Properties of Water- The Universal Solvent: Videos & Practice Problems

Water is known as the universal solvent due to its ability to dissolve various solutes, such as salts and proteins, forming aqueous solutions. In these solutions, water acts as the solvent, while the dissolved substances are solutes. Solutions can be homogeneous, where components are uniformly mixed, or heterogeneous, where they are unevenly distributed. Additionally, substances are classified as hydrophilic, which dissolve well in water, or hydrophobic, which do not. Understanding these concepts is crucial for studying biological systems and their interactions.

Properties of Water- The Universal Solvent

In this video, we're going to continue to talk about the properties of water, specifically how water serves as the universal solvent. Water is described as the universal solvent because it is capable of dissolving so many different types of solutes. We need to differentiate the term "solvent" from the term "solutes," and that's exactly what we're going to do below.

The solvent can be defined as the substance that does the dissolving; it is the substance that is dissolving another substance and is usually found in larger amounts and is typically a liquid. In biological systems that consider life, water is usually the solvent. If you are not sure, just go with water being the solvent, especially in this course. This is another reason why water is known as the universal solvent.

The term "solute," on the other hand, can be defined as the substance that gets dissolved by the solvent and is usually found in smaller amounts. To better understand the distinction between solvent and solute, let's look at our example image, which shows table salt (sodium chloride, NaCl) dissolving in water. Notice in the image on the left, we show a salt shaker with table salt, and on the right, we demonstrate the addition of table salt to a cup of water.

Zooming into the salt shaker, we already know from our previous lessons about ionic bonds that sodium chloride consists of a sodium cation (positively charged) forming an ionic bond with a chloride anion (negatively charged). The intact ionic bond is visually represented by a yellow, highlighted dotted line. When we add this table salt to water, it can dissolve because water, being the liquid, serves as the solvent while the sodium chloride becomes the solute.

Upon adding sodium chloride to the water, you'll notice that the ionic bonds have been disrupted; there are no ionic bonds forming between these ions. On the left, we have the sodium cation, and on the right, the chloride anion, both being surrounded by water molecules that have disrupted the ionic bonds. These disruptions allow us to say that the table salt has been dissolved.

Considering the combination of the solute (sodium chloride) and the solvent (water), we refer to this as a solution. The solution is the combination of both the solute and the solvent. This forms an aqueous solution, a term that refers to a solution where water is serving as the solvent. In biological systems that consider life, water typically serves as the solvent, and such systems often utilize aqueous solutions.

You may have noticed that the water molecules form what is known as a hydration shell around each of the solute ions being dissolved. The hydration shell is simply a layer of water molecules surrounding each ion. Water's ability to dissolve many different types of solutes, such as proteins, nucleic acids, and carbohydrates, justifies its title as a universal solvent, even though it cannot dissolve everything. This concludes our brief introduction to water as the universal solvent and distinguishing the terms solvent, solute, and solution. We'll get some practice applying this knowledge as we move forward. I'll see you all in our next video.

A solution in which water is the solvent is called a(n) _______________ solution.

• A. Polar.
• B. Aqueous.
• C. Hydrophobic.
• D. Complete.

Answer: (B)

The substance in a mixture that is dissolved is called the:

• A. Solution.
• B. Solvent.
• C. Solute.
• D. Aqueous solution.

Answer: (C)

What is the charge of the solute molecule in the image below based on the polarity of water?

• A. Positively charged.
• B. Negatively charged.
• C. Uncharged.
• D. Non-polar and hydrophobic.

Answer: (B)

Homogenous vs. Heterogenous Solutions

In this video, we're going to differentiate between homogeneous solutions and heterogeneous solutions. Homogeneous solutions have the root "homo," which means the same. Thus, homogeneous solutions are uniformly mixed solutions where all parts are the same throughout the container, or in other words, all parts are evenly distributed throughout the container.

On the other hand, heterogeneous solutions have the root "hetero," a root that means different. Hence, heterogeneous solutions are mixed solutions where the parts are different throughout the container. Or in other words, the parts are unevenly distributed throughout the container.

If we take a look at our example image down below, we'll be able to better differentiate between homogeneous solutions and heterogeneous solutions. Notice on the left-hand side, we're showing you a beaker of water that has two different solutes. Notice that it has red solutes and blue solutes. These solutes are pretty evenly distributed throughout the beaker, which makes this a uniform mixture and a homogeneous solution. We can go ahead and label the left as a homogeneous solution.

Now looking at the right side of our image, notice that we also have a beaker of water with the same two solutes. This time, the red solutes are towards the top of the beaker and the blue solutes are towards the bottom of the beaker. These solutes are not evenly distributed throughout the container, making this a heterogeneous solution. We can go ahead and label it as such.

This here concludes our brief lesson differentiating homogeneous and heterogeneous solutions, and we'll be able to get some practice applying this as we move forward. So, I'll see you all in our next video.

The components of a heterogenous solution are ________________ distributed throughout.

• A. Equally.
• B. Unequally.
• C. Uniformly.

Answer: (B)

Hydrophilic vs. Hydrophobic

In this video we're going to differentiate between the terms hydrophilic and hydrophobic. And so what's important to note is that although we've described water as the universal solvent, partially because it's so good at dissolving so many different types of solutes, water cannot dissolve all substances. In fact, water can really only dissolve hydrophilic substances. And so the term hydrophilic describes substances that readily dissolve in water really nicely due to having an affinity or an attraction to water. We can actually see this within the roots of the word hydrophilic because the root "hydro" is a root that means water and the root "philic" is a root that means loving. And so hydrophilic substances are water-loving substances that dissolve really nicely in water. Now it turns out that the polar and charged molecules are the molecules that tend to be hydrophilic. So, for example, salts and ions are examples of these hydrophilic substances that dissolve really nicely in water.

Now, once again, water cannot dissolve all substances and substances that do not dissolve well in water are referred to as hydrophobic substances. And so the term hydrophobic describes substances that do not readily dissolve in water very nicely. Once again, we can see this within the roots of the word hydrophobic because the root "hydro" once again means water and the root "phobic" means fearing, and so people that have a phobia are going to have an extreme fear of something. And so hydrophobic substances are water-fearing substances that do not readily dissolve in water and will try to separate out from the water. Now it turns out that it is going to be the nonpolar substances or molecules that tend to be hydrophobic. For example, fats, oils, and waxes, which are all examples of different types of lipids, are all hydrophobic or display some hydrophobic nature and so we're going to talk a lot more about lipids later in our course.

But for now, let's take a look at our example image down below so that we can better differentiate between hydrophilic and hydrophobic. And so what we're going to do is look at salt versus oil mixed with water. On the left-hand side notice what we're showing you is our table salt being mixed into a cup of water. Recall from our previous lesson videos that table salt is sodium chloride. So we have a sodium cation and a chloride anion, and they are being surrounded by these hydration shells or these water molecules that are disrupting the ionic bond between them. And so the sodium chloride is dissolved in the water. And because it is dissolved in the water, and because the sodium and chloride are charged particles, they are going to be hydrophilic, and so the salt here is hydrophilic. Now on the right-hand side, notice what we're showing you is some vegetable oil being mixed into a cup of water. Now if you try this at home, what you'll notice is that no matter how much you try to stir in the vegetable oil and mix it into that cup of water, the vegetable oil will always separate out into a separate layer. And so this is because the oil is going to be made of nonpolar molecules and those nonpolar molecules are going to be hydrophobic or water-fearing meaning that they will separate out and not dissolve well in water and so we can label this as hydrophobic.

And so this here concludes our brief lesson differentiating hydrophilic from hydrophobic substances, and we'll be able to get some practice applying these concepts moving forward. So, I'll see you all in our next video.

Hydrophobic molecules:

• A. Are polar covalent molecules.
• B. Easily dissolve in water.
• C. Are nonpolar water 'fearing' molecules.
• D. Are nonpolar water 'loving' molecules.

Answer: (C)

Here’s what students ask on this topic:

Why is water considered the universal solvent?

Water is considered the universal solvent because it can dissolve a wide variety of substances. This ability is due to its polar nature, where the oxygen atom has a partial negative charge, and the hydrogen atoms have partial positive charges. This polarity allows water molecules to surround and interact with various solutes, such as salts, proteins, and carbohydrates, effectively breaking their bonds and dissolving them. In biological systems, water's role as a solvent is crucial for facilitating chemical reactions and transporting nutrients and waste products.

What is the difference between a solvent and a solute?

A solvent is the substance that does the dissolving in a solution, typically present in a larger amount and usually a liquid. In biological systems, water is the most common solvent. A solute, on the other hand, is the substance that gets dissolved by the solvent and is usually present in a smaller amount. For example, in a saltwater solution, water is the solvent, and sodium chloride (table salt) is the solute.

What are homogeneous and heterogeneous solutions?

Homogeneous solutions are mixtures where the components are uniformly distributed throughout the container, resulting in a consistent composition. An example is salt dissolved in water. Heterogeneous solutions, however, have components that are unevenly distributed, leading to different compositions in different parts of the container. An example is a mixture of oil and water, where the oil forms a separate layer on top of the water.

What is the difference between hydrophilic and hydrophobic substances?

Hydrophilic substances are those that readily dissolve in water due to their affinity for water molecules. These substances are usually polar or charged, such as salts and ions. Hydrophobic substances, on the other hand, do not dissolve well in water and tend to separate from it. These substances are typically non-polar, such as fats, oils, and waxes. Understanding these properties is essential for studying biological systems, as they influence how molecules interact within cells and tissues.

What is an aqueous solution?

An aqueous solution is a solution in which water acts as the solvent. The term 'aqueous' refers to water, and in these solutions, water dissolves various solutes, such as salts, proteins, and carbohydrates. Aqueous solutions are common in biological systems, where water facilitates chemical reactions and transports substances within organisms. For example, blood is an aqueous solution containing dissolved nutrients, gases, and waste products.