Properties of Water- Cohesion and Adhesion - Online Tutor, Practice Problems & Exam Prep

Cohesion and adhesion are key properties of water. Cohesion refers to water molecules sticking together through hydrogen bonds, while adhesion describes water's ability to cling to other polar surfaces, like glass. These interactions create surface tension, which is the resistance to breaking the surface of a liquid. This phenomenon allows certain organisms to exploit water's surface tension, as seen when a paperclip floats despite being denser than water. Understanding these properties is essential for grasping water's role in biological systems and its significance for life.

Properties of Water- Cohesion and Adhesion

In this video, we're going to begin our lesson on the properties of water, specifically on cohesion and adhesion. Cohesion is defined as the ability for water molecules to stick together, basically water molecules sticking to other water molecules. We can tell this because the root "co" in cohesion means "together." When water molecules hydrogen bond with other water molecules they stick together, and we refer to this as cohesion.

Adhesion, on the other hand, is the ability for water molecules to stick to other molecules that are not water. For example, water molecules sticking to glass. If we look at our image below, we can get a better understanding of the cohesion and adhesion of water. Notice we are showing a glass of water on the left-hand side, and we are zooming into the bottom of this glass of water, which is what the middle image is showing. Notice all these water molecules are represented as blue circles, and the green lines connecting these water molecules represent hydrogen bonds between different water molecules. These green lines allow water molecules to stick together and represent cohesion.

Also notice we have purple lines connecting the water molecules to the glass. When water molecules stick to other molecules that are not water, such as glass, we refer to this as adhesion. It is important to note that water does not adhere to all molecules. Water will only adhere to specific types of molecules that are polar and/or charged objects. Glass is indeed a polar object. Collectively, the cohesion and adhesion of water create surface tension.

Surface tension can be defined as a measure of the difficulty in breaking the surface of a liquid with force. The cohesion and adhesion of water create a surface tension that requires some amount of force to break this surface and submerge into the water. Some organisms are able to take advantage of this surface tension. Over here on the right-hand side, we're showing an image of the surface tension of water. Notice there is a paper clip that is more dense than the liquid water; the paperclip should sink to the bottom of the cup of water. However, because it has not broken the surface tension, this paperclip is actually on top of the surface of the liquid water. The water molecules, through adhesion and cohesion, stick together and create a surface that this paperclip is lying on. If you place the paperclip on the surface correctly, it will lie on the surface without breaking the surface tension. However, if you apply enough force, the paperclip will break the surface tension and sink to the bottom of the glass of water.

The cohesion and adhesion abilities of water are due to water's polarity and its ability to form hydrogen bonds. As we move forward in our course, we will continue to talk more and more about the properties of water that are important for life. So, that concludes this video and I'll see you all in our next one.

Properties of Water- Cohesion and Adhesion Example 1

Alright. So here we have an example problem that wants us to fill in the blank in this sentence using one of these 4 potential answer options down below. And the example problem says, cohesion, surface tension, and adhesion are properties of water molecules that blank. And option a says increases with temperature. Now in our last lesson video, we never mentioned that these properties, cohesion, surface tension, and adhesion, will actually increase with temperature, and in fact, this is not going to be true. So we can eliminate option a for that reason. Option b says that it will increase with pH, and once again, we never mentioned this in our previous lesson videos, and this is simply not going to be true. So now we're between either option c or option d, and option c says, are a result of non-polar covalent bonding. But, of course, we know from our previous lesson videos that water molecules are held together using polar covalent bonds, not non-polar covalent bonds, and so the non-polar here makes this part false. And so, of course, this only leaves option d here as the correct answer, and so cohesion, surface tension, and adhesion are all properties of water molecules that are a result of hydrogen bonding. And so option d here is the correct answer to this practice problem. And really, it's the hydrogen bonding that water molecules are capable of forming that allow water to have cohesive and adhesive properties and to create a relatively high surface tension. And so this here concludes this example problem, and I'll see you all in our next video.

Which of the following effects can occur because of the high surface tension of water?

a) Lakes cannot freeze solid in winter even with extremely low temperatures.

b) A spider can walk across the surface of a small pond.

c) Organisms can resist temperature changes, although they give off heat due to chemical reactions.

d) Sweat can evaporate from the skin, helping to keep people from overheating.

• A. Lakes cannot freeze solid in winter even with extremely low temperatures.
• B. A spider can walk across the surface of a small pond.
• C. Oganisms can resist temperature changes, although they give off heat due to chemical reactions.
• D. Sweat can evaporate from the skin, helping to keep people from overheating.

Cohesive forces in liquid water occur when:

a) The H atoms on molecules of H₂O hydrogen bond to O atoms on adjacent molecules of H₂O.

b) The H atoms on molecules of H₂O hydrogen bond to other H atoms on adjacent molecules of H₂O.

c) The atoms on molecules of H₂O hydrogen bond to other O atoms on adjacent molecules of H₂O.

d) None of the above are correct.

• A. The H atoms on molecules of H₂O hydrogen bond to O atoms on adjacent molecules of H₂O.
• B. The H atoms on molecules of H₂O hydrogen bond to other H atoms on adjacent molecules of H₂O.
• C. The atoms on molecules of H₂O hydrogen bond to other O atoms on adjacent molecules of H₂O.
• D. None of the above are correct.

Here’s what students ask on this topic:

What is the difference between cohesion and adhesion in water?

Cohesion and adhesion are two key properties of water. Cohesion refers to the ability of water molecules to stick to each other due to hydrogen bonding. This is why water forms droplets and has surface tension. Adhesion, on the other hand, is the ability of water molecules to stick to other substances that are polar or charged, such as glass. This property is crucial for processes like capillary action, where water can move up thin tubes against gravity. Both cohesion and adhesion are essential for various biological processes, including nutrient transport in plants.

How does surface tension relate to cohesion and adhesion in water?

Surface tension is a result of the cohesive and adhesive properties of water. Cohesion causes water molecules to stick together, forming a 'skin' on the surface that resists external force. Adhesion allows water to stick to other surfaces, contributing to the overall surface tension. For example, a paperclip can float on water because the cohesive forces between water molecules create a surface strong enough to support it. If enough force is applied, the surface tension breaks, and the paperclip sinks. Surface tension is crucial for various biological phenomena, such as the ability of insects to walk on water.

Why can a paperclip float on water despite being denser than water?

A paperclip can float on water due to the surface tension created by the cohesive and adhesive properties of water. Cohesion causes water molecules to stick together, forming a surface that resists external force. Adhesion helps water molecules stick to the paperclip, further supporting it. When placed gently on the water's surface, the paperclip does not break the surface tension, allowing it to float. However, if enough force is applied, the surface tension breaks, and the paperclip sinks. This phenomenon illustrates the strength of water's surface tension.

What role do hydrogen bonds play in the cohesion and adhesion of water?

Hydrogen bonds are crucial for both the cohesion and adhesion of water. In cohesion, hydrogen bonds form between water molecules, causing them to stick together. This is why water forms droplets and exhibits surface tension. In adhesion, hydrogen bonds allow water molecules to stick to other polar or charged surfaces, such as glass. These bonds are relatively strong, making water an excellent solvent and enabling processes like capillary action. Understanding hydrogen bonds is essential for grasping water's unique properties and its significance in biological systems.

How do cohesion and adhesion contribute to capillary action?

Capillary action is the ability of water to flow in narrow spaces without the assistance of external forces. This phenomenon is driven by both cohesion and adhesion. Adhesion allows water molecules to stick to the walls of a narrow tube, while cohesion causes water molecules to stick to each other. Together, these forces enable water to move upward against gravity. Capillary action is essential for various biological processes, such as the transport of water and nutrients in plants. Understanding these properties helps explain how water can move through tiny spaces in living organisms.