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

Water exhibits unique properties of cohesion and adhesion due to hydrogen bonding. Cohesion refers to water molecules sticking to each other, while adhesion involves water molecules adhering to other polar or charged surfaces, like glass. These properties contribute to water's high surface tension, allowing objects like paper clips to float on its surface. Understanding these characteristics is crucial as they play a significant role in water's function as a solvent for life, impacting biological processes and ecosystems.

Properties of Water- Cohesion and Adhesion

In this video, we're going to begin our lesson on the properties of water, specifically cohesion and adhesion. Now, cohesion is specifically referring to the ability for water molecules to stick together. Essentially, for water molecules to stick to other water molecules, water sticking to water. Now, adhesion, on the other hand, is the ability for water molecules to stick to other molecules that are not water. So, for example, water sticking to glass.

And so, if we take a look at our image down below over here on the left-hand side, notice that we're showing you an example of the cohesion and adhesion of water. And so, we're specifically taking a look at a glass of water like this one over here, and we're zooming in to the bottom of the glass of water over here on the right-hand side. And so, notice that when the water molecules stick to other water molecules represented by these green lines that you see throughout right here, this represents cohesion. Once again, cohesion is the ability for water molecules to stick together, water sticking to more water. And this happens because of hydrogen bonding.

Recall, water molecules can hydrogen bond to other water molecules. And so, once again, water's hydrogen bonding is going to be very very important for its properties. Now, when water molecules stick to other molecules that are not water, for example, water sticking to the glass, that is an example, of course, of adhesion when water molecules stick to other molecules that are not water since glass is not water. And so, water will specifically adhere to objects that are either polar or charged, and glass is certainly a polar object. Now, the cohesive and adhesive abilities of water are due to its ability to hydrogen bond, And so water is capable of hydrogen bonding with the glass and that's what allows it to adhere to the glass.

And together, the cohesive and adhesive ability of water gives water a relatively high surface tension. And surface tension is really just a measure of the difficulty in breaking the surface of a liquid with force. And so, notice down below over here on the right-hand side of our image, we're showing you a little example of the surface tension of water. And so, notice that this paper clip right here has been laid down on the surface so gently in a way that it does not break the surface of the liquid water. And so, this water is really acting like a surface for the paper clip.

And so, these cohesive adhesive abilities that create high surface tension is really quite a unique property for liquid water. And most liquids do not display these cohesive and adhesive properties. And so, this is something that we should be beneficial, for because these properties are going to be really critical in the ability for water to act as a solvent for life. And so, this here concludes our introduction to the properties of water, cohesion, and adhesion. And as we move forward in our course, we'll continue to talk more and more about the properties of water.

So I'll see you all in our next video.

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 four potential answer options down below. The example problem says, cohesion, surface tension, and adhesion are properties of water molecules that blank. 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 nonpolar covalent bonding. But of course, we know from our previous lesson videos that water molecules are held together using polar covalent bonds, not nonpolar covalent bonds, and so the nonpolar 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. 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.

Here’s what students ask on this topic:

What is the difference between cohesion and adhesion in water?

Cohesion refers to the ability of water molecules to stick to each other due to hydrogen bonding. This is why water droplets form and why water has a high surface tension. Adhesion, on the other hand, is the ability of water molecules to stick to other substances that are not water, such as glass. This occurs because water can form hydrogen bonds with other polar or charged surfaces. Together, these properties enable water to act as a solvent and play a crucial role in various biological processes.

How does hydrogen bonding contribute to water's cohesive and adhesive properties?

Hydrogen bonding is the key to water's cohesive and adhesive properties. In cohesion, hydrogen bonds form between water molecules, allowing them to stick together. This is why water has a high surface tension. In adhesion, water molecules form hydrogen bonds with other polar or charged surfaces, such as glass. This allows water to adhere to these surfaces. These hydrogen bonds are relatively strong, making water an excellent solvent and crucial for many biological processes.

Why does water have a high surface tension?

Water has a high surface tension due to its cohesive properties, which are a result of hydrogen bonding between water molecules. These hydrogen bonds create a 'film' on the surface of the water, making it difficult to break. This is why objects like paper clips can float on water if placed gently. The high surface tension is unique to water and is essential for various biological processes, such as the movement of water in plants through capillary action.

What role do cohesion and adhesion play in biological processes?

Cohesion and adhesion are crucial for many biological processes. Cohesion allows water molecules to stick together, facilitating the transport of water and nutrients in plants through capillary action. Adhesion helps water molecules stick to the walls of plant vessels, aiding in the upward movement of water from roots to leaves. These properties also contribute to water's role as a solvent, enabling it to dissolve and transport various substances essential for life.

How do cohesion and adhesion affect water's function as a solvent?

Cohesion and adhesion enhance water's ability to act as a solvent. Cohesion allows water molecules to stick together, forming a continuous column in plant vessels, which is essential for nutrient transport. Adhesion enables water to stick to other polar or charged substances, helping it dissolve a wide range of solutes. These properties make water an excellent solvent, crucial for various biochemical reactions and processes in living organisms.