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 substances, 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 specifically refers to the ability of 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 of water molecules to stick to other molecules that are not water. For example, water sticking to glass. And so, if we take a look at our image down below 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 on the bottom of the glass of water 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 of 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 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 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 are 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 of 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 4 potential answer options down below. And the example problem says, cohesion, surface tension, and adhesion are properties of water molecules that ____. 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 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) 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 refers to the ability of water molecules to stick to each other due to hydrogen bonding. This means that water molecules are attracted to other water molecules, creating a cohesive force. 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 molecules. Together, these properties contribute to water's high surface tension, allowing it to act as a solvent and support various biological processes.

How does hydrogen bonding contribute to the properties of water?

Hydrogen bonding is crucial for the unique properties of water. In cohesion, hydrogen bonds form between water molecules, allowing them to stick together. In adhesion, water molecules form hydrogen bonds with other polar or charged substances, enabling them to adhere to surfaces like glass. These hydrogen bonds also contribute to water's high surface tension, making it difficult to break the surface of the liquid. This high surface tension allows objects like paper clips to float on water and plays a significant role in water's function as a solvent in biological systems.

Why is surface tension important in water?

Surface tension is a measure of the difficulty in breaking the surface of a liquid with force. In water, high surface tension is due to the cohesive forces between water molecules, which are a result of hydrogen bonding. This property is important because it allows water to form droplets, enables insects to walk on water, and supports small objects like paper clips on its surface. High surface tension also plays a critical role in biological processes, such as the movement of water through plant vessels and the formation of cell membranes.

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

Cohesion and adhesion significantly enhance water's role as a solvent. Cohesion allows water molecules to stick together, facilitating the formation of a continuous column of water in plant vessels, aiding in nutrient transport. Adhesion enables water to stick to other polar or charged substances, helping it dissolve a wide range of solutes. These properties ensure that water can effectively transport nutrients, waste products, and other molecules within biological systems, making it an essential solvent for life.

What are some real-life examples of cohesion and adhesion in water?

Real-life examples of cohesion include the formation of water droplets and the ability of water to form a continuous column in plant vessels, aiding in nutrient transport. Adhesion can be observed when water sticks to the surface of a glass or when it climbs up a paper towel dipped in water. These properties are also evident in capillary action, where water moves through narrow spaces against gravity, such as in soil or plant roots. Together, cohesion and adhesion play vital roles in various natural and biological processes.