 The bad news that the cost of going to UC is going up. I thought I'd just tell you what I would do if I were in charge. And when I present what I would do, you'll see why I'm not in charge. If I were in charge, it would be free. But if you weren't serious, you'd be gone. No repeats. You flunk one course. Cyanara. Because if it's free, there are going to be a lot of people who are willing to take your shoes. So you don't goof around. You don't march around. You don't do anything except work. And you try to improve yourself as much as you possibly can. And then, after you graduate, if you go to graduate or professional school, we defer things. But after you graduate, we take 5% of what you earn for the next 10 years. If I don't teach you anything worthwhile, and you're a barista at Starbucks, I don't get paid off. But if I teach you something incredibly valuable, and you get a high-paying job, then I get rewarded for doing that. On the other hand, if you take 4 years of college and then you get sick or hit by a car, and you're on disability, you aren't on the hook for 50,000 bucks. But now you can't possibly pay back. If you don't have the stress, you have an opportunity, everyone can go. But if you don't work, you're out of there. That's how I would do it. We'd have to settle on the percentage. We'd have to make the numbers work. But it could be done. Okay, I keep hearing on the news all these people dying. And what's getting alarming is that they aren't that much older than I am. So it's starting to become sort of a constant drumbeat. Don and Summer died, and so and so died. The question is, did they do something wrong, or were they unlucky, or some combination of both? The answer is, you usually make your own luck. You remember the ancients saying, Man sana in cook pro sana, a sound mind and a sound body. That's the Aristotelian ideal. And that's what you should strive for. And you shouldn't assume that that's going to be easy. No one said easy. Adversity is your friend. What makes you tougher and makes you have the ability to withstand all the knocks that you're going to get in life. You don't want things too easy. Maybe that's why the rich movie stars and rock stars don't live long. Things are too easy and they're unmotivated to do anything. Without the motivation, you don't do anything, and then you die. People who retire early die quicker. They think, yeah, great, I can now retire early. Statistically, they die much quicker than people who keep working. That's kind of the same thing. Let's have a look. I just had to inject a little bit about something that concerns me. I keep seeing on these clips, clean natural gas. And I'm sure you all think it's probably a positive opinion of it. I don't know. You may have forgotten the San Bruno blow up that leveled all those houses. But that doesn't happen that often. And there is a lot of natural gas that can be obtained by unconventional methods. And I'd just like to have a look. The method that they're using all over the United States now is called hydraulic fracturing. I'll tell you a little bit about it. You access so-called shale gas. And boy, is it being carried out at huge scale. Many people in the United States do not own the mineral rights to their property. You own the land on top. But if I discover gold under your house, I can drill in from the side and mine it. Because you do not own the mineral rights. I didn't sell you that. And that's very important because most people don't read the fine print on what they do or don't own. I don't know why that's white. That's a new one. Well, let's hope it doesn't continue. Air pollution, groundwater pollution, and possibly earthquakes are concerned. They've had swarms of earthquakes in Oklahoma where they didn't have any before. And the methane that we get is very useful in industrial processes for heat. They're now using this gas to refine oil. They can refine the oil so cheaply into gasoline that they can afford then to ship it in ships. The gasoline to Mexico and put the Mexican refineries out of business. So we're shipping gasoline down there because the price is higher. That raises our price, by the way. And then also to generate electricity, unless San Onofre comes online, the AES natural gas peaker plant out in Huntington Beach is going to be fired up again. And then we'll start having the brown haze and various things that we have avoided while that's been off. If everyone switches on the air in the summer, the grid will go down unless you have enough power. Air conditioning takes a trillion watts. The price has fallen and we have jobs. Jobs for the boys. And the jobs don't require a great deal of education. So they could be ideal for certain sectors. You have to be careful if you're doing a job that you're doing something constructive and not destructive. And sometimes it's hard to tell. The gas companies pay off farmers. Farming's kind of in a slump some years. Some guy comes along and says, look, we'll pay 100k cash. All you have to do is let us set up this little, little rig here. We'll drill way down. We'll get the gas. We'll take off. Everything will be as it was, except you'll be richer. And of course, if you don't own the mineral rights, they just come along and set up a rig. There's a guy in Colorado who has this huge, noisy gas drilling rig 150 feet from his house. It's producing incredible air pollution. I'll get to that in a minute. His eyes itch. Feels like somebody went down his sternum with a toilet brush. Worries about the health of his kids. The reason why it's 150 feet away is because the law was written about 100 years ago. And they figured that if an oil derrick fell over 150 feet away, it wouldn't hit your house. The law's still on the books. And so there you go. The scale is enormous. I'll give you a little map in a minute. But it's millions and millions of gallons of water, thousands of feet of drilling, and all over the place. It's a big boom. So then if, if is natural gas our energy panacea, even if there's a lot of it, if I'm a diabetic it doesn't matter if I have a thousand chocolate cakes. Maybe not. So here's an article. One thing you should do is you should go to the library and you should learn how to use a proper search engine like PubMed or ISI Web of Science or these various search engines. And you should, you should find topics that interest you and then find articles written in refereed journals. Not a blog. A refereed journal. Somebody else who's an expert read the manuscript and said, yeah, there may be some problems with it, but or you may want to do this experiment and then we'll let you publish it, etc. and read those and if you can't understand them then you know you need to learn a lot more. When you first start out you won't be able to understand a thing about the article. It'll have notation, jargon, abbreviations, etc. But gradually as you read more of them you'll start to come up to speed and you'll be able to educate yourself then. And that's really a huge benefit of the access, the electronic access that we have. And of course books are not half bad either and there are plenty of them in the Science Library. Here's an article that came out in 2011. Methane and the greenhouse gas footprint of natural gas from shale formations. If you're interested in what's going on then this is an interesting article. And they say, okay, we evaluate the greenhouse gas footprint of natural gas obtained by high volume hydraulic fracturing from shale formations focusing on methane emissions. I've blown this up a little so it's easier to read. Methane itself, not CO2, but methane itself is a powerful greenhouse gas with a global warming potential that is far greater than that of carbon dioxide particularly over the time horizon of the first few decades following emission. Methane contributes substantially to the greenhouse gas footprint of shale gas on shorter timescales dominating it on a 20 year time horizon. The footprint for shale gas is greater than that for conventional gas or oil when viewed on any time horizon, but particularly over 20 years. And here's the bad part. Compared to coal, that's the worst of the worst. The footprint of shale gas is at least 20% greater and perhaps more than twice as great on the 20 year time horizon. And it's comparable when compared over 100 years. The problem is, as I've mentioned several times why chemists don't like to work with gases, is gases always leak. No matter what you do, you have leaks. And if you're bringing up millions and millions of cubic feet of natural gas all of which you're going to burn by the way into CO2 anyhow which isn't a good idea, but let's leave that out. And a few percent leak. And it's 20 times more potent than the CO2 you produce from it. Then you've doubled your greenhouse gas footprint. In other words, you're going to autoclave the whole planet by doing that. And here's a graph from this paper, the 20 year time horizon. They have a low estimate, grams of carbon per megajoule of energy. A high estimate depends how much leaks and a lot of stuff. And this is the methane, the purple is the huge part. This is the CO2 after you burn it. And this is indirect CO2. Indirect CO2 is, last time I checked when you set up a drilling rig you have to power it somehow. While if you power it with diesel, you're creating a ton of CO2. And it takes a lot of muscle to drill down 8,000 feet and then pump in billions of gallons of water to do the hydraulic fracturing. Let's have a look. This is what they do. They start up here, then they come down. And then they've got tricky technology now. This is why it's unconventional so they can turn the corner and they can drill in to this big layer of dark looking Marcellus shale that has a lot of gas trapped in it in tiny pores. Then they set off some high explosives. Usually they don't mention that, but that's pretty much part of mining last time I checked. There's a lot of explosions that go on. And then they pump down a ton of water and other stuff. And the other stuff pollutes the water and the water gets polluted here as well because the reason this is shale is that this is an ancient marine formation and so it's got a ton of salt in it and other things. And when the water comes back up it's polluted. You can't drink it, you can't use it for farming, you can't do anything with it, you have to treat it. And that treatment is going to cost energy and it could be a lot. In fact you could come out in the hole if you aren't careful. This is what a real rig looks like. They're big, they're loud and they wreck the air for a long ways around because when you have methane leak out you get a lot of ozone formation and that's what makes your eyes itch and your throat burn and so forth. That's the air pollution on a very bad day when it looks grayish and you can't see anything, that's ozone in the troposphere. That's known to be bad. There are organisms I think that can live on hydrogen cyanide but nothing can live on ozone. Ozone kills everything. So they drill 8,000 feet down, lots of pipes going down there, then 11,000 feet sideways and then millions of gallons of what they call frack fluid which has things like hydrochloric acid and all sorts of things in it. And here are the trucks delivering all the stuff and all the truck drivers have jobs and here they've cleared this area, this used to be green like this and now it looks like that. There's an environmental consequence for doing that because you have to build all these roads into everywhere, wreck the forest as you go and then this is... Each little dot here like smallpox is a well in West Virginia but these are all hitting this gigantic ancient shale deposit that's underground that has a lot of gas in it. This is just West Virginia and there's Pennsylvania and they're arguing about New York, there's Colorado, there's Montana, all these other places because now they know how to prospect for these shale formations and when they find one, if they have the mineral rights, they buy them and then they drill and if the government owns the mineral rights and the government's broke, the government may sell it because it's worth some money. That's how things tend to go. Okay, let's do some review problems. Practice problem 47, very topical. Let's purify some back frack. Back frack is the water that comes bubbling back out after you've pumped it down there with all those chemicals plus it's dissolved whatever happens to be down there which you may not know exactly until it comes back up what it is. I think at first they were throwing it in the rivers and then people objected to that because that was having a very big environmental impact. Then the mining company said, fine, what we'll do is we'll divert the frack water to the municipal water treatment plants and that drove the municipal water treatment guys crazy because the last step when you're treating wastewater usually is you chlorinate the water to make sure it doesn't have any bacteria especially if it's from sewage and things like that and normally that's okay, no big deal but this has some bromide sometimes from the shale itself and if you treat bromide with chlorine you get bromine and then that reacts with various things that are in the water and you can get methyl bromide methyl bromide is just what they've outlawed as a fumigant for strawberries because it has a high vapor pressure and it is carcinogenic as all get out it's a DNA methylation agent it's known bad news you don't want that in the water that you're going to be drinking and growing stuff with so that's out and so now the proposal, at least I read it on one brochure the proposal is well we'll purify it by RO we'll use reverse osmosis well let's figure out then how much energy that takes because we know a little bit about osmotic pressure and reverse osmosis let's just take a case study here and figure out what it would take okay so I'm assuming that it's got 3.5% sodium chloride this is on average and 0.2% sodium bromide it's got a lot of other stuff arsenic, barium things that chemists don't like to deal with but they can be taken out if you want to work you can clean things up it's just like cleaning up your room you have to want to do it and it takes work and there are levels of clean if you want it to be like an operating theater it's a lot more work than if you just want it to look good because somebody's dropping by for a cup of tea well we've got our osmotic pressure equation pi for a fancy p equals i that just keeps track of how many moles of particles times the concentration times r times t and we'll assume two moles of ions each from sodium chloride and sodium bromide it's not quite two because remember these charged particles tend to try to stick together a little bit and so they aren't totally independent and the osmotic pressure assumes they're totally independent and let's assume 300 kelvin depending where they're doing it if they're doing it in the summer that's going to be quite accurate okay three and a half weight percent there are 35 grams of sodium chloride and two grams of sodium bromide per kilogram of solution which is nearly a liter of solution so we'll assume it is the concentrations thus are approximately because we need the molar mass we've got 35 grams per liter times one mole 58.44 grams for sodium chloride that's .6 molar I think we did that with seawater earlier and then we've got sodium bromide two grams and then that's .019 molar the total number of particles or ions is then two times the sum of these because they're both producing two moles of ions when one mole of salt dissolves and therefore it's 1.24 molar and then I just put this in put in R, make sure all the units go away and I find the osmotic pressure is 30 and a half atmospheres that means I've got to push on the water with at least that much pressure to get it to go back so I can overcome the tendency of the fresh water to rush into the salt water and push it back the other way and get fresh water out of course I have to have a suitable semipermeable membrane and that has to not tear or then all my polluted water comes through and it has to not clog or else I can't jam anything through and then I need a huge pump it's like pumping up a bike tire as you start pumping and the tire gets full it gets harder and harder to pump and you notice your arms get tired and there's an energy cost to doing that let's have a look then at what that might be though the 30.5 is the minimum pressure we must apply and let's just use that minimum pressure and let's just force 100 million gallons of water through at that pressure the minimum we need the volume of 100 million gallons in liters 378.5 million liters and then let's just estimate just using p times v so much pressure so much volume going through pv is an energy unit and we can convert it to joules by taking the ratio of the listed values of the gas constant that's kind of a handy way to convert from liter atmospheres to joules just use the ratio of the gas constant 30.5 atmospheres I have 378 million liters the ratio of 8.314 to .082 I get 1.2 times 10 to the 12 joules that's 1.2 trillion if we had a 10 megawatt reverse osmosis system it would have to run for 120,000 seconds or about 1.25 days this is just very very very crude analysis we can do better because we can actually look up what some of the pros on reverse osmosis have said and the best estimate that I got reading the most recent literature is that it takes 5.6 kilowatt hours to purify a cubic meter for seawater if we use that 100 million gallons is about 378,000 cubic meters and so we'll need to purify just 100 million gallons and there's a lot more water involved than that believe me we need 2 million kilowatt hours of electricity which has to come from somewhere presumably by burning the gas we've just fracked so we're going round and round in a circle and a lot of stuff's getting used up yes, sure this one? yes because when sodium chloride dissolves I get Na plus and Cl minus remember, colligative properties depend on the number of particles but not their type just the total number of particles in there that's what dictates it therefore if I have a mixture of things I just have to figure out the total molarity of all the particles and that's what I need to know to figure out the freezing point depression the boiling point elevation the osmotic pressure I don't care what they are I just care how much yes well I assumed 300 Kelvin but I had to assume a temperature for the purpose of this calculation if I assume a high temperature it's going to be a lot more work and then on a hot day it may be more than 300 Kelvin the amount of work I'm going to have to put is going to depend on how hot it is if it's a hot day in Tennessee or something it might be a good day to not run it for example or I might want to run it in the winter so anyway 5.6 kilowatt hours 2 million kilowatt hours and even at 7 cents a kilowatt hour if you're a big user you might get that rate I don't know that's going to add up I figured I had a 10 megawatt machine and that's 10 million joules per second and I know how many joules of energy I need to push it all through and so I divide the two and I get the number of seconds and it came out to be about 120,000 in round numbers yes no it's two and I add up the total molarity of sodium bromide and sodium chloride first and then each of them produces two moles of ions sodium chloride sodium bromide two each okay so I added up the total concentration and then multiplied by two if I have a salt like calcium chloride that produces three moles of ions then what I have to do is set that aside figure out how many moles of calcium chloride are there and then multiply that by three and then add it in to the total the total dissolved solids as they call it in these waters is very high some of them come out like the great salt lake in other words the chloride is the maximum amount of chloride you can dissolve in water because these are dried out ocean deposits they could have tons of salt in there and in actual fact the water this polluted water is so full of other stuff sediment particles of mud stuff that's a nightmare for a reverse osmosis system because particles of mud and clay are just what you don't want with your nice semipermeable membrane because they just clog the membrane and that's it you're out of luck no water goes through and now you're sitting there oh well let's change the membrane so you have to first have a settling tank you have to let the sediment settle you have to make sure and then you have to make sure that your membrane is not letting through any other nasty guys maybe it keeps out sodium and chloride and bromide but lets through something else because it wasn't designed with that in mind so you have to check it and then you have to replace the membranes and you have to put a bunch of guys on it and they have to watch it they have to test the water that comes out to make sure it's okay and all that costs money and it could be a lot of money so the tendency will be to not do any of it because if it costs money and I don't have to do it there's no law that says I have to do it I don't practice problem 48 in this problem we'll make sure we can keep fracking in Montana in the winter this was actually another proposed solution I know what we'll do with all the salty water we'll put it in some big you know basin and we'll let it dry and then we'll scoop up all the salt and we'll salt all the roads in the eastern U.S. in the winter time with it and de-ice the roads and we'll be doing great public service unfortunately there's arsenic and other contaminants in there that they aren't going to let you just spray around everywhere so that they get into everybody's crop and everybody's well water and everything else you're still going to have to clean it up but anyway here we have a problem the cryoscopic constant for water is 1.86 degrees per molal suppose that a stretch of road in Montana is 70 feet wide and 10 miles long and has a one inch thick layer of ice on it if the ambient temperature is 20 degrees Fahrenheit and boy does it get colder than that up there I remember one winter in Utah we laughed every day because every day the coldest place in the inner mountain west on the on the weather was big tiny Wyoming and most of the winter it was never above zero Fahrenheit it was minus something and that's cold I don't know if you've ever been in minus five degrees Fahrenheit but if you aren't dressed for it you're in immediate trouble if you come out in your bathrobe to get the newspaper and the door swing shut you might have an instant panic if the door locked and you're living in the middle of nowhere it's that serious it's that cold you can die of exposure but let's assume it's 20 Fahrenheit the question is I'm in charge and I need to know at the start of the day the guy calls me up with the truck he says how many 50 pound bags of salt do I need today boss I know what the job is I know how much snow fell I have historical records of what happens with the roads and I know that if I leave the roads icy we're going to have a lot of accidents and a lot of misery so I've got to de-ice the roads how many 50 pound bags of salt should the trucks use spreading it evenly to make sure the road is de-iced but without using excess salt because salt is very bad it kills all the plants nearby I don't want to use more than I need and then there are all these conversion units 1 degree C is 1.8 degrees F 1 mile is 50 5,280 feet 1 inch is 2.54 centimeters 1 kilogram is 2.2 pounds and the density of ice is 0.9168 grams per centimeter this is a great problem let's figure out how we're going to do it well we have to depress the freezing point which is normally for pure water 32 Fahrenheit we have to depress the freezing point to 20 Fahrenheit if we depress the freezing point below 20 that means the ice melts and that's what we want it melts and it just runs off the road and we know what the expression is for freezing point depression it's delta T which is always listed as a positive number because we always know the freezing point goes down so we're saying delta T is some positive number because molality is positive and the cryoscopic constant is positive but we know that this positive is how far down it went in temperature because it always depresses the delta T we need well 12 degrees Fahrenheit that's 32 minus 20 and then convert to Celsius we need 6.67 degrees Celsius and therefore based on our freezing point depression formula we know how many moles of particles we need the molality of particles we need is the freezing point depression we want divided by the cryoscopic constant 6.67 divided by 1.86 degrees C goes away molal to the minus 1 is underneath so it's molal so we need 3.584 molal moles per kilogram of particles that means we need half as much salt per kilogram of water and here I'm going to leave you something to do over the weekend which is to finish this problem I'll tell you how to finish it but I will not tell you the answer one second here's how we finish it we know the density of ice we know the volume of ice we've got 1 inch 70 feet 10 miles convert that to kilograms of ice volume times density so figure out how much the volume of ice on that road is in cubic centimeters by converting all the units and not screwing it up and then multiply that by 0.9168 to figure out how many grams of ice are on the road and then divide by a thousand to get the number of kilograms of ice on the road then you know for each kilogram of ice you need 1.792 moles of sodium chloride you know the molar mass of sodium chloride so you know how many grams of sodium chloride you need you back convert that into pounds because the guy driving the truck if you tell him what it is in grams he's lost and then you divide by 50 and say look Joe load up a thousand bags over and out and that's what they do and if you get it wrong if you don't get the factor of 2 you put on twice as much salt as you need that costs you a ton of money and wrecks the environment and if you get it wrong and don't put on enough they drive and waste all that diesel fuel spraying the solution out the salting the road and then it still has it so it's important to get it right okay yes can I repeat all that guess what it's going to be on film and I promise you that we'll have all the lectures up pronto so just play it back okay play it back and then go through it yes because of I yes because I get 2 moles of particles from one mole of sodium chloride and so I don't need as much sodium chloride as because I'm lucky I get twice as much freezing point depression with sodium chloride okay and be prepared to solve something like this on next Tuesday okay just a fun problem converting units fiddling around and actually getting a practical answer yes well we have the entire class to do the midterm yeah pretty much as soon as we hand things out pretty much we'll have the entire class we'll try to hand things out as fast as we can and you can work like crazy yes yes it will be I don't know how much more but it'll yeah yeah I can't hear you the website for the lecture video the first ones are on our class website go down to the bottom click and you can find and this will be whatever lecture it is I think this is 12 okay you want to play this one back in particular okay let's press on practice problem 49 aha what is this one benzene benzene boy there's been a long history of things like benzene benzene used to be used as a solvent in organic chemistry labs like crazy everybody used it except benzene well it's known that benzene is poisonous but benzene is also a class A carcinogen and one day a crate of benzene came in and it was marked different than before it was just benzene analytical grade ready to roll this one was brightly colored like if you don't pay your power bill and it said all these hazardous warnings and I thought it would have been nice to know that back then and there's a moral to that story if the science hasn't been done you're on your own it could be hazardous or not nobody knows yet and therefore the wisest thing is to be cautious don't expose yourself to all kinds of new things just because they're new if there's no evidence about what they may or may not do you have to be kind of kind of cautious I'm still here though so probably wasn't that bad I also washed my hands with chloroform one time another class A carcinogen because I had something nasty on my hands which was even worse and it was bugging me because it was staining my skin bright yellow and I thought that's probably not good I know get it off with chloroform you could never do that these days either that was a very long time ago benzene here in skeletal formation has a carbon and a hydrogen at each position so it's C6H6 and I've drawn it here as alternating single and double bonds but it in fact is a perfect hexagon so it can't possibly be single and double alternating or it would be distorted so the bonds swap around as you may know that's called resonance and here we have a list of all the mean bond enthalpy's for a C H bond 412 for a C C single bond 348 kilojoules per mole C C double bond 614 CO double bond almost 800 O O double bond in oxygen 495 and an OH single bond 463 and with this table here I can work out the enthalpy of combustion of benzene I can estimate it first we have to balance the complete combustion reaction I have 6 carbons therefore the first I always write CO2 and H2O for a complete combustion I have 6 carbons and that means I got to have a 6 there I have 6 hydrogens H this is the only thing with hydrogen so I need 3 of these guys and then all I do is carefully count up the oxygen which won't matter for the combustion reaction enthalpy because oxygen has well actually I take that all back this matters a lot because we need to know how many oxygen bonds we're breaking because we aren't doing it by formation I've got 12 oxygens here plus 3 that's 15 this is molecular oxygen so I need 15 halves the next thing we have to do is we have to count and boy you've got to be careful if you're under pressure because if you miscount you get it wrong you can know exactly how to do it but if you miscount or you flub it with the calculator you just get it wrong anyway still wrong we count all the bonds and the reactants and products for benzene those are the single lines 3 carbon-carbon double bonds those are the double lines and then we've got 6 hydrogens around the ring so that's 6 carbon-hydrogen single bonds for oxygen we've got 7.5 we're just using the numbers 7.5 00 double bonds for carbon dioxide we've got 6 of them but each has 2 CO double bonds again we've got to count the bonds so that's 12 CO double bonds and for water we've got 2 OH single bonds but we've got 3 of them so we've got 6 OH bonds and just as an aside chemists often write notation of the form AXN like SO4 or PO4 or CLO4 NO3 there's lots of things like that whenever it's written like that AXN it means that all the X's are independently stuck onto the A like the spokes of a bicycle into the hub and that's how you can count the bonds if you're just given the formula if it's not written like that it still may be like that H2O for historical reasons we don't write OH2 that would be consistent but we're so used to calling it H2O that we keep it in that order but that's got an H and H and then the oxygen and if you don't know how they're bonded you can't count the number of bonds if you just have a formula and you don't know who's bonded to whom you can't count the number of bonds and so you can't get it done so you have to know the structure to be able to count alright let's then take these and let's count them up I don't think it's too bad let's break all the reactant bonds we got three carbon single bonds three carbon double bonds six carbon hydrogen single bonds and seven and a half 00 double bonds and that turns out that up to quite a lot 9,070.5 kilojoules per mole and then let's take all the energy to break the product bonds we've got 12 carbon oxygen double bonds that's 12 times 799 plus 6 hydrogen hydrogen oxygen single bonds 6 times 463 that's even bigger 12,366 we're making the products though we aren't breaking the products into atoms what we're doing conceptually is we're breaking the reactants into atoms and then we're reassembling the atoms in another way like tinkered toys into the products therefore we don't want this plus energy to make the products we get this energy back when we make them and therefore the delta H of combustion is 9,070.5 minus the 12 366 and that's minus 3,295.5 kilojoules per mole that's our estimate I looked in the CRC and the literature value is minus 3,273 kilojoules per mole it's off by 22 or so a benzene by this figure appears to be more stable than what we figured that might be these numbers are kind of big it might be because of our approximate nature of the calculation using these averages over a library of compounds but in fact benzene is more stable than we would have predicted and that has consequences because benzene is more stable and also benzene stuck together to make bigger things like pyrenes and molecules like that are also more stable and that means for example in cigarette smoke where you don't have complete combustion you have particles that have a lot of things like Ben's pyrene and things like that on them and if you take a mouse and you take Ben's pyrene and you paint it on their skin they get cancer right where you painted it not good stuff if you're ever working with that you have to be extremely careful because if you get it on your skin that can be it now you're exposed ok practice problem 50 let's go way back was it just so beautiful or so horrible interesting how you can think back seems so long ago doesn't it how far we've come barium titanate is a piezoelectric material a piezoelectric material is a material that if you put an electrical force on it if you put an electric potential on it it will mechanically deform or if you mechanically deform it it will start generating an electric potential you may have heard the phrase piezoelectric tweeters because they use some of these materials in loudspeakers because they put a voltage on and it mechanically deforms at the same frequency as the voltage that shakes the air and then you hear the cymbal crash and the fidelity can be quite good here's a material barium titanate and here it is in this big unit cell here and the question is if this is the unit cell for barium titanate what is the molecular formula for barium titanate it sort of depends on how good your brain is at figuring out where spheres are usually we would try to put some planes through a dark circle through the thing but I'll just tell you that these oxygens are on the middle of the faces they're on the edge they aren't inside these guys here are on the exact corner and this guy here is totally inside the box we're going to use that to get the formula remember although we draw it like this it's not shaved off because it has to be a perfect cube so when we put them together we make an entire crystal we can't have extra stuff hanging out over the edges so we can only count what's inside the box not what's outside although we tend not to draw it that way because that turns out to be even more confusing than drawing it this way people have a hard time seeing okay let's look the barium atoms are on the corners they're intersected by three planes therefore they only count one eighth or if you imagine it's only the inner part on the corner the outer parts are all gone that's one eighth there's eight of them so there's one barium atom the titanium atoms completely inside and so there's one titanium per unit cell and the six oxygen atoms are on the six faces they have one plane through them so they count half there's six of them six times a half is three and the charges also help us although the charges are not always listed with the unit cell sometimes they aren't there but in this case they are it was listed plus two for barium well it's that's an alkaline earth metal plus four for titanium that's a common oxidation state for titanium and then three times two minus for oxygen this is six positive and six negative the salts neutral just like sodium chloride is neutral sodium plus chloride minus and so the formula is B A T I O 3 and that's why it's called barium titanate it's purportedly being used as part of the new capacitor storage systems being investigated for next generation vehicles so next generation vehicles they may have a big for electric vehicle they may have a big capacitor in the vehicle too in addition to the battery and when you really need to go the capacitor discharges it supplies you a lot of power very quickly and then while you're coasting downhill the car is smart enough to charge the capacitor back up like it does the battery yeah I give it to you because you aren't a chemist yet but the reason why it's called barium titanate and sodium chloride when you see the one that has the I U M that's first yeah so D young very young okay otherwise it'd be called titanium barium or something like that if it were backwards but for now we won't split hairs okay if you get the right number of atoms we'll take it okay alright let's see aha a temperature sensitive oops I meant compound I'll fix that a temperature sensitive compound that is wet I can't heat it to dry it because if I heat it it decomposes it cooks now I made this stuff in the lab and the last thing I want to do on the last step to dry it out to weigh it is to cook it and so I want to get rid of the water but not by heating it up to 100 so that the water vapor pressure is one atmosphere but I just want to heat it up to 40 and if I know the enthalpy of vaporization of water then I should know if I have a pump in a speedback what pressure I need to hold on the pump in order to be able to drive the water off only at 40 Celsius I don't want the pressure to be higher than the vapor pressure of water at 40 Celsius if it's higher the water will go back onto the compound if my pressure is lower because I'm pumping fast enough then the water will just wander off and I'll dry it out and I won't wreck the compound and this is done all the time in the lab and we need an equation then that relates delta H of vaporization to temperature and I see these are in Celsius be careful while we have such an equation the Clausius-Clapeyron equation and it says if I know the vapor pressure at one temperature then I can predict the vapor pressure at another temperature as long as I know delta H but I know delta H and I know R should be fairly easy the only thing I have to be careful of is this 40 40 Celsius if I'm in a hurry I might put 1 over 100, 1 over 40 and I'll get into trouble right away so let's insert all the numbers I'm calling conditions 1 conditions 1 is water at 100 Celsius and 1 atmosphere pressure so I put p1 1 atmosphere p2 I want to figure out this is delta H in joules this is R in joules from all goes away Kelvin to the minus 1 that kills this good the log of something is dimensionless I convert the 100 to 373.15 and I convert the 40 to 313.15 and then I solve all this stuff and I get a number plus 2.5104 and then I take the exponential function of both sides which just gets rid of the log I have 1 atmosphere divided by p2 is equal to the exponential function or e to the 2.5 I punch e to the 2.5 on my calculator I get 12.31 therefore p2 is 1 over 12.31 p2 is 0.0812 atmospheres or 61.7 often times the meter will actually be listed in tour just because people find it easier to read 60 more than 0.08 something in atmospheres maybe too big a unit I know the vapor pressure of water is one atmosphere at its boiling point that I do know and we can achieve this with any decent pump now we had to make some assumptions that the material itself has very low vapor pressure if the material has high vapor pressure pump it off too and you have to be careful sometimes depending what you've got otherwise you end up pumping your product into the pump oil of the pump and then people get very angry with you when you pump things into the pump oil because that wrecks the pump oil for the next person okay last one 52 a careless scientist measured the vapor pressure of toluene that's the stuff in airplane glue that kids got into for a while none of them were chemists I assure you chemists do not sniff anything ever measured the vapor pressure of toluene in atmospheres here the boiling point of toluene is about 110 to me this data looks okay and then after the measurement now the goal of the project was to excuse me determine delta H of vaporization for toluene well I've got all this data this is much much better than two points because if I can plot this data as a straight line I can then do linear aggression and I can get a great line through all of it and then I can get the slope of that line and that's minus delta H over r so I can get it just have to do a little analysis well here's what happened he plots log p versus one over t and comes to you and says help boss help it's not straight it's going wrong he took the log okay I guess first of all what's wrong with this graph the axes are not labeled with the units whenever you see a graph where the axes are not labeled stand back don't start looking at the graph try to figure out what the units were he had things like 20 degrees and I notice he's got 0.5 and I notice that 1 over 20 is 0.05 and so I figured this guy's adult what he's done is he's plotted the log of the pressure okay but he's plotted it versus 1 over t in Celsius and that's why it's curved because it has to be 1 over t in Kelvin and he's careless because he didn't put the units here which would be k minus 1 or in his case degrees c to the minus 1 if you would have seen degrees c to the minus 1 you would have said hey that's wrong we never plot anything in chemistry like that we always use Kelvin and therefore if you go back and do it and so here's the conclusion the data's okay the graph doesn't have units we can see that the log of the pressure is okay because you can take the log of that and the reference pressure is 1 atmosphere but it's in Celsius okay and what I'd like you to do is go back convert it to Kelvin plot it and see if it's straight and then here are the last important points for Tuesday first same seating chart second we have to do some spot roll taking therefore make sure you have your ID because somebody will come around say you're in G7 or you Joe Blow third practice and finally don't count on looking things up in your notes that's a slow algorithm and I hope you do well