Properties of Water- Density - Online Tutor, Practice Problems & Exam Prep

Water's unique properties, particularly its density, are crucial for life. Liquid water has a high density due to closely packed molecules forming and breaking hydrogen bonds, while solid ice is less dense because it forms a stable lattice structure, allowing it to float. This phenomenon enables ice to insulate liquid water below, sustaining aquatic life during freezing conditions. Understanding these concepts is vital for grasping the significance of water in ecological systems and its role in supporting life through extreme temperature fluctuations.

Properties of Water- Density

In this video, we're going to continue to talk about the properties of water, specifically, its density and comparing the density of liquid water to solid ice. And so liquid water molecules are really highly packed together, meaning that they have a high density, and they're constantly forming and breaking hydrogen bonds. Whereas solid water molecules in the ice form are much less packed, and that means that they are less dense and this is because solid water molecules actually expand and this is because they form very stable hydrogen bonds in a lattice structure, and the lattice structure is what allows the water molecules to expand. Now this is important because solid ice is actually going to have a much lower density than liquid water, and things that have a lower density in liquids are going to float. And so this means that solid ice is going to float in liquid water, and this is incredibly important for life because it means that water is going to freeze from the top to the bottom. And so when it freezes from top to bottom it creates a layer of ice on the top, and that layer of ice on the top is capable of insulating the liquid water, that is below the surface, and this is incredibly important to sustain life.

And so if we take a look at our image down below, notice that we're showing you an example of how density of liquid water, compares to solid ice. And so over here we have an image that shows you both solid ice up here at the top floating on top of the liquid water that is down below. And so what you'll notice is that if we zoom into the liquid water down below, notice that the water molecules are really highly packed into this little, small area. And so the liquid water molecules are really highly dense because they're so highly packed, and these liquid water molecules, they are constantly forming and breaking hydrogen bonds, constantly breaking and reforming. Whereas if we zoom in specifically to the ice here that's floating on top, notice that its water molecules are in a lattice structure and they are much less packed, they are much less dense. And so solid ice is going to be less dense and because it's less dense, this is what allows it to float on top of the liquid water that's down below. And so, it's less dense because it forms stable hydrogen bonds in a lattice structure instead of forming hydrogen bonds that constantly break and reform.

And so once again, this is really important because water will freeze from top to bottom, and so the ice layer that freezes on top is capable of insulating the liquid water down below and that can sustain life. Especially imagine, in the past million years ago, our planet went through extreme temperature fluctuations and there were ice ages that existed. And during the ice ages, our oceans would have frozen completely solid if it were not for this amazing ability for water to freeze from top to bottom, create an insulating layer that keeps the liquid water down below in a liquid form, allowing life to survive those ice ages. And so this is really really important. And so this here concludes our lesson on the density of water, comparing liquid water density to solid ice density, and we'll be able to get some practice as we move forward in our course. So I'll see you all in our next video.

Properties of Water- Density Example 1

Alright. So here we have an example problem that's asking why does ice float in liquid water? And we've got these four potential answer options down below. Now after reading through some of these answer options, there are a few that we can eliminate right off the bat, such as option c here, which says that the ionic bonds between the molecules in ice prevent the ice from sinking. But of course, we know that water is not an ion because it does not have full charges. It only has partial charges. So it's not an ion, which means that it cannot form ionic bonds. And so because it says ionic bonds here, we should have been able to eliminate answer option c right away. Now answer option d here says, the lattice structure of ice causes it to be more dense than liquid water. But once again recall from our last lesson video that solid ice is actually less dense, not more dense than liquid water. And so for this reason right here, we can eliminate answer option d. So now we're between either option a or option b, and notice option a says the high surface tension of liquid water makes the ice float. But even ice that penetrates the liquid surface and goes beyond, the surface tension, it breaks the surface tension, that ice that breaks the surface tension will still ultimately end up floating once again. So it's not the surface tension that's allowing ice to float. And so option a, although it might be a tempting answer option, is not going to be true. And so the real reason that ice floats on liquid water is because stable hydrogen bonds keep water molecules of ice farther apart than water molecules of liquid water. And so because water molecules of ice are farther apart, it means that it is less dense, solid ice is less dense than liquid water molecules which are more dense. And so things that are less dense will float. And so option b is going to be the correct answer for this example problem. And that concludes this example, so I'll see you all in our next video.

Solid substances are normally more dense than liquid substances. However, solid ice is LESS dense than liquid water. Why is this characteristic of solid ice important for life?

a) This characteristic allows lakes to freeze solid.

b) This characteristic allows the surface water of lakes to freeze.

c) This characteristic ensures that salt water does not freeze.

d) This characteristic is not important for life.

• A. This characteristic allows lakes to freeze solid.
• B. This characteristic allows the surface water of lakes to freeze.
• C. This characteristic ensures that salt water does not freeze.
• D. This characteristic is not important for life.

Here’s what students ask on this topic:

Why does ice float on water?

Ice floats on water because it is less dense than liquid water. In liquid water, molecules are closely packed together, constantly forming and breaking hydrogen bonds, resulting in high density. In contrast, when water freezes, the molecules form a stable lattice structure with hydrogen bonds that are more spread out. This lattice structure causes the molecules to be less densely packed, making ice less dense than liquid water. As a result, ice floats on the surface of liquid water, which is crucial for insulating the water below and sustaining aquatic life during freezing conditions.

How does the density of water change when it freezes?

When water freezes, its density decreases. In its liquid state, water molecules are tightly packed due to the constant formation and breaking of hydrogen bonds. However, as water transitions to its solid state (ice), the molecules arrange themselves into a stable lattice structure. This structure is less dense because the molecules are more spread out compared to their arrangement in liquid water. Consequently, ice is less dense than liquid water, which is why it floats. This decrease in density upon freezing is a unique property of water and is vital for insulating aquatic environments during cold periods.

What is the significance of water's density for aquatic life during freezing conditions?

Water's density is crucial for aquatic life during freezing conditions because it allows ice to float on the surface of liquid water. As water freezes from the top down, the ice layer that forms on the surface acts as an insulating barrier. This insulation prevents the entire body of water from freezing solid, maintaining liquid water beneath the ice. This liquid water provides a habitat for aquatic organisms to survive even in extreme cold. Without this property, bodies of water would freeze completely, making it impossible for aquatic life to endure harsh winter conditions.

How do hydrogen bonds affect the density of water in its liquid and solid states?

Hydrogen bonds significantly influence the density of water in its liquid and solid states. In liquid water, hydrogen bonds are constantly forming and breaking, allowing water molecules to be closely packed together, resulting in high density. In contrast, in the solid state (ice), water molecules form stable hydrogen bonds that create a lattice structure. This structure is less dense because the molecules are more spread out compared to their arrangement in liquid water. Therefore, the stable hydrogen bonds in ice reduce its density, causing it to float on liquid water. This unique behavior is essential for insulating aquatic environments during freezing conditions.

Why is the lattice structure of ice important for its density?

The lattice structure of ice is important for its density because it causes the water molecules to be more spread out compared to their arrangement in liquid water. In liquid water, molecules are closely packed due to the constant formation and breaking of hydrogen bonds, resulting in high density. However, when water freezes, the molecules form a stable lattice structure with hydrogen bonds that are more spread out. This arrangement decreases the density of ice, making it less dense than liquid water. As a result, ice floats on water, which is crucial for insulating the liquid water below and sustaining aquatic life during freezing conditions.