so our last topic is colloids and colloids are dispersed substances not dissolved so what that means is you have small groupings of the colloid or colloids could also include very large molecules like hemoglobin that actually are large enough to scatter light and so examples of colloids include fog we see plenty of that in the valley when the liquid is dispersing into the solvent which is air and that's what recreates the fogs it's actually very tiny water droplets that are being dispersed throughout the air smoke is also an example of a colloid where the particulate it's actually small particles of uh from combustion processes are created so little chunks of carbon or residual from combustion are actually dispersed into the air and the water droplets coalesce onto those and that's what creates the colloid and then there's an example for another example for example whipped cream which is considered to be a foam right so these are aerosols this is a foam a foam is actually a gas dispersed into a liquid so when you get whipped cream and there's other examples this is simply an excerpt from a table in the book soap is also a colloid soap for example sodium sterate is what technically is a soap it's actually produced from the action of sodium hydroxide potassium hydroxide on fat uh but this is an example of sodium stearate contains 18 carbon atoms two three four five six seven eight nine ten eleven twelve thirteen forty fifteen sixteen 17 i think i miscounted in there but there should be 18 carbon atoms in here and then it has a carboxylate functional group on the end that's a carboxylic acid group that looks like this very similar to acetic acid has a negative charge this part is very strongly polar now this part is very strongly nonpolar if you can be strongly nonpolar and when you take soap and you throw it in water then what ends up happening is is the nonpolar parts are hydrophobic and so what they do is they get away from the water hydrophobic is the term we use for things which don't like to to mix with the water so this non-polar region of the soap molecule tends to hide itself away in this in a structure known as a micelle so the outside part is the polar head and then the long chains what we often refer to as the tails all point towards the inside and create what's this sort of spherical structure called a micelle now this is the structure of a soap molecule or soap as it takes when it goes into water and that's why it creates what's called again a colloidal dispersion a dispersion of molecules within water if you take a light and you shine it on a soap solution what ends up happening is that the light will scatter in the soap solution here and this is just a water on the other side a little bit food coloring it i believe but the colloid the colloidal dispersion you can see in the soap solution this sort of scattering of light that's the brightness that you see in the solution what's actually happening is the light waves are coming in and striking the particles and then leaving the sides of the solution so it actually looks like it's glows so soaps will do this we take a soap solution you can do it the laser it's a little harder to see with the laser because it's so intense but you can do with a laser and you can see the scattering of light that is created when you make a soap solution well these money cells are actually the reason why soap works to remove grease from food containers that have contained food that has so this is a really old video so it's a little uh low quality but it gets the point across pretty nicely this represents a micelle from soap and this represents a glob of oil let's say on a piece of fabric or on a dish and this is the how the soap actually acts to remove this oil from the surface a soap micelle consists of a group of surfactant molecules with hydrophobic tails pointing inward and hydrophilic polar heads pointing outward the micelle absorbs nonpolar oily liquids and carries them away as an oil in water colloidal dispersion so the nonpolar portions of the micelle actually absorb the oil droplet from the surface and because it's charged on the outside it effectively masks the nonpolar region on the inside my cells are also used for a number of other interesting applications and they're being looked at for drug delivery mechanisms because you can put something that's non-polar on the inside and dissolve it into a solution and make a suspension out of it anyways that about does it for the lecture if you have any questions you feel free to send me a message