Liquid Chemicals: Surface-Active Agents - Online Tutor, Practice Problems & Exam Prep

Surfactants, or surface-active agents, are amphipathic molecules that lower surface tension in liquids, aiding in microbial control. They consist of hydrophilic heads and hydrophobic tails, forming micelles that trap oils and microbes for removal. Soaps, biodegradable fatty acid-based surfactants, effectively degerm but do not kill microbes, while detergents, synthetic and non-biodegradable, prevent soap scum and fabric damage. Quaternary ammonium compounds (quats) are cationic detergents with antimicrobial properties, disrupting microbial membranes. Understanding these agents is crucial for effective cleaning and microbial management.

Liquid Chemicals: Surface-Active Agents

In this video, we're going to begin our lesson on the use of surface active agents, or surfactants, as liquid chemicals for controlling microbial growth. Surface active agents are commonly referred to as just surfactants. These surface active agents or surfactants are really just chemical agents that lower the surface tension of a liquid or solid in which they have been dissolved. These surface active agents or surfactants consist of amphipathic molecules themselves. Recall from our previous lesson videos that the term amphipathic means that the molecule contains both hydrophilic and hydrophobic groups. In fact, these surfactant molecules have a hydrophilic head and a long hydrophobic tail group.

If we take a look at our image down below, notice that these molecules that you see here are the surfactant molecules. They have once again a head group and a tail group branching off. The head group is hydrophilic. It is going to have either a positive or a negative charge on it and will be able to associate with water, and this is water right here. When we add these surfactant molecules to water, they take this particular orientation where the hydrophilic heads are all facing towards the water, and the hydrophobic tails are facing towards the air because they're going to associate with the surface of the water.

Through the addition of enough surfactant molecules, it actually allows for something known as a micelle to form. A micelle is really just a spherical-shaped group of amphipathic molecules. As you can see down below, this structure right here is the micelle. These molecules, when enough have been added, associate with each other to form this micelle. This micelle creates a hydrophobic core right here in the middle. The hydrophobic tails are all facing towards each other to create a hydrophobic core, and the hydrophilic heads are all facing towards the outside and interacting with the water. Now usually, water and oil do not mix very well together. However, with the use of these surface active agents and surfactants, and adding enough to form micelles, these micelles can allow for hydrophobic substances like oil, for example, to be mechanically washed away using polar solvents like water.

Moving forward in our course, we're going to talk about two main types of surfactants. We will talk about soaps, which are one main type of surfactant. We will also talk about detergents, which are another type of surfactant. A specific type of detergent that we will talk about are quats, which are really quaternary ammonium compounds that we'll get to talk more about moving forward in our course. Ultimately, through the formation of these micelles, hydrophobic substances like oil can get trapped in the hydrophobic core. Then water can wash away the entire micelle to get rid of that oil. These micelles can also trap bacteria as well and other substances as well to help wash away microbes and help to control microbial growth.

This here concludes our brief introduction to surface active agents or surfactants. We'll be able to learn more about them and talk more about different types of surfactants including soaps, detergents, and quats as we move forward in our course. So, I'll see you all in our next video.

Soaps & Detergents

In this video, we're going to continue to talk about surface active agents or surfactants by briefly introducing soaps and detergents. Soaps can be defined as biodegradable natural surfactant molecules that are actually fatty acids, and they contain a salt atom or an atom that tends to form salts, such as, for example, sodium or potassium ions. It's important to note that soaps alone are not antimicrobials, which means that soaps alone do not kill microbes. However, soaps can still be very effective at controlling microbial growth because soaps are very effective degermers, which means that soaps are very good at removing microbes from the surface of an object, such as removing microbes from the surface of your hands when you wash your hands with soap. But again, the soaps on their own do not kill microbes.

Occasionally, soaps can be mixed with antimicrobials, so sometimes you'll find antimicrobial soaps in the store. But again, the soaps on their own are not antimicrobial and do not kill microbes, but they are really good at degerming or removing microbes from the surface, allowing those microbes to be washed away, such as being washed down a drain when you wash your hands. One of the disadvantages of soaps is that soaps tend to form what is known as soap scum. This soap scum can form when the soap interacts with many minerals and salts found in hard water. This soap scum, which tends to form when it interacts with hard water, can deteriorate fabrics and ruin clothing and some surfaces. So, soaps are not always going to be the best reagent to use, and so we don't generally use soaps to wash our clothes.

This is when detergents can come into play. We know that we use detergents to wash our clothes. Unlike soaps, which are biodegradable, detergents are non-biodegradable. Instead of being natural surfactant molecules, detergents are synthetic surfactant molecules that are generally made in a lab. But these detergents have lots of similarities to soaps. One of the big differences is that soaps are fatty acids, whereas detergents are not fatty acids. Instead, these detergents are generally associated with sulfonate groups, a functional group that is less likely to bind minerals and salts in hard water, which means that the sulfonate group or the detergent with the sulfonate group is not going to form scum. This means that detergents will not deteriorate fabrics and will not ruin clothing and surfaces like soaps might do occasionally.

Detergents can be a counter use to soaps. We use detergents to wash our clothes, and we use soaps to wash our hands. These detergents can either be anionic, meaning that they contain negatively charged groups such as the sulfonate group, or they could be cationic, meaning that they have positively charged groups. An example of a positively charged or cationic detergent is quaternary ammonium compounds, which we'll get to talk more about in a different video as we move forward in our course.

For now, if we take a look at our image down below, we'll be able to better distinguish between the soaps and detergents. Notice that the top half of our image is focused on the soap molecule, which is a long hydrocarbon chain with a carboxylic acid group at the end. These soaps tend to form interactions with salt atoms such as sodium and potassium. Here, you can see a bar of soap, and again, the soap itself is not an antimicrobial but is effective at degerming, allowing us to wash our hands with soap and remove the microbes from the surface so that those microbes can be washed away, such as being washed down a drain.

Now, the bottom half of the image shows a detergent molecule. At first glance, the detergent molecule looks very similar. However, notice that it is not a fatty acid, so it does not have a carboxylic acid group at the end like what the soap molecule has. Instead, the detergent molecule has other chemical groups that include the sulfonate group that you see right here. Again, the detergent will not form a scum, and so the detergent will not deteriorate fabrics and will not ruin clothing and surfaces like what soaps might occasionally do. Here we are showing you the detergents that you might use to wash your clothes.

This concludes our brief introduction to soaps and detergents, and we'll be able to get some practice applying these concepts and learn more as we move forward in our course. So, I'll see you all in our next video.

Which of the following statements are FALSE?

• A. Soaps are made from organic materials like animal fats.
• B. Detergents are made from synthetic materials.
• C. Soaps interact with salt molecules in water which leaves a residue after washing.
• D. Soaps and Detergents kill microbes and are effective sterilants.
• E. All of the following are true.

Quats

In this video, we're going to continue to talk about surface active agents or surfactants by specifically introducing quats. Quats is really just an abbreviation for Quaternary Ammonium Compounds. Quats, or Quaternary Ammonium Compounds, are really just cationic detergents. What this means is that these are detergents that have a positive charge associated with them. These quats, or Quaternary Ammonium Compounds, are cationic detergents that are actually safe enough to be used in food preparation. Now these quats, or Quaternary Ammonium Compounds, are amphipathic molecules, which once again recall from our previous lesson videos, just means that they have both hydrophobic groups that are water-fearing and hydrophilic groups that are water-loving.

Taking a look at this image below, notice that we're focusing on these Quaternary Ammonium Compounds or quats. Notice over here on the left-hand side we're showing you a quat molecule. Notice that it is an amphipathic molecule because it has this hydrophobic tail group that is water-fearing and then it also has this hydrophilic head group which is actually a quaternary ammonium group. These quats are amphipathic molecules that have a positively charged quaternary ammonium group.

Now these quats do actually have antimicrobial features, which means they have the ability to destroy or kill microbes. This is because these quats or Quaternary Ammonium Compounds have the ability to disrupt cytoplasmic membranes, and they can do that by inserting into the phospholipid bilayer. If we take a look at this image down below, notice that we're showing you a plasma membrane being disrupted by these quat molecules that are found here. These quat molecules are disrupting the phospholipid bilayer, from associating as it normally would. Therefore, it can create leaks in the membranes and ultimately destroy the microbe.

This here concludes our brief introduction to quats, these positively charged or cationic detergents. 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.

Quaternary ammonium compounds:

• A. Are cationic detergents that help wash surfaces.
• B. Are used as a 22% aqueous solution.
• C. Are extremely toxic to humans.
• D. Are amphipathic molecules with negatively charged hydrophilic portion.