L26 IMFs P6. Liquid Properties

Summary

In this Fogline Academy video, several intriguing properties of liquids are discussed, focusing on their relation to intermolecular forces (IMFs). The video covers a variety of properties beyond just boiling and melting points, such as viscosity and surface tension. The presenter explains how the length of hydrocarbon chains influences viscosity and demonstrates the role of surface tension through various phenomena such as water droplets forming spheres and capillary action in plants. The video also touches upon how these properties are utilized in practical applications like chromatography, offering a comprehensive insight into the dynamic behavior of liquids.

Highlights

• Viscosity in liquids is influenced by intermolecular forces, impacting their ability to flow. ⚗️
• Surface tension causes liquids to minimize their surface area, often forming spherical shapes. 🔵
• Capillary action is driven by cohesive and adhesive forces, allowing liquids to move through narrow spaces, like plant fibers. 📈
• Chromatography utilizes the principle of capillary action to separate mixture components based on their attraction to the substrate. 🧑‍🔬
• Surface tension can support light objects on water, demonstrating the delicate balance of intermolecular forces. 💧

Key Takeaways

• Viscosity varies with the length of hydrocarbon chains - shorter chains have lower viscosity, while longer ones have higher viscosity. 🛢️
• Surface tension influences liquid behavior, leading to spherical droplets and capillary action in plants. 🌱
• Capillary action allows liquids like water to climb up narrow tubes, showcasing cohesive and adhesive forces. 🔍
• Chromatography, a technique for separating mixtures, leverages the capillary effect to distinguish between colored molecules in solutions. 🧪
• Surface tension can even hold denser objects like a paper clip afloat on water until disrupted by substances like soap. 🧼

Overview

In the final episode on liquid properties, Fogline Academy dives into various fascinating aspects beyond boiling and melting points, such as viscosity and surface tension. The video delves into the importance of intermolecular forces in determining the resistance to flow, explaining how this plays a crucial role in the practical application of motor oils and lubricants.

Surface tension is another intriguing property affected by IMFs, causing liquids to naturally assume shapes of minimal surface area, like spheres. This property is at play when insects skim over water surfaces or when executing party tricks like floating a paper clip on water. These phenomena are explained with an engaging, easy-to-understand approach.

Additionally, the concept of capillary action is explored, demonstrating how liquids can climb narrow tubes due to combined cohesive and adhesive forces. This is critically important in natural processes like water elevation in plants and serves as the foundation of chromatography, a key technique in separating mixture components based on their affinity towards different substrates.

Chapters

• 00:00 - 00:30: Introduction to Liquid Properties In this chapter, we briefly summarize various properties of liquids besides the boiling point and melting point. We discuss how these properties are related to the strength of intermolecular forces. One such property is viscosity, which measures the resistance to flow of a liquid.
• 00:30 - 05:00: Viscosity The chapter titled 'Viscosity' discusses the concept of viscosity, explaining that it is a measure of a fluid's resistance to flow. It provides examples of different substances with varying levels of viscosity: water (low viscosity), oils such as motor oil (higher viscosity), and honey (very high viscosity). The chapter notes that substances with higher viscosity flow more slowly under similar forces compared to those with lower viscosity. The transcript suggests that further concepts related to viscosity might be introduced following these initial examples.
• 05:00 - 10:00: Surface Tension The chapter "Surface Tension" discusses the concept of intermolecular forces (IMF) in relation to hydrocarbons, focusing on how these forces affect the viscosity of different hydrocarbons. It highlights the practical application of this knowledge in the use of motor oils, explaining that these are hydrocarbon molecules similar to those being studied, but typically longer. The chapter aims to provide an understanding of why certain hydrocarbons behave differently in terms of viscosity due to their molecular structure.
• 10:00 - 16:30: Capillary Action and Applications The chapter explores the concept of capillary action, focusing on the interactions between hydrocarbons. It explains that shorter chain hydrocarbons have less molecular attraction, which consequently results in lower resistance to flow. This is due to such hydrocarbons having fewer induced dipole attractions between adjacent molecules, a phenomenon described using the molecular velcro analogy. The chapter emphasizes how these characteristics impact fluid dynamics and practical applications.
• 16:30 - 21:00: Chromatography In this chapter, we discuss the concept of viscosity with a specific focus on how intermolecular forces (IMF) affect it. Viscosity refers to the thickness or resistance to flow in a fluid. It is observed that molecules with greater IMF attractions tend to have higher viscosity because these attractions make it difficult for the molecules to slide past each other. The chapter provides examples by listing viscosity values for various substances at room temperature, effectively illustrating the concept.
• 21:00 - 23:00: Conclusion and Recommended Video This chapter discuss the complexities considered by the lubricant industry, particularly in formulating motor oils. It highlights the focus on intermolecular forces and their role in designing lubricants that perform effectively across various conditions. The chapter underscores the challenges of starting a cold engine, where the oil's viscosity is higher, affecting the ease with which molecules flow. As the engine warms up, the dynamics change, demonstrating the necessity for oils that can adapt to temperature variations.

L26 IMFs P6. Liquid Properties Transcription

• 00:00 - 00:30 In this last video, we are going to just briefly  summarize a variety of other properties of liquids   besides the boiling point and melting point and  talk about some of these other properties of   liquids that are also related to the strength of  intermolecular forces. The one of those properties   is viscosity, viscosity is a measurement  of resistance to flow of a liquid, and so
• 00:30 - 01:00 essentially, we would say that water, for  example, has a relatively low viscosity;   it flows pretty easily. Substances that have  somewhat higher viscosity might be oils, motor   oil that you might put in the engine of your car,  and honey has a very high viscosity compared to   these other liquids and so much greater resistance  to flow, and of course, that means that it tends   to flow more slowly under similar forces. Now,  if we want to apply some of our concepts we've
• 01:00 - 01:30 been thinking about in terms of IMF's we could  look at this list of hydrocarbons and think about   which of these would have the highest viscosity in  which would have the lowest viscosity. It's worth   mentioning that motor oils that we use as  lubricating fluids and engines and other machinery   are essentially hydrocarbon molecules like this,  although they tend to be somewhat longer than the
• 01:30 - 02:00 ones we have shown here, but similar concept. So,  of course, we know that shorter chain hydrocarbons   because of that molecular velcro will tend to have  fewer of those induced dipole attractions between   adjacent molecules, and as a result, we would  expect the smallest of these to have the least   attraction between molecules and therefore have  the least resistance to flow or in other words
• 02:00 - 02:30 the lowest viscosity and the largest of these  molecules to have greater IMF attractions between   molecules be harder to get them to slide past  each other and will have the higher viscosity,   which is exactly what we see here when we look at  the list of viscosity values for these different   substances at room temperature. It's probably  worth mentioning that folks who work in the
• 02:30 - 03:00 industry of making lubricants, for example, motor  oils, spend a great deal of time thinking about   these sorts of IMF interactions between molecules  in order to design lubricants that work better   under a range of different operating conditions.  Because, of course, when you start up your engine,   it's cold you've been parked overnight, and so the  viscosity at a low temperature is much higher it's   harder to get the molecules to flow past each  other, but as the engine warms up while you're
• 03:00 - 03:30 driving there's a lot more energy available to  overcome those IMF's and so the viscosity of   the fluid drops as the temperature goes up and  so since you need those lubricating fluids to   lubricate both at a low temperature as the car  is warming up and still provide protection and   higher temperatures there's a lot of science that  goes into developing those lubricating materials. Another property that's important related to IMF's  is the concept of surface tension, and essentially
• 03:30 - 04:00 the concept here is simply that when you have  a fluid a bulk liquid, the conditions or the   environment for the molecules at the surface of  the liquid in contact with say air is different   than the environment for the molecules that are  down in the bulk of the liquid. In particular,   the molecules that are down on the interior bulk  of the liquid are surrounded by molecules on all
• 04:00 - 04:30 sides, so they're pulled relatively equally in  all directions by those attractions; however,   the molecules that are on the surface of  the liquid only have molecules beneath them,   and so when you look at the net pull of all the  other molecules there's a tendency for those   surface molecules to be pulled downward into  the bulk of the liquid. And so, in some sense,   we looked at the individual molecular scale;  all of those molecules near the surface are
• 04:30 - 05:00 constantly trying to fight their way down into  the bulk right, which exposes other molecules to   the surface again, and so there's just a natural  tendency in liquids to reduce surface area that   is there's a natural tendency to have the minimum  surface area possible. And so that reveals itself   in some interesting ways. One of those we see  on the top left is the fact that any liquid will
• 05:00 - 05:30 have a natural tendency when it's not in contact  with other materials to assume a spherical shape,   so a droplet of water, for example, will tend to  form the spherical shape because it turns out that   you learn in geometry class that a sphere  has the minimum surface area for any given   amount of volume and so that shape tends to just  naturally reduce surface area. So if you could get
• 05:30 - 06:00 away from gravity, you would find that droplets  of liquids all tend to form a perfect sphere,   and so one way to sort of take advantage of this  to think about interactions between materials we   see on the bottom left and that is something known  as contact angle that's often used to measure the   interaction between different materials. So  by putting a droplet of liquid, say water,   on a solid material, you can get some measure  of how much interaction and attraction there is
• 06:00 - 06:30 between the molecules of water and the molecules  of that solid material and so the more spherical   the shape of the droplet the less attraction there  is of the water molecules to that material if the   water droplet tends to spread out it changes that  contact angle between the droplet and the solid   surface and so that indicates greater attraction  between the water molecules and that material. And
• 06:30 - 07:00 of course, some other interesting ideas are those  of shown on the top right of just the fact that   in any situation, a liquid, including water, will  tend to prevent or resist having its surface area   increased even when things are pushing on it that  are higher density, and so we see examples of this   and certain insects that kind of skim and skip  across the surface of ponds and things like that
• 07:00 - 07:30 or party tricks like taking a clean paper clip  and floating it on top of the water in a glass of   water. If you place it in there really carefully  and this works particularly well if you coat the   surface of the paper clip with a little oil before  you put it in there because we know that oil and   water don't like the mix and so the paper clip  even though it's more dense than the liquid water
• 07:30 - 08:00 it can actually float on that surface because it  sort of tends to bend the surface of the liquid,   and the water resists that increase in surface  area keeping it floating there. And then it turns   out if you add one drop of detergent, which like  soap, as we've discussed in our fats and soap lab,   provides both a polar and a nonpolar portion  that kind of interacts between the oil and
• 08:00 - 08:30 the water one drop of soap will cause the  paper clip to fall and break through that   surface tension and drop to the bottom. And  speaking of those sort of attractive forces   between materials and the idea of, say, a liquid  sticking to itself or sticking to a solid surface,   one interesting application of this is to think  about the meniscus when you put a liquid in,
• 08:30 - 09:00 say a test tube and in the case of mercury shown  on the left the mercury atoms are much more   attracted to other mercury atoms than they are  to class and as a result, the mercury tends to   ball up if you will inside the tube and so the  the surface of the mercury curves the opposite   direction than we would normally see when we  put water into a test-tube. And as we know,   when we have water in glass because the water  is attracted to glass, the meniscus tends to
• 09:00 - 09:30 curve upwards like sort of a u-shape as the water  climbs up the glass, and so we call those forces   between the molecules in the liquid cohesive  forces whereas the attractions between the   liquid molecules and solid molecules we would  call adhesive forces. And so it turns out one   interesting result of this because water has both  strong, cohesive forces and strong adhesive forces
• 09:30 - 10:00 between water and glass that water can actually  climb up glass capillary tubes and so as the glass   tubes get smaller and smaller in diameter, water  is able to climb further and further up these   small diameter tubes because of this combination  of adhesive and cohesive forces climbing up due to   adhesive forces climbing up the glass and then the  cohesive forces pulling up other liquid molecules
• 10:00 - 10:30 behind. And force of course classic example of  this capillary action is water climbing up fibers   of wood in trees plant fibers because essentially  those fibers are like very small capillaries that   have a lot of OH groups on them and therefore very  attracted to water molecules and so water has a
• 10:30 - 11:00 natural tendency to climb up plant fibers in trees  and other plants, and of course, one material that   we make from those wood fibers or plant fibers  is paper, and so water has a natural tendency   to climb up through those cellulose molecules  in paper and will wick up a dry piece of paper   as it wicks up through those capillaries. And  it turns out that we can take advantage of this
• 11:00 - 11:30 sort of capillary action as it's called in order  to separate mixtures, so for example, you could   take a dot of ink that might actually be a mixture  of a bunch of different colors molecules, put them   on a piece of paper and then dip the end of the  paper into water and the water will climb up the   cellulose fibers dragging solvating and dragging  the molecules of the ink along with it and as it
• 11:30 - 12:00 does so some of those colored molecules may be  more attracted to the paper fibers than other   molecules. And after a while, those different  colors will separate out, and so in this example,   some of those colors who are moving faster than  other ones were, and I think this has actually   been flipped upside down, so I believe it was  the red molecules that were actually moving more
• 12:00 - 12:30 quickly and the blue ones more slowly as the water  traveled up the paper. And we use this sort of   technique known as chromatography in the chemistry  lab and in many different industrial settings in   order to separate out different materials, and  we sometimes use paper but often use various   other solid materials as the substrate that we  pass the solvent through, and so we have things
• 12:30 - 13:00 known as gel chromatography high-pressure liquid  chromatography and various other techniques that   we use in chemistry to separate out mixtures based  on these concepts. And finally, I would encourage   you to go take a look at this particular video  which is a fun video showing wringing out a wet   washcloth in space where it demonstrates many  of the ideas we've been talking about regarding
• 13:00 - 13:30 intermolecular forces, surface tension,  and so forth in a zero-gravity environment.