or fall in a narrow capillary tube.
If an identical tube is placed in a beaker of mercury the surface tends to curve Convex inward.
Remember the reason why mercury don’t wet glass,
In the case of mercury, the Cohesion of mercury molecules is greater or stronger than its adhesion to glass.
So therefore the mercury tends to curve inward and become depressed (fall) in the tube.top↑
Capillarity is brought about cohesion and adhesion force, so water and other liquids that wet glass will rise in a capillary tube because the force of adhesion of the liquid molecules to glass is greater or stronger than thier cohesion to each other.
So therefore water tends to rise up in the glass and curve concave upward.
What am saying is that ;
Liquid that can wet glass will rise in a capillary tube and curve upward(concave) e.g water.
While liquid that cannot wet glass will fall in a capillary tube and curve inward (convex) e.g mercury.top↑
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