1 00:00:00,030 --> 00:00:02,410 The following content is provided under a Creative 2 00:00:02,410 --> 00:00:03,830 Commons license. 3 00:00:03,830 --> 00:00:06,850 Your support will help MIT OpenCourseWare continue to 4 00:00:06,850 --> 00:00:10,520 offer high-quality educational resources for free. 5 00:00:10,520 --> 00:00:13,650 To make a donation, or view additional materials from 6 00:00:13,650 --> 00:00:17,150 hundreds of MIT courses, visit MIT OpenCourseWare at 7 00:00:17,150 --> 00:00:18,400 ocw.mit.edu. 8 00:00:21,000 --> 00:00:24,390 PROFESSOR: So we will have weekly quiz tomorrow. 9 00:00:24,390 --> 00:00:28,100 There's been a lot of coverage, and so to focus you 10 00:00:28,100 --> 00:00:33,170 a bit, I'm going to confine the weekly quiz to glasses and 11 00:00:33,170 --> 00:00:34,100 chemical kinetics. 12 00:00:34,100 --> 00:00:36,040 So you don't have to worry about diffusion. 13 00:00:36,040 --> 00:00:38,300 We'll catch up on that, but I know there's so 14 00:00:38,300 --> 00:00:39,140 much material there. 15 00:00:39,140 --> 00:00:44,270 Let's keep it confined to glasses and chemical kinetics. 16 00:00:44,270 --> 00:00:46,860 And I'll be available today 4:30 to 5:30. 17 00:00:46,860 --> 00:00:51,730 If you can't be at that time, send me a note, and I'm sure 18 00:00:51,730 --> 00:00:54,480 we can figure out a time to get together. 19 00:00:54,480 --> 00:00:57,100 So what I want to do today is to start a new unit. 20 00:00:57,100 --> 00:01:00,810 We're going to start talking today about solutions, and do 21 00:01:00,810 --> 00:01:03,690 some solution chemistry, OK? 22 00:01:03,690 --> 00:01:07,180 Today we talk about solutions. 23 00:01:07,180 --> 00:01:09,330 And you might initially say, why are we 24 00:01:09,330 --> 00:01:10,410 talking about solutions? 25 00:01:10,410 --> 00:01:12,430 This is solid-state chemistry. 26 00:01:12,430 --> 00:01:15,250 I think up until now, you've seen that it's pretty rare 27 00:01:15,250 --> 00:01:17,990 that we use solids in their pure form. 28 00:01:17,990 --> 00:01:20,000 We usually have mixtures. 29 00:01:20,000 --> 00:01:23,050 So for example, when we studied glasses, we modified 30 00:01:23,050 --> 00:01:25,620 the glasses with an alkaline earth oxide. 31 00:01:25,620 --> 00:01:28,250 Well we, in fact, were making a solution of 32 00:01:28,250 --> 00:01:30,170 more than one component. 33 00:01:30,170 --> 00:01:32,800 So it's to get certain properties 34 00:01:32,800 --> 00:01:33,950 that we study solutions. 35 00:01:33,950 --> 00:01:38,380 Secondly, coming out of liquid phase is a way to make solids. 36 00:01:38,380 --> 00:01:40,870 So in terms of processing, we need to understand something 37 00:01:40,870 --> 00:01:42,510 about solutions. 38 00:01:42,510 --> 00:01:45,800 And then lastly, we're going to be studying, towards the 39 00:01:45,800 --> 00:01:49,140 end of the semester, a big unit on biochemistry. 40 00:01:49,140 --> 00:01:51,850 And biochemistry, why, you say, biochemistry? 41 00:01:51,850 --> 00:01:52,950 Why is he doing biochemistry? 42 00:01:52,950 --> 00:01:54,760 I thought this was solid-state chemistry. 43 00:01:54,760 --> 00:01:58,570 We are solid-state devices, but we're made of soft matter. 44 00:01:58,570 --> 00:02:01,640 At least the exoskeleton is soft matter. 45 00:02:01,640 --> 00:02:04,740 The endoskeleton is ceramic, right? 46 00:02:04,740 --> 00:02:07,800 Our bone structure is ceramic. 47 00:02:07,800 --> 00:02:10,370 Hydroxyapatite, calcium hydroxyapatite, and the 48 00:02:10,370 --> 00:02:12,370 outside is a polymer. 49 00:02:12,370 --> 00:02:12,830 So look at this. 50 00:02:12,830 --> 00:02:15,860 Confirmational changes in polymer. 51 00:02:15,860 --> 00:02:19,560 But the chemistry, the biochemistry, so much of it 52 00:02:19,560 --> 00:02:21,140 takes place in aqueous solution. 53 00:02:21,140 --> 00:02:23,060 So hence, we better know something 54 00:02:23,060 --> 00:02:24,960 about aqueous solution. 55 00:02:24,960 --> 00:02:29,430 So to this, we go almost right back to the first day. 56 00:02:29,430 --> 00:02:32,160 You remember, was the second lecture, and we showed this 57 00:02:32,160 --> 00:02:35,720 figure, and all the different categories of matter. 58 00:02:35,720 --> 00:02:38,480 And we started over here with elements, and we moved into 59 00:02:38,480 --> 00:02:41,560 some pure substance compounds, et cetera, et cetera. 60 00:02:41,560 --> 00:02:43,500 Now we're going to move over to here. 61 00:02:43,500 --> 00:02:46,600 So homogeneous mixture containing uniform composition 62 00:02:46,600 --> 00:02:49,650 and properties, as opposed to a heterogeneous mix. 63 00:02:49,650 --> 00:02:50,910 So we're now over here. 64 00:02:50,910 --> 00:02:54,220 We're working our way through the diagram. 65 00:02:54,220 --> 00:02:54,570 All right. 66 00:02:54,570 --> 00:02:58,540 So let's get a couple of basic definitions up. 67 00:02:58,540 --> 00:03:05,240 So the solution is really a mix of at least two 68 00:03:05,240 --> 00:03:06,130 constituents. 69 00:03:06,130 --> 00:03:10,450 One, the majority constituent is called the solvent, and 70 00:03:10,450 --> 00:03:13,330 then we can have one or more solutes. 71 00:03:16,160 --> 00:03:22,190 So the solvent, this is the majority constituent, and then 72 00:03:22,190 --> 00:03:25,095 the solutes are the minority constituents. 73 00:03:25,095 --> 00:03:27,090 And in some instances, it's pretty hard to 74 00:03:27,090 --> 00:03:28,640 tell which is which. 75 00:03:28,640 --> 00:03:30,870 And as far as types of solutions, I 76 00:03:30,870 --> 00:03:31,950 want to broaden this. 77 00:03:31,950 --> 00:03:34,150 You know, when I say solution, you're probably thinking about 78 00:03:34,150 --> 00:03:35,540 aqueous solution. 79 00:03:35,540 --> 00:03:38,660 But I want to take a minute and work through this chart. 80 00:03:38,660 --> 00:03:40,780 And this is all posted, so you don't have to 81 00:03:40,780 --> 00:03:41,540 write it all down. 82 00:03:41,540 --> 00:03:42,480 Just follow with me. 83 00:03:42,480 --> 00:03:47,080 So most of the general chemistry subjects will just 84 00:03:47,080 --> 00:03:48,840 stop at the end of the first line. 85 00:03:48,840 --> 00:03:51,870 They'll treat solutions as aqueous solutions. 86 00:03:51,870 --> 00:03:54,740 But in material science, we think of things broadly. 87 00:03:54,740 --> 00:03:58,000 So a good example of a simple aqueous solution is sodium 88 00:03:58,000 --> 00:03:58,870 chloride and water. 89 00:03:58,870 --> 00:04:03,030 Sodium chloride is the solute and water is the solvent. 90 00:04:03,030 --> 00:04:04,840 But you can have a liquid solute. 91 00:04:04,840 --> 00:04:07,870 So wine-- 92 00:04:07,870 --> 00:04:10,030 in case you've ever encountered this beverage, 93 00:04:10,030 --> 00:04:15,650 it's primarily water, but it can contain up to about 14% 94 00:04:15,650 --> 00:04:19,130 ethyl alcohol, and there are other constituents that give 95 00:04:19,130 --> 00:04:21,040 the color and the flavor and so on. 96 00:04:21,040 --> 00:04:23,490 And you can have a gas in a liquid, and that would be 97 00:04:23,490 --> 00:04:26,050 seltzer, where CO2 is dissolved. 98 00:04:26,050 --> 00:04:26,955 It's actually dissolved. 99 00:04:26,955 --> 00:04:31,820 If you take a look at a bottle of bubbly water on the shelf, 100 00:04:31,820 --> 00:04:32,950 you don't see the bubbles. 101 00:04:32,950 --> 00:04:36,220 The carbon dioxide is actually dissolved. 102 00:04:36,220 --> 00:04:39,720 You can have a gas as a solvent, and air would be an 103 00:04:39,720 --> 00:04:42,840 example of that, where the solvent is nitrogen. 104 00:04:42,840 --> 00:04:46,230 And then we have as solutes oxygen, argon, carbon dioxide, 105 00:04:46,230 --> 00:04:49,740 if you live next to a power plant, it's sulfur dioxide, if 106 00:04:49,740 --> 00:04:51,640 you live next to an aluminum smelter, it's 107 00:04:51,640 --> 00:04:53,692 tetrafluoromethane, and so on. 108 00:04:53,692 --> 00:04:56,160 So we have all kinds of solutes in the air. 109 00:04:56,160 --> 00:04:58,320 And then we can have solid solutions. 110 00:04:58,320 --> 00:05:01,580 And OK, as soon as you see the word solid, you know, that 111 00:05:01,580 --> 00:05:02,870 means you're 3.091. 112 00:05:02,870 --> 00:05:04,460 So what do we see for solids? 113 00:05:04,460 --> 00:05:05,380 Metal alloys. 114 00:05:05,380 --> 00:05:07,110 We saw carbon dissolved in iron. 115 00:05:07,110 --> 00:05:08,640 Well, that's a solution. 116 00:05:08,640 --> 00:05:12,250 It's homogeneous, single phase, just as the definition 117 00:05:12,250 --> 00:05:15,070 on that chart 1.11 said. 118 00:05:15,070 --> 00:05:19,550 Semiconductor, boron doping into silicon, the boron sits 119 00:05:19,550 --> 00:05:20,950 on a silicon lattice site. 120 00:05:20,950 --> 00:05:23,740 So this is a true solution. 121 00:05:23,740 --> 00:05:27,530 The boron is the solute, and silicon is the solvent. 122 00:05:27,530 --> 00:05:28,800 We can have the ceramic. 123 00:05:28,800 --> 00:05:30,450 We talked about the oxygen sensor. 124 00:05:30,450 --> 00:05:34,950 The oxygen sensor is zirconia, which has been stabilized with 125 00:05:34,950 --> 00:05:37,390 the addition of calcium oxide. 126 00:05:37,390 --> 00:05:38,320 As one example. 127 00:05:38,320 --> 00:05:40,720 In contemporary work, they might use another oxide. 128 00:05:40,720 --> 00:05:43,170 But what's the purpose of the calcium oxide? 129 00:05:43,170 --> 00:05:47,250 Well, I told you that it's to increase the vacancy 130 00:05:47,250 --> 00:05:49,190 population, give you a rapid response 131 00:05:49,190 --> 00:05:50,330 on your oxygen sensor. 132 00:05:50,330 --> 00:05:52,740 And as we're going to learn later, that's true, and 133 00:05:52,740 --> 00:05:55,900 there's a second value in putting in the calcium oxide. 134 00:05:55,900 --> 00:05:58,960 And it stabilizes, that's why they use the term stabilize, 135 00:05:58,960 --> 00:06:01,440 it stabilizes the cubic form of zirconia. 136 00:06:01,440 --> 00:06:04,400 Zirconia has a different crystallographic 137 00:06:04,400 --> 00:06:05,340 modifications. 138 00:06:05,340 --> 00:06:08,970 The cubic one is the one that gives us the best ability to 139 00:06:08,970 --> 00:06:12,690 transfer oxygen, and the addition of calcium oxide as a 140 00:06:12,690 --> 00:06:16,430 solute, the calcium ions actually sit on the zirconium 141 00:06:16,430 --> 00:06:19,480 lattice, that's a true solid solution. 142 00:06:19,480 --> 00:06:22,960 It also makes the cubic zirconia stable, and with 143 00:06:22,960 --> 00:06:25,950 Christmas coming, you know, it's the poor man's diamond, 144 00:06:25,950 --> 00:06:28,610 and that's the same material there. 145 00:06:28,610 --> 00:06:31,630 And to modify a glass, as I mentioned earlier, adding a 146 00:06:31,630 --> 00:06:34,360 alkaline earth oxide breaks the silicate network. 147 00:06:34,360 --> 00:06:35,640 That's a solution. 148 00:06:35,640 --> 00:06:38,220 Now here's an inverse one, where the solid is the 149 00:06:38,220 --> 00:06:42,040 solvent, and the liquid is the solute. 150 00:06:42,040 --> 00:06:46,370 So this was dentist's office practice going back to the 151 00:06:46,370 --> 00:06:47,830 time when I was your age. 152 00:06:47,830 --> 00:06:51,390 If you had a feeling, the dentist had silver and mercury 153 00:06:51,390 --> 00:06:55,110 in the dentist's office, and would add liquid mercury to 154 00:06:55,110 --> 00:07:00,630 silver and make up this amalgam, and then jam that 155 00:07:00,630 --> 00:07:01,390 into the tooth. 156 00:07:01,390 --> 00:07:03,560 Actually, that was the B part of the operation. 157 00:07:03,560 --> 00:07:05,870 There was this dentist here in the United States, and if I 158 00:07:05,870 --> 00:07:08,530 could find him, I would like to have a word with him. 159 00:07:08,530 --> 00:07:10,730 But he had this theory. 160 00:07:10,730 --> 00:07:14,720 You see, the amalgam is a metallic alloy. 161 00:07:14,720 --> 00:07:17,110 And so obviously, it has metallic bonding. 162 00:07:17,110 --> 00:07:19,080 And the tooth is-- 163 00:07:19,080 --> 00:07:21,230 it's a ceramic. 164 00:07:21,230 --> 00:07:24,280 So what kind of bonds are going to form between a metal 165 00:07:24,280 --> 00:07:25,270 and a ceramic? 166 00:07:25,270 --> 00:07:28,050 They're not very good. 167 00:07:28,050 --> 00:07:32,640 So this dentist had the theory that the way to increase the 168 00:07:32,640 --> 00:07:36,890 bonding capability of the amalgam to the tooth was to 169 00:07:36,890 --> 00:07:38,960 maximize contact areas. 170 00:07:38,960 --> 00:07:42,210 So when you went in with a tiny, tiny little cavity, the 171 00:07:42,210 --> 00:07:49,530 dentist would drill the tooth out, removing about 75% of the 172 00:07:49,530 --> 00:07:52,700 volume of the tooth, and then they would make this amalgam 173 00:07:52,700 --> 00:07:54,390 and shove that in. 174 00:07:54,390 --> 00:07:59,070 And you'd wear that for about 20 years, until one day you 175 00:07:59,070 --> 00:08:02,680 bite into a muffin that's got a little piece of walnut shell 176 00:08:02,680 --> 00:08:04,760 in it, and the amalgam flexes, and your 177 00:08:04,760 --> 00:08:06,610 thin-walled tooth goes bang! 178 00:08:06,610 --> 00:08:07,760 Like that. 179 00:08:07,760 --> 00:08:11,010 And now you get to go back to the dentist's office for yet 180 00:08:11,010 --> 00:08:13,730 some more medieval treatment. 181 00:08:13,730 --> 00:08:16,510 Actually, things have improved somewhat. 182 00:08:16,510 --> 00:08:17,840 Thanks to material science. 183 00:08:17,840 --> 00:08:20,080 But they're not using this amalgam anymore. 184 00:08:20,080 --> 00:08:21,920 But there are a number of us who are still walking around 185 00:08:21,920 --> 00:08:25,530 with silver and mercury in our mouths, and-- 186 00:08:25,530 --> 00:08:25,850 yeah. 187 00:08:25,850 --> 00:08:27,290 Enough about my dental problems. 188 00:08:27,290 --> 00:08:29,570 Now let's go on to intercalation. 189 00:08:29,570 --> 00:08:31,300 You can put a gas into a solid. 190 00:08:31,300 --> 00:08:33,820 And I told you about this one, where if you want to store 191 00:08:33,820 --> 00:08:35,740 hydrogen, and this is a big problem, if we're going to 192 00:08:35,740 --> 00:08:37,830 talk about hydrogen-powered vehicles. 193 00:08:40,360 --> 00:08:43,385 A problem as big as, how to get the fuel cell cheap 194 00:08:43,385 --> 00:08:45,550 enough, is where are you going to store the hydrogen on the 195 00:08:45,550 --> 00:08:48,840 car, and one of the materials that's been proposed is this 196 00:08:48,840 --> 00:08:52,030 alloy of lanthanum and nickel that can intercalate huge 197 00:08:52,030 --> 00:08:52,990 amounts of hydrogen. 198 00:08:52,990 --> 00:08:54,900 So that forms a solid solution. 199 00:08:54,900 --> 00:08:57,230 So those are examples of solutions, and we're going to 200 00:08:57,230 --> 00:09:00,300 go back and make sure that we cover the basic Gen Chem at 201 00:09:00,300 --> 00:09:00,950 the top here. 202 00:09:00,950 --> 00:09:02,690 But I want you know that solution 203 00:09:02,690 --> 00:09:04,990 chemistry is very broad. 204 00:09:04,990 --> 00:09:08,100 Now when you dissolve something, you actually have 205 00:09:08,100 --> 00:09:11,680 things down at the atomic level. 206 00:09:11,680 --> 00:09:16,330 So for example, in brine, you actually have below two 207 00:09:16,330 --> 00:09:17,910 nanometers as particle size. 208 00:09:17,910 --> 00:09:21,680 You actually have sodium ions and chloride ions dissolved 209 00:09:21,680 --> 00:09:27,070 completely, which means that the solution is clear, 210 00:09:27,070 --> 00:09:29,240 colorless, and transparent to visible light. 211 00:09:29,240 --> 00:09:31,780 Water is clear, colorless, transparent to visible light. 212 00:09:31,780 --> 00:09:34,810 If you had sodium chloride, it remains clear, colorless, 213 00:09:34,810 --> 00:09:36,150 transparent to visible light. 214 00:09:36,150 --> 00:09:39,590 You can't filter, and you can't wait for the sodium 215 00:09:39,590 --> 00:09:43,030 chloride to settle out, because it's bonded within the 216 00:09:43,030 --> 00:09:44,710 structure of the liquid water. 217 00:09:44,710 --> 00:09:46,550 And this has implications. 218 00:09:46,550 --> 00:09:49,340 There's so much water on the planet, but there's not so 219 00:09:49,340 --> 00:09:51,470 much fresh water on the planet. 220 00:09:51,470 --> 00:09:54,570 And desalination can't be accomplished by filtration. 221 00:09:54,570 --> 00:09:58,800 A filter that had a pore size small enough to trap sodium 222 00:09:58,800 --> 00:10:03,390 ions, the pore size would be so small, water molecules 223 00:10:03,390 --> 00:10:04,170 couldn't go through. 224 00:10:04,170 --> 00:10:06,380 So this is the concept. 225 00:10:06,380 --> 00:10:09,560 At the other end, you can get something called a suspension, 226 00:10:09,560 --> 00:10:12,670 where the particle size is greater than about 1,000 227 00:10:12,670 --> 00:10:15,680 nanometers, and blood is a good example of that, where 228 00:10:15,680 --> 00:10:17,390 it's opaque. 229 00:10:17,390 --> 00:10:20,450 Visible light doesn't go through, but you can filter 230 00:10:20,450 --> 00:10:22,650 out some of the matter in blood. 231 00:10:22,650 --> 00:10:25,080 And if you let it sit for a while, it'll settle in it 232 00:10:25,080 --> 00:10:26,450 gravitational field. 233 00:10:26,450 --> 00:10:29,860 And in between, you have this whole zone of colloids. 234 00:10:29,860 --> 00:10:32,540 And so between colloids and suspensions, the only 235 00:10:32,540 --> 00:10:34,640 difference is particle size. 236 00:10:34,640 --> 00:10:37,150 And this whole thing we would just call a dispersion of 237 00:10:37,150 --> 00:10:40,230 another phase, either another solid phase, or 238 00:10:40,230 --> 00:10:41,860 another liquid phase. 239 00:10:41,860 --> 00:10:44,890 And it's kind of an interesting physical chemistry 240 00:10:44,890 --> 00:10:49,070 about the dispersion, what makes it work. 241 00:10:49,070 --> 00:10:51,660 For example, in milk, milk is a good example of a 242 00:10:51,660 --> 00:10:52,610 dispersion. 243 00:10:52,610 --> 00:10:56,650 You have a fatty phase, and you have an aqueous phase. 244 00:10:56,650 --> 00:10:58,470 The aqueous phase, where all the minerals are. 245 00:10:58,470 --> 00:10:58,800 Why? 246 00:10:58,800 --> 00:11:00,510 Because the minerals are-- 247 00:11:00,510 --> 00:11:01,810 what kind of compound? 248 00:11:01,810 --> 00:11:04,850 They're not metallic, they're not covalent. 249 00:11:04,850 --> 00:11:06,030 They're ionic. 250 00:11:06,030 --> 00:11:09,235 The ionic compounds dissolve in the aqueous phase, and then 251 00:11:09,235 --> 00:11:10,940 in the fatty phase, that's where you have the 252 00:11:10,940 --> 00:11:12,600 protein and so on. 253 00:11:12,600 --> 00:11:16,700 But the fatty phase is clear and colorless, and the aqueous 254 00:11:16,700 --> 00:11:17,820 phase is clear and colorless. 255 00:11:17,820 --> 00:11:20,320 And yet milk is white. 256 00:11:20,320 --> 00:11:23,750 It's, as the term implies, it's milky. 257 00:11:23,750 --> 00:11:24,900 Why? 258 00:11:24,900 --> 00:11:26,130 What's going on? 259 00:11:26,130 --> 00:11:28,670 You have a second phase here. 260 00:11:28,670 --> 00:11:34,360 This could be the fatty phase, and this is the aqueous phase. 261 00:11:34,360 --> 00:11:36,510 They're both clear and colorless, but they have 262 00:11:36,510 --> 00:11:38,870 different indices of refraction. 263 00:11:38,870 --> 00:11:43,380 And since this has n fatty phase, and this has n aqueous 264 00:11:43,380 --> 00:11:47,200 phase, this interface scatters the light. 265 00:11:47,200 --> 00:11:50,370 So if you want to start a business, if you want to try 266 00:11:50,370 --> 00:11:57,640 to tailor the index so that the index of the aqueous phase 267 00:11:57,640 --> 00:12:00,790 matches the index of refraction of the fatty phase, 268 00:12:00,790 --> 00:12:03,520 you'd have the two dissolve, one and the other, and it 269 00:12:03,520 --> 00:12:06,060 would be transparent, divisible light. 270 00:12:06,060 --> 00:12:08,160 So you would have milk that isn't milky. 271 00:12:12,870 --> 00:12:14,960 I mean, the public would be very confused. 272 00:12:14,960 --> 00:12:16,300 But anyways. 273 00:12:16,300 --> 00:12:17,100 So that's what you do. 274 00:12:17,100 --> 00:12:20,200 So why does this thing not settle? 275 00:12:20,200 --> 00:12:24,240 Because they do have a density difference, and again, going 276 00:12:24,240 --> 00:12:27,510 back to the days when I was not a college student but a 277 00:12:27,510 --> 00:12:30,650 youngster, there was still this form of milk called 278 00:12:30,650 --> 00:12:31,790 pasteurized milk. 279 00:12:31,790 --> 00:12:34,810 Well, all milk is pasteurized, but this milk was not 280 00:12:34,810 --> 00:12:35,770 homogenized. 281 00:12:35,770 --> 00:12:40,390 And what would happen is, there was this person that 282 00:12:40,390 --> 00:12:41,930 would deliver milk. 283 00:12:41,930 --> 00:12:45,140 This was a borosilicate glass bottle. 284 00:12:45,140 --> 00:12:47,790 And here would be the cream. 285 00:12:47,790 --> 00:12:49,220 The cream would rise to the top. 286 00:12:49,220 --> 00:12:52,120 We have all these expressions in our language. 287 00:12:52,120 --> 00:12:54,970 And then this would be the milk here, and you could skim 288 00:12:54,970 --> 00:12:57,240 this off for coffee or sugar, and then this would be a 289 00:12:57,240 --> 00:12:58,600 low-fat milk. 290 00:12:58,600 --> 00:13:02,530 But people wanted this all mixed, so then they went to 291 00:13:02,530 --> 00:13:04,320 homogenized milk. 292 00:13:04,320 --> 00:13:07,850 So what is homogenized milk? 293 00:13:07,850 --> 00:13:09,330 This is your red cap, now. 294 00:13:09,330 --> 00:13:10,570 All the milk is homogenized. 295 00:13:10,570 --> 00:13:11,360 This was a big thing. 296 00:13:11,360 --> 00:13:12,610 This was simply called pasteurized. 297 00:13:15,090 --> 00:13:16,820 I'm going to get to the physical chemistry here. 298 00:13:16,820 --> 00:13:17,750 It's very interesting. 299 00:13:17,750 --> 00:13:21,100 Because this is lower density, and yet in homogenized milk it 300 00:13:21,100 --> 00:13:23,060 doesn't rise. 301 00:13:23,060 --> 00:13:26,410 So let's take a look at what goes on in the physical 302 00:13:26,410 --> 00:13:30,030 chemistry of homogenized milk, because it's all about these 303 00:13:30,030 --> 00:13:33,820 various systems. So I'm going to take this particle here, 304 00:13:33,820 --> 00:13:36,835 and its sum insoluble cluster. 305 00:13:41,810 --> 00:13:43,550 And I'm not specifying the cluster size. 306 00:13:43,550 --> 00:13:47,610 It's probably greater than about two nanometers. 307 00:13:47,610 --> 00:13:49,690 So there are two forces acting on this. 308 00:13:49,690 --> 00:13:56,170 There's a settling force and there's a buoyancy force. 309 00:13:56,170 --> 00:13:57,920 Obviously, otherwise it wouldn't float. 310 00:13:57,920 --> 00:14:01,570 So there's some kind of a buoyancy force. 311 00:14:01,570 --> 00:14:03,300 Settling force and a buoyancy force. 312 00:14:03,300 --> 00:14:05,920 Well, the settling force, this is just the gravity. 313 00:14:05,920 --> 00:14:06,490 Right? 314 00:14:06,490 --> 00:14:08,620 This is the force of gravity. 315 00:14:08,620 --> 00:14:10,400 And we know the force of gravity. 316 00:14:10,400 --> 00:14:12,560 That goes with the mass. 317 00:14:12,560 --> 00:14:15,420 Come on, get that cell phone out of here. 318 00:14:15,420 --> 00:14:18,720 This force of gravity goes as the mass, and the mass, we 319 00:14:18,720 --> 00:14:21,220 know, goes as the volume. 320 00:14:21,220 --> 00:14:24,070 And the volume goes as the cube of the radius. 321 00:14:24,070 --> 00:14:27,120 I'm assuming this is a spherical particle, all right? 322 00:14:27,120 --> 00:14:28,410 Now, the buoyancy force. 323 00:14:28,410 --> 00:14:30,570 The buoyancy force is the interfacial 324 00:14:30,570 --> 00:14:32,240 force between the two. 325 00:14:32,240 --> 00:14:33,790 There's some binding across here. 326 00:14:33,790 --> 00:14:38,430 Maybe weak van der Waals, or if this fatty phase has 327 00:14:38,430 --> 00:14:41,070 molecules in it that are polar, then there could be 328 00:14:41,070 --> 00:14:43,290 dipole-dipole interaction. 329 00:14:43,290 --> 00:14:45,020 But in any case, there's some kind of an 330 00:14:45,020 --> 00:14:48,470 interfacial force here. 331 00:14:48,470 --> 00:14:52,880 And this is all chemical bonding 332 00:14:52,880 --> 00:14:56,870 between solute and solvent. 333 00:14:59,420 --> 00:15:01,440 But you see, the force is a weak force. 334 00:15:01,440 --> 00:15:03,050 If it were a really strong force, it would 335 00:15:03,050 --> 00:15:04,110 dissolve this thing. 336 00:15:04,110 --> 00:15:07,240 It won't quite dissolve it, but there is some kind of 337 00:15:07,240 --> 00:15:09,480 dipole-dipole weak force. 338 00:15:09,480 --> 00:15:14,840 And this one here is operating across the surface area. 339 00:15:14,840 --> 00:15:15,810 That's the contact. 340 00:15:15,810 --> 00:15:19,790 So this force goes as the area, and area goes as the 341 00:15:19,790 --> 00:15:23,570 square of the radius, whereas mass goes as 342 00:15:23,570 --> 00:15:24,690 the cube of the radius. 343 00:15:24,690 --> 00:15:29,570 So you know, from your math, that r cubed dominates r 344 00:15:29,570 --> 00:15:33,830 squared, but only at large r. 345 00:15:33,830 --> 00:15:35,860 It's not always the case, is it? 346 00:15:35,860 --> 00:15:37,570 Maybe before you got here, you thought that. 347 00:15:37,570 --> 00:15:40,190 But now that you've been at MIT a few months, you know 348 00:15:40,190 --> 00:15:44,860 that r squared can dominate r cubed at small r. 349 00:15:47,560 --> 00:15:49,400 Interfacial forces dominate. 350 00:15:49,400 --> 00:15:52,650 And that's exactly what happens in these dispersions, 351 00:15:52,650 --> 00:15:54,520 and that's why they don't settle out. 352 00:15:54,520 --> 00:15:59,770 Now, homogenized milk is simply milk that has been 353 00:15:59,770 --> 00:16:03,610 agitated in such a way as to reduce the fat globule size 354 00:16:03,610 --> 00:16:08,570 below a critical value so that these interfacial forces hold 355 00:16:08,570 --> 00:16:10,670 the fat globules in suspension. 356 00:16:10,670 --> 00:16:13,310 If you waited long enough, they would agglomerate and 357 00:16:13,310 --> 00:16:17,660 settle, but that time is probably longer than the shelf 358 00:16:17,660 --> 00:16:18,300 life of the milk. 359 00:16:18,300 --> 00:16:22,150 So the milk probably spoils before stuff settles out. 360 00:16:22,150 --> 00:16:26,620 So this is all very important to understand. 361 00:16:26,620 --> 00:16:31,030 The range that exists between insolubility and this sort of 362 00:16:31,030 --> 00:16:34,730 clustering, and suspension, and so on. 363 00:16:34,730 --> 00:16:37,565 By the way, a lot of pharmaceuticals are like this. 364 00:16:37,565 --> 00:16:39,030 A lot of pharmaceuticals. 365 00:16:39,030 --> 00:16:40,670 So when it says, shake well before 366 00:16:40,670 --> 00:16:42,690 using, they're not kidding. 367 00:16:42,690 --> 00:16:46,610 Because the active ingredient will settle. 368 00:16:46,610 --> 00:16:50,210 And you're drinking just the solvent, just the vehicle. 369 00:16:50,210 --> 00:16:54,400 And all of the potency is on the bottom of the bottle. 370 00:16:54,400 --> 00:16:55,660 Shake that thing up! 371 00:16:59,100 --> 00:17:01,760 I can't say what it does to the taste, but 372 00:17:01,760 --> 00:17:03,540 that's another problem. 373 00:17:03,540 --> 00:17:05,140 Actually, I threw in this slide here. 374 00:17:05,140 --> 00:17:07,200 We're not going to spend any time on it, but you can look 375 00:17:07,200 --> 00:17:08,260 at it at some point. 376 00:17:08,260 --> 00:17:10,130 This is a whole taxonomy of colloids. 377 00:17:12,920 --> 00:17:16,090 Solid-liquid emulsions, aerosols, they're all part of 378 00:17:16,090 --> 00:17:21,170 this magic zone between solubility and 379 00:17:21,170 --> 00:17:23,280 just brick, all right? 380 00:17:23,280 --> 00:17:26,310 There's this whole fine, pardon the pun, 381 00:17:26,310 --> 00:17:28,610 the whole fine structure. 382 00:17:28,610 --> 00:17:31,480 OK, So let's get to the chemistry. 383 00:17:31,480 --> 00:17:34,300 Obviously there's something to do with bonding here, right? 384 00:17:34,300 --> 00:17:37,960 So here's a simple experiment, and this is taken right from 385 00:17:37,960 --> 00:17:38,380 the reading. 386 00:17:38,380 --> 00:17:41,850 So I've just taken this episode that is written up in 387 00:17:41,850 --> 00:17:42,280 the reading. 388 00:17:42,280 --> 00:17:44,490 So we've got two beakers here, and in each 389 00:17:44,490 --> 00:17:45,940 beaker, we have a bilayer. 390 00:17:45,940 --> 00:17:51,090 We've poured in some carbon tetrachloride, liquid, and 391 00:17:51,090 --> 00:17:52,410 we've poured in some water. 392 00:17:52,410 --> 00:17:55,990 And these two are immiscible, because carbon tetrachloride 393 00:17:55,990 --> 00:17:59,820 is obviously a non-polar liquid, and water is a polar 394 00:17:59,820 --> 00:18:02,350 liquid with hydrogen bonding capability. 395 00:18:02,350 --> 00:18:06,350 And in one beaker, we introduce crystals of iodine. 396 00:18:06,350 --> 00:18:08,140 In the other beaker, we introduce crystals of 397 00:18:08,140 --> 00:18:09,600 potassium permanganate. 398 00:18:09,600 --> 00:18:12,690 And then we shake them up, and we wait. 399 00:18:12,690 --> 00:18:17,950 And eventually we see that on the left, the iodine dissolves 400 00:18:17,950 --> 00:18:19,350 in the carbon tetrachloride. 401 00:18:19,350 --> 00:18:21,830 And we're using the purple color as an indicator. 402 00:18:21,830 --> 00:18:23,890 And this is kind of cute, because both potassium 403 00:18:23,890 --> 00:18:28,160 permanganate and iodine will render things purple. 404 00:18:28,160 --> 00:18:29,770 So you're comparing purple to purple. 405 00:18:29,770 --> 00:18:31,780 They could have chosen something else, but this is 406 00:18:31,780 --> 00:18:32,710 kind of cute. 407 00:18:32,710 --> 00:18:33,030 All right. 408 00:18:33,030 --> 00:18:35,580 So here you end up with a solution of iodine and carbon 409 00:18:35,580 --> 00:18:38,340 tetrachloride, whereas on the right side, you end up with a 410 00:18:38,340 --> 00:18:41,900 solution of potassium permanganate and water, and 411 00:18:41,900 --> 00:18:44,490 nothing in the carbon tetrachloride. 412 00:18:44,490 --> 00:18:47,840 So what can we infer from this? 413 00:18:47,840 --> 00:18:50,130 Well, let's take a look at the possible interactions. 414 00:18:50,130 --> 00:18:53,950 So first of all let's categorize H2O. 415 00:18:53,950 --> 00:18:59,410 This is polar, it's a polar liquid, with hydrogen bonding 416 00:18:59,410 --> 00:19:00,660 capability. 417 00:19:03,810 --> 00:19:06,990 Carbon tetrachloride is non-polar. 418 00:19:06,990 --> 00:19:08,010 It's very toxic. 419 00:19:08,010 --> 00:19:11,790 When I was a child, we had this in the medicine cabinet. 420 00:19:11,790 --> 00:19:13,005 It's a non-polar solvent. 421 00:19:13,005 --> 00:19:16,040 It's fantastic for getting grease stains off. 422 00:19:16,040 --> 00:19:17,050 Every man had this. 423 00:19:17,050 --> 00:19:19,757 With a little handkerchief, you'd take a little grease 424 00:19:19,757 --> 00:19:21,260 stain off your tie. 425 00:19:21,260 --> 00:19:22,240 You can't buy this stuff. 426 00:19:22,240 --> 00:19:24,560 You can't even guy it for research anymore. 427 00:19:24,560 --> 00:19:25,310 It's too bad. 428 00:19:25,310 --> 00:19:26,620 It's great stuff. 429 00:19:26,620 --> 00:19:27,620 Highly toxic, though. 430 00:19:27,620 --> 00:19:31,690 But you know, there's a time and a place. 431 00:19:31,690 --> 00:19:32,030 All right. 432 00:19:32,030 --> 00:19:33,430 So then here's iodine. 433 00:19:33,430 --> 00:19:36,640 Iodine, we know, is non-polar. 434 00:19:36,640 --> 00:19:39,450 It's a homonuclear molecule, it has to be non-polar. 435 00:19:39,450 --> 00:19:42,330 And so what holds iodine together in the crystal? 436 00:19:42,330 --> 00:19:46,320 There's only one bond, and that's van der Waals, right? 437 00:19:46,320 --> 00:19:52,190 It's a van der Waals solid, whereas potassium permanganate 438 00:19:52,190 --> 00:19:53,960 is an ionic solid. 439 00:19:53,960 --> 00:19:57,420 Potassium permanganate is ionic, and it consists of 440 00:19:57,420 --> 00:20:01,830 potassium cations and permanganate anions. 441 00:20:01,830 --> 00:20:06,280 And what we find is that the non-polar solute dissolves in 442 00:20:06,280 --> 00:20:11,630 the non-polar solvent, and the ionic solute dissolves in the 443 00:20:11,630 --> 00:20:16,220 polar solvent with hydrogen bonding capability. 444 00:20:16,220 --> 00:20:23,000 So from this, we can infer the general rule, which is 445 00:20:23,000 --> 00:20:27,850 encapsulated in the language used in chemistry textbooks. 446 00:20:27,850 --> 00:20:30,125 Like dissolves like. 447 00:20:33,130 --> 00:20:37,340 And what they're really saying here, is that like solutes 448 00:20:37,340 --> 00:20:40,570 dissolve in like solvents. 449 00:20:40,570 --> 00:20:43,410 Solute-solvent is like dissolves like. 450 00:20:43,410 --> 00:20:43,700 OK. 451 00:20:43,700 --> 00:20:46,010 It's a good place to start, but it's 452 00:20:46,010 --> 00:20:47,380 an incomplete picture. 453 00:20:47,380 --> 00:20:49,230 So I want to show you that there's some 454 00:20:49,230 --> 00:20:50,460 sophistication here. 455 00:20:50,460 --> 00:20:52,680 This is taken from one of the other books. 456 00:20:52,680 --> 00:20:56,410 And it shows just the rules for ionic compounds in water. 457 00:20:56,410 --> 00:20:59,540 And I just showed you, from this example, that the ionic 458 00:20:59,540 --> 00:21:01,640 compound dissolved in water. 459 00:21:01,640 --> 00:21:05,070 And what you see here is that some ionic compounds dissolve 460 00:21:05,070 --> 00:21:07,160 in water, but there's a whole set or 461 00:21:07,160 --> 00:21:09,340 insoluble ionic compounds. 462 00:21:09,340 --> 00:21:13,500 So it's not straightforward. 463 00:21:13,500 --> 00:21:17,340 But we know from 3.091, we know that we can make sense of 464 00:21:17,340 --> 00:21:21,550 this on the basis of competition. 465 00:21:21,550 --> 00:21:24,950 Competition between what holds the compound in the solid 466 00:21:24,950 --> 00:21:27,650 state versus what will pull it into the liquid state. 467 00:21:27,650 --> 00:21:31,750 So for example, we can compare sodium chloride, which we know 468 00:21:31,750 --> 00:21:33,160 dissolves in water. 469 00:21:33,160 --> 00:21:36,470 So sodium chloride, as a crystalline solid, will 470 00:21:36,470 --> 00:21:42,600 dissolve to form sodium chloride aqueous solution. 471 00:21:42,600 --> 00:21:47,970 Whereas if you look at magnesium oxide, which is also 472 00:21:47,970 --> 00:21:56,190 an ionic crystal, it does not, to any standard imaginable, 473 00:21:56,190 --> 00:21:59,960 dissolve to form an aqueous solution of magnesium oxide. 474 00:21:59,960 --> 00:22:01,170 And what's the difference here? 475 00:22:01,170 --> 00:22:10,440 The difference here is, compare solvation energy, in 476 00:22:10,440 --> 00:22:12,870 other words, the energy that you got by pulling this into 477 00:22:12,870 --> 00:22:16,670 solution, and forming bonds between sodium and chlorine in 478 00:22:16,670 --> 00:22:20,855 water, with the crystallization energy. 479 00:22:24,810 --> 00:22:25,920 And what's that all about? 480 00:22:25,920 --> 00:22:28,310 Well, that's the Madelung constant, remember? 481 00:22:28,310 --> 00:22:29,970 Madelung constant. 482 00:22:29,970 --> 00:22:35,520 q1 q2 over 4 pi epsilon 0 r, where this 483 00:22:35,520 --> 00:22:36,880 is the cation anion. 484 00:22:36,880 --> 00:22:41,200 And you can see here that sodium chloride has sodium 485 00:22:41,200 --> 00:22:44,870 cations and chloride anions, and there's a certain binding 486 00:22:44,870 --> 00:22:46,320 energy in the crystal. 487 00:22:46,320 --> 00:22:49,710 Magnesium has 2 plus. 488 00:22:49,710 --> 00:22:51,750 Oxide is 2 minus. 489 00:22:51,750 --> 00:22:55,030 The binding energy between magnesium and oxygen is so 490 00:22:55,030 --> 00:22:58,750 great that there's no driving force to dissolve. 491 00:22:58,750 --> 00:23:01,610 Now, I don't expect you to be able to look at this and tell 492 00:23:01,610 --> 00:23:04,470 me whether something's going to dissolve or not. 493 00:23:04,470 --> 00:23:08,570 But if I were to say to you, explain why sodium chloride 494 00:23:08,570 --> 00:23:13,300 forms solutions with water, and magnesium oxide doesn't, 495 00:23:13,300 --> 00:23:16,380 that you could go through this rationalization. 496 00:23:16,380 --> 00:23:18,820 And here's a cartoon from the textbook that tries to 497 00:23:18,820 --> 00:23:20,560 illustrate this solvation. 498 00:23:20,560 --> 00:23:23,460 Here you can see a crystal of sodium chloride, in the 499 00:23:23,460 --> 00:23:27,440 inimitable fashion, as drawn by chemistry books, where the 500 00:23:27,440 --> 00:23:31,655 chloride ion is green, and the sodium ion is blue. 501 00:23:31,655 --> 00:23:32,560 And that's OK. 502 00:23:32,560 --> 00:23:34,930 I can live with the color-coding, as long as we 503 00:23:34,930 --> 00:23:38,310 agree amongst ourselves, these ions are clear and colorless, 504 00:23:38,310 --> 00:23:40,180 because they have octet stability in 505 00:23:40,180 --> 00:23:41,610 their electronic shell. 506 00:23:41,610 --> 00:23:45,030 And here's water, with the hydrogen shown in white, and 507 00:23:45,030 --> 00:23:46,730 the oxygen shown in red. 508 00:23:46,730 --> 00:23:51,930 And you can see that the oxide end, the oxygen end, the delta 509 00:23:51,930 --> 00:23:56,940 negative end of the water, is trying to wrest sodium cation 510 00:23:56,940 --> 00:23:58,850 out of the lattice, and ultimately 511 00:23:58,850 --> 00:24:00,870 surround it by a cage. 512 00:24:00,870 --> 00:24:01,950 And the same thing here. 513 00:24:01,950 --> 00:24:04,400 You see the hydrogen ends of the water trying to pull 514 00:24:04,400 --> 00:24:07,840 chloride out, and ultimately surround it with 515 00:24:07,840 --> 00:24:09,600 a water-like cage. 516 00:24:09,600 --> 00:24:11,850 So this is the competition I was talking about. 517 00:24:11,850 --> 00:24:14,480 In the case of sodium chloride, water wins. 518 00:24:14,480 --> 00:24:17,530 In the case of magnesium oxide, water loses. 519 00:24:17,530 --> 00:24:20,900 The binding energy between magnesium and oxygen and the 520 00:24:20,900 --> 00:24:22,580 crystal dominate. 521 00:24:22,580 --> 00:24:25,010 So you don't see that solvation. 522 00:24:25,010 --> 00:24:25,310 OK. 523 00:24:25,310 --> 00:24:27,430 Let's talk about metrics now. 524 00:24:27,430 --> 00:24:30,100 Let's look at some metrics of solubility. 525 00:24:30,100 --> 00:24:31,850 It's quantifiable. 526 00:24:31,850 --> 00:24:38,230 So we can express a measure of solubility in terms of a 527 00:24:38,230 --> 00:24:40,210 quantity known as molarity. 528 00:24:43,850 --> 00:24:55,165 So we can express moles of solute per liter of solvent. 529 00:24:59,300 --> 00:25:07,300 And this is called molarity, and the symbol is capital M. 530 00:25:07,300 --> 00:25:12,750 So we can say, for example, a 1 molar solution of sodium 531 00:25:12,750 --> 00:25:16,885 chloride in water, we'll write 1 molar NaCl, and then we'll 532 00:25:16,885 --> 00:25:19,100 write subscript aq, meaning aqueous. 533 00:25:19,100 --> 00:25:24,340 So it's an aqueous solution at a concentration of 1 mole of 534 00:25:24,340 --> 00:25:29,170 NaCl per liter. 535 00:25:29,170 --> 00:25:34,460 And the liter is named after a person, so that's capital L, 536 00:25:34,460 --> 00:25:37,200 per liter of solution. 537 00:25:37,200 --> 00:25:40,040 And remember, the solution is the sum of 538 00:25:40,040 --> 00:25:44,480 the water plus solute. 539 00:25:44,480 --> 00:25:48,510 For dilute solutions, there's very little difference between 540 00:25:48,510 --> 00:25:51,200 the total amount of water and the total amount of solution. 541 00:25:51,200 --> 00:25:54,090 But in certain instances, the presence of the solute 542 00:25:54,090 --> 00:25:56,340 actually has a volumetric change on here. 543 00:25:56,340 --> 00:26:00,500 So strictly speaking, it's per liter of solution 544 00:26:00,500 --> 00:26:04,800 And as I've shown you, there are degrees of solubility. 545 00:26:04,800 --> 00:26:10,690 So people represent the threshold of solubility as c 546 00:26:10,690 --> 00:26:12,580 of the solute. 547 00:26:12,580 --> 00:26:15,780 When c of the solute is less than about a million molar, 548 00:26:15,780 --> 00:26:20,770 0.001 molar, we call this insoluble. 549 00:26:20,770 --> 00:26:24,580 So something is vanishingly soluble, we 550 00:26:24,580 --> 00:26:26,165 say that's the value. 551 00:26:26,165 --> 00:26:27,595 So we'll call this the threshold. 552 00:26:30,410 --> 00:26:33,350 And then, something that's quite soluble, we'd say that 553 00:26:33,350 --> 00:26:36,272 the concentration of the solute starts to exceed at 554 00:26:36,272 --> 00:26:38,740 about 0.1 molar. 555 00:26:38,740 --> 00:26:43,035 And then we would say, that qualifies as soluble. 556 00:26:46,480 --> 00:26:51,950 So now let's look at two extremes in solubility, 557 00:26:51,950 --> 00:26:54,100 operating off of this. 558 00:26:54,100 --> 00:26:57,040 So in the one case, we can have complete solubility. 559 00:26:57,040 --> 00:27:01,060 So examples of that, where things are completely miscible 560 00:27:01,060 --> 00:27:02,220 in one another. 561 00:27:02,220 --> 00:27:04,990 Complete solubility. 562 00:27:04,990 --> 00:27:07,080 By the way, some people will use the term miscibility. 563 00:27:10,530 --> 00:27:12,810 When something is miscible it means it's soluble. 564 00:27:12,810 --> 00:27:13,890 Same idea. 565 00:27:13,890 --> 00:27:16,440 If something is insoluble, some people might say it's 566 00:27:16,440 --> 00:27:18,000 immiscible. 567 00:27:18,000 --> 00:27:19,190 Same thing. 568 00:27:19,190 --> 00:27:19,770 OK? 569 00:27:19,770 --> 00:27:25,980 So complete solubility is ethyl alcohol and water. 570 00:27:25,980 --> 00:27:27,575 You can mix them in all proportions. 571 00:27:32,800 --> 00:27:34,050 Continuously variable. 572 00:27:36,480 --> 00:27:40,580 On the solid alloy is silver and gold. 573 00:27:40,580 --> 00:27:43,960 Silver and gold, you can make alloys of any composition 574 00:27:43,960 --> 00:27:47,780 between 100% gold and 100% silver. 575 00:27:47,780 --> 00:27:50,360 Now, that's the exception. 576 00:27:50,360 --> 00:27:54,280 Most cases are situations of limited solubility. 577 00:28:01,900 --> 00:28:09,000 So they go up to a maximum, which we can denote C-star or 578 00:28:09,000 --> 00:28:10,250 C saturation. 579 00:28:13,190 --> 00:28:15,980 This is the maximum solubility. 580 00:28:18,680 --> 00:28:21,590 So an example of something that's sparingly soluble in 581 00:28:21,590 --> 00:28:24,120 water is silver chloride. 582 00:28:24,120 --> 00:28:27,030 Let's look at silver chloride. 583 00:28:27,030 --> 00:28:30,380 So silver chloride, I'm going to start here, silver chloride 584 00:28:30,380 --> 00:28:34,130 as a crystal, and I'm going to dissolve that in water. 585 00:28:34,130 --> 00:28:38,520 So that gives me AgCl aq. 586 00:28:38,520 --> 00:28:40,980 So that's just simply the formation of an aqueous 587 00:28:40,980 --> 00:28:42,900 solution of silver chloride. 588 00:28:42,900 --> 00:28:47,240 And when the reaction moves from left to right, we call 589 00:28:47,240 --> 00:28:50,670 that dissolution. 590 00:28:50,670 --> 00:28:53,110 The silver chloride is dissolving, and when the 591 00:28:53,110 --> 00:28:57,190 system moves from right to left, we call that-- 592 00:28:57,190 --> 00:29:01,840 now here I'm going to nitpick with the book. 593 00:29:01,840 --> 00:29:04,420 The book calls the left reaction crystallization. 594 00:29:07,030 --> 00:29:08,490 And that's correct. 595 00:29:08,490 --> 00:29:11,080 It is crystallization in this case, because silver chloride 596 00:29:11,080 --> 00:29:12,050 is a crystal. 597 00:29:12,050 --> 00:29:18,150 But it is possible, in other systems, to have the solute 598 00:29:18,150 --> 00:29:20,560 come out of solution, and make a solid that is 599 00:29:20,560 --> 00:29:21,980 noncrystalline. 600 00:29:21,980 --> 00:29:26,200 And you know that all crystals are solids, but not all solids 601 00:29:26,200 --> 00:29:26,840 are crystals. 602 00:29:26,840 --> 00:29:28,180 You can have an amorphous solid. 603 00:29:28,180 --> 00:29:31,040 So what would happen if you were to bring out of solution 604 00:29:31,040 --> 00:29:32,080 an amorphous solid? 605 00:29:32,080 --> 00:29:34,000 It would be silly to call it crystallization. 606 00:29:34,000 --> 00:29:39,420 So I prefer to use the term precipitation. 607 00:29:39,420 --> 00:29:41,620 And there's another term that you can use, and I learned 608 00:29:41,620 --> 00:29:44,680 this one from reading the literature of geochemistry. 609 00:29:44,680 --> 00:29:48,980 What the geochemists call the reaction going from solution 610 00:29:48,980 --> 00:29:53,140 to make a solid, they say the system exsolves. 611 00:29:53,140 --> 00:29:55,470 This is dissolve, this is exsolve. 612 00:29:55,470 --> 00:29:58,950 So this is called exsolution. 613 00:29:58,950 --> 00:30:01,440 It's amazing what you can do when you know a 614 00:30:01,440 --> 00:30:02,610 little bit of Latin. 615 00:30:02,610 --> 00:30:03,560 So this exsolves. 616 00:30:03,560 --> 00:30:06,530 So that's the exsolution, or the crystallization reaction. 617 00:30:06,530 --> 00:30:09,590 Now I'm going to show you what won Arrhenius his Nobel prize. 618 00:30:09,590 --> 00:30:12,570 Arrhenius did not get the Nobel prize for his brilliant 619 00:30:12,570 --> 00:30:14,790 work on activation energy. 620 00:30:14,790 --> 00:30:18,300 He got his Nobel prize on the theory of electrolytic 621 00:30:18,300 --> 00:30:21,150 dissociation, which was, people knew that you could 622 00:30:21,150 --> 00:30:24,670 dissolve salts and water, but they didn't know how. 623 00:30:24,670 --> 00:30:26,940 And it was Arrhenius who said that the salts go into 624 00:30:26,940 --> 00:30:30,240 solution by dissociating and forming ions. 625 00:30:30,240 --> 00:30:38,190 So goes in as Ag plus Ag plus aq plus chloride ion-- 626 00:30:38,190 --> 00:30:39,700 thank you. 627 00:30:39,700 --> 00:30:42,930 And that, ladies and gentleman, was a Nobel prize 628 00:30:42,930 --> 00:30:44,500 for Arrhenius. 629 00:30:44,500 --> 00:30:47,880 And you can see that there's a relationship between the 630 00:30:47,880 --> 00:30:50,530 amount of silver chloride and the amount of ions. 631 00:30:50,530 --> 00:30:53,960 So there's a mass balance there, that the concentration 632 00:30:53,960 --> 00:30:58,310 of silver chloride dissolved, in fact, equals, in this case, 633 00:30:58,310 --> 00:31:04,520 by stoichiometry, the concentration of Ag plus, 634 00:31:04,520 --> 00:31:07,820 because of the nature of the dissociation reaction on a 635 00:31:07,820 --> 00:31:08,930 mass balance basis. 636 00:31:08,930 --> 00:31:11,880 And that also equals the concentration of the 637 00:31:11,880 --> 00:31:15,050 chloride ion, OK? 638 00:31:15,050 --> 00:31:20,590 So that's the way we can look at the system. 639 00:31:20,590 --> 00:31:25,510 And how do we know that this thing has limited solubility? 640 00:31:25,510 --> 00:31:30,390 Well, there's various ways of measuring it, and one of them 641 00:31:30,390 --> 00:31:31,740 involves conductivity. 642 00:31:31,740 --> 00:31:33,820 Here's the conductivity of pure water. 643 00:31:33,820 --> 00:31:36,830 And you know that water has very, very poor conductivity, 644 00:31:36,830 --> 00:31:39,640 and in fact, what's happening here, when we add silver 645 00:31:39,640 --> 00:31:42,680 chloride is, we're adding charge carriers, because the 646 00:31:42,680 --> 00:31:44,220 audience are charged species. 647 00:31:44,220 --> 00:31:45,720 So they can carry charge. 648 00:31:45,720 --> 00:31:49,050 And you can see that this is a measure of conductivity as a 649 00:31:49,050 --> 00:31:51,920 function of silver chloride concentration. 650 00:31:51,920 --> 00:31:55,840 And as you add silver chloride to higher and higher values, 651 00:31:55,840 --> 00:31:57,500 the conductivity goes up. 652 00:31:57,500 --> 00:32:00,730 And look at even the tiniest amount of silver chloride has 653 00:32:00,730 --> 00:32:03,490 a conductivity that's about, what, half an order of 654 00:32:03,490 --> 00:32:05,380 magnitude higher than the conductivity 655 00:32:05,380 --> 00:32:07,340 of pure water itself. 656 00:32:07,340 --> 00:32:10,700 So I would say that this is akin to doping, isn't it? 657 00:32:10,700 --> 00:32:14,400 So up here, when you've got 10 to the minus 6 Siemens per 658 00:32:14,400 --> 00:32:17,810 centimeter conductivity, that aqueous solution is 659 00:32:17,810 --> 00:32:20,720 demonstrating the extrinsic behavior. 660 00:32:20,720 --> 00:32:22,680 This is very similar to doping. 661 00:32:22,680 --> 00:32:26,780 And at some point, we get to this value here, around 10 to 662 00:32:26,780 --> 00:32:31,300 the minus 5 moles of silver chloride per liter, and then 663 00:32:31,300 --> 00:32:35,350 adding more silver chloride has no impact on conductivity. 664 00:32:35,350 --> 00:32:38,150 Which tells you that you've hit saturation. 665 00:32:38,150 --> 00:32:41,540 This is akin to adding more and more sugar to the cup of 666 00:32:41,540 --> 00:32:44,190 tea, until finally the sugar just falls to the bottom. 667 00:32:44,190 --> 00:32:46,470 You can stir all you want, but you won't get it to dissolve, 668 00:32:46,470 --> 00:32:48,890 because you've hit saturation. 669 00:32:48,890 --> 00:32:54,680 So that indicates the presence of a saturated solution. 670 00:32:54,680 --> 00:33:01,820 And so we can talk about that value, and we can say that for 671 00:33:01,820 --> 00:33:07,650 silver chloride, the concentration at saturation is 672 00:33:07,650 --> 00:33:15,070 equal to 1.3 times 10 to the minus 5 moles per liter. 673 00:33:15,070 --> 00:33:18,160 Moles of silver chloride per liter. 674 00:33:18,160 --> 00:33:21,940 And obviously, that's equal to, according to that, it's 675 00:33:21,940 --> 00:33:24,680 equal to the silver ion concentration. 676 00:33:24,680 --> 00:33:27,650 I'm going to use square brackets to indicate moles of 677 00:33:27,650 --> 00:33:30,850 silver, ion per liter of solution, which 678 00:33:30,850 --> 00:33:33,380 is also equal to-- 679 00:33:33,380 --> 00:33:37,960 pardon me-- it's also equal to the chloride ion concentration 680 00:33:37,960 --> 00:33:39,530 at saturation. 681 00:33:39,530 --> 00:33:41,280 Now I'm going to ask you a simple question. 682 00:33:41,280 --> 00:33:45,840 Suppose I've got a beaker here, and I know the maximum I 683 00:33:45,840 --> 00:33:50,100 can get here, the maximum is 1.3 times 10 to the minus 5. 684 00:33:50,100 --> 00:33:51,950 Now this is a really simple question. 685 00:33:51,950 --> 00:33:56,060 Suppose I am about to add silver chloride-- 686 00:33:56,060 --> 00:33:59,130 let's say this is 1 liter already. 687 00:33:59,130 --> 00:33:59,710 All right? 688 00:33:59,710 --> 00:34:00,890 I've got one liter. 689 00:34:00,890 --> 00:34:03,880 And you'd tell me, well, you can put in 1.3 times 10 to the 690 00:34:03,880 --> 00:34:06,490 minus 5 moles to get the saturation. 691 00:34:06,490 --> 00:34:10,220 Suppose instead of 1 liter of pure water, I had 1 liter of 692 00:34:10,220 --> 00:34:15,530 water already containing, say, 1 times 10 to the minus 5 693 00:34:15,530 --> 00:34:18,230 molar silver chloride. 694 00:34:18,230 --> 00:34:20,050 Well, that's kind of obvious, isn't it? 695 00:34:20,050 --> 00:34:24,700 I'm only going to be able to put 0.3 moles in, because 0.3 696 00:34:24,700 --> 00:34:26,520 times 10 to the minus 5, because I've already got 697 00:34:26,520 --> 00:34:27,910 silver chloride in there. 698 00:34:27,910 --> 00:34:28,960 That's easy. 699 00:34:28,960 --> 00:34:31,490 Now let's make the question a little more interesting. 700 00:34:31,490 --> 00:34:34,520 Suppose instead of a certain amount of silver chloride in 701 00:34:34,520 --> 00:34:38,810 there, I have no silver chloride in there. 702 00:34:38,810 --> 00:34:43,010 But I've got, say, 0.1 molar sodium chloride. 703 00:34:46,080 --> 00:34:47,090 It's a salt. 704 00:34:47,090 --> 00:34:48,840 It's a difference salt. 705 00:34:48,840 --> 00:34:52,830 So the question is, does the presence of a different salt 706 00:34:52,830 --> 00:34:57,950 have an impact on how much silver chloride I can put into 707 00:34:57,950 --> 00:34:58,862 this solution? 708 00:34:58,862 --> 00:35:00,960 And the answer is, yes. 709 00:35:00,960 --> 00:35:02,720 The answer is yes. 710 00:35:02,720 --> 00:35:09,130 So what we find is that the presence of the other salt, in 711 00:35:09,130 --> 00:35:13,210 this case, has an impact, because sodium chloride goes 712 00:35:13,210 --> 00:35:17,240 in as sodium plus, and chloride minus. 713 00:35:17,240 --> 00:35:21,070 So there's already a boatload of chloride ion in there, and 714 00:35:21,070 --> 00:35:23,980 that has an impact on this relationship. 715 00:35:23,980 --> 00:35:27,620 So how do we answer the question, what is the 716 00:35:27,620 --> 00:35:30,100 solubility of silver chloride in the presence of other 717 00:35:30,100 --> 00:35:31,710 chloride ions? 718 00:35:31,710 --> 00:35:36,510 And for that, we define something called the 719 00:35:36,510 --> 00:35:37,760 solubility product. 720 00:35:40,530 --> 00:35:43,980 And you need it in order to answer the question, how do 721 00:35:43,980 --> 00:35:47,500 you determine the solubility of a solute when there are 722 00:35:47,500 --> 00:35:50,260 other solutes present already? 723 00:35:50,260 --> 00:35:55,140 And it's denoted capital K, lowercase sp, subscript. 724 00:35:55,140 --> 00:35:56,470 Solubility product. 725 00:35:56,470 --> 00:36:00,770 And it's equal to simply the ion products of the 726 00:36:00,770 --> 00:36:01,520 constituents. 727 00:36:01,520 --> 00:36:04,320 So the solubility product of silver chloride is the product 728 00:36:04,320 --> 00:36:07,470 of the silver ion concentration, and the 729 00:36:07,470 --> 00:36:09,620 chloride ion concentration. 730 00:36:09,620 --> 00:36:16,760 And you know that in a solution of silver chloride 731 00:36:16,760 --> 00:36:24,210 alone, if nothing else, that the concentration of silver 732 00:36:24,210 --> 00:36:26,910 ion equals the concentration of chloride ion. 733 00:36:26,910 --> 00:36:30,600 That's the whole business of dissolving by itself. 734 00:36:30,600 --> 00:36:34,300 And so I can then just say that Ksp. 735 00:36:34,300 --> 00:36:38,020 will then equal the concentration of silver ion 736 00:36:38,020 --> 00:36:42,910 squared, which we also know is equal to the concentration of 737 00:36:42,910 --> 00:36:44,240 silver chloride aqueous. 738 00:36:44,240 --> 00:36:46,050 See, all of these are the same. 739 00:36:46,050 --> 00:36:47,720 So this solubility is the same. 740 00:36:47,720 --> 00:36:52,370 I can just put that in, which is just concentration of 741 00:36:52,370 --> 00:36:55,220 silver chloride. 742 00:36:55,220 --> 00:36:56,530 Square that. 743 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 744 00:37:02,710 --> 00:37:08,080 solubility product of 1.8 times 10 to the minus 10. 745 00:37:08,080 --> 00:37:13,510 So now I can use this in order to determine how much 746 00:37:13,510 --> 00:37:17,400 solubility I get in the presence of another salt. 747 00:37:17,400 --> 00:37:22,340 So in this case, I'm going to put 0.1 molar sodium chloride. 748 00:37:22,340 --> 00:37:24,870 And these are strong salts, so we're going to get complete 749 00:37:24,870 --> 00:37:26,090 dissociation. 750 00:37:26,090 --> 00:37:35,010 Gives me 0.1 molar sodium ion, and 0.1 molar chloride ion, 751 00:37:35,010 --> 00:37:36,080 when it dissociates. 752 00:37:36,080 --> 00:37:37,330 Now you see the difference. 753 00:37:37,330 --> 00:37:42,240 Because the silver chloride, by itself, gives me 10 to the 754 00:37:42,240 --> 00:37:44,750 minus 5 molar chloride ions. 755 00:37:44,750 --> 00:37:48,360 When I add sodium chloride, I get 4 as a 756 00:37:48,360 --> 00:37:49,890 magnitude more chloride. 757 00:37:49,890 --> 00:37:53,160 So let's go back to the Ksp. 758 00:37:53,160 --> 00:37:56,180 So Ksp, this is for silver chloride. 759 00:37:56,180 --> 00:37:59,550 Ksp for silver chloride is going to be equal to the 760 00:37:59,550 --> 00:38:04,100 silver concentration and the chloride concentration. 761 00:38:04,100 --> 00:38:07,930 And in this case, the silver concentration is just equal to 762 00:38:07,930 --> 00:38:09,700 whatever that solubility is. 763 00:38:09,700 --> 00:38:11,850 Because there's only source of silver ion, 764 00:38:11,850 --> 00:38:13,000 and it's silver chloride. 765 00:38:13,000 --> 00:38:14,440 So I can write that as 766 00:38:14,440 --> 00:38:17,410 concentration of silver chloride. 767 00:38:17,410 --> 00:38:19,350 That's good. 768 00:38:19,350 --> 00:38:20,870 And now this one here is what? 769 00:38:20,870 --> 00:38:22,310 I've got two sources. 770 00:38:22,310 --> 00:38:25,590 I've got silver chloride, I I've got sodium chloride. 771 00:38:25,590 --> 00:38:27,600 So it's going to equal this thing here. 772 00:38:27,600 --> 00:38:32,580 0.1 plus whatever I get from silver chloride. 773 00:38:32,580 --> 00:38:35,560 And it's vanishingly small, isn't it? 774 00:38:35,560 --> 00:38:38,200 The concentration of silver chloride, whatever it is. 775 00:38:38,200 --> 00:38:42,770 This is nothing, so I'm just going to neglect it. 776 00:38:42,770 --> 00:38:43,850 It's dominated now. 777 00:38:43,850 --> 00:38:47,230 The chlorine is flooded by the silver chloride. 778 00:38:47,230 --> 00:38:48,940 And this product is a constant. 779 00:38:48,940 --> 00:38:51,300 That's still equal to 10 to the minus 10. 780 00:38:51,300 --> 00:38:56,920 So I can turn this around and solve for the concentration of 781 00:38:56,920 --> 00:38:59,650 silver chloride, which is equal to the 782 00:38:59,650 --> 00:39:02,780 concentration of silver io. 783 00:39:02,780 --> 00:39:05,370 And that's equal to, what is it, 10 to of the minus 10 784 00:39:05,370 --> 00:39:10,170 divided by 0.1, which then gives me-- 785 00:39:10,170 --> 00:39:12,000 what's the number here? 786 00:39:12,000 --> 00:39:13,390 Plug that in. 787 00:39:13,390 --> 00:39:17,390 And I end up with 10 to the 1.8 times 10 788 00:39:17,390 --> 00:39:20,300 to the minus 9 molar. 789 00:39:20,300 --> 00:39:20,830 Right? 790 00:39:20,830 --> 00:39:21,350 So look. 791 00:39:21,350 --> 00:39:26,970 Look at what's happened by having the chloride present 792 00:39:26,970 --> 00:39:30,660 from sodium chloride in such a large amount. 793 00:39:30,660 --> 00:39:32,360 It's repressed. 794 00:39:32,360 --> 00:39:35,460 It has repressed the dissolution. 795 00:39:35,460 --> 00:39:40,130 The presence of chloride then has a negative impact on 796 00:39:40,130 --> 00:39:43,490 solubility, and instead of having 10 to the minus 5 797 00:39:43,490 --> 00:39:46,350 molar, it's down to 10 to the the minus 9 molar. 798 00:39:46,350 --> 00:39:51,570 And this effect of repressing solubility by adding a second 799 00:39:51,570 --> 00:39:56,030 solute is called the common ion effect, OK? 800 00:39:56,030 --> 00:40:09,790 Solubility repression by second solute is known as the 801 00:40:09,790 --> 00:40:13,100 common ion effect. 802 00:40:13,100 --> 00:40:15,140 And this is used in processing. 803 00:40:15,140 --> 00:40:20,680 If I want to trigger the precipitation-- 804 00:40:20,680 --> 00:40:22,980 see, if I started with a solution containing 10 to the 805 00:40:22,980 --> 00:40:26,330 minus 5 molar of silver chloride, and I throw in some 806 00:40:26,330 --> 00:40:28,170 sodium chloride, it'll start 807 00:40:28,170 --> 00:40:30,690 precipitating out silver chloride. 808 00:40:30,690 --> 00:40:33,040 So if I wanted to make a fine precipitate of silver 809 00:40:33,040 --> 00:40:35,530 chloride, I make a pregnant solution. 810 00:40:35,530 --> 00:40:37,920 And I could drop the temperature, because you can 811 00:40:37,920 --> 00:40:40,790 imagine that solubility is a function of temperature, or I 812 00:40:40,790 --> 00:40:43,580 could keep it isothermal, throw in some sodium chloride, 813 00:40:43,580 --> 00:40:46,030 and out comes silver chloride. 814 00:40:46,030 --> 00:40:52,610 So since the common ion effect on it and its value in 815 00:40:52,610 --> 00:40:54,540 processing. 816 00:40:54,540 --> 00:40:54,970 OK. 817 00:40:54,970 --> 00:40:55,940 Good. 818 00:40:55,940 --> 00:41:03,820 Well, I think I'm going to hold it there. 819 00:41:03,820 --> 00:41:07,490 I"ll show you just one more thing. 820 00:41:07,490 --> 00:41:10,730 If you've got stoichiometry like this-- 821 00:41:10,730 --> 00:41:13,040 this is a difluoride of magnesium. 822 00:41:13,040 --> 00:41:16,930 If it goes into solution, you get magnesium cation plus 2 823 00:41:16,930 --> 00:41:18,200 fluoride anions. 824 00:41:18,200 --> 00:41:22,240 And so if I wrote the Ksp for this reaction, it would be the 825 00:41:22,240 --> 00:41:28,450 product of the magnesium concentration and the fluoride 826 00:41:28,450 --> 00:41:30,000 ion concentration. 827 00:41:30,000 --> 00:41:32,580 Because there's the two here, this is squared. 828 00:41:32,580 --> 00:41:38,860 So this, too, will transfer up there, and then throw in some 829 00:41:38,860 --> 00:41:42,860 sodium fluoride, and cause the other thing to exsolve, and 830 00:41:42,860 --> 00:41:43,910 away we go. 831 00:41:43,910 --> 00:41:44,080 All right. 832 00:41:44,080 --> 00:41:45,680 I've got a couple of things to show you. 833 00:41:45,680 --> 00:41:47,400 We're talking a lot about Arrhenius. 834 00:41:47,400 --> 00:41:50,860 This is a book I have. It's an English translation of a book 835 00:41:50,860 --> 00:41:54,540 written by Arrhenius in the late 1800s, and it was printed 836 00:41:54,540 --> 00:41:57,480 in English around 1908. 837 00:41:57,480 --> 00:41:59,710 And Arrhenius was a genius. 838 00:41:59,710 --> 00:42:02,390 He wrote on all sorts of topics here. 839 00:42:02,390 --> 00:42:04,840 Biology, physics, you name it. 840 00:42:04,840 --> 00:42:08,430 And one of the things and he was interested in was the 841 00:42:08,430 --> 00:42:10,470 origins of the earth. 842 00:42:10,470 --> 00:42:14,450 So this chapter is called, Celestial Bodies as Abodes of 843 00:42:14,450 --> 00:42:18,670 Organisms. Already speculating on whether you could have life 844 00:42:18,670 --> 00:42:23,520 as we know it exist elsewhere in the universe. 845 00:42:23,520 --> 00:42:26,340 And one of the things he talks about is global warming. 846 00:42:26,340 --> 00:42:28,400 So this is Arrhenius on global warming. 847 00:42:28,400 --> 00:42:30,780 I'll read you the last paragraph of this chapter. 848 00:42:30,780 --> 00:42:34,240 There had been some major volcanic eruptions that had 849 00:42:34,240 --> 00:42:37,600 caused cooling when Krakatoa in 1883 and 850 00:42:37,600 --> 00:42:39,390 Martinique in 1902. 851 00:42:39,390 --> 00:42:45,300 Major plumes of soot that caused dramatic decreases in 852 00:42:45,300 --> 00:42:46,550 temperature. 853 00:42:46,550 --> 00:42:49,400 So now here comes the last paragraph. 854 00:42:49,400 --> 00:42:53,280 We often hear lamentations that the coal stored up in the 855 00:42:53,280 --> 00:42:56,320 earth is wasted by the present generation-- 856 00:42:56,320 --> 00:42:58,020 remember, this is written 100 years ago-- 857 00:42:58,020 --> 00:42:59,910 without any thought of the future. 858 00:42:59,910 --> 00:43:03,110 And we are terrified by the awful destruction of life and 859 00:43:03,110 --> 00:43:07,920 property which is followed the volcanic eruptions of our day. 860 00:43:07,920 --> 00:43:10,500 We may find a kind of consolation in the 861 00:43:10,500 --> 00:43:12,480 consideration that adheres in every other case. 862 00:43:12,480 --> 00:43:14,780 There is good mixed with the evil. 863 00:43:14,780 --> 00:43:16,920 By the influence of the increasing percentage of 864 00:43:16,920 --> 00:43:20,660 carbonic acid in the atmosphere-- that's CO2-- 865 00:43:20,660 --> 00:43:24,220 we may hope to enjoy ages with more equitable and better 866 00:43:24,220 --> 00:43:25,540 climates.-- 867 00:43:25,540 --> 00:43:29,150 Remember, he's a Swede; it's cold-- 868 00:43:29,150 --> 00:43:32,350 especially as regards the colder regions of the earth, 869 00:43:32,350 --> 00:43:35,510 ages when the earth will bring forth much more abundant crops 870 00:43:35,510 --> 00:43:37,640 than at present for the benefit of 871 00:43:37,640 --> 00:43:40,050 rapidly propagating mankind. 872 00:43:40,050 --> 00:43:41,930 So it's interesting to see the world-- 873 00:43:41,930 --> 00:43:42,910 it's a great book to read. 874 00:43:42,910 --> 00:43:46,140 And you can see people in the 1830s were already calculating 875 00:43:46,140 --> 00:43:49,600 heat transfer coefficients to how much 876 00:43:49,600 --> 00:43:51,400 the earth was changing. 877 00:43:51,400 --> 00:43:52,970 We're going to post these to the website. 878 00:43:52,970 --> 00:43:55,230 This was, last year, in the New York Times. 879 00:43:55,230 --> 00:43:57,640 Every Tuesday they have a science section. 880 00:43:57,640 --> 00:43:59,260 And this was about glass. 881 00:43:59,260 --> 00:44:04,420 And very, actually, with your 3.091 knowledge, you'll read 882 00:44:04,420 --> 00:44:07,600 this like a newspaper, and it'll be very easy. 883 00:44:07,600 --> 00:44:09,590 And they go through the structure. 884 00:44:09,590 --> 00:44:11,770 Here's the structure of a window glass. 885 00:44:11,770 --> 00:44:13,420 You can see the network, former network 886 00:44:13,420 --> 00:44:14,970 modifier, and so on. 887 00:44:14,970 --> 00:44:18,630 And they talk about how difficult it is from a first 888 00:44:18,630 --> 00:44:23,160 principle's standpoint to model the structure of glass. 889 00:44:23,160 --> 00:44:27,210 These oxide glasses are complex and not easy to model. 890 00:44:27,210 --> 00:44:29,990 So when you're trying to engineer the glasses, instead 891 00:44:29,990 --> 00:44:33,430 of trial and error, it's hard to do so by theory. 892 00:44:33,430 --> 00:44:37,820 And it talks about some efforts at theory, and so on. 893 00:44:37,820 --> 00:44:41,380 And the last thing I want to talk about is 894 00:44:41,380 --> 00:44:42,640 bulk metallic glasses. 895 00:44:42,640 --> 00:44:48,170 You recall that I showed you metallic glass that was made 896 00:44:48,170 --> 00:44:53,550 by melting gold silicon, and dripping it onto a 897 00:44:53,550 --> 00:44:58,000 water-cooled copper wheel that was zooming around to give us 898 00:44:58,000 --> 00:45:01,830 a cooling rate of about a million degrees a second. 899 00:45:01,830 --> 00:45:06,020 And those strips had to be very, very 900 00:45:06,020 --> 00:45:07,210 thin, the metal strips. 901 00:45:07,210 --> 00:45:13,110 Because you've got liquid dripping down, and we're 902 00:45:13,110 --> 00:45:15,330 pulling the solid away, and there's a 903 00:45:15,330 --> 00:45:18,600 finite thickness here. 904 00:45:18,600 --> 00:45:20,250 Let's use a Greek letter, xi. 905 00:45:20,250 --> 00:45:22,210 There's a finite thickness xi. 906 00:45:22,210 --> 00:45:25,680 Because what's happening is that this is the water-cooled 907 00:45:25,680 --> 00:45:29,100 copper wheel, and you're extracting heat here. 908 00:45:29,100 --> 00:45:32,370 But eventually, the thermal conductivity of the metal is 909 00:45:32,370 --> 00:45:33,690 the limiter. 910 00:45:33,690 --> 00:45:35,080 In other words, I don't care how cold. 911 00:45:35,080 --> 00:45:37,240 You can put this in liquid helium if you want. 912 00:45:37,240 --> 00:45:40,660 You can't get the heat through the metal fast enough. 913 00:45:40,660 --> 00:45:44,350 And what happens is, when you look down here, the lower part 914 00:45:44,350 --> 00:45:46,820 is amorphous and the upper part is crystalline. 915 00:45:46,820 --> 00:45:48,450 So you don't end up with metallic glass. 916 00:45:48,450 --> 00:45:51,370 You end up with some metallic glass, and the upper part is 917 00:45:51,370 --> 00:45:52,510 crystalline. 918 00:45:52,510 --> 00:45:56,120 So what happens when you end up with the limitation being 919 00:45:56,120 --> 00:45:58,080 the thermal conductivity of the metal? 920 00:45:58,080 --> 00:46:00,010 At that point, you're finished. 921 00:46:00,010 --> 00:46:04,330 And this was typically on the order of microns. 922 00:46:04,330 --> 00:46:06,520 And then they got up to, sort of, submillimeter. 923 00:46:06,520 --> 00:46:07,190 And that was it. 924 00:46:07,190 --> 00:46:09,770 So the glass that I showed you was foil. 925 00:46:09,770 --> 00:46:11,640 Now what happened was, with more research-- 926 00:46:11,640 --> 00:46:12,200 so here we are. 927 00:46:12,200 --> 00:46:14,950 This is Pol Duwez at Caltech, gold silicon. 928 00:46:14,950 --> 00:46:17,460 And this is the thickness in centimeters. 929 00:46:17,460 --> 00:46:22,250 So you were down here at some tens of microns, all right? 930 00:46:22,250 --> 00:46:28,260 Now, in the '60s, research at Harvard uncovered a set of 931 00:46:28,260 --> 00:46:31,760 palladium alloys that had better thermal conductivity 932 00:46:31,760 --> 00:46:36,560 and, remember the first day, about the analogy to the 933 00:46:36,560 --> 00:46:37,800 musical chairs? 934 00:46:37,800 --> 00:46:40,350 These things have slightly more complicated crystal 935 00:46:40,350 --> 00:46:41,320 structures. 936 00:46:41,320 --> 00:46:44,660 So for a given cooling rate, the metal has more difficulty 937 00:46:44,660 --> 00:46:46,460 finding the proper lattice site. 938 00:46:46,460 --> 00:46:48,760 And they were able to make metallic glasses that were on 939 00:46:48,760 --> 00:46:51,650 the order of 0.1 centimeters. 940 00:46:51,650 --> 00:46:53,470 That's still fairly thin. 941 00:46:53,470 --> 00:46:58,555 And then back to Caltech in the late '80s, early '90s, and 942 00:46:58,555 --> 00:47:03,740 a man by name of Bill Johnson was able to develop a set of 943 00:47:03,740 --> 00:47:07,300 alloys that can be made in bulk form. 944 00:47:07,300 --> 00:47:09,290 Totally amorphous metal. 945 00:47:09,290 --> 00:47:11,290 And these are known as bulk metallic glasses. 946 00:47:11,290 --> 00:47:15,540 And look at the complexity of the alloy designation. 947 00:47:15,540 --> 00:47:17,360 So now you see, well, why are they doing this? 948 00:47:17,360 --> 00:47:20,430 Because look, this is strength versus elastic limit. 949 00:47:20,430 --> 00:47:22,430 So you can either have things like polymers, that you can 950 00:47:22,430 --> 00:47:25,830 stretch very, very far, but they don't have much strength. 951 00:47:25,830 --> 00:47:29,560 Or you can have things like certain steels, that are very, 952 00:47:29,560 --> 00:47:33,560 very strong, but you can't bend them very far. 953 00:47:33,560 --> 00:47:36,330 And bulk metallic glass has put you right up here. 954 00:47:36,330 --> 00:47:39,000 You have strong alloys that have very, very 955 00:47:39,000 --> 00:47:40,040 high elastic limits. 956 00:47:40,040 --> 00:47:43,410 So they make great golf clubs and tennis rackets and so on, 957 00:47:43,410 --> 00:47:46,400 because they can flex way back, store enormous energy, 958 00:47:46,400 --> 00:47:47,650 and then spring. 959 00:47:50,160 --> 00:47:52,460 So here are some bulk metallic glasses, and 960 00:47:52,460 --> 00:47:54,130 here's a classic one. 961 00:47:54,130 --> 00:47:58,565 This is zirconium, titanium, copper, nickel, beryllium. 962 00:47:58,565 --> 00:48:00,060 All right, now how do we get that? 963 00:48:00,060 --> 00:48:05,900 Well, zirconium and titanium are body-centered cubic, we've 964 00:48:05,900 --> 00:48:09,740 got copper and nickel are face-centered cubic, and 965 00:48:09,740 --> 00:48:13,540 beryllium is hexagonal close-packed. 966 00:48:13,540 --> 00:48:17,130 So the idea here is the principle of confusion. 967 00:48:17,130 --> 00:48:19,840 So the alloy is fighting with itself. 968 00:48:19,840 --> 00:48:22,100 You know, am I face-centered cubic, am I body-centered 969 00:48:22,100 --> 00:48:23,780 cubic, am I hexagonal? 970 00:48:23,780 --> 00:48:28,650 And this confusion about what the crystal structure is to be 971 00:48:28,650 --> 00:48:32,440 leads to quenching and the disorder of a liquid state, 972 00:48:32,440 --> 00:48:34,840 and preventing the formation of grain boundaries, 973 00:48:34,840 --> 00:48:36,520 dislocations and so on. 974 00:48:36,520 --> 00:48:39,880 So I want to show you one example besides golf clubs. 975 00:48:39,880 --> 00:48:45,220 Dave, could we cut to the document camera here? 976 00:48:45,220 --> 00:48:48,310 Get this thing down. 977 00:48:48,310 --> 00:48:50,890 So this is a-- 978 00:48:50,890 --> 00:48:53,280 I'm not endorsing the product at all, but you know, this is 979 00:48:53,280 --> 00:48:55,720 one of the companies that makes, this 980 00:48:55,720 --> 00:48:57,090 is SanDisk, I think. 981 00:48:57,090 --> 00:48:59,870 And they make these flash memories. 982 00:48:59,870 --> 00:49:02,820 This just looks like a another piece of metal, and in fact, 983 00:49:02,820 --> 00:49:05,270 it's very disarming, because they call 984 00:49:05,270 --> 00:49:06,820 this model the Titanium. 985 00:49:06,820 --> 00:49:09,430 Well, it has about 13% titanium. 986 00:49:09,430 --> 00:49:11,900 The interesting thing here, what's so cool about this, 987 00:49:11,900 --> 00:49:13,900 this is bulk metallic glass. 988 00:49:13,900 --> 00:49:17,360 And what's attractive about the fact that it's bulk 989 00:49:17,360 --> 00:49:21,800 metallic glass is, that it can be shaped by casting, from the 990 00:49:21,800 --> 00:49:24,810 liquid state to very, very fine precision. 991 00:49:24,810 --> 00:49:27,680 So you see all of these slots and everything, and on the 992 00:49:27,680 --> 00:49:31,830 side, all of this kind of stuff, and on the end. 993 00:49:31,830 --> 00:49:34,770 All of this is done by casting from the liquid 994 00:49:34,770 --> 00:49:37,320 state, in one operation. 995 00:49:37,320 --> 00:49:38,290 And this is a clam shell. 996 00:49:38,290 --> 00:49:39,250 There's two pieces here. 997 00:49:39,250 --> 00:49:41,660 I don't know if you can see, but there's two pieces that 998 00:49:41,660 --> 00:49:43,000 have been sandwiched together. 999 00:49:43,000 --> 00:49:44,530 You can see on the edge there. 1000 00:49:44,530 --> 00:49:48,300 And the impact that has on manufacturing costs is 1001 00:49:48,300 --> 00:49:51,900 phenomenal, because normally you make the basic shells, 1002 00:49:51,900 --> 00:49:54,220 then you have to drill, and you've got to 1003 00:49:54,220 --> 00:49:55,320 auger out, and so on. 1004 00:49:55,320 --> 00:49:57,320 This thing, one step operation, 1005 00:49:57,320 --> 00:50:00,400 including the labeling. 1006 00:50:00,400 --> 00:50:03,330 There's no subsequent processing. 1007 00:50:03,330 --> 00:50:06,810 And this is done by a company out in Michigan 1008 00:50:06,810 --> 00:50:09,220 called Liquid Metal. 1009 00:50:09,220 --> 00:50:11,630 And they've licensed the technology and so on. 1010 00:50:11,630 --> 00:50:13,610 And again, I'm not trying to make a commercial thing, but 1011 00:50:13,610 --> 00:50:18,790 I'm just trying to show you that these ideas of changing 1012 00:50:18,790 --> 00:50:22,200 properties for engineered materials, you know, are 1013 00:50:22,200 --> 00:50:24,870 around us everywhere. 1014 00:50:24,870 --> 00:50:26,410 And this is relatively recent. 1015 00:50:26,410 --> 00:50:27,920 Bulk metallic glass. 1016 00:50:27,920 --> 00:50:31,830 Fantastic example of structure property relations. 1017 00:50:31,830 --> 00:50:33,080 OK.