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

Water exhibits unique properties due to its molecular structure, particularly in terms of density. Liquid water molecules are tightly packed and constantly form and break hydrogen bonds, resulting in higher density. In contrast, solid ice forms stable hydrogen bonds, creating a lattice structure that spaces molecules further apart, leading to lower density. This allows ice to float on water, which is crucial for aquatic life as it insulates the liquid below, preventing it from freezing. Understanding these properties is essential for grasping the significance of water in sustaining life.

Density of Liquid Water vs. Solid Ice

In this video, we're going to continue to talk about the properties of water by focusing specifically on density and comparing the density of liquid water to the density of solid ice. And so what's important to know is that the liquid water molecules are actually very highly packed together, and these highly packed liquid water molecules are constantly forming and breaking new hydrogen bonds. Now, on the other hand, solid water molecules that are found in solid ice are less packed. And so, because they are less packed, they are more spread apart and therefore they are more expanded. Solid ice will expand in comparison to liquid water.

Now the reason for this less compaction and the expansion of the solid water molecules is because the solid water molecules form stable hydrogen bonds, and so these stable hydrogen bonds are not constantly forming and breaking like they do in liquid water. And so these stable hydrogen bonds allow the water molecules in solid ice to form a lattice structure that keeps the solid ice water molecules more spread apart and again, more expanded. Now this expansion of the solid ice water molecules allows solid ice to have a lower density in comparison to liquid water, and of course substances that have a lower density in comparison to a liquid are going to actually float. Thus, this is what causes solid ice to float in liquid water.

And so, the next time you go to a restaurant and you get a glass of water with ice, and your ice cubes float to the top of your glass of water, now you know it's because the solid ice cubes, the water in the solid ice cubes are more expanded and less dense than the liquid water molecules in your glass of water. Also, another important feature of this density comparison between liquid water and solid water is that this is going to allow water to freeze from top to bottom, which is incredibly crucial when it comes to life, and it will also allow the solid ice that is on top to insulate the liquid that is below the surface in order to sustain life. And so by insulating it, it's able to keep that water warmer and prevent it from freezing.

And so, if we look at our image down below, we'll be able to tie in a lot of the things that we’ve talked about and look at the density of liquid water versus the density of solid ice. And so notice on the left we have an image that's showing you both solid ice and liquid water as well. If we look at the liquid water, if we zoom into it, notice that the water molecules in the liquid water are very compacted and highly densed in comparison to the water molecules in solid ice. And so what we can say here is that the liquid water is actually going to be more dense in comparison to the water molecules in the solid ice.

Also, the hydrogen bonds, abbreviated here as H bonds, are constantly breaking and reforming in liquid water. And so, that is what allows them to be able to be more compacted. Now, when we look at the water molecules in solid ice, notice that these water molecules are more spread apart; they're not as highly packed together, not as highly dense. And so these more spaced out, more expanded water molecules in solid ice allow the solid ice to be less dense. And, because it is less dense, it is going to float in liquid water. Solid ice floats in liquid water.

Now, the reason that these water molecules in solid ice are able to expand is because they are able to form stable hydrogen bonds and those stable hydrogen bonds are not constantly breaking and reforming, so they're able to remain in a specific position that creates a lattice structure. This enables the water molecules to expand and become less dense. And so once again, this is very important because when solid ice is less dense, it will float to the top, which means water will freeze from top to bottom, in this fashion that you see here, and when it freezes from top to bottom, the top layer of ice can insulate the liquid water that is below allowing for life to be sustained during the winters and things like that. And so that is incredibly important for life.

This year concludes our brief lesson on the density of water and comparing the density of liquid water to solid ice. We'll be able to get some practice applying these concepts as we move forward. 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 4 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 solid ice, water molecules form stable hydrogen bonds, creating a lattice structure that spreads the molecules apart. This expansion results in a lower density compared to liquid water, where molecules are tightly packed and constantly forming and breaking hydrogen bonds. The lower density of ice allows it to float on the denser liquid water, which is crucial for insulating the water below and sustaining aquatic life during cold conditions.

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

Water's density is crucial for aquatic life because it allows ice to float, forming an insulating layer on the surface of bodies of water. This insulation prevents the water below from freezing solid, maintaining a habitable environment for aquatic organisms during winter. Additionally, the density of water affects the stratification of lakes and oceans, influencing nutrient distribution and the overall health of aquatic ecosystems.

How do hydrogen bonds affect the density of water and ice?

Hydrogen bonds play a key role in determining the density of water and ice. In liquid water, hydrogen bonds are constantly forming and breaking, allowing water molecules to be tightly packed, resulting in higher density. In contrast, in solid ice, hydrogen bonds are stable and form a lattice structure that spreads the molecules apart, leading to lower density. This difference in hydrogen bonding behavior is why ice is less dense and floats on liquid water.

Why is the density of water important for the environment?

The density of water is important for the environment because it influences the behavior of water in natural settings. For example, the fact that ice is less dense than liquid water and floats helps insulate bodies of water, protecting aquatic life during cold periods. Additionally, the density of water affects thermal stratification in lakes and oceans, which is essential for nutrient cycling and the overall health of aquatic ecosystems. Understanding water's density is crucial for grasping its role in sustaining life on Earth.

What causes the density difference between liquid water and solid ice?

The density difference between liquid water and solid ice is caused by the arrangement and behavior of water molecules. In liquid water, molecules are tightly packed due to constantly forming and breaking hydrogen bonds, resulting in higher density. In solid ice, water molecules form stable hydrogen bonds, creating a lattice structure that spreads the molecules apart, leading to lower density. This structural difference is why ice is less dense and floats on liquid water.