Cohesion and adhesion of water

Both cohesion and adhesion are properties that are observed in molecules in various phenomena, objects and substances. Naturally water is a perfect example to study them, for this reason we present below information on cohesion and adhesion in water .

DefinitionTendency of water molecules to stick to each other.Two surfaces of the same or different substances conjugate when they come into contact.
ExampleAn insect can stay on the surface of the water thanks to the tension.Drainage of the tear ducts in the eyes or sending water towards the treetops.

The cohesion and adhesion properties can be observed in multiple phenomena. In principle, cohesion is the attraction between molecules that holds the particles of a substance together, that is, there is an attractive force between adjacent particles within the same body. Instead, adhesion is the property of matter by which two surfaces of the same or different substances are conjugated or joined when they come into contact, being held together by intermolecular forces.

Therefore, a clear difference between cohesion and adhesion is that their unions are of different nature: the first within the same body; the second between the surface of two different ones. However, these phenomena may be sufficiently linked to study.

Cohesion in water

We speak of cohesion in water because its molecules have that tendency, that is, to stick together . So cohesion refers to the attraction that molecules have for others of the same type. In this case, the water molecules exhibit this property by having the ability to form hydrogen bonds between them.

And this itself generates the phenomenon of surface tension. What is it about? It results from the tendency of the surface of a liquid to resist rupture when subjected to stress or tension. Water molecules on the surface, at an interface between water and air, form hydrogen bonds with their neighbors, just like those found inside the liquid (think of any container, like a glass). However, as one side is exposed to air, there will be fewer water molecules to bind with and the bonds between them will be stronger.

Then, the surface tension, a product of the cohesiveness of water, causes small spherical drops to form in it and even allows it to support small objects if they are carefully placed on the aqueous surface. Good examples are a pin, a piece of paper, or even certain insects that deposit themselves.

Example of cohesion in water

Cohesion in water can be glimpsed with a multitude of simple experiments. A good example is when a glass or any container is filled to the maximum with the mentioned liquid. If the limit is reached and a few more drops are carefully added, it will be seen that before everything overflows, a small hump or dome is formed, which is the product of the same cohesion. It is fragile, but it can be sustained if it is not excessively broken with that precarious balance.

Adhesion in water

Adhesion is the attraction of molecules of one type to molecules of another and this can be quite strong in water, especially when the other molecules are positively or negatively charged. So we can say how water has a tendency to stick to itself, which shows its cohesiveness; it also does so with other types of molecules.

It is important to emphasize that water has its own adhesive characteristics. That is, it is a phenomenon in which many factors participate, such as the temperature of the adhesive, the compatibility of the substance and who acts as the adhesive, the treatments of the same surface, etc. A good example to observe adhesion are the same drops of water that adhere to the glass, for example on a rainy day; but also the movement of water towards the treetops as a clear natural phenomenon.

Example of water adhesion

Adhesion allows water to rise through thin glass tubes, called capillaries, placed inside containers. This upward movement against gravity is known as capillarity and depends basically on the attraction between the water molecules and the glass walls of the tube from the adhesive point of view. Since, as announced above, cohesion also occurs in the interactions of water molecules with each other.

Then certain water molecules are attracted more strongly to glass, due to its important polarity. Therefore, this simple experiment gives a clear visual image of the phenomenon: the water will always have its highest point where it makes contact with the glass in the tube and always its lowest in the center, where it is just far from the glass itself. And that can be verified in any container, regardless of its width (although it is true that if you play with the capillaries the phenomenon is more evident). That curvature, more pronounced or not, formed by a liquid in a tube is called a meniscus.

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