all right so today what we're going to be going over is melting point so we got our trusty uh melting point tubes here sounds great and we also have our melting point apparatus which you'll see in a little bit but um basically what we want to do is do a melting point of caffeine which has a very high melting point uh value and we also want to do a melting point of benzoic acid which is about 100 degrees lower okay so i would say like we have a high melting point and we have a low melting point and um after we get that what i want to do is also uh stick with benzoic acid because it's got a reasonable temperature to work with not too hot um but then make it impure and see how that affects the temperature at which it melts and also the temperature the melting point range and then in addition to that we're going to uh well basically the way we're going to do that is we're going to have a very very very impure sample meaning like almost 50 50 mixture of benzoic acid and caffeine and then we're also going to do um a mixture of majority benzoic acid with a little bit of caffeine in there and see how that affects the melting point range and then we'll be able to compare the two and then we'll get a great understanding about how melting point works and how it's affected in terms of impurity because most of the time when you make this your chemicals in your organic compounds in a laboratory you're going to have a lot of byproducts and so um you're going to get some impure samples and it's it's a skill to actually purify organic substances and it's very difficult and so once you get really good you'll be able to get those pure samples but in the meantime let's try and figure out a way to determine if they're pure or not using the physical properties and melting point's a great way to do that and so let's do it here we go put a little bit of my caffeine sample that we recrystallize you can see those lovely uh truffula tree leaves right they're nice and needly what i did was i put them inside of this mortar so that way i can kind of smash it down with the pestle and make sure that we have it finely ground up before we get started on the melting point okay so this process is fairly straightforward you basically just push down and kind of squiggle it around we're just basically grinding the solid material with the mortar and pestle and so that way it's fine it's like a nice fine powder so that way when we put it into our melting point too one of these bad boys they there's no room for air to get lodged in there and kind of interfere with our melting point okay so we've got our sample here we've got our capillary two notice this end right here is actually closed off you can kind of see it's got it looks like a bubble kind of on the top and then this and right here is open so we're going to want to put this end down into the sample that has been pulverized with the mortar and pestle and then we're going to kind of just scrape it so sometimes you can scrape it and it'll scoop inside sometimes you gotta just literally like kind of smash the sample like that sometimes you're gonna have to deal with some static clean you can kind of see it a little bit right there and then now what i typically do is i take this and i gently tap on the bench okay now this does work pretty efficiently what you can also do is place this particular tube inside of like a rubber tube hold that rubber tube straight up and then you just drop it down and this guy falls a couple feet maybe three feet and it bounces on the bench top much harder and it pushes the sample down you can see that this is about about i say to it's probably not packed perfectly but two maybe almost three millimeters and that's totally okay when we're trying to prepare a melting point tube um remember the goal was like one to two and if we have about three that is okay as well the goal really is just get a small amount in here and you don't we want to make sure that it's well packed so that way we don't have any air bubbles in there that are going to affect the numbers that we obtain and then so you can kind of continue to pack this what you can also do is sorry i'm going to go to remove the video go to the melting point apparatus and place it inside of this little test or this little spot right here this hole and you can click tube tapper what that does is it kind of shakes it and your sample drops down so it's fancy pretty cool not all of them have this but this one does so if you have the opportunity go ahead and try that and you should be good to go to go ahead and place that in one of those three holes and now that we've got our sample prepared you hopefully can now just eyeball approximately how much sample you need in this particular melting point tube you don't want to come get to a ruler and then just measure one two millimeters every single time that's crazy just tap tap tap boom you're good to go right so um again not to you don't have to get too crazy and be very precise on this just uh get some sample in there make sure that it's nice and packed and then go ahead and uh get your melting point and what you can do you can also just prep multiple samples to get multiple trials done and so um record that melting point value multiple times that way you can get a good average and then that's always best when you're trying to collect data so cool let's go all right so this is our melting point apparatus um basically it's a digital um melting point apparatus so it's got a digital thermometer as opposed to the traditional one and then what we're going to do is can you see these three holes right here sorry let me scoot over a little bit one two and then three so those are those are three separate holes for three different samples because we can do them all at the same time if we wanted or we could do three at a time i guess but first what we want to do before we insert a sample is take a look at the settings and so let's look from the top view as you can see right here there's a there's a number that's displayed and that's actually the temperature of the room this is at room temperature it hasn't been used yet and so when we want to get the melting point of a given sample we have to know at least approximately or we don't need to know but ideally we wouldn't we would know approximately what that melting point should be and so now that way what we can do is set a start temperature so i can this start temperature is currently set to 220 degrees celsius okay and now what that means is that this this is going to heat up very very very fast to 220 degrees and then what we can do after that is set a ramp rate right here press that button and then this says 5.0 and that's degrees celsius per minute so what that means is that it's going to go from the start temperature to 20 and it's going to ramp up at a rate of 5 degrees celsius per 1 minute until we hit a stop temperature that we set and i have it currently set to 255.0 degrees celsius and so um basically the reason why i have them set to these specific temperatures is uh well actually i didn't set this one let's go back let's go down to 200. we have two samples that we're going to test the melting point of and their melting point should be around 230 or so but let's see what they actually are and so we don't want to get too close to in terms of the starting temperature because if they are either we were wrong on the melting point or if the sample is very impure there is going to be a melting point depression and so it could be much lower than the actual literature value and so we want to make sure that we can account for that by starting at a lower rate or at a lower temperature and then five degrees per minute is actually slow but it is slow and controlled and that's kind of what we want when we are checking the melting point of something if it's if it's something we have no clue about then what you would typically do is start at room temperature do the ramp rate at maybe like 10 degrees and you can change this by using these up and down arrows so i could do 10 degrees per minute or even up to 20 degrees per minute and what this will allow me to do is get an idea as to where that melting point is so let's say we start at room temperature we don't want to go at a rate of 5 degrees per minute and go all the way up to 250 degrees because i would we would just be here forever so what we can do is set it to 20 degrees per minute and then only wait like a few minutes until we get to 250 degrees and realize hey this is a very high melting point let's go ahead and do another sample and then do our start temperature at let's say 200 degrees and then go do a ramp rate of five bring that back down do a stop temp of maybe 255 and then what you want to do after that is hit start this is a start and a stop button so you want to hit that right now it says cooling so we'll press that again and it says preheat so what that means is that you'll see this number start to skyrocket up to 200 degrees celsius which is our start temperature okay and then once we're ready you press that green start button okay so i went ahead and started the caffeine already and you can see the temperature is rising it's at uh 210 degrees celsius so let's see if we can take a look into this window see what it looks like and there it goes let me see if i can focus there we go you can see the caffeine through the window and it's currently just chilling right just a nice little solid there for you okay so to me it looks like it's kind of softening here it's difficult to see maybe in the camera but what we've got is a temperature of 227 so we're getting close to the temp the melting point of caffeine let's see if we can't get a better look at that solid material we can start to see something happening perhaps it's keeping a close eye on it once you see that first drop of liquid you want to record that value what i would suggest during this whole process is actually just recording any observations you see and at which temperature so uh since i'm the one in control of the temperature as well as the video i will i see some stuff happening it's 2 34. and whoa it's happening fast and last drop let's see the last drop of clear liquid it's happening almost gone almost gone that was cool 237.6 see how cool was that right but you see how fast that can happen now this was a crystallized sample so that's why it's going to happen fast because it is fairly pure because it's such an awesome job of recrystallizing it okay so this is actually a um setup for benzoic acid so there's a spider right there you see it right there got them spiderman spiderman at spider in the chemistry lab and they're survived i feel like if i got bit i could probably get some spider-man powers um anyway it's at a hundred degrees because uh benzoic acid's uh melting point is a little bit lower it's uh i'll let you look that up it's like a hundred and something but um what i have is the start temp is that 100 degrees i have the ramp rate at five and i have my stop temp at whatever i'm just going to make sure that i go ahead and press stop when we're all done here but let's take a look inside of this lens to make sure our sample is actually all groovy nothing wrong with that right it looks like a nice little solid sometimes when you put it in here if you take a look and it's melted you did something wrong and maybe you started at a lower temperature or you had so much liquid in there that from the recrystallization process that it actually just started heating up the liquid and then the solute or the the solid material actually became soluble in it so sometimes you see that with water but what i'm going to do now is i'm going to go ahead and press start you can see here that it says melt that means this temperature right here is going to start to go up at a rate of five degrees per minute okay and so we're going to keep a close eye on the sample and then we'll see what happens okay see you then so as we watch our sample through this lens we want to obviously make sure we have our goggles on because uh practice lab safety but as we're watching this we want to think about all of the possibilities that can occur the different factors so there's there's a few things you want to learn over time how to identify so obviously the substance can melt but it can also decompose there's a there's something called shrinking uh or sweating and uh shrinking and or sweating are basically when the solar material is kind of no longer adhering to the glass but almost like pulls away from it and so we want to make sure that's shrinking sorry then we want to make sure that we can identify that and differentiate that between actually melting okay another thing is sweating so let's say we recrystallize this in ethanol or something if we had a little bit of residual solvent or because we didn't dry it well or the solvent was incorporated into the crystal lattice as we heat it that solvent will kind of be set free especially if it has like a lower the boiling point is below what we're actually working with then when we start to see that ethanol in this in this particular example then it might look like it's melting but it's actually just sweating and so we're gonna have to be able to identify that but again i think it's really important just to record anything and everything that you see any change um that you think you might see and then you can kind of reflect back like okay well as something started happening around let's say 85 degrees and you're like well that's actually and then the sample didn't melt until 125 degrees well maybe that was actually not the melting process starting but maybe sweating because ethanol does boil around that time and so or you can reflect back in that manner but you can only do that if you take really good observations and notes and write them down in your laboratory notebook okay so i touched up on shrinking or shrinkage uh that's pulling away from the glass sweating and then decomposition so oftentimes your samples may decompose rather as they are melting or melts because they did decompose and then you can start to see something happen it just i would record something it says the 120 point it was about one 120.00 uh left and then let's just keep observing i would say i'm watching this through the screen as well so that we're actually seeing the same thing i would feel comfortable in identifying it as a melting at least a drop 122 and then we got all the like the rest of that solid material is melting melting melting so remember when you are recording the melting point you want to record the range this first drop of liquid that you see was at 122 and then we want to see that when the last piece of solid turns into a clear liquid which is 120 4.3 and so that would technically be our melting point range so go ahead and record that value all right so that was awesome right so um happens so fast too and um the purity of the sample is going to dictate how quickly a substance melts at least uh in terms of like that melting point range that melting point range was uh we had 122 122.0 for the first drop of liquid that i've saw and then it finished off the all of the solid material melted into a clear liquid at 120 four okay so that's only two degrees and that way that melting point range is very small and that's because this is a very pure substance as we add more of an impurity to this that melting point range is going to be larger and larger and larger it might start maybe at like 115 or definitely just just significantly lower than 122 and this is because the presence of an impurity um affects the intermolecular forces between the pure subs like the benzoic acid for example and you can also think of it so remember that the melting point of a substance is also the same as the freezing point right so think about water when water is on the roads they tend to throw salt on it right and so that's because when you throw salt onto water it depresses the freezing point for the melting point and so um it can be maybe instead of zero degrees celsius minus 10 degrees celsius and so if that's depressing the presence of that impurity salt actually lowers the the melting point of water and so it melts the water of the ice on the roads and obviously makes it safer for us to drive okay and so you can think of impurities in our organic substances as doing the exact same thing that sauce does salt does to water it's going to depress that melting or freezing point obviously to a certain point there's only so far down that it can go but the larger that melting point range the more impure that it is so if having a melting point range of uh maybe like two to four degrees celsius is actually really good and that means that that substance is pretty pure right and so um what we want to do is kind of give you an example or show proof of that so we did benzoic acid now what i want to do is kind of doped benzoic acid with a little sample of caffeine and see how that affects that melting point okay we want to take a look at that and see what it does okay so what i've got here is the sample of caffeine that i've ground ground up as well as the sample of benzoic acid so now i'm just going to combine the two and then we will gather our sample of um our melting point too and in our melting point tube and then we'll take a look at the melting point and see how it's affected so you don't need to see how i just pretty much can buy them but i put all that caffeine right in that mortar or mortar and then we'll uh i'll mix it up really well with the pestle all right so i got our sample yeah um you can't see it but i can see it it's perfect um and so let's go ahead and throw that on the melting point apparatus and we'll see what happens okay all right so i went ahead and started this video and we have two samples so there's one on the left that's a almost like a 50 50 mixture of caffeine and benzoic acid well on the right we have a a little larger proportion of benzoic acid with respect to the caffeine so we'll call that benzoic acid with a small caffeine impurity while the one on the left is about a 50 50 mixture of both and we have a the melting started at 62 already so uh it's significantly lower because i'm anticipating the 50 50 mixture to have a significantly lower melting point just because of that large difference in melting points between the two okay so let's keep an eye on it and see what happens all right so i'm going to speed up the rate of this video so that way you don't have to sit here but i want to see uh i want you to kind of observe the whole time that way we can see what happens i feel like i see something going on with the sample on the left so i would record a value of 75 degrees just something happened right and i don't anticipate really like much sweating perhaps shrinking but it looks like something it doesn't look like it's adhering to the glass as much and a day i would say that's probably melting so again here's the temperature at 77. still not much going on on the structure on i'm sorry the sample on the right yeah that looks pretty pretty clear to me that it's melting not very fast though right so we are approaching 80 degrees and it looks as though the sample is getting smaller so more and more of that is melting we have quite a bit of it gone starting very early in the process that depression of the melting point was very significant in this 50-50 mixture so now i can definitely see liquid on the bottom that's 82.6 degrees depending on how you want to record it we're just making a lot of observations and recording as much as possible to make a very good conclusion in the end still nothing really going on on the sample on the right but this one on the left is definitely melting i feel like an announcer i wish i was better at a sports announcer all right he's coming in he's uh he's starting to liquify we got a 50 50 mixture on the left approximately of caffeine and carboxylic acid i'm sorry benzoic acid which is a carboxylic acid um still melting still melting he's heating up it's getting hot in here [Music] definitely going to want to speed this up but wow check that out 88.6 degrees and he's a structure on the right or the sample on the right it's not wanting to change i'm not gonna lie i'm focusing on the one on the left so if you've noticed a change in the structure on the example on the right you could definitely record that i feel like it might be a little looks a little wet right say maybe sweating maybe starting to melt i would definitely just write something down around like 85 that's structured on the sample on the right this one on the left it's not completely melted just yet it's so close so close and we're at 92 degrees so we're still moving up okay struggling you can see that this range is huge and that's a good indication of an impure sample bubbles all right so this is definitely one of those procedures where you have to be extremely patient and you don't want to just ramp it up to 10 degrees per minute because that's just gonna i mean you're not going to get great results you want to put in just a few minutes of extra time just to get some good results to make sure that your final conclusion is very definitive okay and it is one of those things that just patience is a virtue and that's the case for all organic chemistry you could either be doing reactions that take forever you got to be patient or you can do reactions that just don't work and you have to be patient in that sense because fail after fail after fail eventually you'll get that that reaction to go to completion and you'll be so happy i can't tell if that's melted or not so hold on let me move this i don't think it is i don't think it is actually so right now we are currently at 99 degrees so we are still moving that looks melted let's just focus on the fact that this has changed so much the values from pure benzoic acid to impure benzoic acid have changed so much in this process of uh kind of going uh with a little adding a little caffeine and you know what's interesting about adding caffeine caffeine's melting point is significantly higher than benzoic acids yet it doesn't raise the melting point it actually lowers the melting point and that's because it doesn't matter what the melting point of the inferior substance is it's just the presence of the empty or substance affects the intermolecular forces and therefore it causes a melting point or freezing point depression as we can see here currently we are at 108 and i'm not sure that this is completely melted on the left i still see a little crystal in there the one on the right is definitely melting but we're still at 109.6 now we're at 110. i want to say that this guy might be the one on the left you see it kind of glaring in the back or it's sparkly shining bright like a diamond still there okay let's call that one down on the left that is 112.4 what a range on that one the one on the right we're still we're still cruising we've got quite a bit of sample in there it's not budging so let's uh i'm going to just zoom to the end and we'll show you the final process of the melting all right so we're approaching 120. so let's take a look at our sample sorry about that there we go we got that focus going it is melting melting melting almost done there almost there almost there so remember we're shooting for 124 the final benzoic acid melting point that's what it was when it was pure at the upper end we're at 122.3 which is where it started melting last time now we are going to tell that is a solid material right there on top it's very difficult to see but i'm going to keep going it's at 124 right now let's take a look sorry about that yeah this is just uh yeah we're good 124 is dead all right so you can see how the impurities affected the melting point range all right so you can see how the melting point range is affected by the presence of an impurity even if that impurity has a much higher melting point and so this again goes back to just the presence of a solute in a liquid for example uh causes a freezing point depression and the freezing point and the melting point are the same temperature and so um the presence of caffeine which has a melting point of about 233 degrees celsius actually didn't raise the melting point of benzoic acid from 124 up to something higher but it actually lowered it to have a much larger range okay and so you can see that the percentage or um yeah i guess the rough percentage as we have an increase and percentage of the impurity we get a much larger range or even just totally getting the entire melting point out of whack as you saw the sample with 50 50 approximate 5050 mixture resulted in a melting point um significantly lower than 124 while the majority of benzoic acid with a little bit of caffeine in there that resulted in a final melting point close to 124 about there but also starting significantly lower so we had a very large range for that melting point and that's because of the impurity of caffeine being in that melting point apparatus tube and so hopefully this was helpful in at least kind of seeing a variety of uh scenarios where we got the pure sample we got the low sam low temperature melting point at the higher temperature melting point we've got um the impure samples with the varying percentages and kind of how that can affect it and so uh really when it comes to being successful at melting points it's not tough it's not very hard it's just takes some time and some some effort and some practice and so you're going to get that hopefully from this video visualizing it is really helpful because now all you do is press buttons in the laboratory you'll be good to go