Properties of Water- Cohesion and Adhesion - Video Tutorials & Practice Problems
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concept
Properties of Water- Cohesion and Adhesion
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Video transcript
In this video we're going to begin our lesson on the properties of water, specifically on cohesion and adhesion. And so cohesion is defined as the ability for water molecules to stick together, basically water molecules sticking to other water molecules. Now we can tell this because the root co in cohesion is a root that means together. And so when water molecules hydrogen bond with other water molecules they stick together and we refer to this as cohesion. Now 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. And so if we take a look at our image down below we can get a better understanding of the cohesion and adhesion of water. And so notice we're showing you on the left hand side a glass of water and we're zooming into the bottom of this glass of water and that is what this middle image is showing. And so notice we can see all of these water molecules are being represented as blue circles. And notice that connecting these water molecules are these green lines, and these green lines represent hydrogen bonds that form between water molecules, so different water molecules. And so these green lines are allowing water molecules to stick together and so we are showing these green lines as cohesion. The green lines represent cohesion. Now, also notice that we have these purple lines and these purple lines are connecting the water molecules to the glass. And so when water molecules stick to other molecules that are not water, for example water sticking to glass, we refer to this as adhesion. Now it is important to note that water does not adhere to all molecules. Water will only adhere to specific types of molecules that are going to be polar and or charged objects. And so it turns out that glass is indeed a polar object. Now, collectively, the cohesion and adhesion of water create surface tension. And so surface tension can be defined as a measure of the difficulty in breaking the surface of a liquid with force. And so it turns out that the cohesion and adhesion of water creates somewhat of a surface tension, meaning that it requires some amount of force to break, this surface and, submerge into the water. And so, what you'll note is that some organisms are able to take advantage of this surface tension. And also, over here on the right hand side we're showing you an image of the surface tension of water. And so notice that we have a paper clip that's right here. And this paperclip, is actually more dense than the liquid water so the paperclip should sink to the bottom of this cup of water. But you'll notice that this paper clip is actually on top of the surface of this liquid water and that's because it has not broken the surface tension. And so, the water molecules through adhesion, and cohesion are able to stick together and create a surface that this paper clip is lying on. And if you put the paper clip on the surface in the right way then the paper clip will be able to lie on the surface without breaking the surface tension. But if you apply enough force, then the paper clip will break the surface tension and sink to the bottom of the glass of water. And so, again, this cohesion and adhesion abilities of water is due to water's polarity and water's ability to form hydrogen bonds. And as we move forward in our course, we're going to 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.
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example
Properties of Water- Cohesion and Adhesion Example 1
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1m
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Video transcript
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 blink. 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.
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Problem
Problem
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.
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Problem
Problem
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.