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 that constantly form and break hydrogen bonds. In contrast, solid ice has a lower density because its molecules form a stable lattice structure, allowing it to float. This phenomenon enables ice to insulate the 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 maintaining life during extreme temperature fluctuations.

Density of Liquid Water vs. Solid Ice

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. Liquid water molecules are packed closely together, meaning they have a high density, and they're constantly forming and breaking hydrogen bonds. In contrast, solid water molecules in ice are less packed, resulting in lower density. This is because ice molecules expand by forming very stable hydrogen bonds in a lattice structure. The lattice structure allows the water molecules to expand. This is important because solid ice has a much lower density than liquid water, causing it to float.

Solid ice floating in liquid water is incredibly important for life because it means that water freezes from the top down. When it freezes in this way, it creates a layer of ice on top, which insulates the liquid water below, sustaining life. If we look at the image below, notice that it shows an example of how the density of liquid water compares to solid ice. You will see solid ice floating on top of the liquid water. If we zoom into the liquid water below, you can see that the water molecules are very densely packed in a small area.

The density of liquid water molecules is high because they are tightly packed. These molecules constantly form and break hydrogen bonds. On the other hand, if we examine the ice floating on top, you will notice that its water molecules are arranged in a lattice structure and are much less packed, making the ice less dense. The ability of ice to be less dense is due to forming stable hydrogen bonds in a lattice structure, rather than forming bonds that constantly break and reform. This feature is crucial because water freezing from the top down ensures the insulating ice layer on the surface, which can sustain life.

Especially imagine how, millions of years ago, our planet experienced extreme temperature fluctuations, including ice ages. During these ice ages, our oceans would have frozen completely solid if not for the remarkable ability of water to freeze from top to bottom, creating an insulating layer that keeps the liquid water below in a liquid state, allowing life to survive those harsh conditions. This is critically important.

This concludes our lesson on the density of water, comparing liquid water density to solid ice density. We will be able to get some practice as we move forward in our course. 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 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 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 denser. 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.

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 its solid form, water molecules form a stable lattice structure, which causes them to be less tightly packed compared to the constantly forming and breaking hydrogen bonds in liquid water. This lower density allows ice to float on the denser liquid water. This phenomenon is crucial for insulating the water below, helping to sustain aquatic life during freezing conditions.

How does the density of water change from liquid to solid?

The density of water decreases when it changes from liquid to solid. In liquid water, molecules are closely packed together, constantly forming and breaking hydrogen bonds, resulting in high density. When water freezes, the molecules form a stable lattice structure, causing them to be less tightly packed and thus less dense. This decrease in density allows ice to float on liquid water, which is essential for insulating the water below and sustaining life during cold periods.

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, creating an insulating layer on the surface. This insulation prevents the entire body of water from freezing solid, maintaining a liquid environment below the ice where aquatic organisms can survive. This property is especially important during extreme temperature fluctuations, such as ice ages, ensuring the continuity of life in aquatic ecosystems.

How do hydrogen bonds affect the density of water?

Hydrogen bonds significantly affect the density of water. In liquid water, hydrogen bonds are constantly forming and breaking, allowing molecules to be closely packed and resulting in high density. In solid ice, hydrogen bonds form a stable lattice structure, causing the molecules to be less tightly packed and thus less dense. This difference in hydrogen bonding patterns between liquid and solid water explains why ice is less dense and floats on liquid water.

Why is the lattice structure of ice important?

The lattice structure of ice is important because it causes the water molecules to be less densely packed compared to liquid water. This structure results in ice having a lower density, allowing it to float on liquid water. The floating ice forms an insulating layer on the surface, which is crucial for maintaining liquid water below and sustaining aquatic life during freezing conditions. This property has been vital for the survival of life through historical ice ages and extreme temperature fluctuations.