Lecture 13. Physical Equilibrium, Pt. III.
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00:00
WasserLösungAdenosylmethioninBiskalcitratumAmmoniakVancomycinWasserErdrutschKörpertemperaturDeltaStickstoffatomRauschgiftChemische VerbindungenKonkrement <Innere Medizin>StoffmengenanteilWursthülleFülle <Speise>Elektronische ZigarettePeriodateKrankengeschichteUnterdrückung <Homöopathie>KochsalzDipol <1,3->ChemieanlageSchmierfettAnomalie <Medizin>FettSenseComputeranimation
09:59
Gelöster organischer StoffWasserLösungBiskalcitratumNaphthalinPhenylgruppeBenzolringElektrolytlösungAlkoholische LösungNatriumchloridKaugummiNanopartikelChemische EigenschaftElektrolytlösungMolekulargewichtsbestimmungStoffmengeGlucoseLösungWasserKochsalzDeltaNatriumchloridZellfusionAlkoholische LösungNatriumKörpertemperaturOrganisches LösungsmittelBukett <Wein>WursthülleBenzolringSonnenschutzmittelKohlenhydratchemieVancomycinKonkrement <Innere Medizin>ChlorideStratotypChemische ReaktionArzneimittelBrandsilberEdelgasPeriodateKluftflächeLeukozytenultrafiltratNahtoderfahrungPotenz <Homöopathie>ZuckerDruckabhängigkeitComputeranimation
19:58
NatriumchloridBenzolringOrganisches LösungsmittelMannosePCTDruckbelastungOsmoseSemipermeable MembranPlasmamembranDruckabhängigkeitMolekülPoröser StoffTerminations-CodonBukett <Wein>VerdünnerKrebsforschungHydroxybuttersäure <gamma->Phantom <Medizin>ElektronentransferAlkoholische LösungFülle <Speise>KonzentratProteineStratotypPeriodateAzokupplungElektronische ZigaretteDruckabhängigkeitStoffmengenanteilRoheisenGradingWasserChlorideElektrolytlösungChemischer ProzessWursthülleBukett <Wein>CalciumSynthesekautschukSchelfeisÖlWildbachPlasmamembranImpfung <Chemie>SonnenschutzmittelBenzolringNatriumchloridMolvolumenMolekülOsmoseLösungCalciumchloridKochsalzAdvanced glycosylation end productsSemipermeable MembranVancomycinNatriumIonenkanalSiedenComputeranimation
29:57
OsmoseDruckbelastungBiskalcitratumPlasmamembranAlkoholische LösungSystemische Therapie <Pharmakologie>DruckabhängigkeitAktives ZentrumMeeresspiegelWildbachAlkoholische LösungMolvolumenFülle <Speise>Computeranimation
31:05
MolvolumenAlkoholische LösungRübenzuckerMeerwasserLösungWässrige LösungDruckabhängigkeitBiskalcitratumGolgi-ApparatHarnstoffCalcineurinLammfleischAbführmittelMühleGlucoseOsmoseAtomZündholzInfusionVancomycinSonnenschutzmittelElektrolytische DissoziationKörpertemperaturMedroxyprogesteronAnomalie <Medizin>BenzolringToluolLebensmittelvergiftungMonoklonaler AntikörperAltbierClick-ChemieHexaneOctaneMischenEntzündungNeprilysinLöslichkeitElektrolytlösungDruckbelastungPCTMas <Biochemie>Bukett <Wein>WasserNatriumChlorideNatriumchloridNanopartikelAzokupplungNatriumStoffmengenanteilFülle <Speise>WasserMolvolumenKochsalzBenzolringMannoseOsmoseDruckabhängigkeitMolekülT <2,4,5->ToluolLösungWasserstoffCobaltoxideGletscherzungeSystemische Therapie <Pharmakologie>WursthülleKohlenstofffaserKüstengebietElektronische ZigaretteHeck-ReaktionVancomycinRübenzuckerGradingKohlenhydratchemieChemische FormelQuerprofilBoyle-Mariotte-GesetzBetäubungsmittelNatriumchloridErdrutschElektrolytlösungMischenMeerwasserentsalzungSemipermeable MembranWässrige LösungChemischer ProzessBukett <Wein>BruchverhaltenTachyphylaxieAdamantanPeriodateSammler <Technik>Aktives ZentrumGlucoseAlkoholische LösungStratotypMeerMineralKonzentratInjektionslösungUnterdrückung <Homöopathie>Hope <Diamant>GanglagerstätteIsotopenmarkierungBiologisches MaterialWasserwelle <Haarbehandlung>EisflächeQuellgebietMeerwasserKörpertemperaturBrillenglasToll-like-RezeptorenVerzweigte VerbindungenVerbrennungMeteoritGangart <Erzlagerstätte>StahlPasteComputeranimation
Transkript: English(automatisch erzeugt)
00:07
So let's go ahead and start. Last time we were together, we talked a little bit about, just initially about boiling point elevation and freezing point depression.
00:22
Today we're going to actually do some calculations with that. But this is a conceptual picture of what is happening. So this solid line is the phase diagram for water in this case, and what happens is that when we add something,
00:44
so pure water, this is pure water right there, okay, and you have to understand that when things are pure, we can actually measure a vapor pressure. We can actually measure things, and so we know, in fact, that this is true. If you start adding stuff,
01:02
then you don't have pure vapor or pure liquid. And so you can affect the vapor pressure, you can affect the boiling point, you can affect the freezing point. So in this case, if you look at this, the dotted line or the dashed line here is where we slide down as we add more and more, or as we reduce the mole fraction
01:23
of the pure compound by adding salt, by adding something, it slides right down this curve right here, okay? So this kind of widens like this, slides down, and if we look at then, folks, remember, one atmosphere is boiling, okay?
01:40
So this line out here, as we drop it this way, moves in that direction, this line moves this way. This is one atmosphere, and so the boiling point actually increases, and look at what happens here. This slides this way, the freezing point decreases, okay? So this is the conceptual, this is the picture of what's happening.
02:02
We call this the delta temperature of the boiling point, so this is delta Tb here, meaning how much does it change, and this is the delta of the freezing point. Notice that this is, in Waters' case, this is bigger than this, okay?
02:21
So this is what's actually happening, and now we're going to go ahead and look at some of the, I've sort of said this, you've got to know this, folks, right there, write it down, nice and simple, mole owls, okay?
03:03
Mole owls, K sub B, I have to give you, okay? I have to give you that. It's different for everything, although that's not quite, that is true, but I don't have to give it to you.
03:24
I could ask you to calculate it. In fact, right now, I want you to calculate it. Okay? If delta T is equal to a half a degree C, so 0.5C, and you have 10 molar, what is K sub E?
03:44
So, 0.5 here, and this is a 10. Easy. So all you've got to do, once again, folks,
04:02
I have to give you, or you have to have information that allows you to know two out of three, okay? So as long as you know 0.5 degrees here and 10 molar here, you can figure out what K sub B is, and what is K sub B in that case? Who got the answer?
04:21
0.05, okay? So, K sub B is going to be in what units? We've got degrees over here, and we've got moles here, okay? So it's going to be degrees per mole, or per mole owl, okay? So, once again, you can calculate this, all right?
04:40
Don't freak out if you're asked a question where you're given the temperature change and the molality, or I could ask you the molality, okay? If temperature change, folks, is, I'm going to make, yes? Really loud. Depends, okay? If I just asked for the change in temperature,
05:01
one degree Kelvin is one degree Celsius, okay? So any time you're talking about deltas, unless I specifically say, what is the temperature change in Kelvin, or what is the temperature change in Celsius? That, but you can't use, well I guess you could use Fahrenheit.
05:22
If I was asking, if I were asking you, what is the K sub B, and I said that this is one degree Fahrenheit, then you would give me the K sub B in Fahrenheit, but I wouldn't do that. So once again, folks, all kinds of permutations here as to what I can ask, simple questions, simple math, okay?
05:46
So as she said over here, the units then are going to be in degrees C per molal, okay, or degrees K, doesn't matter. Does everybody understand why it doesn't matter?
06:01
Okay. I guess I should say, does anybody not understand? Okay, do this, using the equation that I just gave you. Take out your calculators and do this problem.
06:58
Okay, just in case you don't know, nitrogen is 14,
07:02
so this whole thing is 14 plus 3 is 17.
07:40
Well that's almost a mol, right? That's almost a mol, and that's a fifth of a mol, so it should be about one over .2. So that's kind of, I'm not going to be like, at times that should be about two and a half.
08:10
Okay, let's see what the answer is. Once again, it never hurts to just have a little bit of a clue as to what you think it's going to be, okay?
08:20
So look at this. I said that 17 grams per mol for this. Everybody got that? So that's not quite a mol, okay? Eleven grams, 17 grams, half a mol or whatever, half to one mol. And it's over 200 grams of water. For mol als, it's supposed to be over a kilogram.
08:40
So that's .2 kilograms right there. So it's about .5 moles, .7 moles over .2. So you're going to have a molality of like two and a half or three or something like that. So it's then going to be three times this. So you should have a number around one and a half degrees. Let's see if I'm right. Okay, so here's, so you've got about two-thirds
09:04
of a mol divided by .2 kilograms. So you've got 3.3 mol al, 3.3 times 5.2, about 1.7. So we got that?
09:20
How many want me to slow down? How many think they got that? Okay, all right. So once again, it's a very simple, straightforward calculation. Okay? Nothing tricky about it. Now folks, I can get, I can make it a lot trickier, okay? But, so delta T, that could be a 170, 1.74 K, 1.74 C. I don't see any reason
09:51
to change things, folks. If I give you torr, if I give you a Clausius-Clapeyron equation and I give you torr, you know, I wouldn't, you know,
10:00
I'd leave it in torr, okay, unless I ask, what is the atmosphere, what is in atmospheres, what is it in bars, whatever, okay? Okay, now we just did this one, we're going to do this one now, okay? And it's the same thing, okay? But, the K is different, okay?
10:21
The effect that something has on the boiling point is not necessarily the same effect. They're going opposite directions. You're lowering the freezing point and you're raising the boiling point. But, they don't have the same K sub, or Ks, there it is. Same equation, okay, in this case, delta T of fusion
10:44
or freezing is equal to K sub F times the molality. Write that down because you're going to have a problem to do right now.
11:00
So, delta T sub F, freezing or fusion, I don't care what you call it, is K sub F times the molality. Same as before, degrees per molal, do this.
11:28
Everybody should be calculating this. If you just watch me do it, I don't think it's as effective.
11:46
Whichever's bigger is the solute, or the solvent, I mean, sorry. So, we've got, calculate the freezing point of the solution of 5 grams of this and that many grams of this dissolved in 200. This is your solvent right here. Solvent's always the big one.
12:11
And what you don't know is that these are both solids. This is a solid, and this is a solid, okay? And so, this is the only thing that's a liquid. It's the only thing with a vapor pressure.
13:05
And once again, calculate the freezing point of a solution of 5 grams of diphenyl, C12H10, and 7 and a half grams of naphthalene, C10H8 dissolved in 200 grams of benzene.
13:21
It has a freezing point of 5.5. So, similar to water, but it's got a big case of F, okay?
13:52
So, once again, if we, we have to figure out the mole fraction, right? We have to figure out the mole. So, we've got 5 grams divided by 154 grams per mole, plus 7 and a half grams divided by 128.
14:02
So, we've got about .1 moles, or mole owls, no moles, of these two things that we're then putting in to .2 kilograms, okay? So, the molality is about .45.
14:29
Here's that equation again. And you remember what the case of F was.
14:40
I think it was 5.12 degrees per mole owl. So, that's 5.12 times this. Delta T is going to be about 2 degrees, okay? So, delta T is going to be 2 degrees.
15:00
Now, don't forget, I'm not sure what the question was, but if it asks what is the new freezing point, then you have to take whatever that change in temperature was, if it's 2 or 3 degrees, subtract it from 5.5, okay? So, let's see.
15:22
Look at that, okay? So, you have the molality here, you've got this here. Delta T is equal to 2.33. Subtract it from this. How many got 3.17? Good. Okay, now, so folks, on an exam, once again, you have to get the whole answer, all right?
15:42
So, if you had just gotten this, you'd get, maybe this is a six-point question, and I don't know, what do you think Joe said, three or four points? Okay? You know, I, once again, it's simple then to subtract this from that. All of you can do it, but that's the answer.
16:01
So, make sure you read the question. Make sure that you know what is being asked, because I might ask, you know, how many moles of this, how many grams of this, you get it all the way to the end. Now, if you go past it, okay, let's just say there's some calculation where the question is how many grams of, you know,
16:22
sugar, and you get that exact answer, and then you go past that, and you give me actually what the number of moles was of that, and we'll just go ahead and give you full credit for that, okay? Because you worked through it. We'll see. I might take off one point for being a knucklehead.
16:41
Yeah. Okay. Colligative properties, okay? So, what's interesting with these boiling point, freezing point, all these things, is that some things break into two pieces, all right? Look at this. Sodium chloride, NaCl, Na plus, Cl minus, okay?
17:07
So, we have electrolytes, and we have non-electrolytes. A non-electrolyte is something that when you put it into the solution, into the solvent, it doesn't break apart.
17:21
It dissolves like sugar, okay? Sugar, in like granulated sugar, you put it in water, and it disappears, right? It disappears, but it stays exactly as glucose at 180 grams per mole. Sodium chloride breaks into two pieces, sodium chloride.
17:43
We call this an electrolyte because look at this. You've got a negative charge here and a positive charge here and a negative charge here. You put that in salt. If you had a water bath where you had an electrode here and an electrode here, and you measured the potential across it, okay, you're not going to get a lot of electricity going through that water, okay?
18:02
Not nearly as much if you start dumping some salt into it, okay, because then you have all these ions that can carry a current one way or another, okay? So that's what we call this an electrolyte. An electrolyte is something that actually breaks apart. Non-electrolyte is just sugar, okay?
18:20
So, look at this. We have one mole out of this, but we end up with one mole out of this and one mole out of this. We have to consider that, okay? So, colligative properties are properties that depend only on the number of solute particles, okay, and not the nature of the solute particles.
18:41
So, one mole out sodium chloride, two mole outs of ions, right? Because we have one mole out from the chloride and one mole out from the sodium. So, you actually have two moles outs of ions, and what we have is what we call the van Hoff factor,
19:01
and it's actually, yes? Well, it's a, it's a, it's not great, but it's better. Salt water conducts electricity better than water, than pure water, okay? There are other things that conduct even better, but yes. The more salt you put in something,
19:21
the better it conducts electricity. So, this van Hoff, okay, is the actual number of particles, okay? So, it's sort of like the actual number, which is one, you have one of these, let's say, and it breaks into two, oh, sorry, the actual number of particles, sorry, it's the opposite, actual divided by,
19:42
if it weren't dividing into two. So, this would be, for this one, it's going to be two over one, and you get a two for van Hoff for that. So, for non-electrolytes, folks, they don't break apart. You put the sugar in, it stays as sugar, so the van Hoff factor is one, okay?
20:02
NaCl is two. What if you have something that's got three or four things on it, like calcium chloride? You get one calcium that comes off as a plus two, you get two chlorides, so it actually breaks into three pieces, okay?
20:22
So, it's very important. Now, on an exam, folks, I will either say it's an electrolyte or it's a non-electrolyte, and if it's an electrolyte, I would have to tell you that it is completely dissolved. Okay? Assume 100% dissociation, okay?
20:47
So, if I said sodium chloride, you know, is completely dissociated, then the van Hoff factor would be two, okay? Unless I'm asking you to calculate the van Hoff, okay?
21:01
But, in this case, in most cases, where I'm just asking a specific question, then I would have to say that it's completely dissociated. In that case, if you've got calcium chloride, you'd need to know that that goes to three, okay? So, here are just some constants.
21:20
These are just, you don't need to know these. These will be given to you on the exam, but if we look at the freezing point, K sub F, water, 1.86, look at benzene, three times more. So, you can lower the freezing point of benzene by a factor of three with the same amount of, you know,
21:43
solute as you can with water. Look at this one. Sactohexane is huge, okay, and these are the ones for making the boiling point go higher. You notice that these tend to be smaller than these, okay? But, they'll be given. They'll be given to you. Let's just show that they're all different, okay?
22:05
Okay, osmotic pressure, this is another equation you're going to need to know. I kind of think osmotic pressure is pretty cool, okay? You have a semi-permeable membrane. That means that certain things that you go through,
22:22
like look at this, you notice that the red things are too big to go through the holes, okay, too big to go through the holes, but the, in this case, we're going to have this as water. So, here's the water. The water can get through these little holes or channels. The solute can't, okay?
22:44
So, this is sodium chloride or something like this. You've got the electrolytes here, and they can't get this way, okay? But, the solvent can go either direction. And so, what you have is you have this semi-permeable membrane, and what happens is if you have the solvent
23:02
on this side, and then you've got the solution over here, things want to move in this direction, okay? Things can move this way because they're trying to, I'm not sure that we, we haven't talked about it, shall we? Anyway, trust me, they do that.
23:21
So, we can calculate the osmotic pressure, okay? And, the osmotic pressure is going to be dependent on what is the concentration here of the actual solute, okay?
23:41
And, these folks are not very strong, okay? I'll tell you a story now. So, when I was in the fourth grade, I, we grew up on a, like an old McDonald farm, you know, we had chickens
24:02
and pigs and goats and that kind of stuff. But, Renee Marinkovich had an egg farm, and so, she brought in, it turns out that every now and then a chicken lays an egg that doesn't have a shell on it, okay? Anybody ever heard of that?
24:20
Nobody, okay. You have, okay, good. So, what happens is you get that, if you've ever like done a boiled egg, and you start peeling off the shell, sometimes there's like that really, really thin little, almost like a plastic-y rubber, how many of you ever noticed that, you know? Okay. Well, that's what holds the yolk
24:42
and the white and stuff inside the shell, okay? Well, it turns out that every now and then, chickens lay, I don't know why, if it's the same chicken always, or what, but a completely calcium-less egg, okay? And, it's got just a little bit of,
25:02
you can kind of squeeze it, anyway, we got to pass it around in class, it's a big deal, and when you're fourth grade. And, then, our teacher just put it in a thing of water, okay? And, it was not hard, okay? In other words, how many have ever noticed that when you boil an egg, there's usually
25:21
like a little part that is like missing? You ever notice that like on the end, there's like a little dimple, okay? You ever notice that? How many of you have ever, come on, raise your hand, that it's not perfectly shaped like an egg?
25:41
There's like a little, okay, that's because that little membrane, that it's not completely full inside the egg, so you take away, inside the shell, so you take away the shell, and you can kind of squeeze it, okay, it had like maybe a cc or so of volume. Must have freaked her out.
26:01
So, anyway, the, so you could squeeze it, and there was a little bit of volume. So, he puts this in a thing of water. Really? At least somebody's interested. And guess, now don't, no, you shouldn't say really
26:22
after I say this part. And then, after a couple hours, he pulled it out, and it was hard. Thank you. Yeah. Yes, really. And, it was because of this, okay? You had this semi-permeable membrane
26:41
that the water molecules could go through, but the other stuff, the proteins and whatever else was in there, couldn't. And so, it could kind of slowly go through here, and it actually just filled it up to where it was, you know, had water in it. Okay, big deal. So, the story didn't go over very well. But, as a fourth grader, I thought it was pretty cool. But, you can generate this pressure here,
27:02
and that's called the, called the osmotic pressure, and that's what I'm going to expect you to be able to calculate. Now, here's something that I should get a really out of. If I have a closed system, and I've got something with just like pure water, and then I've got something that got pure water and solvent, I mean,
27:20
some stuff in it, some salt, let's say, and this is closed off, the next day, guess what looks like this? This is completely gone, completely gone. Magic. Can I get a really? Yeah. And, that's because, once again, here's a good question.
27:43
Do this. Oh, and never mind. We'll do one in a minute. This is pure, okay, if we go back to something that we did last class, if the vapor pressure of water at room temperature is 20 degree, or is 20 torr, okay,
28:00
pure water at room temperature is 20 torr, and we add some stuff to it, remember it was like P is equal to some chi or X times P zero, okay, and that chi is the mole fraction. So, if we add a whole bunch of salt or something to this, and it turns out that the pressure
28:21
from this has less pressure than this. Okay, this is pure, this is not pure. So, this has a higher vapor pressure, more water molecules jump out of here and just get up here, and then this has lower vapor pressure, they jump into here, you can actually make that happen. Okay. You don't care.
28:41
There was a 60s term that I almost just said, but I swore last night in class, so that's probably not a good idea. Here it is, write it down, you don't care. You'll care on Thursday, folks. So, the vapor, the osmolytic pressure, now folks,
29:06
okay everybody stop, I got to warn you, this is the one time that we use molar, that's a big M, moles per liter, not mole out, don't screw that up, molar, I actually happen
29:24
to like molars a lot easier, there's a lot easier to calculate. Then R and T, now if this is pressure that we're talking about, what R do you think we're going to use? No, 0.08205 liter atmospheres per degree mole,
29:42
that's got pressure in it, okay? So, molarity and an R that has the one that we use with the universal gas constant and PV equals nRT.
30:02
What pressure of what system? Okay, so what we had, this, I've got one, I've got an example, I think the next one, okay, so here's the osmolytic pressure, so you've got something that's one molarity or molarity of one
30:21
and here's the pure solvent, okay? So, which way are things going to flow? The solvent, the solute stuff can't get through that, those holes, so things are always going to go this way and the difference between the level of this and this, so we start off at the same, the difference between here and here is going to be the osmolytic pressure.
30:42
Look at that, that's the osmolytic pressure right there, okay? There it is, okay, sorry about the R there, this is given to me by your, we'll talk about that in a second, but that's what happened, that is the difference,
31:01
the difference right there is the osmolytic pressure and we're calling that pi, okay, do this. So, here's the equation right there,
32:14
how many of you received an e-mail from me last night? How many don't know, raise your hand, it's okay,
32:20
if you don't know you didn't, how many didn't check your e-mail between about 8 o'clock last night and right now? Okay, so I sent you today's notes, okay, because the class, the last night's class that I taught because they've got an exam tomorrow, I'd said that I'd get the notes posted today and they said,
32:43
oh that's too late, so check on your, you know, they haven't, probably haven't been posted on the website, but they should have gone to everybody because I sent it to both classes, check your e-mail a couple times a day, who knows, I might do something crazy and like I said it's going to be an exam or something on Thursday, or say, what?
33:07
Pay attention, okay, so the average osmolytic pressure of seawater, okay, this is one of these wordy, wordy word problems that has way too much stuff in it, okay,
33:22
all this isotonic stuff, so the question is, calculate the molar concentration, molar, moles per liter, aqueous solution of sucrose that is isotonic with seawater, okay, isotonic just means that it's got the same osmolytic pressure, okay, so that means that this value right here is a 30,
33:41
30 atmospheres right there, okay, so 30 atmospheres, we're calculating this, we know what this is and we know what this is, does it get any simpler? No, you just rearrange, you got m on one side, you got π, notice you just take this rt onto this side, over here, so it's going to be π over rt, 30 atmospheres,
34:04
0.8201 liter atmospheres per degree mole times the 298, there it is right there, the molarity that you need to generate 30 atmospheres is 1.23 molar, simple, do we agree?
34:21
Okay, anybody want me to do this again or talk about this? It's very straightforward, but you have to remember folks, it's the only one, the only equation that we'll be using, probably chapter 8 and chapter 9, where we're using molarity, okay, so that's the trick, okay, is molarity,
34:43
it's not a trick, it's just, and that's life, okay, do this,
35:11
last night somebody asked me what intravenous meant, for all you doctor wannabes, it means in your veins,
35:41
and in case you've forgotten, carbon is 12, hydrogen is 1, oxygen is 16, so folks, you've got that right there,
36:48
that's the pressure, okay, you've got the pressure, you've got the temperature, so all you've got to do is figure out the molarity, pretty darn easy, so don't forget, you've got to have it in Kelvin, okay,
37:04
those delta T's were changes, anytime you use a T, it's Kelvin, so we have 310, van Hoft was one because it's a non-electrolyte, so we've got this, I'll let you know what this I is
37:20
in a minute, we haven't talked about that too much, but this would be the van Hoft, which is a 1, and so that's what they've got a 1 here for, but basically you've got π is equal to I over RT, and M is equal to this many atmospheres times the 1 times this divided by that, the molarity is .3, okay,
37:46
so how many got .3? Good, good, good, good, good, how many got the next answer? So the question, once again, was how much glucose, and that's, I would hope on an exam I would ask it a little bit more
38:01
specific, I would say how many grams of glucose, or how many moles of glucose, okay, so this problem goes on, and after you've got this, then there's how much glucose, okay, and you need 54.1 grams, and that's one where, as I said, if I ask for grams, and you only give me moles,
38:22
you'll lose a couple points, if I ask for moles, and you give me grams, and you circle this, you're at the mercy of the TA to actually know that this, you had to have this to get this, that may or may not happen folks, okay, so make sure you read the problem thoroughly, okay,
38:44
got that answer, so I think this is just way cool, okay, so we're talking about reverse osmosis, or osmotic pressure, so if you add more pressure, okay,
39:00
look at it, you have a semi-permeable membrane here, and you put salt water here, look at this, you can actually apply pressure, push this, and you can actually push the water molecules through this, okay, and not the salt, so you can actually make drinkable water with a device like this, okay,
39:23
now the bad news, okay, is that these things generally are a little on the not so strong side, okay, think of that egg that I told you about 20 minutes ago, okay, as I said, it had about 1 cc of space, okay, in it,
39:41
and it took a couple hours to get 1 cc of water to go through that membrane, okay, and it's not something that if you applied a whole lot of pressure to, that it would be able to withstand a lot of pressure, so you can't have one of these things that have some super strong person, you know, do this or stand on it, it would just blow that right out, okay,
40:02
so we can't have a desalination plant off the coast here, and turn salt water into drinkable water in a very easy fashion, it's a very slow process, okay, obviously if they could come up with something that was really good at separating out the salts
40:23
on this side, and on this side you get the fresh water, then a lot of our water problems, at least those of us and countries that live close to the ocean, that would solve a huge problem, but I think this is pretty cool, so I'm going to make you look at it, okay, now, Raoult's Law,
40:42
I love Raoult's Law, there is a Raoult's Law question on the exam, we did Raoult's Law earlier, but that's where we had something like a salt or something that was added to a liquid, it was a one, one of the things had a vapor pressure, the other didn't, okay, now, we got two things,
41:04
two things that got a vapor pressure, okay, so we have benzene, we have toluene, now, mole fraction, mole fraction, I was, I got to the end of the lecture last night, a student came up to me,
41:26
completely confused about mole fraction, okay, so I thought I was doing a great job, and then she completely bummed me out, okay, it's a 60s term,
41:42
so, so let me just spend just a minute or two talking about mole fraction, okay, so, you can't have more than 100% of something, I don't care what these athletes on TV say, they give 110%, you know,
42:04
that just shows how smart they are, okay, I mean, for crying out loud, politicians say it too, I mean, it's ridiculous, you give 100%, no, I've never given 100% at anything I've ever done, I mean, look, I mean, it's probably,
42:24
I mean, it's true, I mean, I studied like a wild man at UCLA, you know, 40, 50, 60 hours a week, but I could have studied another hour, okay, so I wasn't at 100%, so the point is, is that a few of us, I don't care who you are, an Olympian, gave 100%,
42:46
maybe they would die if they did, I don't know, anyway, but you can't give more than 100%, okay, you can't have more than 100%, okay, can I have more than 100% class participation?
43:01
Look at the seats, do you think somebody's going to come in from archaeology and sit in this lecture? When I'm given a lecture, heck no, they would be lost, lost, I mean, not just lost mentally, but lost physically, okay, so 100% is the most, the mole fraction folks can never ever get above one,
43:24
okay, the mole fraction can never get above one, okay, so I asked this young woman who came up to me, who seemed completely confused, I said, okay, look, and there were 15 people in the lecture hall, okay,
43:42
and I said, what is the mole fraction of men in this room? Okay, there were 11 men and there were five women, okay, so 11 men, five women, I said, what's the mole fraction, she said 11, 11, I didn't ask how many men were
44:06
in the room, I said, what is the mole fraction, what is the fraction of men in the room, okay, so let's make it easy on me, let's say that there were 10 people in the room, and there were 7 men and 3 women, I can do that math, okay, it's going to be 7 plus 3 is 10,
44:27
that goes to the denominator, and then however many men you had, in that case, 7, 7 over 10, .7 is the mole fraction of men in the room, okay, .7, I'm going to ask somebody in the front row, you,
44:44
Nancy, what then is the mole fraction of women in that room, .7 for men, what is it for women, .3, yes, when you have two things folks, two things, all you got to do is
45:00
if you know what one of them is, you automatically know the other, if it's .1, the other has to be .9, if that concept is hard for you, I mean I'm not being funny, I'm just saying that you got
45:20
to understand folks, that mole fraction, everything adds up to one, okay, now, so, men and women in this room, the mole fraction is probably about .5 and about .5, okay, maybe, if I said what is the mole
45:47
fraction of, got to be careful here, people wearing sweatshirts, versus people wearing glasses,
46:01
or people wearing glasses, and something else, now if I tell you, if I got three things, and I say okay, the mole fraction of people wearing sweatshirts is .2, then the other two or three things have to add up to .8, but how do I know what fraction those are, okay,
46:23
so if you're given three or four things, coming up with a mole fraction of each of them is not very easy, but two is easy, it's just whatever the mole fraction was of the one, take away from one, does everybody get that, okay,
46:42
you better, it's on the exam tomorrow, on Thursday, so here we have a two component system, we have benzene and we have toluene, this is the mole fraction of benzene, pure benzene, what this tells us is that at some temperature, okay, let's say room temperature,
47:02
benzene has a vapor pressure of about 750 torr, right there, that's when it's pure benzene, 1.0, okay, 1.0, pure benzene, when there's zero benzene,
47:20
then there's zero pressure for benzene, okay, so if I have zero benzene, I have no contribution to the pressure from benzene, if I have 100% benzene, it's all benzene, it's pure and that's the vapor pressure of pure benzene and therefore the vapor pressure of benzene inside this, okay,
47:43
now let's instead say I'm going to go to mole fraction of .2, so it's .2 between benzene and doesn't matter what else, okay, .2, I'm going to ask you, what do you guess or estimate, this guy right here, yeah, what are you going
48:01
to, and that's the guy, what are you going to estimate is the vapor pressure contribution to the system by benzene when we are right here at .2, what do you think? 200, perfect answer, so if you are
48:21
at .2 mole fraction, you just kind of look on here and go, okay, well it's right in this area right here, about 200 torr, okay, if we're at .6, it's about 500, okay, that's how you do this chart, this folks is the mole fraction
48:42
for benzene, okay, there's another one down here that you can't see because it's not here but it should be there, where this is a 0, 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0, it's going to say chi of toluene, so this is where there's no toluene here,
49:03
it's 100% benzene, 0% toluene, then we go this way, this is 100% toluene, 0% benzene, so this is a mole fraction of 1 for toluene and what is its vapor pressure at room temperature, for toluene it's about 300, we got that, 300, okay,
49:26
so, Amne, at .4 mole fraction of, no sorry, this is .6 mole fraction for toluene, what would be the contribution to pressure for toluene, 200,
49:41
right, okay, and the guy next to her, what, so you're right Amne, 200, for you, now we're looking at what is, this was at .6, okay, for toluene, the rest has to be .4, so now what is the contribution of a mole fraction of .4 from benzene, okay, so you add them
50:04
up, 200 plus 300 is 500, watch this, right there, that line folks is the sum of the two, that's how this thing works, okay, simple, okay,
50:20
so all you're doing is multiplying the pure by the mole fraction, okay, and that's what all this is going to say, right there, okay, P total is equal to the pressure from benzene, which is going to be the chi times the pure plus the
50:41
toluene, which is going to be the chi times the pure, okay, and if it's an ideal system, then that line is straight, sometimes it looks like this and like this if it's not ideal, I like ideal things, I live in an ideal world, okay, which makes it easier for you folks, so, once again, there's the equation right there, P total, chi A plus,
51:03
chi AP of the pure plus chi B of the pure B, you got that written down, because I think we got a problem coming up, do it, okay,
53:16
so folks, you look at this question,
53:20
and the first thing I want you to do is to just estimate what is the pressure, okay, what's the most the pressure could absolutely be, 94.6 torr, okay, if you had pure benzene, you'd have 94.6 torr,
53:41
if you have pure toluene, you've got 29 torr, okay, you can never get higher than the highest one, okay, if you go back to that chart before, you'll see that's possible, okay, it's done, so we got almost 100 and we got 30, then you look at, you say, okay, which one has the highest percentage,
54:01
which has the bigger mole fraction, the toluene or the benzene, toluene, okay, so that means there's more of this, right, a bigger number times this, okay, so that means that the answer you're going to get is going to be closer to 29 than it is to 94, so the answer means it's going to be, that tells me the answer should be 50-ish, maybe 45
54:24
to 55 or 60, okay, just as an estimate, okay, I know it's got to be between these two, so, and look at this, percent, folks, how do you convert percent to mole fraction? You divide by 100, the mole fraction
54:40
of toluene is .666666, so what is the mole fraction of benzene, okay, all you got to do is subtract .6666 from 1, okay, so it's just going to be .6666 times this plus .3333
55:07
times this, add them up, you get the total pressure, let's see what we get, there it is right there, okay, 51, did we get that, how many got that, okay, good, now,
55:24
guess what folks, I'm old, I'm cranky, and by the way, for those who come to office hours, I got to call in at noon today to see if I've got jury duty today at 1 o'clock, so if I'm not in a bad enough mood as it is,
55:41
I might have to go to jury duty at 1 o'clock, boy, pity the poor fool whose case I get on, yeah, book him, okay, so, I'm not going to give you what the mole fraction is, why would I do that, okay, instead I might say, well,
56:03
you've got this many grams of benzene, okay, and this many grams of toluene, right, that would make it a little tougher, but still, you'd say, okay, I got to divide the number of, let's do that, it's a good question, too late for the exam, but it's similar, okay, look at this, let's go back to this, right there, okay, everything stays the same,
56:25
except this time, I'm going to tell you that you have 50 grams of benzene and 50 grams of toluene, okay, 50 grams of, I'll write that down, 50 grams of benzene, 50 grams of toluene, the molecular formula
56:40
for benzene is C6H6, C6, I bit myself, I didn't say sex, I said six, let me start over, C6H6, toluene, C7H8,
57:04
I said eight, not hate, for all you haters, now I want to know what is the pressure, okay, so I've given you 50-50, benzene C6H6, toluene C7H8, okay,
57:23
what is the pressure, so let me help you, for those of you who are stumped, you've got to come over the mole fraction, how many moles of benzene in 50 grams of benzene,
57:42
how many moles of toluene in 50 grams of toluene, I'm asking a question, it's not a hypothetical question, Jessica, what's the answer, how many moles of benzene, you got that yet, okay, who's got how many moles of benzene, 0.6, 0.64, is that right, okay, so let's just,
58:06
okay, 0.64 moles of benzene, so I can tell you right now, since the molecular weight of toluene is bigger, toluene is going to be right around .5, what is the moles of toluene, what do you get,
58:23
okay, so .54, okay, so .54 moles of one, .64 moles of the other, so what do you do, you add them up, .64 plus .54 equals, you know, 1.08, and then you just say okay, 1.08,
58:46
toluene was .64, so it's going to be .64 over 1.08, you got a mole fraction of, you know, .60 or something like that, what is the answer, how about you, I'm counting you two guys, .1, okay, how many,
59:06
so we're going to add .54 plus .64, so the mole fraction of benzene is what, .54, okay, .54, and therefore,
59:21
the mole fraction of toluene must be .46, multiplied by these two things, .54 times that, .46 times this, add them up, and you come up with a vapor pressure, a total vapor pressure, what's the answer? Golly guy, okay, I got to have a new go-to person, yes?
59:45
64.4, looks, I mean at least it's between these two, so does everybody see how we did that? So this time, folks, I actually gave you a mass, and the mass, you figure out how many moles, okay?
01:00:01
Hold on a second. I've got to check my schedule here because I just came up with a brilliant, a brilliant other question, but I don't know if I've got time to do it. I don't. Okay. Too bad. Brilliant's passed. Okay. So, okay, now, do this one. This one not so
01:00:27
easy. For those of you who remember algebra, remember eighth grade math, it's easy, but unfortunately, many of you are going to have forgotten it. So, in this case, folks, you've
01:01:57
got something that's got a pure vapor pressure of 125, you've got another one that's got
01:02:01
a pure vapor pressure of 165, one of 125, and I tell you that the total is equal to this. A little bit different. A little bit tougher. Simple. Simple. And after we're done, you're going to go, oh, gosh, I can't believe I didn't get this right.
01:02:28
What's the answer? What is it? Say it really loud. Point two, what are you guys calculating?
01:02:42
So I guess I should see what the question was. What is the mole fraction of hexane? Point two. I believe you're right. So, for those who forgot their, and it's okay to have forgotten something, like I said, we went over this earlier today that, look,
01:03:00
here's what, here's the equation. I gave you 133 torr. That's not going to be equal to the mole fraction of benzene times 165 torr, which was given, plus the mole fraction of toluene times 125 torr. So you know the answer, okay, this and this, if you had all of this, if this was a one, this would be 165 over here. If this, then you
01:03:23
would have, if this was a one here, then this would be 125. So you got 133. We know that the mole fraction of benzene plus the mole fraction toluene equals one, so benzene mole fraction is equal to this minus this. So this is what you do, folks. Remember
01:03:41
the old, I say, I think eighth grade I remember this, where you say, okay, well I'm going to assign one thing as an X, and the other one minus X. You got two things, that works. If you got three things, it doesn't work. Okay? So, go to here, you set it up, this is what you got. I gave you, I said the pressure of this mixture
01:04:06
is 133 torr, so it's going to be X times 165, okay, and then one minus X times 125. So if we multiply that all through, I, if I take a 125 torr times one, I get
01:04:22
a 125. So I move that 125 to the other side, so I got 133 torr minus 125, is equal to, and here I've got an X times 165, and minus X 125, so I got that, so I can subtract that and I get 40X, subtract this, I got 8 torr, so X is equal
01:04:42
to 8 over 40, which is equal to .2. Okay? Since we know that benzene is blah blah blah, so we know that this is 0.2, and therefore timing has to be 0.8. So, you got it in your notes, everybody was sent to you last night, be sure you go over this folks,
01:05:02
because guess what's on the exam? I'm not giving you what the mole fraction is, you got to do this. Yeah. You get it? Okay. All right, so, we're not even close to being done, so don't even think of backing up. Okay. I already said
01:05:24
that. So, these are the equations, this is just a little overview, these are the equations that I told you you needed to know. Vapor pressure lowering, this is when you have only one component that has a vapor pressure, it's like water and
01:05:42
sugar. Sugar has none. So, you have the mole fraction times the purer is equal to the pressure. Boiling point elevation, this is for non-electrolytes. Delta TB is equal to KBM, boiling point, freezing point depression, same thing, and osmotic pressure. Okay? You've gotten all these, I'm just
01:06:02
reminding you. Okay? Now, for electrolytes, they all have an I in them, folks. Okay? Because electrolytes break into pieces. So, it's the same equation, it's
01:06:22
just that you've got I. You can always use I for all, you don't have to remember the other stuff. Just remember this. But just remember that an, a non-electrolyte, I is equal to one. Okay? For sugar, I is one. So, you can just do a one there, times this, times this, gives you that, no problem. So, this is how it all works. Now, vapor pressure lowering. Okay?
01:06:46
Look, I've got an I and I've got a question mark right there. What I'm saying is, is that how do we need to have an I in this? Okay? The answer is sort of. It's, it's implied because of that chi right
01:07:06
there, okay? So, do this. I'm going to go to the next slide.
01:08:10
You just keep working on it, don't cheat. Okay, let's go over this.
01:09:17
Once again, folks, it's all mole fraction. Everything's a mole fraction, okay?
01:09:22
So, first question. And this seemed to throw a lot of people last night. How many, if I give you one liter of water, one liter of water, okay, I don't see a liter bottle, but I got a half a liter over here, okay? Let's just assume this is one liter.
01:09:40
If I give you one liter of water, at four degrees, it weighs one kilogram, okay? How many moles of water in my one liter of water? How many moles of water in my one liter of water? Well, there's a thousand grams in a liter, molecular weight of water is 18, so a thousand
01:10:02
by 18 is 55.5. So, in a liter of water, or one kilogram, there are 55.5 moles of water, okay? So that's, to do this problem, we have to know how many moles, okay? In a two mole aisle solution of sodium chloride,
01:10:24
okay, two mole aisle means we got 2.2, but the sodium breaks into two pieces. So, that two right there, folks, is sort of, is the I, okay? So it's implied when we use mole fractions, so you don't actually have an I in that equation
01:10:41
because that's what χ is, okay? So look, we've got total number of particles from sodium chloride in a 2.2 mole aisle solution is going to be 4.4 moles, okay? So we have 4.4 moles of sodium chloride, we just now say, okay, well, I got a, for
01:11:08
the mole fraction, remember, it's just the two together, is in the denominator, so it's 4.4 from this many moles, 5.5 from that many moles, divided with the 4.4 in the numerator, so we got this is the mole fraction of sodium chloride in that solution.
01:11:28
Okay? We then multiply that times the value we were getting of 1754, and that is the decrease
01:11:41
in the vapor pressure, okay? How many got this right? How many would have gotten it right if I gave you more time? Okay, that's better. Now, so what's the problem with this? Do we, yes? Okay, because it was given,
01:12:16
you've got 2.2 mole out, right? The definition is that you've got 2.2 moles per kilogram.
01:12:26
Kilogram of water. That's the definition, okay? Now it seems simple, right? So now you got that, all right, so that's where the 1000 grams came from, okay?
01:12:40
Now, this is how much the boiling point was lowered, okay? I would have preferred a question to say what is the new boiling point, okay? In that case, instead of multiplying that pressure times the little mole fraction, you would multiply it by whatever one minus
01:13:04
this is. So let's try that right now. Do one minus that number, you get .92 something. What do you get? .926. Now multiply .926 times 1754, and you're going to get a number of
01:13:25
about 16. 16 torr. So the vapor pressure of water is now going to be 16 torr. So the way the question before was asked is what is the decrease in the vapor pressure of water as opposed to what is the vapor pressure of the water, okay? So two different
01:13:45
questions. Okay, study, study, study, folks. I love Clausius-Clapeyron, I love Routh's law and Henry's law.