welcome back to the chemistry lecture series and in this particular segment we're going to discuss about solubility and visibility i'm going to use the term interchangeably because it's kind of easy to use but technically there's a difference between the two terminology so something that is soluble would partially mix with one another so for example table salt or nacl and water are soluble so stable salt is soluble in water but it's not miscible and i know that's the case because i can add a little bit of salt and i know it's going to dissolve completely but then if i add way too much then what happens is that the solubility is going to stop i'm going to have a chunk of salt on the bottom of my water glass right so if you keep adding a lot of salt it would stop dissolving at some point whereas if you have something that is completely miscible like isopropanol and water isopropanol by the way is just rubbing alcohol you can have a one percent solution of isopropanol it's going to dissolve completely you can have a 99.9999 of isopropanol and it would still dissolve completely that is it's going to be soluble in all proportion and again like i mentioned typically we're just going to use the term solubility to describe this ability as well but technically there's a difference between the two terms it's just kind of something that in practice versus a formal definition and my suspicion is that miscible is not some word that's easy to pronounce so people just call it soluble because it's a lot easier and roll off the tongue better now with that definition kind of distinction the rule for solubility and miscibility is simple enough like dissolves like that is too compound that have the same level of polarity and structure and so on are more likely to dissolve in one another so for example if i were to have a polar molecule and another polar molecule so for example water is very polar right and i also have let's say an ethanol which is also polar and alcohol is one of those polar functional groups and what you'll find is that they're going to mix with one another in pretty much all proportion we can also have something that is completely nonpolar and another nonpolar molecule so let's say i'm going to have a cyclohexane versus hexane right they're both completely nonpolar alkane is one of those nonpolar group and they're going to dissolve with one another and pretty much at a hundred percent composition so they're going to dissolve with one another they're going to dissolve with one another but if you have water and say hexane you'll find that they will not dissolve because water is polar and hexane is nonpolar right so that's going to be the rule and the scope that i want you to know it's like solubility for our purposes is that polar and polar will dissolve and nonpolar and nonpolar will dissolve with one another but you can't have a mix between polar and nonpolar that's it that's the limit of solubility that i wanted to be able to know for the purposes of our class because solubility is actually very hard to to predict and in fact polarity is not just a binary whether something is polar or nonpolar it is a gradation of level right so for example water is probably on the very polar n and the reason why it's very polar is because you can have hydrogen bonding and so on and things that are like hexane and cyclohexane or alkanes are on the non-polar side of our functional groups it's completely nonpolar now the ethanol that i have before is roughly somewhere in between so what you'll find is that while water and hexane will not dissolve with one another you can dissolve water and ethanol just fine and you can also dissolve ethanol and hexane just fine so and the reason for that is that the ethanol lies somewhere in between that level of complication is not where the scope that i want to get to whether you have to predict something is miscible versus soluble that's kind of a bit beyond the scope of our class but if i were to kind of give you a problem that looks something like this right so in this case the solubility of water and solubility in hexane so if i were to ask the question well which one is more soluble in water ethanol excuse me methanol or hexanol then you would say oh most likely methanol is more soluble in water because a hexanol here because we have now a mixture of functional group if we have a methanol it's simply going to look like this right this is polar and we have a little bit of alkane which is a bit nonpolar and if we have cyclohexane that looks excuse me one hexanol what we have is that we have smaller polar group and then we have a larger nonpolar here so as we grow the nonpolar region of our organic molecule you should expect that the solubility in this case in water should decrease because it becomes more and more nonpolar and the reverse is also true that is if we were to look at the solubility of the same compound methanol and cyclo one one hexanol inside hexane in this case which is completely nonpolar what you'll find is that the methanol is only partially soluble in hexane but will dissolve but in the other hand cyclohexanol excuse me i keep saying cyclohexanol but i'm meant to say hexanol is going to be pretty much dissolved completely in hexane because their structure is very similar to one another and in this case the large nonpolar region dominates the solubility so uh i will not predict i will ask not ask you to predict which one what is the number but i will um but i will probably ask you okay which one is more soluble in water with one of these two or which one is more less more soluble in hexane between these two compounds