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Video transcript

we've already talked about the notion that a water molecule has polarity to it one end has a partially negative charge and the other hand has partially positive charges and we talked about how this leads to hydrogen bonds and we alluded to the fact that hey maybe these hydrogen bonds give us all sorts of neat properties of water and what I want to talk about in this video is one of those very important properties and that's water at waters ability to be a solvent waters ability to be a solvent and this means that it's easy for certain things to be dissolved inside of water and that's super important because that's how a lot of the chemistry occurs by things getting dissolved in water and then interacting and bumping with other things and this is actually what's happening inside of cells in the cytoplasm the cytoplasm which is mostly water is a solvent which allows a bunch of interactions to happen between different types of molecules let's think about why water is a good solvent and what types of things it can dissolve easily and what types of things it might not be able to dissolve so easily so the key feature that makes water a good solvent or at least a good solvent for a large class of molecules is its is it's polarity if I were to take some sodium chloride so often known as table salt so let me so if I were to take sodium NaCl sodium chloride sodium chloride the sodium and chloride are attracted by ionic bonds the sodium right over here has a positive charge it has a electron stripped from it and the chloride has a let me write that in let me write that in a different color so the sodium has a positive charge because it has an electron stripped from it and the chloride it is an anion it has a negative charge it is a negatively charged ion because it gains an Electra electron but they are attracted to each other this has a positive charge this has a negative charge this is called an ionic bond but if you put sodium chloride in water something very interesting happens this is something that we've all experienced take some take some table salt and put it in water and see what happens it will dissolve and why does it dissolve well let's let's just draw it out so this is the sodium right over here so that's the sodium it has a positive charge it has a positive charge and then this is this is the chloride right over here it has a negative charge what's going to happen if you put it inside of the water let me do that negative charge in the green what's going to happen when you put it inside of water well you could imagine the negative ends of the water molecules are going to be attracted to the sodium ion so it's going to look something like this so you have the oxygen oxygen oxygen oxygen oxygen I'm clearly not drawing things to scale but this will just give you the idea these all this at this end of the water molecule all has a partially negative charge partially negative charge so it's going to be attracted to the sahte the positive sodium ion and then the hydrogen ends the hydrogen ends are going to have a partial positive charge and then they're going to be repelled they are going to be repelled from the positive sodium ion so it's going to look something like this it's going to look something like this and you're going to have partial positive charge on the outside partial positive charge on the outside and now these hydrogen's over here this will just interact with water the way that it would typically with the hydrogen bonding the molecules just flowing past each other so the fact that the sodium the sodium ion here it's an ion it has charge it is it is able to dissolve in the water very easily because it is attracted to the partially negative ends of the water molecule now similar thing is going to happen with the chloride ion and we call a negative ion an anion so over here over here and actually let me let me get some let me move it over a little bit so that I have some space so the chloride anion let me let me move it over a little bit so right well maybe I'll move it over maybe I'll move it right over here so the chloride the chloride anion let me see I'm having with my selection tool alright so there we go the chloride anion it has a negative charge so it's going to be it's going to be attracted to the positive end of the water molecules so you could imagine something like this so the hydrogen ends the hydrogen ends are going to be attracted to it they have a partially positive charge they have a partially positive charge of course you have the oxygen end that has a partially negative charge it has a partially negative charge and I could I could draw more of these hydrogen hydrogen attracted there you have the oxygen over let me do that in the I want to keep my colors consistent the oxygen right over there you have the hydrogen once again this isn't drawn to scale hydrogen it is bonded to the oxygen and so once again you can form this I guess you can almost imagine this this these the shell of water molecules is going to be attracted to it it's going to be and it's going to be attracted for the I guess you could say the the partially positive end which is where the hydrogen atoms are is what's going to be attracted to this negative ion so this is partial positive over here and then on the partially negative side outside of this shell you can imagine she's going to interact with the water just the way any water molecule would and so it's going to be able to flow very easily so you probably see something interesting here if something has charged if it hasn't if it's an ion or if something has some polarity it's very easy to dissolve it inside of water and in this case and just to have some some terminology here in this case water is the water is the solvent so water is the solvent so the solvent is water and the thing that's being dissolved in the water we call that a solute so we call this the solute so the sodium chloride that those that is it could view sodium chloride as a solute or you could say that the sodium sodium ions are solid and so are the chloride so are the chloride ions that is also solid that's also you can consider to be the solute and so you say well what kind of things dissolve well well things that have charged or that are polar and things that are charged Poehler and tend to dissolve well in water there's another thing a word we use for them we say that they are hydrophilic so we could say that this right over here is hydro hydro philic and if you look at the word roots hydro is referring to water so hydro is referring to water and philic means loving so this literally means water loving water water loving hydrophilic and so you might be asking okay everything we've talked about you know we've seen water molecules that's polar we're looking at charged ions okay we could get that we can get why they would be hydrophilic they can incorporate themselves well into the water but what are examples of things that would not incorporate themselves well in the water well in general things that don't have charge or that aren't polar aren't going to be able to dissolve in water all that well and a good example is hydrocarbons so if you took some hexane and hexane is a major constituent of car gasoline so hexane Hex the the prefix means six carbons so c1 let me do this in a another color so if we have one two three four five six carbons so one two three four five six carbons and then they're all all the other bonds are with hydrogen's so let me draw this as well as I can carbon at least typically forms four bonds so hydrogen hydrogen hydrogen hydrogen hydrogen hydrogen hydrogen this is this right over here is hexane this thing has no polarity to it it doesn't form hydrogen bonds it doesn't have any polarity and so if you were to take hexane and throw it into water it's not going to dissolve that well it's actually going to kind of beat up and you would see that if you actually threw some gasoline inside of water so things like hexane we would call hydrophobic hydrophobic so this right over here is hydro phobic hydrophobic a little reball up to avoid getting in touch to minimize its contact with the water because the water is attracted to itself and it's not so attracted to this stuff right over here and hydrophobic you still have hydro meaning water and then phobic is means fearing so this right over here is water fearing that's why it's hard to to mix things like water and oil or gasoline and water
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