so we are going to be talking about the concept of uh polarity and solubility in this video now in previous videos i think i've mentioned that polarity just basically means something that has charge or charges and a polar molecule is basically a molecule that has a charge or charges conversely a nonpolar molecule does not have a charge and in terms of revision one such molecule that we looked at was water as i'm drawing the water molecules over here you notice that the hydrogen atom has delta positive charges and the oxygen atom has delta negative charges the reason for that was mentioned in the previous video on hydrogen bonds and because water has partially positive and partially negative charges water is referred to as a dipole therefore water is a polar molecule now solubility is basically the ability of a substance to dissolve in a solvent this is under chemistry in biological molecule chapter 2 solubility and polarity are usually linked with each other so of course we have to ask ourselves the question uh what does polarity have to do with solubility this is the purpose of today's video now while there are many different types of solvent on earth we are only going to focus on water the reason why we are focusing on water is because water is an important solvent of life why water is an important solvent of life i'm gonna explain that later in another video you see we have too many things to explain so i'm gonna keep it very simple we're just gonna talk about uh solubility of substances in water now let's take two situations we have salt we also have oil if we were to put salt in a beaker of water and if we were to put oil in another beaker of water and we stir it uh which substance is able to dissolve in water very simply put you know the answer to this if you put salt in water and stir it the salt will dissolve in water but oil will not dissolve in water the oil as you can see there's a layer of oil forming at the top but on the beak on the left you can't even see the salt because the salt has already for the lack of a better word the salt has vanished and it's dissolved in the water so one of the main questions we have to look at here is what actually affects solubility of substances in water what makes salt uh able to dissolve in water and why can't oil dissolve in water that's what we have to look at so the most important thing that we have to know here is the fact that water is a dipole affects the solubility of other substances what that means is the fact that water has a partially positive charge and partially negative charge that's the reason why salt is able to dissolve in water and that's the reason also why oil is unable to dissolve in water so what does water's charges have to do with salt and oil let's look at salt so salt itself for example sodium chloride forms a giant lattice network that's not important what is important to know is the sodium chloride has positive charges from the sodium ion and negative charges from the chloride ion now if i were to basically put salt into water a beak of water then going over that and in that beak of water it contains water molecules you can see those water molecules right there and they're forming hydrogen bonds with each other and those dotted lines now what happens when i put salt inside water the salt submerges into the water i'm just drawing a few water molecules there if we notice what actually happens is the sodium chloride starts to break apart where one sodium chloride ion sorry one sodium chloride molecule is able to interact with the charges of the water molecule so like for example the positive end of the sodium chloride is able to interact with the partially negative charge on water and the chloride ion the negative side of the chloride ion is able to interact with the partially positive charge from the water molecules so what actually happens here i'm just i'm just adding on just having to make it a bit bigger as we can see the sodium chloride disperses and interacts and moves along the water molecules the reason is because sodium chloride has charges and water also have charges as well salt is polar therefore it can interact with water molecules and water molecules is a dipole so the uh just to repeat it again the partially negative section of water is able to interact with the positive charge on the sodium chloride and the partially positive side of the water molecule is able to interact with the negative charge of the sodium chloride i have highlighted two sections over there so you can see that and this allows the sodium chloride salt to just basically move in the water quite freely and interact with the water and therefore it dissolves in water molecules so sodium chloride is a polar molecule that can interact with water and it's referred to as something called hydrophilic the concept of hydrophilic just basically means that it is water loving therefore because it's polar it can interact with water and its hydrophilic salt or sodium chloride in this case is able to dissolve in water if we were to look at oil however and oil is a non-polar molecule and if we were to put oil into water remember yeah by the way what is nonpolar non-polar basically means it doesn't have any charge so if we were to put oil into water and we were to shake the beaker of water at first you can see the oil particles break apart yes they are breaking apart they are dispersing in water so you might think hey this is the same this is also the same as sodium chloride so they are able to dissolve in water but no they can't the reason is because the water molecule is unable to interact with the oil particles because the oil particles do not have charge but the only thing water can do is the water molecules can interact with another water molecule because both the water molecules have charges and they can form hydrogen bonds with each other so in this case what will actually start to happen is i'm zooming in a little bit as you can see here as the water molecules start forming hydrogen bonds with each other they push the lipids away or they push the oil away the reason why they're pushing the oil away is just to make room for themselves to form the hydrogen bonds so it's kind of like a click where water just does not want to interact with oil uh well not to say it doesn't want to interact with oil it just cannot interact with oil or lipid and when the water molecules form hydrogen bonds with each other they start to push oil away and because oil is less dense than water they start to they start to be dispersed towards the top that's why oil is always on the surface of water due to its density and the interesting thing over here is uh the oil molecules will then start to interact with each other and that interaction is known as a hydrophobic interaction therefore oil which is a nonpolar molecule does not have charge it's unable to interact with water and it's referred to as hydrophobic hydro meaning water phobic meaning heating so it just does not it is unable to dissolve in water so the polarity of water affects the solubility of other substances water was salt was able to dissolve in water because salt can interact with water and oil cannot dissolve in water because oil is unable to interact with water that's simply what it is so long story short polar molecules can interact with water and therefore can dissolve in water nonpolar molecules cannot interact with water and therefore they cannot dissolve in water that's uh this is just basically a simple overview of it examples of polar molecules will be things like sugars amino acids and some salts like sodium chloride and examples of non-polar molecules will be things like oils fats and polysaccharides yes something that i want you to notice here is alpha glucose and starch even though both of them are carbohydrates alpha glucose is soluble in water but amylose which is starch when they're linked together they become insoluble in water if you look at our previous video on polysaccharides we talked about it as well so that's basically it