WEBVTT 00:00:00.030 --> 00:00:02.410 The following content is provided under a Creative 00:00:02.410 --> 00:00:03.830 Commons license. 00:00:03.830 --> 00:00:06.850 Your support will help MIT OpenCourseWare continue to 00:00:06.850 --> 00:00:10.520 offer high-quality educational resources for free. 00:00:10.520 --> 00:00:13.650 To make a donation, or view additional materials from 00:00:13.650 --> 00:00:17.150 hundreds of MIT courses, visit MIT OpenCourseWare at 00:00:17.150 --> 00:00:18.400 ocw.mit.edu. 00:00:21.000 --> 00:00:24.390 PROFESSOR: So we will have weekly quiz tomorrow. 00:00:24.390 --> 00:00:28.100 There's been a lot of coverage, and so to focus you 00:00:28.100 --> 00:00:33.170 a bit, I'm going to confine the weekly quiz to glasses and 00:00:33.170 --> 00:00:34.100 chemical kinetics. 00:00:34.100 --> 00:00:36.040 So you don't have to worry about diffusion. 00:00:36.040 --> 00:00:38.300 We'll catch up on that, but I know there's so 00:00:38.300 --> 00:00:39.140 much material there. 00:00:39.140 --> 00:00:44.270 Let's keep it confined to glasses and chemical kinetics. 00:00:44.270 --> 00:00:46.860 And I'll be available today 4:30 to 5:30. 00:00:46.860 --> 00:00:51.730 If you can't be at that time, send me a note, and I'm sure 00:00:51.730 --> 00:00:54.480 we can figure out a time to get together. 00:00:54.480 --> 00:00:57.100 So what I want to do today is to start a new unit. 00:00:57.100 --> 00:01:00.810 We're going to start talking today about solutions, and do 00:01:00.810 --> 00:01:03.690 some solution chemistry, OK? 00:01:03.690 --> 00:01:07.180 Today we talk about solutions. 00:01:07.180 --> 00:01:09.330 And you might initially say, why are we 00:01:09.330 --> 00:01:10.410 talking about solutions? 00:01:10.410 --> 00:01:12.430 This is solid-state chemistry. 00:01:12.430 --> 00:01:15.250 I think up until now, you've seen that it's pretty rare 00:01:15.250 --> 00:01:17.990 that we use solids in their pure form. 00:01:17.990 --> 00:01:20.000 We usually have mixtures. 00:01:20.000 --> 00:01:23.050 So for example, when we studied glasses, we modified 00:01:23.050 --> 00:01:25.620 the glasses with an alkaline earth oxide. 00:01:25.620 --> 00:01:28.250 Well we, in fact, were making a solution of 00:01:28.250 --> 00:01:30.170 more than one component. 00:01:30.170 --> 00:01:32.800 So it's to get certain properties 00:01:32.800 --> 00:01:33.950 that we study solutions. 00:01:33.950 --> 00:01:38.380 Secondly, coming out of liquid phase is a way to make solids. 00:01:38.380 --> 00:01:40.870 So in terms of processing, we need to understand something 00:01:40.870 --> 00:01:42.510 about solutions. 00:01:42.510 --> 00:01:45.800 And then lastly, we're going to be studying, towards the 00:01:45.800 --> 00:01:49.140 end of the semester, a big unit on biochemistry. 00:01:49.140 --> 00:01:51.850 And biochemistry, why, you say, biochemistry? 00:01:51.850 --> 00:01:52.950 Why is he doing biochemistry? 00:01:52.950 --> 00:01:54.760 I thought this was solid-state chemistry. 00:01:54.760 --> 00:01:58.570 We are solid-state devices, but we're made of soft matter. 00:01:58.570 --> 00:02:01.640 At least the exoskeleton is soft matter. 00:02:01.640 --> 00:02:04.740 The endoskeleton is ceramic, right? 00:02:04.740 --> 00:02:07.800 Our bone structure is ceramic. 00:02:07.800 --> 00:02:10.370 Hydroxyapatite, calcium hydroxyapatite, and the 00:02:10.370 --> 00:02:12.370 outside is a polymer. 00:02:12.370 --> 00:02:12.830 So look at this. 00:02:12.830 --> 00:02:15.860 Confirmational changes in polymer. 00:02:15.860 --> 00:02:19.560 But the chemistry, the biochemistry, so much of it 00:02:19.560 --> 00:02:21.140 takes place in aqueous solution. 00:02:21.140 --> 00:02:23.060 So hence, we better know something 00:02:23.060 --> 00:02:24.960 about aqueous solution. 00:02:24.960 --> 00:02:29.430 So to this, we go almost right back to the first day. 00:02:29.430 --> 00:02:32.160 You remember, was the second lecture, and we showed this 00:02:32.160 --> 00:02:35.720 figure, and all the different categories of matter. 00:02:35.720 --> 00:02:38.480 And we started over here with elements, and we moved into 00:02:38.480 --> 00:02:41.560 some pure substance compounds, et cetera, et cetera. 00:02:41.560 --> 00:02:43.500 Now we're going to move over to here. 00:02:43.500 --> 00:02:46.600 So homogeneous mixture containing uniform composition 00:02:46.600 --> 00:02:49.650 and properties, as opposed to a heterogeneous mix. 00:02:49.650 --> 00:02:50.910 So we're now over here. 00:02:50.910 --> 00:02:54.220 We're working our way through the diagram. 00:02:54.220 --> 00:02:54.570 All right. 00:02:54.570 --> 00:02:58.540 So let's get a couple of basic definitions up. 00:02:58.540 --> 00:03:05.240 So the solution is really a mix of at least two 00:03:05.240 --> 00:03:06.130 constituents. 00:03:06.130 --> 00:03:10.450 One, the majority constituent is called the solvent, and 00:03:10.450 --> 00:03:13.330 then we can have one or more solutes. 00:03:16.160 --> 00:03:22.190 So the solvent, this is the majority constituent, and then 00:03:22.190 --> 00:03:25.095 the solutes are the minority constituents. 00:03:25.095 --> 00:03:27.090 And in some instances, it's pretty hard to 00:03:27.090 --> 00:03:28.640 tell which is which. 00:03:28.640 --> 00:03:30.870 And as far as types of solutions, I 00:03:30.870 --> 00:03:31.950 want to broaden this. 00:03:31.950 --> 00:03:34.150 You know, when I say solution, you're probably thinking about 00:03:34.150 --> 00:03:35.540 aqueous solution. 00:03:35.540 --> 00:03:38.660 But I want to take a minute and work through this chart. 00:03:38.660 --> 00:03:40.780 And this is all posted, so you don't have to 00:03:40.780 --> 00:03:41.540 write it all down. 00:03:41.540 --> 00:03:42.480 Just follow with me. 00:03:42.480 --> 00:03:47.080 So most of the general chemistry subjects will just 00:03:47.080 --> 00:03:48.840 stop at the end of the first line. 00:03:48.840 --> 00:03:51.870 They'll treat solutions as aqueous solutions. 00:03:51.870 --> 00:03:54.740 But in material science, we think of things broadly. 00:03:54.740 --> 00:03:58.000 So a good example of a simple aqueous solution is sodium 00:03:58.000 --> 00:03:58.870 chloride and water. 00:03:58.870 --> 00:04:03.030 Sodium chloride is the solute and water is the solvent. 00:04:03.030 --> 00:04:04.840 But you can have a liquid solute. 00:04:04.840 --> 00:04:07.870 So wine-- 00:04:07.870 --> 00:04:10.030 in case you've ever encountered this beverage, 00:04:10.030 --> 00:04:15.650 it's primarily water, but it can contain up to about 14% 00:04:15.650 --> 00:04:19.130 ethyl alcohol, and there are other constituents that give 00:04:19.130 --> 00:04:21.040 the color and the flavor and so on. 00:04:21.040 --> 00:04:23.490 And you can have a gas in a liquid, and that would be 00:04:23.490 --> 00:04:26.050 seltzer, where CO2 is dissolved. 00:04:26.050 --> 00:04:26.955 It's actually dissolved. 00:04:26.955 --> 00:04:31.820 If you take a look at a bottle of bubbly water on the shelf, 00:04:31.820 --> 00:04:32.950 you don't see the bubbles. 00:04:32.950 --> 00:04:36.220 The carbon dioxide is actually dissolved. 00:04:36.220 --> 00:04:39.720 You can have a gas as a solvent, and air would be an 00:04:39.720 --> 00:04:42.840 example of that, where the solvent is nitrogen. 00:04:42.840 --> 00:04:46.230 And then we have as solutes oxygen, argon, carbon dioxide, 00:04:46.230 --> 00:04:49.740 if you live next to a power plant, it's sulfur dioxide, if 00:04:49.740 --> 00:04:51.640 you live next to an aluminum smelter, it's 00:04:51.640 --> 00:04:53.692 tetrafluoromethane, and so on. 00:04:53.692 --> 00:04:56.160 So we have all kinds of solutes in the air. 00:04:56.160 --> 00:04:58.320 And then we can have solid solutions. 00:04:58.320 --> 00:05:01.580 And OK, as soon as you see the word solid, you know, that 00:05:01.580 --> 00:05:02.870 means you're 3.091. 00:05:02.870 --> 00:05:04.460 So what do we see for solids? 00:05:04.460 --> 00:05:05.380 Metal alloys. 00:05:05.380 --> 00:05:07.110 We saw carbon dissolved in iron. 00:05:07.110 --> 00:05:08.640 Well, that's a solution. 00:05:08.640 --> 00:05:12.250 It's homogeneous, single phase, just as the definition 00:05:12.250 --> 00:05:15.070 on that chart 1.11 said. 00:05:15.070 --> 00:05:19.550 Semiconductor, boron doping into silicon, the boron sits 00:05:19.550 --> 00:05:20.950 on a silicon lattice site. 00:05:20.950 --> 00:05:23.740 So this is a true solution. 00:05:23.740 --> 00:05:27.530 The boron is the solute, and silicon is the solvent. 00:05:27.530 --> 00:05:28.800 We can have the ceramic. 00:05:28.800 --> 00:05:30.450 We talked about the oxygen sensor. 00:05:30.450 --> 00:05:34.950 The oxygen sensor is zirconia, which has been stabilized with 00:05:34.950 --> 00:05:37.390 the addition of calcium oxide. 00:05:37.390 --> 00:05:38.320 As one example. 00:05:38.320 --> 00:05:40.720 In contemporary work, they might use another oxide. 00:05:40.720 --> 00:05:43.170 But what's the purpose of the calcium oxide? 00:05:43.170 --> 00:05:47.250 Well, I told you that it's to increase the vacancy 00:05:47.250 --> 00:05:49.190 population, give you a rapid response 00:05:49.190 --> 00:05:50.330 on your oxygen sensor. 00:05:50.330 --> 00:05:52.740 And as we're going to learn later, that's true, and 00:05:52.740 --> 00:05:55.900 there's a second value in putting in the calcium oxide. 00:05:55.900 --> 00:05:58.960 And it stabilizes, that's why they use the term stabilize, 00:05:58.960 --> 00:06:01.440 it stabilizes the cubic form of zirconia. 00:06:01.440 --> 00:06:04.400 Zirconia has a different crystallographic 00:06:04.400 --> 00:06:05.340 modifications. 00:06:05.340 --> 00:06:08.970 The cubic one is the one that gives us the best ability to 00:06:08.970 --> 00:06:12.690 transfer oxygen, and the addition of calcium oxide as a 00:06:12.690 --> 00:06:16.430 solute, the calcium ions actually sit on the zirconium 00:06:16.430 --> 00:06:19.480 lattice, that's a true solid solution. 00:06:19.480 --> 00:06:22.960 It also makes the cubic zirconia stable, and with 00:06:22.960 --> 00:06:25.950 Christmas coming, you know, it's the poor man's diamond, 00:06:25.950 --> 00:06:28.610 and that's the same material there. 00:06:28.610 --> 00:06:31.630 And to modify a glass, as I mentioned earlier, adding a 00:06:31.630 --> 00:06:34.360 alkaline earth oxide breaks the silicate network. 00:06:34.360 --> 00:06:35.640 That's a solution. 00:06:35.640 --> 00:06:38.220 Now here's an inverse one, where the solid is the 00:06:38.220 --> 00:06:42.040 solvent, and the liquid is the solute. 00:06:42.040 --> 00:06:46.370 So this was dentist's office practice going back to the 00:06:46.370 --> 00:06:47.830 time when I was your age. 00:06:47.830 --> 00:06:51.390 If you had a feeling, the dentist had silver and mercury 00:06:51.390 --> 00:06:55.110 in the dentist's office, and would add liquid mercury to 00:06:55.110 --> 00:07:00.630 silver and make up this amalgam, and then jam that 00:07:00.630 --> 00:07:01.390 into the tooth. 00:07:01.390 --> 00:07:03.560 Actually, that was the B part of the operation. 00:07:03.560 --> 00:07:05.870 There was this dentist here in the United States, and if I 00:07:05.870 --> 00:07:08.530 could find him, I would like to have a word with him. 00:07:08.530 --> 00:07:10.730 But he had this theory. 00:07:10.730 --> 00:07:14.720 You see, the amalgam is a metallic alloy. 00:07:14.720 --> 00:07:17.110 And so obviously, it has metallic bonding. 00:07:17.110 --> 00:07:19.080 And the tooth is-- 00:07:19.080 --> 00:07:21.230 it's a ceramic. 00:07:21.230 --> 00:07:24.280 So what kind of bonds are going to form between a metal 00:07:24.280 --> 00:07:25.270 and a ceramic? 00:07:25.270 --> 00:07:28.050 They're not very good. 00:07:28.050 --> 00:07:32.640 So this dentist had the theory that the way to increase the 00:07:32.640 --> 00:07:36.890 bonding capability of the amalgam to the tooth was to 00:07:36.890 --> 00:07:38.960 maximize contact areas. 00:07:38.960 --> 00:07:42.210 So when you went in with a tiny, tiny little cavity, the 00:07:42.210 --> 00:07:49.530 dentist would drill the tooth out, removing about 75% of the 00:07:49.530 --> 00:07:52.700 volume of the tooth, and then they would make this amalgam 00:07:52.700 --> 00:07:54.390 and shove that in. 00:07:54.390 --> 00:07:59.070 And you'd wear that for about 20 years, until one day you 00:07:59.070 --> 00:08:02.680 bite into a muffin that's got a little piece of walnut shell 00:08:02.680 --> 00:08:04.760 in it, and the amalgam flexes, and your 00:08:04.760 --> 00:08:06.610 thin-walled tooth goes bang! 00:08:06.610 --> 00:08:07.760 Like that. 00:08:07.760 --> 00:08:11.010 And now you get to go back to the dentist's office for yet 00:08:11.010 --> 00:08:13.730 some more medieval treatment. 00:08:13.730 --> 00:08:16.510 Actually, things have improved somewhat. 00:08:16.510 --> 00:08:17.840 Thanks to material science. 00:08:17.840 --> 00:08:20.080 But they're not using this amalgam anymore. 00:08:20.080 --> 00:08:21.920 But there are a number of us who are still walking around 00:08:21.920 --> 00:08:25.530 with silver and mercury in our mouths, and-- 00:08:25.530 --> 00:08:25.850 yeah. 00:08:25.850 --> 00:08:27.290 Enough about my dental problems. 00:08:27.290 --> 00:08:29.570 Now let's go on to intercalation. 00:08:29.570 --> 00:08:31.300 You can put a gas into a solid. 00:08:31.300 --> 00:08:33.820 And I told you about this one, where if you want to store 00:08:33.820 --> 00:08:35.740 hydrogen, and this is a big problem, if we're going to 00:08:35.740 --> 00:08:37.830 talk about hydrogen-powered vehicles. 00:08:40.360 --> 00:08:43.385 A problem as big as, how to get the fuel cell cheap 00:08:43.385 --> 00:08:45.550 enough, is where are you going to store the hydrogen on the 00:08:45.550 --> 00:08:48.840 car, and one of the materials that's been proposed is this 00:08:48.840 --> 00:08:52.030 alloy of lanthanum and nickel that can intercalate huge 00:08:52.030 --> 00:08:52.990 amounts of hydrogen. 00:08:52.990 --> 00:08:54.900 So that forms a solid solution. 00:08:54.900 --> 00:08:57.230 So those are examples of solutions, and we're going to 00:08:57.230 --> 00:09:00.300 go back and make sure that we cover the basic Gen Chem at 00:09:00.300 --> 00:09:00.950 the top here. 00:09:00.950 --> 00:09:02.690 But I want you know that solution 00:09:02.690 --> 00:09:04.990 chemistry is very broad. 00:09:04.990 --> 00:09:08.100 Now when you dissolve something, you actually have 00:09:08.100 --> 00:09:11.680 things down at the atomic level. 00:09:11.680 --> 00:09:16.330 So for example, in brine, you actually have below two 00:09:16.330 --> 00:09:17.910 nanometers as particle size. 00:09:17.910 --> 00:09:21.680 You actually have sodium ions and chloride ions dissolved 00:09:21.680 --> 00:09:27.070 completely, which means that the solution is clear, 00:09:27.070 --> 00:09:29.240 colorless, and transparent to visible light. 00:09:29.240 --> 00:09:31.780 Water is clear, colorless, transparent to visible light. 00:09:31.780 --> 00:09:34.810 If you had sodium chloride, it remains clear, colorless, 00:09:34.810 --> 00:09:36.150 transparent to visible light. 00:09:36.150 --> 00:09:39.590 You can't filter, and you can't wait for the sodium 00:09:39.590 --> 00:09:43.030 chloride to settle out, because it's bonded within the 00:09:43.030 --> 00:09:44.710 structure of the liquid water. 00:09:44.710 --> 00:09:46.550 And this has implications. 00:09:46.550 --> 00:09:49.340 There's so much water on the planet, but there's not so 00:09:49.340 --> 00:09:51.470 much fresh water on the planet. 00:09:51.470 --> 00:09:54.570 And desalination can't be accomplished by filtration. 00:09:54.570 --> 00:09:58.800 A filter that had a pore size small enough to trap sodium 00:09:58.800 --> 00:10:03.390 ions, the pore size would be so small, water molecules 00:10:03.390 --> 00:10:04.170 couldn't go through. 00:10:04.170 --> 00:10:06.380 So this is the concept. 00:10:06.380 --> 00:10:09.560 At the other end, you can get something called a suspension, 00:10:09.560 --> 00:10:12.670 where the particle size is greater than about 1,000 00:10:12.670 --> 00:10:15.680 nanometers, and blood is a good example of that, where 00:10:15.680 --> 00:10:17.390 it's opaque. 00:10:17.390 --> 00:10:20.450 Visible light doesn't go through, but you can filter 00:10:20.450 --> 00:10:22.650 out some of the matter in blood. 00:10:22.650 --> 00:10:25.080 And if you let it sit for a while, it'll settle in it 00:10:25.080 --> 00:10:26.450 gravitational field. 00:10:26.450 --> 00:10:29.860 And in between, you have this whole zone of colloids. 00:10:29.860 --> 00:10:32.540 And so between colloids and suspensions, the only 00:10:32.540 --> 00:10:34.640 difference is particle size. 00:10:34.640 --> 00:10:37.150 And this whole thing we would just call a dispersion of 00:10:37.150 --> 00:10:40.230 another phase, either another solid phase, or 00:10:40.230 --> 00:10:41.860 another liquid phase. 00:10:41.860 --> 00:10:44.890 And it's kind of an interesting physical chemistry 00:10:44.890 --> 00:10:49.070 about the dispersion, what makes it work. 00:10:49.070 --> 00:10:51.660 For example, in milk, milk is a good example of a 00:10:51.660 --> 00:10:52.610 dispersion. 00:10:52.610 --> 00:10:56.650 You have a fatty phase, and you have an aqueous phase. 00:10:56.650 --> 00:10:58.470 The aqueous phase, where all the minerals are. 00:10:58.470 --> 00:10:58.800 Why? 00:10:58.800 --> 00:11:00.510 Because the minerals are-- 00:11:00.510 --> 00:11:01.810 what kind of compound? 00:11:01.810 --> 00:11:04.850 They're not metallic, they're not covalent. 00:11:04.850 --> 00:11:06.030 They're ionic. 00:11:06.030 --> 00:11:09.235 The ionic compounds dissolve in the aqueous phase, and then 00:11:09.235 --> 00:11:10.940 in the fatty phase, that's where you have the 00:11:10.940 --> 00:11:12.600 protein and so on. 00:11:12.600 --> 00:11:16.700 But the fatty phase is clear and colorless, and the aqueous 00:11:16.700 --> 00:11:17.820 phase is clear and colorless. 00:11:17.820 --> 00:11:20.320 And yet milk is white. 00:11:20.320 --> 00:11:23.750 It's, as the term implies, it's milky. 00:11:23.750 --> 00:11:24.900 Why? 00:11:24.900 --> 00:11:26.130 What's going on? 00:11:26.130 --> 00:11:28.670 You have a second phase here. 00:11:28.670 --> 00:11:34.360 This could be the fatty phase, and this is the aqueous phase. 00:11:34.360 --> 00:11:36.510 They're both clear and colorless, but they have 00:11:36.510 --> 00:11:38.870 different indices of refraction. 00:11:38.870 --> 00:11:43.380 And since this has n fatty phase, and this has n aqueous 00:11:43.380 --> 00:11:47.200 phase, this interface scatters the light. 00:11:47.200 --> 00:11:50.370 So if you want to start a business, if you want to try 00:11:50.370 --> 00:11:57.640 to tailor the index so that the index of the aqueous phase 00:11:57.640 --> 00:12:00.790 matches the index of refraction of the fatty phase, 00:12:00.790 --> 00:12:03.520 you'd have the two dissolve, one and the other, and it 00:12:03.520 --> 00:12:06.060 would be transparent, divisible light. 00:12:06.060 --> 00:12:08.160 So you would have milk that isn't milky. 00:12:12.870 --> 00:12:14.960 I mean, the public would be very confused. 00:12:14.960 --> 00:12:16.300 But anyways. 00:12:16.300 --> 00:12:17.100 So that's what you do. 00:12:17.100 --> 00:12:20.200 So why does this thing not settle? 00:12:20.200 --> 00:12:24.240 Because they do have a density difference, and again, going 00:12:24.240 --> 00:12:27.510 back to the days when I was not a college student but a 00:12:27.510 --> 00:12:30.650 youngster, there was still this form of milk called 00:12:30.650 --> 00:12:31.790 pasteurized milk. 00:12:31.790 --> 00:12:34.810 Well, all milk is pasteurized, but this milk was not 00:12:34.810 --> 00:12:35.770 homogenized. 00:12:35.770 --> 00:12:40.390 And what would happen is, there was this person that 00:12:40.390 --> 00:12:41.930 would deliver milk. 00:12:41.930 --> 00:12:45.140 This was a borosilicate glass bottle. 00:12:45.140 --> 00:12:47.790 And here would be the cream. 00:12:47.790 --> 00:12:49.220 The cream would rise to the top. 00:12:49.220 --> 00:12:52.120 We have all these expressions in our language. 00:12:52.120 --> 00:12:54.970 And then this would be the milk here, and you could skim 00:12:54.970 --> 00:12:57.240 this off for coffee or sugar, and then this would be a 00:12:57.240 --> 00:12:58.600 low-fat milk. 00:12:58.600 --> 00:13:02.530 But people wanted this all mixed, so then they went to 00:13:02.530 --> 00:13:04.320 homogenized milk. 00:13:04.320 --> 00:13:07.850 So what is homogenized milk? 00:13:07.850 --> 00:13:09.330 This is your red cap, now. 00:13:09.330 --> 00:13:10.570 All the milk is homogenized. 00:13:10.570 --> 00:13:11.360 This was a big thing. 00:13:11.360 --> 00:13:12.610 This was simply called pasteurized. 00:13:15.090 --> 00:13:16.820 I'm going to get to the physical chemistry here. 00:13:16.820 --> 00:13:17.750 It's very interesting. 00:13:17.750 --> 00:13:21.100 Because this is lower density, and yet in homogenized milk it 00:13:21.100 --> 00:13:23.060 doesn't rise. 00:13:23.060 --> 00:13:26.410 So let's take a look at what goes on in the physical 00:13:26.410 --> 00:13:30.030 chemistry of homogenized milk, because it's all about these 00:13:30.030 --> 00:13:33.820 various systems. So I'm going to take this particle here, 00:13:33.820 --> 00:13:36.835 and its sum insoluble cluster. 00:13:41.810 --> 00:13:43.550 And I'm not specifying the cluster size. 00:13:43.550 --> 00:13:47.610 It's probably greater than about two nanometers. 00:13:47.610 --> 00:13:49.690 So there are two forces acting on this. 00:13:49.690 --> 00:13:56.170 There's a settling force and there's a buoyancy force. 00:13:56.170 --> 00:13:57.920 Obviously, otherwise it wouldn't float. 00:13:57.920 --> 00:14:01.570 So there's some kind of a buoyancy force. 00:14:01.570 --> 00:14:03.300 Settling force and a buoyancy force. 00:14:03.300 --> 00:14:05.920 Well, the settling force, this is just the gravity. 00:14:05.920 --> 00:14:06.490 Right? 00:14:06.490 --> 00:14:08.620 This is the force of gravity. 00:14:08.620 --> 00:14:10.400 And we know the force of gravity. 00:14:10.400 --> 00:14:12.560 That goes with the mass. 00:14:12.560 --> 00:14:15.420 Come on, get that cell phone out of here. 00:14:15.420 --> 00:14:18.720 This force of gravity goes as the mass, and the mass, we 00:14:18.720 --> 00:14:21.220 know, goes as the volume. 00:14:21.220 --> 00:14:24.070 And the volume goes as the cube of the radius. 00:14:24.070 --> 00:14:27.120 I'm assuming this is a spherical particle, all right? 00:14:27.120 --> 00:14:28.410 Now, the buoyancy force. 00:14:28.410 --> 00:14:30.570 The buoyancy force is the interfacial 00:14:30.570 --> 00:14:32.240 force between the two. 00:14:32.240 --> 00:14:33.790 There's some binding across here. 00:14:33.790 --> 00:14:38.430 Maybe weak van der Waals, or if this fatty phase has 00:14:38.430 --> 00:14:41.070 molecules in it that are polar, then there could be 00:14:41.070 --> 00:14:43.290 dipole-dipole interaction. 00:14:43.290 --> 00:14:45.020 But in any case, there's some kind of an 00:14:45.020 --> 00:14:48.470 interfacial force here. 00:14:48.470 --> 00:14:52.880 And this is all chemical bonding 00:14:52.880 --> 00:14:56.870 between solute and solvent. 00:14:59.420 --> 00:15:01.440 But you see, the force is a weak force. 00:15:01.440 --> 00:15:03.050 If it were a really strong force, it would 00:15:03.050 --> 00:15:04.110 dissolve this thing. 00:15:04.110 --> 00:15:07.240 It won't quite dissolve it, but there is some kind of 00:15:07.240 --> 00:15:09.480 dipole-dipole weak force. 00:15:09.480 --> 00:15:14.840 And this one here is operating across the surface area. 00:15:14.840 --> 00:15:15.810 That's the contact. 00:15:15.810 --> 00:15:19.790 So this force goes as the area, and area goes as the 00:15:19.790 --> 00:15:23.570 square of the radius, whereas mass goes as 00:15:23.570 --> 00:15:24.690 the cube of the radius. 00:15:24.690 --> 00:15:29.570 So you know, from your math, that r cubed dominates r 00:15:29.570 --> 00:15:33.830 squared, but only at large r. 00:15:33.830 --> 00:15:35.860 It's not always the case, is it? 00:15:35.860 --> 00:15:37.570 Maybe before you got here, you thought that. 00:15:37.570 --> 00:15:40.190 But now that you've been at MIT a few months, you know 00:15:40.190 --> 00:15:44.860 that r squared can dominate r cubed at small r. 00:15:47.560 --> 00:15:49.400 Interfacial forces dominate. 00:15:49.400 --> 00:15:52.650 And that's exactly what happens in these dispersions, 00:15:52.650 --> 00:15:54.520 and that's why they don't settle out. 00:15:54.520 --> 00:15:59.770 Now, homogenized milk is simply milk that has been 00:15:59.770 --> 00:16:03.610 agitated in such a way as to reduce the fat globule size 00:16:03.610 --> 00:16:08.570 below a critical value so that these interfacial forces hold 00:16:08.570 --> 00:16:10.670 the fat globules in suspension. 00:16:10.670 --> 00:16:13.310 If you waited long enough, they would agglomerate and 00:16:13.310 --> 00:16:17.660 settle, but that time is probably longer than the shelf 00:16:17.660 --> 00:16:18.300 life of the milk. 00:16:18.300 --> 00:16:22.150 So the milk probably spoils before stuff settles out. 00:16:22.150 --> 00:16:26.620 So this is all very important to understand. 00:16:26.620 --> 00:16:31.030 The range that exists between insolubility and this sort of 00:16:31.030 --> 00:16:34.730 clustering, and suspension, and so on. 00:16:34.730 --> 00:16:37.565 By the way, a lot of pharmaceuticals are like this. 00:16:37.565 --> 00:16:39.030 A lot of pharmaceuticals. 00:16:39.030 --> 00:16:40.670 So when it says, shake well before 00:16:40.670 --> 00:16:42.690 using, they're not kidding. 00:16:42.690 --> 00:16:46.610 Because the active ingredient will settle. 00:16:46.610 --> 00:16:50.210 And you're drinking just the solvent, just the vehicle. 00:16:50.210 --> 00:16:54.400 And all of the potency is on the bottom of the bottle. 00:16:54.400 --> 00:16:55.660 Shake that thing up! 00:16:59.100 --> 00:17:01.760 I can't say what it does to the taste, but 00:17:01.760 --> 00:17:03.540 that's another problem. 00:17:03.540 --> 00:17:05.140 Actually, I threw in this slide here. 00:17:05.140 --> 00:17:07.200 We're not going to spend any time on it, but you can look 00:17:07.200 --> 00:17:08.260 at it at some point. 00:17:08.260 --> 00:17:10.130 This is a whole taxonomy of colloids. 00:17:12.920 --> 00:17:16.090 Solid-liquid emulsions, aerosols, they're all part of 00:17:16.090 --> 00:17:21.170 this magic zone between solubility and 00:17:21.170 --> 00:17:23.280 just brick, all right? 00:17:23.280 --> 00:17:26.310 There's this whole fine, pardon the pun, 00:17:26.310 --> 00:17:28.610 the whole fine structure. 00:17:28.610 --> 00:17:31.480 OK, So let's get to the chemistry. 00:17:31.480 --> 00:17:34.300 Obviously there's something to do with bonding here, right? 00:17:34.300 --> 00:17:37.960 So here's a simple experiment, and this is taken right from 00:17:37.960 --> 00:17:38.380 the reading. 00:17:38.380 --> 00:17:41.850 So I've just taken this episode that is written up in 00:17:41.850 --> 00:17:42.280 the reading. 00:17:42.280 --> 00:17:44.490 So we've got two beakers here, and in each 00:17:44.490 --> 00:17:45.940 beaker, we have a bilayer. 00:17:45.940 --> 00:17:51.090 We've poured in some carbon tetrachloride, liquid, and 00:17:51.090 --> 00:17:52.410 we've poured in some water. 00:17:52.410 --> 00:17:55.990 And these two are immiscible, because carbon tetrachloride 00:17:55.990 --> 00:17:59.820 is obviously a non-polar liquid, and water is a polar 00:17:59.820 --> 00:18:02.350 liquid with hydrogen bonding capability. 00:18:02.350 --> 00:18:06.350 And in one beaker, we introduce crystals of iodine. 00:18:06.350 --> 00:18:08.140 In the other beaker, we introduce crystals of 00:18:08.140 --> 00:18:09.600 potassium permanganate. 00:18:09.600 --> 00:18:12.690 And then we shake them up, and we wait. 00:18:12.690 --> 00:18:17.950 And eventually we see that on the left, the iodine dissolves 00:18:17.950 --> 00:18:19.350 in the carbon tetrachloride. 00:18:19.350 --> 00:18:21.830 And we're using the purple color as an indicator. 00:18:21.830 --> 00:18:23.890 And this is kind of cute, because both potassium 00:18:23.890 --> 00:18:28.160 permanganate and iodine will render things purple. 00:18:28.160 --> 00:18:29.770 So you're comparing purple to purple. 00:18:29.770 --> 00:18:31.780 They could have chosen something else, but this is 00:18:31.780 --> 00:18:32.710 kind of cute. 00:18:32.710 --> 00:18:33.030 All right. 00:18:33.030 --> 00:18:35.580 So here you end up with a solution of iodine and carbon 00:18:35.580 --> 00:18:38.340 tetrachloride, whereas on the right side, you end up with a 00:18:38.340 --> 00:18:41.900 solution of potassium permanganate and water, and 00:18:41.900 --> 00:18:44.490 nothing in the carbon tetrachloride. 00:18:44.490 --> 00:18:47.840 So what can we infer from this? 00:18:47.840 --> 00:18:50.130 Well, let's take a look at the possible interactions. 00:18:50.130 --> 00:18:53.950 So first of all let's categorize H2O. 00:18:53.950 --> 00:18:59.410 This is polar, it's a polar liquid, with hydrogen bonding 00:18:59.410 --> 00:19:00.660 capability. 00:19:03.810 --> 00:19:06.990 Carbon tetrachloride is non-polar. 00:19:06.990 --> 00:19:08.010 It's very toxic. 00:19:08.010 --> 00:19:11.790 When I was a child, we had this in the medicine cabinet. 00:19:11.790 --> 00:19:13.005 It's a non-polar solvent. 00:19:13.005 --> 00:19:16.040 It's fantastic for getting grease stains off. 00:19:16.040 --> 00:19:17.050 Every man had this. 00:19:17.050 --> 00:19:19.757 With a little handkerchief, you'd take a little grease 00:19:19.757 --> 00:19:21.260 stain off your tie. 00:19:21.260 --> 00:19:22.240 You can't buy this stuff. 00:19:22.240 --> 00:19:24.560 You can't even guy it for research anymore. 00:19:24.560 --> 00:19:25.310 It's too bad. 00:19:25.310 --> 00:19:26.620 It's great stuff. 00:19:26.620 --> 00:19:27.620 Highly toxic, though. 00:19:27.620 --> 00:19:31.690 But you know, there's a time and a place. 00:19:31.690 --> 00:19:32.030 All right. 00:19:32.030 --> 00:19:33.430 So then here's iodine. 00:19:33.430 --> 00:19:36.640 Iodine, we know, is non-polar. 00:19:36.640 --> 00:19:39.450 It's a homonuclear molecule, it has to be non-polar. 00:19:39.450 --> 00:19:42.330 And so what holds iodine together in the crystal? 00:19:42.330 --> 00:19:46.320 There's only one bond, and that's van der Waals, right? 00:19:46.320 --> 00:19:52.190 It's a van der Waals solid, whereas potassium permanganate 00:19:52.190 --> 00:19:53.960 is an ionic solid. 00:19:53.960 --> 00:19:57.420 Potassium permanganate is ionic, and it consists of 00:19:57.420 --> 00:20:01.830 potassium cations and permanganate anions. 00:20:01.830 --> 00:20:06.280 And what we find is that the non-polar solute dissolves in 00:20:06.280 --> 00:20:11.630 the non-polar solvent, and the ionic solute dissolves in the 00:20:11.630 --> 00:20:16.220 polar solvent with hydrogen bonding capability. 00:20:16.220 --> 00:20:23.000 So from this, we can infer the general rule, which is 00:20:23.000 --> 00:20:27.850 encapsulated in the language used in chemistry textbooks. 00:20:27.850 --> 00:20:30.125 Like dissolves like. 00:20:33.130 --> 00:20:37.340 And what they're really saying here, is that like solutes 00:20:37.340 --> 00:20:40.570 dissolve in like solvents. 00:20:40.570 --> 00:20:43.410 Solute-solvent is like dissolves like. 00:20:43.410 --> 00:20:43.700 OK. 00:20:43.700 --> 00:20:46.010 It's a good place to start, but it's 00:20:46.010 --> 00:20:47.380 an incomplete picture. 00:20:47.380 --> 00:20:49.230 So I want to show you that there's some 00:20:49.230 --> 00:20:50.460 sophistication here. 00:20:50.460 --> 00:20:52.680 This is taken from one of the other books. 00:20:52.680 --> 00:20:56.410 And it shows just the rules for ionic compounds in water. 00:20:56.410 --> 00:20:59.540 And I just showed you, from this example, that the ionic 00:20:59.540 --> 00:21:01.640 compound dissolved in water. 00:21:01.640 --> 00:21:05.070 And what you see here is that some ionic compounds dissolve 00:21:05.070 --> 00:21:07.160 in water, but there's a whole set or 00:21:07.160 --> 00:21:09.340 insoluble ionic compounds. 00:21:09.340 --> 00:21:13.500 So it's not straightforward. 00:21:13.500 --> 00:21:17.340 But we know from 3.091, we know that we can make sense of 00:21:17.340 --> 00:21:21.550 this on the basis of competition. 00:21:21.550 --> 00:21:24.950 Competition between what holds the compound in the solid 00:21:24.950 --> 00:21:27.650 state versus what will pull it into the liquid state. 00:21:27.650 --> 00:21:31.750 So for example, we can compare sodium chloride, which we know 00:21:31.750 --> 00:21:33.160 dissolves in water. 00:21:33.160 --> 00:21:36.470 So sodium chloride, as a crystalline solid, will 00:21:36.470 --> 00:21:42.600 dissolve to form sodium chloride aqueous solution. 00:21:42.600 --> 00:21:47.970 Whereas if you look at magnesium oxide, which is also 00:21:47.970 --> 00:21:56.190 an ionic crystal, it does not, to any standard imaginable, 00:21:56.190 --> 00:21:59.960 dissolve to form an aqueous solution of magnesium oxide. 00:21:59.960 --> 00:22:01.170 And what's the difference here? 00:22:01.170 --> 00:22:10.440 The difference here is, compare solvation energy, in 00:22:10.440 --> 00:22:12.870 other words, the energy that you got by pulling this into 00:22:12.870 --> 00:22:16.670 solution, and forming bonds between sodium and chlorine in 00:22:16.670 --> 00:22:20.855 water, with the crystallization energy. 00:22:24.810 --> 00:22:25.920 And what's that all about? 00:22:25.920 --> 00:22:28.310 Well, that's the Madelung constant, remember? 00:22:28.310 --> 00:22:29.970 Madelung constant. 00:22:29.970 --> 00:22:35.520 q1 q2 over 4 pi epsilon 0 r, where this 00:22:35.520 --> 00:22:36.880 is the cation anion. 00:22:36.880 --> 00:22:41.200 And you can see here that sodium chloride has sodium 00:22:41.200 --> 00:22:44.870 cations and chloride anions, and there's a certain binding 00:22:44.870 --> 00:22:46.320 energy in the crystal. 00:22:46.320 --> 00:22:49.710 Magnesium has 2 plus. 00:22:49.710 --> 00:22:51.750 Oxide is 2 minus. 00:22:51.750 --> 00:22:55.030 The binding energy between magnesium and oxygen is so 00:22:55.030 --> 00:22:58.750 great that there's no driving force to dissolve. 00:22:58.750 --> 00:23:01.610 Now, I don't expect you to be able to look at this and tell 00:23:01.610 --> 00:23:04.470 me whether something's going to dissolve or not. 00:23:04.470 --> 00:23:08.570 But if I were to say to you, explain why sodium chloride 00:23:08.570 --> 00:23:13.300 forms solutions with water, and magnesium oxide doesn't, 00:23:13.300 --> 00:23:16.380 that you could go through this rationalization. 00:23:16.380 --> 00:23:18.820 And here's a cartoon from the textbook that tries to 00:23:18.820 --> 00:23:20.560 illustrate this solvation. 00:23:20.560 --> 00:23:23.460 Here you can see a crystal of sodium chloride, in the 00:23:23.460 --> 00:23:27.440 inimitable fashion, as drawn by chemistry books, where the 00:23:27.440 --> 00:23:31.655 chloride ion is green, and the sodium ion is blue. 00:23:31.655 --> 00:23:32.560 And that's OK. 00:23:32.560 --> 00:23:34.930 I can live with the color-coding, as long as we 00:23:34.930 --> 00:23:38.310 agree amongst ourselves, these ions are clear and colorless, 00:23:38.310 --> 00:23:40.180 because they have octet stability in 00:23:40.180 --> 00:23:41.610 their electronic shell. 00:23:41.610 --> 00:23:45.030 And here's water, with the hydrogen shown in white, and 00:23:45.030 --> 00:23:46.730 the oxygen shown in red. 00:23:46.730 --> 00:23:51.930 And you can see that the oxide end, the oxygen end, the delta 00:23:51.930 --> 00:23:56.940 negative end of the water, is trying to wrest sodium cation 00:23:56.940 --> 00:23:58.850 out of the lattice, and ultimately 00:23:58.850 --> 00:24:00.870 surround it by a cage. 00:24:00.870 --> 00:24:01.950 And the same thing here. 00:24:01.950 --> 00:24:04.400 You see the hydrogen ends of the water trying to pull 00:24:04.400 --> 00:24:07.840 chloride out, and ultimately surround it with 00:24:07.840 --> 00:24:09.600 a water-like cage. 00:24:09.600 --> 00:24:11.850 So this is the competition I was talking about. 00:24:11.850 --> 00:24:14.480 In the case of sodium chloride, water wins. 00:24:14.480 --> 00:24:17.530 In the case of magnesium oxide, water loses. 00:24:17.530 --> 00:24:20.900 The binding energy between magnesium and oxygen and the 00:24:20.900 --> 00:24:22.580 crystal dominate. 00:24:22.580 --> 00:24:25.010 So you don't see that solvation. 00:24:25.010 --> 00:24:25.310 OK. 00:24:25.310 --> 00:24:27.430 Let's talk about metrics now. 00:24:27.430 --> 00:24:30.100 Let's look at some metrics of solubility. 00:24:30.100 --> 00:24:31.850 It's quantifiable. 00:24:31.850 --> 00:24:38.230 So we can express a measure of solubility in terms of a 00:24:38.230 --> 00:24:40.210 quantity known as molarity. 00:24:43.850 --> 00:24:55.165 So we can express moles of solute per liter of solvent. 00:24:59.300 --> 00:25:07.300 And this is called molarity, and the symbol is capital M. 00:25:07.300 --> 00:25:12.750 So we can say, for example, a 1 molar solution of sodium 00:25:12.750 --> 00:25:16.885 chloride in water, we'll write 1 molar NaCl, and then we'll 00:25:16.885 --> 00:25:19.100 write subscript aq, meaning aqueous. 00:25:19.100 --> 00:25:24.340 So it's an aqueous solution at a concentration of 1 mole of 00:25:24.340 --> 00:25:29.170 NaCl per liter. 00:25:29.170 --> 00:25:34.460 And the liter is named after a person, so that's capital L, 00:25:34.460 --> 00:25:37.200 per liter of solution. 00:25:37.200 --> 00:25:40.040 And remember, the solution is the sum of 00:25:40.040 --> 00:25:44.480 the water plus solute. 00:25:44.480 --> 00:25:48.510 For dilute solutions, there's very little difference between 00:25:48.510 --> 00:25:51.200 the total amount of water and the total amount of solution. 00:25:51.200 --> 00:25:54.090 But in certain instances, the presence of the solute 00:25:54.090 --> 00:25:56.340 actually has a volumetric change on here. 00:25:56.340 --> 00:26:00.500 So strictly speaking, it's per liter of solution 00:26:00.500 --> 00:26:04.800 And as I've shown you, there are degrees of solubility. 00:26:04.800 --> 00:26:10.690 So people represent the threshold of solubility as c 00:26:10.690 --> 00:26:12.580 of the solute. 00:26:12.580 --> 00:26:15.780 When c of the solute is less than about a million molar, 00:26:15.780 --> 00:26:20.770 0.001 molar, we call this insoluble. 00:26:20.770 --> 00:26:24.580 So something is vanishingly soluble, we 00:26:24.580 --> 00:26:26.165 say that's the value. 00:26:26.165 --> 00:26:27.595 So we'll call this the threshold. 00:26:30.410 --> 00:26:33.350 And then, something that's quite soluble, we'd say that 00:26:33.350 --> 00:26:36.272 the concentration of the solute starts to exceed at 00:26:36.272 --> 00:26:38.740 about 0.1 molar. 00:26:38.740 --> 00:26:43.035 And then we would say, that qualifies as soluble. 00:26:46.480 --> 00:26:51.950 So now let's look at two extremes in solubility, 00:26:51.950 --> 00:26:54.100 operating off of this. 00:26:54.100 --> 00:26:57.040 So in the one case, we can have complete solubility. 00:26:57.040 --> 00:27:01.060 So examples of that, where things are completely miscible 00:27:01.060 --> 00:27:02.220 in one another. 00:27:02.220 --> 00:27:04.990 Complete solubility. 00:27:04.990 --> 00:27:07.080 By the way, some people will use the term miscibility. 00:27:10.530 --> 00:27:12.810 When something is miscible it means it's soluble. 00:27:12.810 --> 00:27:13.890 Same idea. 00:27:13.890 --> 00:27:16.440 If something is insoluble, some people might say it's 00:27:16.440 --> 00:27:18.000 immiscible. 00:27:18.000 --> 00:27:19.190 Same thing. 00:27:19.190 --> 00:27:19.770 OK? 00:27:19.770 --> 00:27:25.980 So complete solubility is ethyl alcohol and water. 00:27:25.980 --> 00:27:27.575 You can mix them in all proportions. 00:27:32.800 --> 00:27:34.050 Continuously variable. 00:27:36.480 --> 00:27:40.580 On the solid alloy is silver and gold. 00:27:40.580 --> 00:27:43.960 Silver and gold, you can make alloys of any composition 00:27:43.960 --> 00:27:47.780 between 100% gold and 100% silver. 00:27:47.780 --> 00:27:50.360 Now, that's the exception. 00:27:50.360 --> 00:27:54.280 Most cases are situations of limited solubility. 00:28:01.900 --> 00:28:09.000 So they go up to a maximum, which we can denote C-star or 00:28:09.000 --> 00:28:10.250 C saturation. 00:28:13.190 --> 00:28:15.980 This is the maximum solubility. 00:28:18.680 --> 00:28:21.590 So an example of something that's sparingly soluble in 00:28:21.590 --> 00:28:24.120 water is silver chloride. 00:28:24.120 --> 00:28:27.030 Let's look at silver chloride. 00:28:27.030 --> 00:28:30.380 So silver chloride, I'm going to start here, silver chloride 00:28:30.380 --> 00:28:34.130 as a crystal, and I'm going to dissolve that in water. 00:28:34.130 --> 00:28:38.520 So that gives me AgCl aq. 00:28:38.520 --> 00:28:40.980 So that's just simply the formation of an aqueous 00:28:40.980 --> 00:28:42.900 solution of silver chloride. 00:28:42.900 --> 00:28:47.240 And when the reaction moves from left to right, we call 00:28:47.240 --> 00:28:50.670 that dissolution. 00:28:50.670 --> 00:28:53.110 The silver chloride is dissolving, and when the 00:28:53.110 --> 00:28:57.190 system moves from right to left, we call that-- 00:28:57.190 --> 00:29:01.840 now here I'm going to nitpick with the book. 00:29:01.840 --> 00:29:04.420 The book calls the left reaction crystallization. 00:29:07.030 --> 00:29:08.490 And that's correct. 00:29:08.490 --> 00:29:11.080 It is crystallization in this case, because silver chloride 00:29:11.080 --> 00:29:12.050 is a crystal. 00:29:12.050 --> 00:29:18.150 But it is possible, in other systems, to have the solute 00:29:18.150 --> 00:29:20.560 come out of solution, and make a solid that is 00:29:20.560 --> 00:29:21.980 noncrystalline. 00:29:21.980 --> 00:29:26.200 And you know that all crystals are solids, but not all solids 00:29:26.200 --> 00:29:26.840 are crystals. 00:29:26.840 --> 00:29:28.180 You can have an amorphous solid. 00:29:28.180 --> 00:29:31.040 So what would happen if you were to bring out of solution 00:29:31.040 --> 00:29:32.080 an amorphous solid? 00:29:32.080 --> 00:29:34.000 It would be silly to call it crystallization. 00:29:34.000 --> 00:29:39.420 So I prefer to use the term precipitation. 00:29:39.420 --> 00:29:41.620 And there's another term that you can use, and I learned 00:29:41.620 --> 00:29:44.680 this one from reading the literature of geochemistry. 00:29:44.680 --> 00:29:48.980 What the geochemists call the reaction going from solution 00:29:48.980 --> 00:29:53.140 to make a solid, they say the system exsolves. 00:29:53.140 --> 00:29:55.470 This is dissolve, this is exsolve. 00:29:55.470 --> 00:29:58.950 So this is called exsolution. 00:29:58.950 --> 00:30:01.440 It's amazing what you can do when you know a 00:30:01.440 --> 00:30:02.610 little bit of Latin. 00:30:02.610 --> 00:30:03.560 So this exsolves. 00:30:03.560 --> 00:30:06.530 So that's the exsolution, or the crystallization reaction. 00:30:06.530 --> 00:30:09.590 Now I'm going to show you what won Arrhenius his Nobel prize. 00:30:09.590 --> 00:30:12.570 Arrhenius did not get the Nobel prize for his brilliant 00:30:12.570 --> 00:30:14.790 work on activation energy. 00:30:14.790 --> 00:30:18.300 He got his Nobel prize on the theory of electrolytic 00:30:18.300 --> 00:30:21.150 dissociation, which was, people knew that you could 00:30:21.150 --> 00:30:24.670 dissolve salts and water, but they didn't know how. 00:30:24.670 --> 00:30:26.940 And it was Arrhenius who said that the salts go into 00:30:26.940 --> 00:30:30.240 solution by dissociating and forming ions. 00:30:30.240 --> 00:30:38.190 So goes in as Ag plus Ag plus aq plus chloride ion-- 00:30:38.190 --> 00:30:39.700 thank you. 00:30:39.700 --> 00:30:42.930 And that, ladies and gentleman, was a Nobel prize 00:30:42.930 --> 00:30:44.500 for Arrhenius. 00:30:44.500 --> 00:30:47.880 And you can see that there's a relationship between the 00:30:47.880 --> 00:30:50.530 amount of silver chloride and the amount of ions. 00:30:50.530 --> 00:30:53.960 So there's a mass balance there, that the concentration 00:30:53.960 --> 00:30:58.310 of silver chloride dissolved, in fact, equals, in this case, 00:30:58.310 --> 00:31:04.520 by stoichiometry, the concentration of Ag plus, 00:31:04.520 --> 00:31:07.820 because of the nature of the dissociation reaction on a 00:31:07.820 --> 00:31:08.930 mass balance basis. 00:31:08.930 --> 00:31:11.880 And that also equals the concentration of the 00:31:11.880 --> 00:31:15.050 chloride ion, OK? 00:31:15.050 --> 00:31:20.590 So that's the way we can look at the system. 00:31:20.590 --> 00:31:25.510 And how do we know that this thing has limited solubility? 00:31:25.510 --> 00:31:30.390 Well, there's various ways of measuring it, and one of them 00:31:30.390 --> 00:31:31.740 involves conductivity. 00:31:31.740 --> 00:31:33.820 Here's the conductivity of pure water. 00:31:33.820 --> 00:31:36.830 And you know that water has very, very poor conductivity, 00:31:36.830 --> 00:31:39.640 and in fact, what's happening here, when we add silver 00:31:39.640 --> 00:31:42.680 chloride is, we're adding charge carriers, because the 00:31:42.680 --> 00:31:44.220 audience are charged species. 00:31:44.220 --> 00:31:45.720 So they can carry charge. 00:31:45.720 --> 00:31:49.050 And you can see that this is a measure of conductivity as a 00:31:49.050 --> 00:31:51.920 function of silver chloride concentration. 00:31:51.920 --> 00:31:55.840 And as you add silver chloride to higher and higher values, 00:31:55.840 --> 00:31:57.500 the conductivity goes up. 00:31:57.500 --> 00:32:00.730 And look at even the tiniest amount of silver chloride has 00:32:00.730 --> 00:32:03.490 a conductivity that's about, what, half an order of 00:32:03.490 --> 00:32:05.380 magnitude higher than the conductivity 00:32:05.380 --> 00:32:07.340 of pure water itself. 00:32:07.340 --> 00:32:10.700 So I would say that this is akin to doping, isn't it? 00:32:10.700 --> 00:32:14.400 So up here, when you've got 10 to the minus 6 Siemens per 00:32:14.400 --> 00:32:17.810 centimeter conductivity, that aqueous solution is 00:32:17.810 --> 00:32:20.720 demonstrating the extrinsic behavior. 00:32:20.720 --> 00:32:22.680 This is very similar to doping. 00:32:22.680 --> 00:32:26.780 And at some point, we get to this value here, around 10 to 00:32:26.780 --> 00:32:31.300 the minus 5 moles of silver chloride per liter, and then 00:32:31.300 --> 00:32:35.350 adding more silver chloride has no impact on conductivity. 00:32:35.350 --> 00:32:38.150 Which tells you that you've hit saturation. 00:32:38.150 --> 00:32:41.540 This is akin to adding more and more sugar to the cup of 00:32:41.540 --> 00:32:44.190 tea, until finally the sugar just falls to the bottom. 00:32:44.190 --> 00:32:46.470 You can stir all you want, but you won't get it to dissolve, 00:32:46.470 --> 00:32:48.890 because you've hit saturation. 00:32:48.890 --> 00:32:54.680 So that indicates the presence of a saturated solution. 00:32:54.680 --> 00:33:01.820 And so we can talk about that value, and we can say that for 00:33:01.820 --> 00:33:07.650 silver chloride, the concentration at saturation is 00:33:07.650 --> 00:33:15.070 equal to 1.3 times 10 to the minus 5 moles per liter. 00:33:15.070 --> 00:33:18.160 Moles of silver chloride per liter. 00:33:18.160 --> 00:33:21.940 And obviously, that's equal to, according to that, it's 00:33:21.940 --> 00:33:24.680 equal to the silver ion concentration. 00:33:24.680 --> 00:33:27.650 I'm going to use square brackets to indicate moles of 00:33:27.650 --> 00:33:30.850 silver, ion per liter of solution, which 00:33:30.850 --> 00:33:33.380 is also equal to-- 00:33:33.380 --> 00:33:37.960 pardon me-- it's also equal to the chloride ion concentration 00:33:37.960 --> 00:33:39.530 at saturation. 00:33:39.530 --> 00:33:41.280 Now I'm going to ask you a simple question. 00:33:41.280 --> 00:33:45.840 Suppose I've got a beaker here, and I know the maximum I 00:33:45.840 --> 00:33:50.100 can get here, the maximum is 1.3 times 10 to the minus 5. 00:33:50.100 --> 00:33:51.950 Now this is a really simple question. 00:33:51.950 --> 00:33:56.060 Suppose I am about to add silver chloride-- 00:33:56.060 --> 00:33:59.130 let's say this is 1 liter already. 00:33:59.130 --> 00:33:59.710 All right? 00:33:59.710 --> 00:34:00.890 I've got one liter. 00:34:00.890 --> 00:34:03.880 And you'd tell me, well, you can put in 1.3 times 10 to the 00:34:03.880 --> 00:34:06.490 minus 5 moles to get the saturation. 00:34:06.490 --> 00:34:10.220 Suppose instead of 1 liter of pure water, I had 1 liter of 00:34:10.220 --> 00:34:15.530 water already containing, say, 1 times 10 to the minus 5 00:34:15.530 --> 00:34:18.230 molar silver chloride. 00:34:18.230 --> 00:34:20.050 Well, that's kind of obvious, isn't it? 00:34:20.050 --> 00:34:24.700 I'm only going to be able to put 0.3 moles in, because 0.3 00:34:24.700 --> 00:34:26.520 times 10 to the minus 5, because I've already got 00:34:26.520 --> 00:34:27.910 silver chloride in there. 00:34:27.910 --> 00:34:28.960 That's easy. 00:34:28.960 --> 00:34:31.490 Now let's make the question a little more interesting. 00:34:31.490 --> 00:34:34.520 Suppose instead of a certain amount of silver chloride in 00:34:34.520 --> 00:34:38.810 there, I have no silver chloride in there. 00:34:38.810 --> 00:34:43.010 But I've got, say, 0.1 molar sodium chloride. 00:34:46.080 --> 00:34:47.090 It's a salt. 00:34:47.090 --> 00:34:48.840 It's a difference salt. 00:34:48.840 --> 00:34:52.830 So the question is, does the presence of a different salt 00:34:52.830 --> 00:34:57.950 have an impact on how much silver chloride I can put into 00:34:57.950 --> 00:34:58.862 this solution? 00:34:58.862 --> 00:35:00.960 And the answer is, yes. 00:35:00.960 --> 00:35:02.720 The answer is yes. 00:35:02.720 --> 00:35:09.130 So what we find is that the presence of the other salt, in 00:35:09.130 --> 00:35:13.210 this case, has an impact, because sodium chloride goes 00:35:13.210 --> 00:35:17.240 in as sodium plus, and chloride minus. 00:35:17.240 --> 00:35:21.070 So there's already a boatload of chloride ion in there, and 00:35:21.070 --> 00:35:23.980 that has an impact on this relationship. 00:35:23.980 --> 00:35:27.620 So how do we answer the question, what is the 00:35:27.620 --> 00:35:30.100 solubility of silver chloride in the presence of other 00:35:30.100 --> 00:35:31.710 chloride ions? 00:35:31.710 --> 00:35:36.510 And for that, we define something called the 00:35:36.510 --> 00:35:37.760 solubility product. 00:35:40.530 --> 00:35:43.980 And you need it in order to answer the question, how do 00:35:43.980 --> 00:35:47.500 you determine the solubility of a solute when there are 00:35:47.500 --> 00:35:50.260 other solutes present already? 00:35:50.260 --> 00:35:55.140 And it's denoted capital K, lowercase sp, subscript. 00:35:55.140 --> 00:35:56.470 Solubility product. 00:35:56.470 --> 00:36:00.770 And it's equal to simply the ion products of the 00:36:00.770 --> 00:36:01.520 constituents. 00:36:01.520 --> 00:36:04.320 So the solubility product of silver chloride is the product 00:36:04.320 --> 00:36:07.470 of the silver ion concentration, and the 00:36:07.470 --> 00:36:09.620 chloride ion concentration. 00:36:09.620 --> 00:36:16.760 And you know that in a solution of silver chloride 00:36:16.760 --> 00:36:24.210 alone, if nothing else, that the concentration of silver 00:36:24.210 --> 00:36:26.910 ion equals the concentration of chloride ion. 00:36:26.910 --> 00:36:30.600 That's the whole business of dissolving by itself. 00:36:30.600 --> 00:36:34.300 And so I can then just say that Ksp. 00:36:34.300 --> 00:36:38.020 will then equal the concentration of silver ion 00:36:38.020 --> 00:36:42.910 squared, which we also know is equal to the concentration of 00:36:42.910 --> 00:36:44.240 silver chloride aqueous. 00:36:44.240 --> 00:36:46.050 See, all of these are the same. 00:36:46.050 --> 00:36:47.720 So this solubility is the same. 00:36:47.720 --> 00:36:52.370 I can just put that in, which is just concentration of 00:36:52.370 --> 00:36:55.220 silver chloride. 00:36:55.220 --> 00:36:56.530 Square that. 00:36:56.530 --> 00:37:02.710 So if I square 1.3 times 10 to the minus 5, I end up with a 00:37:02.710 --> 00:37:08.080 solubility product of 1.8 times 10 to the minus 10. 00:37:08.080 --> 00:37:13.510 So now I can use this in order to determine how much 00:37:13.510 --> 00:37:17.400 solubility I get in the presence of another salt. 00:37:17.400 --> 00:37:22.340 So in this case, I'm going to put 0.1 molar sodium chloride. 00:37:22.340 --> 00:37:24.870 And these are strong salts, so we're going to get complete 00:37:24.870 --> 00:37:26.090 dissociation. 00:37:26.090 --> 00:37:35.010 Gives me 0.1 molar sodium ion, and 0.1 molar chloride ion, 00:37:35.010 --> 00:37:36.080 when it dissociates. 00:37:36.080 --> 00:37:37.330 Now you see the difference. 00:37:37.330 --> 00:37:42.240 Because the silver chloride, by itself, gives me 10 to the 00:37:42.240 --> 00:37:44.750 minus 5 molar chloride ions. 00:37:44.750 --> 00:37:48.360 When I add sodium chloride, I get 4 as a 00:37:48.360 --> 00:37:49.890 magnitude more chloride. 00:37:49.890 --> 00:37:53.160 So let's go back to the Ksp. 00:37:53.160 --> 00:37:56.180 So Ksp, this is for silver chloride. 00:37:56.180 --> 00:37:59.550 Ksp for silver chloride is going to be equal to the 00:37:59.550 --> 00:38:04.100 silver concentration and the chloride concentration. 00:38:04.100 --> 00:38:07.930 And in this case, the silver concentration is just equal to 00:38:07.930 --> 00:38:09.700 whatever that solubility is. 00:38:09.700 --> 00:38:11.850 Because there's only source of silver ion, 00:38:11.850 --> 00:38:13.000 and it's silver chloride. 00:38:13.000 --> 00:38:14.440 So I can write that as 00:38:14.440 --> 00:38:17.410 concentration of silver chloride. 00:38:17.410 --> 00:38:19.350 That's good. 00:38:19.350 --> 00:38:20.870 And now this one here is what? 00:38:20.870 --> 00:38:22.310 I've got two sources. 00:38:22.310 --> 00:38:25.590 I've got silver chloride, I I've got sodium chloride. 00:38:25.590 --> 00:38:27.600 So it's going to equal this thing here. 00:38:27.600 --> 00:38:32.580 0.1 plus whatever I get from silver chloride. 00:38:32.580 --> 00:38:35.560 And it's vanishingly small, isn't it? 00:38:35.560 --> 00:38:38.200 The concentration of silver chloride, whatever it is. 00:38:38.200 --> 00:38:42.770 This is nothing, so I'm just going to neglect it. 00:38:42.770 --> 00:38:43.850 It's dominated now. 00:38:43.850 --> 00:38:47.230 The chlorine is flooded by the silver chloride. 00:38:47.230 --> 00:38:48.940 And this product is a constant. 00:38:48.940 --> 00:38:51.300 That's still equal to 10 to the minus 10. 00:38:51.300 --> 00:38:56.920 So I can turn this around and solve for the concentration of 00:38:56.920 --> 00:38:59.650 silver chloride, which is equal to the 00:38:59.650 --> 00:39:02.780 concentration of silver io. 00:39:02.780 --> 00:39:05.370 And that's equal to, what is it, 10 to of the minus 10 00:39:05.370 --> 00:39:10.170 divided by 0.1, which then gives me-- 00:39:10.170 --> 00:39:12.000 what's the number here? 00:39:12.000 --> 00:39:13.390 Plug that in. 00:39:13.390 --> 00:39:17.390 And I end up with 10 to the 1.8 times 10 00:39:17.390 --> 00:39:20.300 to the minus 9 molar. 00:39:20.300 --> 00:39:20.830 Right? 00:39:20.830 --> 00:39:21.350 So look. 00:39:21.350 --> 00:39:26.970 Look at what's happened by having the chloride present 00:39:26.970 --> 00:39:30.660 from sodium chloride in such a large amount. 00:39:30.660 --> 00:39:32.360 It's repressed. 00:39:32.360 --> 00:39:35.460 It has repressed the dissolution. 00:39:35.460 --> 00:39:40.130 The presence of chloride then has a negative impact on 00:39:40.130 --> 00:39:43.490 solubility, and instead of having 10 to the minus 5 00:39:43.490 --> 00:39:46.350 molar, it's down to 10 to the the minus 9 molar. 00:39:46.350 --> 00:39:51.570 And this effect of repressing solubility by adding a second 00:39:51.570 --> 00:39:56.030 solute is called the common ion effect, OK? 00:39:56.030 --> 00:40:09.790 Solubility repression by second solute is known as the 00:40:09.790 --> 00:40:13.100 common ion effect. 00:40:13.100 --> 00:40:15.140 And this is used in processing. 00:40:15.140 --> 00:40:20.680 If I want to trigger the precipitation-- 00:40:20.680 --> 00:40:22.980 see, if I started with a solution containing 10 to the 00:40:22.980 --> 00:40:26.330 minus 5 molar of silver chloride, and I throw in some 00:40:26.330 --> 00:40:28.170 sodium chloride, it'll start 00:40:28.170 --> 00:40:30.690 precipitating out silver chloride. 00:40:30.690 --> 00:40:33.040 So if I wanted to make a fine precipitate of silver 00:40:33.040 --> 00:40:35.530 chloride, I make a pregnant solution. 00:40:35.530 --> 00:40:37.920 And I could drop the temperature, because you can 00:40:37.920 --> 00:40:40.790 imagine that solubility is a function of temperature, or I 00:40:40.790 --> 00:40:43.580 could keep it isothermal, throw in some sodium chloride, 00:40:43.580 --> 00:40:46.030 and out comes silver chloride. 00:40:46.030 --> 00:40:52.610 So since the common ion effect on it and its value in 00:40:52.610 --> 00:40:54.540 processing. 00:40:54.540 --> 00:40:54.970 OK. 00:40:54.970 --> 00:40:55.940 Good. 00:40:55.940 --> 00:41:03.820 Well, I think I'm going to hold it there. 00:41:03.820 --> 00:41:07.490 I"ll show you just one more thing. 00:41:07.490 --> 00:41:10.730 If you've got stoichiometry like this-- 00:41:10.730 --> 00:41:13.040 this is a difluoride of magnesium. 00:41:13.040 --> 00:41:16.930 If it goes into solution, you get magnesium cation plus 2 00:41:16.930 --> 00:41:18.200 fluoride anions. 00:41:18.200 --> 00:41:22.240 And so if I wrote the Ksp for this reaction, it would be the 00:41:22.240 --> 00:41:28.450 product of the magnesium concentration and the fluoride 00:41:28.450 --> 00:41:30.000 ion concentration. 00:41:30.000 --> 00:41:32.580 Because there's the two here, this is squared. 00:41:32.580 --> 00:41:38.860 So this, too, will transfer up there, and then throw in some 00:41:38.860 --> 00:41:42.860 sodium fluoride, and cause the other thing to exsolve, and 00:41:42.860 --> 00:41:43.910 away we go. 00:41:43.910 --> 00:41:44.080 All right. 00:41:44.080 --> 00:41:45.680 I've got a couple of things to show you. 00:41:45.680 --> 00:41:47.400 We're talking a lot about Arrhenius. 00:41:47.400 --> 00:41:50.860 This is a book I have. It's an English translation of a book 00:41:50.860 --> 00:41:54.540 written by Arrhenius in the late 1800s, and it was printed 00:41:54.540 --> 00:41:57.480 in English around 1908. 00:41:57.480 --> 00:41:59.710 And Arrhenius was a genius. 00:41:59.710 --> 00:42:02.390 He wrote on all sorts of topics here. 00:42:02.390 --> 00:42:04.840 Biology, physics, you name it. 00:42:04.840 --> 00:42:08.430 And one of the things and he was interested in was the 00:42:08.430 --> 00:42:10.470 origins of the earth. 00:42:10.470 --> 00:42:14.450 So this chapter is called, Celestial Bodies as Abodes of 00:42:14.450 --> 00:42:18.670 Organisms. Already speculating on whether you could have life 00:42:18.670 --> 00:42:23.520 as we know it exist elsewhere in the universe. 00:42:23.520 --> 00:42:26.340 And one of the things he talks about is global warming. 00:42:26.340 --> 00:42:28.400 So this is Arrhenius on global warming. 00:42:28.400 --> 00:42:30.780 I'll read you the last paragraph of this chapter. 00:42:30.780 --> 00:42:34.240 There had been some major volcanic eruptions that had 00:42:34.240 --> 00:42:37.600 caused cooling when Krakatoa in 1883 and 00:42:37.600 --> 00:42:39.390 Martinique in 1902. 00:42:39.390 --> 00:42:45.300 Major plumes of soot that caused dramatic decreases in 00:42:45.300 --> 00:42:46.550 temperature. 00:42:46.550 --> 00:42:49.400 So now here comes the last paragraph. 00:42:49.400 --> 00:42:53.280 We often hear lamentations that the coal stored up in the 00:42:53.280 --> 00:42:56.320 earth is wasted by the present generation-- 00:42:56.320 --> 00:42:58.020 remember, this is written 100 years ago-- 00:42:58.020 --> 00:42:59.910 without any thought of the future. 00:42:59.910 --> 00:43:03.110 And we are terrified by the awful destruction of life and 00:43:03.110 --> 00:43:07.920 property which is followed the volcanic eruptions of our day. 00:43:07.920 --> 00:43:10.500 We may find a kind of consolation in the 00:43:10.500 --> 00:43:12.480 consideration that adheres in every other case. 00:43:12.480 --> 00:43:14.780 There is good mixed with the evil. 00:43:14.780 --> 00:43:16.920 By the influence of the increasing percentage of 00:43:16.920 --> 00:43:20.660 carbonic acid in the atmosphere-- that's CO2-- 00:43:20.660 --> 00:43:24.220 we may hope to enjoy ages with more equitable and better 00:43:24.220 --> 00:43:25.540 climates.-- 00:43:25.540 --> 00:43:29.150 Remember, he's a Swede; it's cold-- 00:43:29.150 --> 00:43:32.350 especially as regards the colder regions of the earth, 00:43:32.350 --> 00:43:35.510 ages when the earth will bring forth much more abundant crops 00:43:35.510 --> 00:43:37.640 than at present for the benefit of 00:43:37.640 --> 00:43:40.050 rapidly propagating mankind. 00:43:40.050 --> 00:43:41.930 So it's interesting to see the world-- 00:43:41.930 --> 00:43:42.910 it's a great book to read. 00:43:42.910 --> 00:43:46.140 And you can see people in the 1830s were already calculating 00:43:46.140 --> 00:43:49.600 heat transfer coefficients to how much 00:43:49.600 --> 00:43:51.400 the earth was changing. 00:43:51.400 --> 00:43:52.970 We're going to post these to the website. 00:43:52.970 --> 00:43:55.230 This was, last year, in the New York Times. 00:43:55.230 --> 00:43:57.640 Every Tuesday they have a science section. 00:43:57.640 --> 00:43:59.260 And this was about glass. 00:43:59.260 --> 00:44:04.420 And very, actually, with your 3.091 knowledge, you'll read 00:44:04.420 --> 00:44:07.600 this like a newspaper, and it'll be very easy. 00:44:07.600 --> 00:44:09.590 And they go through the structure. 00:44:09.590 --> 00:44:11.770 Here's the structure of a window glass. 00:44:11.770 --> 00:44:13.420 You can see the network, former network 00:44:13.420 --> 00:44:14.970 modifier, and so on. 00:44:14.970 --> 00:44:18.630 And they talk about how difficult it is from a first 00:44:18.630 --> 00:44:23.160 principle's standpoint to model the structure of glass. 00:44:23.160 --> 00:44:27.210 These oxide glasses are complex and not easy to model. 00:44:27.210 --> 00:44:29.990 So when you're trying to engineer the glasses, instead 00:44:29.990 --> 00:44:33.430 of trial and error, it's hard to do so by theory. 00:44:33.430 --> 00:44:37.820 And it talks about some efforts at theory, and so on. 00:44:37.820 --> 00:44:41.380 And the last thing I want to talk about is 00:44:41.380 --> 00:44:42.640 bulk metallic glasses. 00:44:42.640 --> 00:44:48.170 You recall that I showed you metallic glass that was made 00:44:48.170 --> 00:44:53.550 by melting gold silicon, and dripping it onto a 00:44:53.550 --> 00:44:58.000 water-cooled copper wheel that was zooming around to give us 00:44:58.000 --> 00:45:01.830 a cooling rate of about a million degrees a second. 00:45:01.830 --> 00:45:06.020 And those strips had to be very, very 00:45:06.020 --> 00:45:07.210 thin, the metal strips. 00:45:07.210 --> 00:45:13.110 Because you've got liquid dripping down, and we're 00:45:13.110 --> 00:45:15.330 pulling the solid away, and there's a 00:45:15.330 --> 00:45:18.600 finite thickness here. 00:45:18.600 --> 00:45:20.250 Let's use a Greek letter, xi. 00:45:20.250 --> 00:45:22.210 There's a finite thickness xi. 00:45:22.210 --> 00:45:25.680 Because what's happening is that this is the water-cooled 00:45:25.680 --> 00:45:29.100 copper wheel, and you're extracting heat here. 00:45:29.100 --> 00:45:32.370 But eventually, the thermal conductivity of the metal is 00:45:32.370 --> 00:45:33.690 the limiter. 00:45:33.690 --> 00:45:35.080 In other words, I don't care how cold. 00:45:35.080 --> 00:45:37.240 You can put this in liquid helium if you want. 00:45:37.240 --> 00:45:40.660 You can't get the heat through the metal fast enough. 00:45:40.660 --> 00:45:44.350 And what happens is, when you look down here, the lower part 00:45:44.350 --> 00:45:46.820 is amorphous and the upper part is crystalline. 00:45:46.820 --> 00:45:48.450 So you don't end up with metallic glass. 00:45:48.450 --> 00:45:51.370 You end up with some metallic glass, and the upper part is 00:45:51.370 --> 00:45:52.510 crystalline. 00:45:52.510 --> 00:45:56.120 So what happens when you end up with the limitation being 00:45:56.120 --> 00:45:58.080 the thermal conductivity of the metal? 00:45:58.080 --> 00:46:00.010 At that point, you're finished. 00:46:00.010 --> 00:46:04.330 And this was typically on the order of microns. 00:46:04.330 --> 00:46:06.520 And then they got up to, sort of, submillimeter. 00:46:06.520 --> 00:46:07.190 And that was it. 00:46:07.190 --> 00:46:09.770 So the glass that I showed you was foil. 00:46:09.770 --> 00:46:11.640 Now what happened was, with more research-- 00:46:11.640 --> 00:46:12.200 so here we are. 00:46:12.200 --> 00:46:14.950 This is Pol Duwez at Caltech, gold silicon. 00:46:14.950 --> 00:46:17.460 And this is the thickness in centimeters. 00:46:17.460 --> 00:46:22.250 So you were down here at some tens of microns, all right? 00:46:22.250 --> 00:46:28.260 Now, in the '60s, research at Harvard uncovered a set of 00:46:28.260 --> 00:46:31.760 palladium alloys that had better thermal conductivity 00:46:31.760 --> 00:46:36.560 and, remember the first day, about the analogy to the 00:46:36.560 --> 00:46:37.800 musical chairs? 00:46:37.800 --> 00:46:40.350 These things have slightly more complicated crystal 00:46:40.350 --> 00:46:41.320 structures. 00:46:41.320 --> 00:46:44.660 So for a given cooling rate, the metal has more difficulty 00:46:44.660 --> 00:46:46.460 finding the proper lattice site. 00:46:46.460 --> 00:46:48.760 And they were able to make metallic glasses that were on 00:46:48.760 --> 00:46:51.650 the order of 0.1 centimeters. 00:46:51.650 --> 00:46:53.470 That's still fairly thin. 00:46:53.470 --> 00:46:58.555 And then back to Caltech in the late '80s, early '90s, and 00:46:58.555 --> 00:47:03.740 a man by name of Bill Johnson was able to develop a set of 00:47:03.740 --> 00:47:07.300 alloys that can be made in bulk form. 00:47:07.300 --> 00:47:09.290 Totally amorphous metal. 00:47:09.290 --> 00:47:11.290 And these are known as bulk metallic glasses. 00:47:11.290 --> 00:47:15.540 And look at the complexity of the alloy designation. 00:47:15.540 --> 00:47:17.360 So now you see, well, why are they doing this? 00:47:17.360 --> 00:47:20.430 Because look, this is strength versus elastic limit. 00:47:20.430 --> 00:47:22.430 So you can either have things like polymers, that you can 00:47:22.430 --> 00:47:25.830 stretch very, very far, but they don't have much strength. 00:47:25.830 --> 00:47:29.560 Or you can have things like certain steels, that are very, 00:47:29.560 --> 00:47:33.560 very strong, but you can't bend them very far. 00:47:33.560 --> 00:47:36.330 And bulk metallic glass has put you right up here. 00:47:36.330 --> 00:47:39.000 You have strong alloys that have very, very 00:47:39.000 --> 00:47:40.040 high elastic limits. 00:47:40.040 --> 00:47:43.410 So they make great golf clubs and tennis rackets and so on, 00:47:43.410 --> 00:47:46.400 because they can flex way back, store enormous energy, 00:47:46.400 --> 00:47:47.650 and then spring. 00:47:50.160 --> 00:47:52.460 So here are some bulk metallic glasses, and 00:47:52.460 --> 00:47:54.130 here's a classic one. 00:47:54.130 --> 00:47:58.565 This is zirconium, titanium, copper, nickel, beryllium. 00:47:58.565 --> 00:48:00.060 All right, now how do we get that? 00:48:00.060 --> 00:48:05.900 Well, zirconium and titanium are body-centered cubic, we've 00:48:05.900 --> 00:48:09.740 got copper and nickel are face-centered cubic, and 00:48:09.740 --> 00:48:13.540 beryllium is hexagonal close-packed. 00:48:13.540 --> 00:48:17.130 So the idea here is the principle of confusion. 00:48:17.130 --> 00:48:19.840 So the alloy is fighting with itself. 00:48:19.840 --> 00:48:22.100 You know, am I face-centered cubic, am I body-centered 00:48:22.100 --> 00:48:23.780 cubic, am I hexagonal? 00:48:23.780 --> 00:48:28.650 And this confusion about what the crystal structure is to be 00:48:28.650 --> 00:48:32.440 leads to quenching and the disorder of a liquid state, 00:48:32.440 --> 00:48:34.840 and preventing the formation of grain boundaries, 00:48:34.840 --> 00:48:36.520 dislocations and so on. 00:48:36.520 --> 00:48:39.880 So I want to show you one example besides golf clubs. 00:48:39.880 --> 00:48:45.220 Dave, could we cut to the document camera here? 00:48:45.220 --> 00:48:48.310 Get this thing down. 00:48:48.310 --> 00:48:50.890 So this is a-- 00:48:50.890 --> 00:48:53.280 I'm not endorsing the product at all, but you know, this is 00:48:53.280 --> 00:48:55.720 one of the companies that makes, this 00:48:55.720 --> 00:48:57.090 is SanDisk, I think. 00:48:57.090 --> 00:48:59.870 And they make these flash memories. 00:48:59.870 --> 00:49:02.820 This just looks like a another piece of metal, and in fact, 00:49:02.820 --> 00:49:05.270 it's very disarming, because they call 00:49:05.270 --> 00:49:06.820 this model the Titanium. 00:49:06.820 --> 00:49:09.430 Well, it has about 13% titanium. 00:49:09.430 --> 00:49:11.900 The interesting thing here, what's so cool about this, 00:49:11.900 --> 00:49:13.900 this is bulk metallic glass. 00:49:13.900 --> 00:49:17.360 And what's attractive about the fact that it's bulk 00:49:17.360 --> 00:49:21.800 metallic glass is, that it can be shaped by casting, from the 00:49:21.800 --> 00:49:24.810 liquid state to very, very fine precision. 00:49:24.810 --> 00:49:27.680 So you see all of these slots and everything, and on the 00:49:27.680 --> 00:49:31.830 side, all of this kind of stuff, and on the end. 00:49:31.830 --> 00:49:34.770 All of this is done by casting from the liquid 00:49:34.770 --> 00:49:37.320 state, in one operation. 00:49:37.320 --> 00:49:38.290 And this is a clam shell. 00:49:38.290 --> 00:49:39.250 There's two pieces here. 00:49:39.250 --> 00:49:41.660 I don't know if you can see, but there's two pieces that 00:49:41.660 --> 00:49:43.000 have been sandwiched together. 00:49:43.000 --> 00:49:44.530 You can see on the edge there. 00:49:44.530 --> 00:49:48.300 And the impact that has on manufacturing costs is 00:49:48.300 --> 00:49:51.900 phenomenal, because normally you make the basic shells, 00:49:51.900 --> 00:49:54.220 then you have to drill, and you've got to 00:49:54.220 --> 00:49:55.320 auger out, and so on. 00:49:55.320 --> 00:49:57.320 This thing, one step operation, 00:49:57.320 --> 00:50:00.400 including the labeling. 00:50:00.400 --> 00:50:03.330 There's no subsequent processing. 00:50:03.330 --> 00:50:06.810 And this is done by a company out in Michigan 00:50:06.810 --> 00:50:09.220 called Liquid Metal. 00:50:09.220 --> 00:50:11.630 And they've licensed the technology and so on. 00:50:11.630 --> 00:50:13.610 And again, I'm not trying to make a commercial thing, but 00:50:13.610 --> 00:50:18.790 I'm just trying to show you that these ideas of changing 00:50:18.790 --> 00:50:22.200 properties for engineered materials, you know, are 00:50:22.200 --> 00:50:24.870 around us everywhere. 00:50:24.870 --> 00:50:26.410 And this is relatively recent. 00:50:26.410 --> 00:50:27.920 Bulk metallic glass. 00:50:27.920 --> 00:50:31.830 Fantastic example of structure property relations. 00:50:31.830 --> 00:50:33.080 OK.