1 00:00:17,217 --> 00:00:22,222 Today, we are going to continue thinking about reactions. 2 00:00:24,791 --> 00:00:27,160 Just to remind you, what did we do on Friday? 3 00:00:27,160 --> 00:00:30,864 So we introduced-- here's what we did last time. 4 00:00:30,864 --> 00:00:33,833 We talked about constant-- we talked about reactions. 5 00:00:33,833 --> 00:00:38,805 And there, on Friday, we were really interested in rates-- 6 00:00:38,805 --> 00:00:40,206 how fast is it happening. 7 00:00:40,206 --> 00:00:43,977 So we talked about things that affect the reaction rate-- 8 00:00:43,977 --> 00:00:45,178 concentration. 9 00:00:45,178 --> 00:00:49,949 Concentration versus time, and how you can measure that. 10 00:00:49,949 --> 00:00:56,322 And you can have rate loss based on experimental measurements. 11 00:00:56,322 --> 00:00:59,459 And that can tell you the reaction order. 12 00:00:59,459 --> 00:01:02,429 We talked about zero, first, second-order reactions, 13 00:01:02,429 --> 00:01:04,664 the rate constant, and then we also 14 00:01:04,664 --> 00:01:07,801 talked about the temperature dependence. 15 00:01:07,801 --> 00:01:10,603 And at the very end, the role of a catalyst in lowering 16 00:01:10,603 --> 00:01:13,506 that activation barrier. 17 00:01:13,506 --> 00:01:17,277 Today, we're going to talk about how things dissolve. 18 00:01:17,277 --> 00:01:22,949 So we're going to talk about solubility, 19 00:01:22,949 --> 00:01:26,453 and this has to do with reactions because something 20 00:01:26,453 --> 00:01:29,122 dissolving is a reaction. 21 00:01:29,122 --> 00:01:31,524 But what's going to happen is we're 22 00:01:31,524 --> 00:01:35,829 going to talk about how that reaction finds its happy place. 23 00:01:35,829 --> 00:01:38,565 And we know a happy place is a good thing, 24 00:01:38,565 --> 00:01:41,768 and it's called equilibrium. 25 00:01:41,768 --> 00:01:43,902 And so that's going to involve talking about things 26 00:01:43,902 --> 00:01:48,475 like equilibrium constants, dissolution, 27 00:01:48,475 --> 00:01:50,743 we're going to look at some examples 28 00:01:50,743 --> 00:01:52,512 with ionic compounds-- so salts. 29 00:01:52,512 --> 00:01:55,381 We're going to be dissolving salts in water 30 00:01:55,381 --> 00:01:59,252 and looking at how to think about how much of that 31 00:01:59,252 --> 00:02:01,955 dissolves in terms of the equilibrium 32 00:02:01,955 --> 00:02:03,890 constant for the reaction. 33 00:02:03,890 --> 00:02:06,326 So that's the goal today. 34 00:02:06,326 --> 00:02:10,263 I want to start, though, by talking about why this matters, 35 00:02:10,263 --> 00:02:14,667 and that's directly related to your goodie bag. 36 00:02:14,667 --> 00:02:19,939 So this is something some of you may have seen. 37 00:02:19,939 --> 00:02:22,475 The data here in from the '50s is 38 00:02:22,475 --> 00:02:27,881 from the Mauna Loa measurements, the top of a volcano. 39 00:02:27,881 --> 00:02:31,718 And this is CO2 concentration, parts per million 40 00:02:31,718 --> 00:02:32,986 in the atmosphere. 41 00:02:32,986 --> 00:02:36,256 But if you dig into the ice-- 42 00:02:36,256 --> 00:02:37,891 we're going to be doing a lot of that 43 00:02:37,891 --> 00:02:41,194 here in Boston over the next three months. 44 00:02:41,194 --> 00:02:45,531 But if you dig deeper into the ice, in the cores, 45 00:02:45,531 --> 00:02:49,402 you go back in time, and it's a beautiful thing. 46 00:02:49,402 --> 00:02:53,973 The ice as you go down is ancient atmosphere. 47 00:02:53,973 --> 00:02:56,075 That's cool-- because there's little bubbles. 48 00:02:56,075 --> 00:02:59,679 Remember, we talked about the half life 49 00:02:59,679 --> 00:03:06,152 of carbon-14 that's trapped from a living thing breathing it in. 50 00:03:06,152 --> 00:03:08,855 Well, you can trap directly the little bubbles 51 00:03:08,855 --> 00:03:12,025 of atmosphere in the ice, and that's what happens. 52 00:03:12,025 --> 00:03:15,328 And that's why we know what CO2 levels-- we're going back 53 00:03:15,328 --> 00:03:16,629 almost a million years here. 54 00:03:16,629 --> 00:03:19,232 It's 800,000 years of data. 55 00:03:19,232 --> 00:03:23,570 And this is a graph that I think many of you have seen. 56 00:03:23,570 --> 00:03:27,073 It's going up, a lot. 57 00:03:27,073 --> 00:03:27,974 And here it is. 58 00:03:27,974 --> 00:03:31,511 Now, this is just zooming in on the last 50 59 00:03:31,511 --> 00:03:36,049 or so-- this is just the data, the Mauna Loa data. 60 00:03:36,049 --> 00:03:38,084 And The reason is because here we also 61 00:03:38,084 --> 00:03:39,352 have another kind of data. 62 00:03:39,352 --> 00:03:42,222 So there's a lot of attention paid on CO2, 63 00:03:42,222 --> 00:03:44,224 and there should be. 64 00:03:44,224 --> 00:03:48,328 There is a lot less attention paid to what 65 00:03:48,328 --> 00:03:51,731 that is doing to our oceans. 66 00:03:51,731 --> 00:03:54,334 And this is a reaction that we will talk about more when 67 00:03:54,334 --> 00:03:55,735 we talk about acidification. 68 00:03:55,735 --> 00:03:57,337 So when we talk about acids and bases, 69 00:03:57,337 --> 00:03:59,405 which is coming up later-- 70 00:03:59,405 --> 00:04:02,242 later being Wednesday and next week-- 71 00:04:02,242 --> 00:04:03,376 we'll talk more about this. 72 00:04:03,376 --> 00:04:05,345 But I just want to tell you that when 73 00:04:05,345 --> 00:04:08,548 you have CO2 in the atmosphere going up, 74 00:04:08,548 --> 00:04:12,852 then you also have CO2 in the ocean going up. 75 00:04:12,852 --> 00:04:14,587 So the CO2 in the ocean-- 76 00:04:14,587 --> 00:04:20,959 the CO2 in the atmosphere is getting absorbed by the ocean. 77 00:04:20,959 --> 00:04:22,328 So what? 78 00:04:22,328 --> 00:04:26,499 No, it's a lot of what, because what happens 79 00:04:26,499 --> 00:04:28,835 is the CO2 in the ocean-- 80 00:04:28,835 --> 00:04:31,137 the more CO2 in the ocean-- 81 00:04:31,137 --> 00:04:35,207 is making the ocean more acidic. 82 00:04:35,207 --> 00:04:37,510 So if you just write this number down-- 83 00:04:37,510 --> 00:04:39,479 because it's so astonishing. 84 00:04:46,152 --> 00:04:58,064 Past 200 years, the ocean has become 30% more acidic. 85 00:05:03,903 --> 00:05:15,448 Now that is the fastest-known change in the ocean chemistry 86 00:05:15,448 --> 00:05:19,419 in 50 million years. 87 00:05:25,992 --> 00:05:30,830 That's a big and very sudden change. 88 00:05:30,830 --> 00:05:36,369 So the ocean is absorbing about 22 million tons per day of CO2. 89 00:05:36,369 --> 00:05:37,970 And that number is going up. 90 00:05:37,970 --> 00:05:40,506 Why does that matter? 91 00:05:40,506 --> 00:05:41,974 Maybe it will do to the oceans what 92 00:05:41,974 --> 00:05:44,644 it's doing to the atmosphere and making things a little warmer. 93 00:05:44,644 --> 00:05:49,215 No, it's doing more, because when it acidifies, 94 00:05:49,215 --> 00:05:51,183 then it has a direct impact on things 95 00:05:51,183 --> 00:05:56,189 like this, which is a pteropod. 96 00:05:56,189 --> 00:05:59,058 You look at the food chain of the ocean-- there 97 00:05:59,058 --> 00:06:00,793 are three things at the bottom. 98 00:06:00,793 --> 00:06:03,429 That's one of them. 99 00:06:03,429 --> 00:06:04,864 I mean, there's plants. 100 00:06:04,864 --> 00:06:06,799 There's photosynthesis. 101 00:06:06,799 --> 00:06:09,502 And then there's the bottom of the food chain. 102 00:06:09,502 --> 00:06:11,371 Now you know what's going to happen 103 00:06:11,371 --> 00:06:15,541 when the bottom of the food chain disappears. 104 00:06:15,541 --> 00:06:18,678 This is one of the main kinds of animals 105 00:06:18,678 --> 00:06:20,046 that lives at the bottom of ocean 106 00:06:20,046 --> 00:06:24,384 because they've got these very small calcium carbonate shells. 107 00:06:24,384 --> 00:06:27,954 If you make the ocean just a little 108 00:06:27,954 --> 00:06:33,393 more acidic, like we're doing, those shells don't survive, 109 00:06:33,393 --> 00:06:37,029 and those animals don't survive. 110 00:06:37,029 --> 00:06:40,266 So that's what happens to a pteropod. 111 00:06:40,266 --> 00:06:42,835 At the rate we're going-- 112 00:06:42,835 --> 00:06:47,473 like decades of time from now-- that's what happens. 113 00:06:47,473 --> 00:06:50,643 So what you have in your goodie bag 114 00:06:50,643 --> 00:06:55,014 is a way to see this a little bit more accelerated. 115 00:06:55,014 --> 00:06:56,349 So here's your goodie bag. 116 00:06:56,349 --> 00:06:58,217 So I wanted you to-- 117 00:06:58,217 --> 00:07:01,354 I wanted you to see what's happening in the ocean, 118 00:07:01,354 --> 00:07:03,289 and you have now the tools to do that. 119 00:07:03,289 --> 00:07:07,593 So in your goodie bag, you've got citric powder. 120 00:07:07,593 --> 00:07:10,062 Imagine you take a lot of limes, and you squeeze them, 121 00:07:10,062 --> 00:07:11,297 and then you dry it all out. 122 00:07:11,297 --> 00:07:12,598 And that's what you got-- 123 00:07:12,598 --> 00:07:14,400 citric acid. 124 00:07:14,400 --> 00:07:18,104 Now you're going to mix that with water to change the ph. 125 00:07:18,104 --> 00:07:20,907 And you're going to dissolve this powder. 126 00:07:20,907 --> 00:07:23,709 That's the topic of today's lecture-- dissolution 127 00:07:23,709 --> 00:07:25,445 and equilibrium. 128 00:07:25,445 --> 00:07:27,079 So you're going to mix that into water, 129 00:07:27,079 --> 00:07:32,018 and you've got a scale from a previous goodie bag. 130 00:07:32,018 --> 00:07:34,821 So my hope is that you've been using that on a daily basis. 131 00:07:34,821 --> 00:07:37,824 You take it with you places, and you can use that again here. 132 00:07:37,824 --> 00:07:40,560 And you'll need that, because I want you to see 133 00:07:40,560 --> 00:07:43,329 how these shells dissolve. 134 00:07:43,329 --> 00:07:46,899 And if you lower the acidity more-- 135 00:07:46,899 --> 00:07:48,167 we don't want to wait 40-- 136 00:07:48,167 --> 00:07:49,902 well, you can wait 45 days, but I 137 00:07:49,902 --> 00:07:52,972 want you to be able to do these experiments in minutes. 138 00:07:52,972 --> 00:07:57,610 So we're going to go a little lower in acidity, in ph, 139 00:07:57,610 --> 00:07:59,445 but you're going to get the same result. 140 00:07:59,445 --> 00:08:01,013 You're going to dissolve these shells. 141 00:08:05,852 --> 00:08:09,021 Some of you are going on planes, and there's 142 00:08:09,021 --> 00:08:14,126 white powder and a scale involved in this goodie bag. 143 00:08:14,126 --> 00:08:18,831 Please don't put that in your carry-on. 144 00:08:18,831 --> 00:08:19,832 It's just not a good-- 145 00:08:19,832 --> 00:08:21,701 it really isn't a good idea. 146 00:08:21,701 --> 00:08:27,006 We have data-- students sending me pictures with the airport 147 00:08:27,006 --> 00:08:29,709 screening person. 148 00:08:29,709 --> 00:08:33,546 So I love the excitement of thinking 149 00:08:33,546 --> 00:08:35,948 about this over Thanksgiving, but put it in your suitcase 150 00:08:35,948 --> 00:08:37,250 if you're going to take it home. 151 00:08:39,986 --> 00:08:43,456 That's my why this matters. 152 00:08:43,456 --> 00:08:45,358 So we're dissolving stuff today. 153 00:08:45,358 --> 00:08:46,325 That's the topic. 154 00:08:46,325 --> 00:08:48,327 How do things dissolve? 155 00:08:48,327 --> 00:08:52,064 There's a citric powder, that citric acid 156 00:08:52,064 --> 00:08:55,434 that's going to make water more acidic. 157 00:08:55,434 --> 00:08:58,170 And again, we're going to move into acids and bases next. 158 00:08:58,170 --> 00:09:00,339 Today we're just talking about dissolution. 159 00:09:00,339 --> 00:09:02,475 And so here's citric acid. 160 00:09:02,475 --> 00:09:03,142 There it is. 161 00:09:03,142 --> 00:09:05,278 Now over Thanksgiving, I thought I'd throw this in, 162 00:09:05,278 --> 00:09:07,613 because you might have sugar at the table. 163 00:09:07,613 --> 00:09:10,950 You know to call it a c12h22o11. 164 00:09:10,950 --> 00:09:12,285 Don't ask for the sugar. 165 00:09:12,285 --> 00:09:14,053 If you want to add some sugar to something, 166 00:09:14,053 --> 00:09:16,789 ask for it by molecular name. 167 00:09:16,789 --> 00:09:18,424 But the question is why do these things 168 00:09:18,424 --> 00:09:20,626 dissolve in the first place. 169 00:09:20,626 --> 00:09:26,032 There is acetic acid, citric acid, there's sugar. 170 00:09:26,032 --> 00:09:27,900 These are molecules that look like that. 171 00:09:27,900 --> 00:09:30,269 Why do they dissolve in the first place? 172 00:09:30,269 --> 00:09:35,040 And the answer is because of the things 173 00:09:35,040 --> 00:09:39,045 that we learned about bonding and about things 174 00:09:39,045 --> 00:09:43,783 like whether a molecule is polar or not. 175 00:09:43,783 --> 00:09:47,219 Or in this case, whether you've got the possibility 176 00:09:47,219 --> 00:09:49,589 to hydrogen bond or not. 177 00:09:52,391 --> 00:09:54,460 And so if you look at both of these, 178 00:09:54,460 --> 00:09:59,332 you can see that they both have a whole bunch of oh groups 179 00:09:59,332 --> 00:10:02,735 that look a whole lot like things we've seen 180 00:10:02,735 --> 00:10:04,971 that like to hydrogen bond. 181 00:10:04,971 --> 00:10:06,839 You see those ohs on the end there, 182 00:10:06,839 --> 00:10:12,912 both for sugar, around the outside, and for citric acid. 183 00:10:12,912 --> 00:10:17,984 And so what happens is if I put a sugar molecule into water, 184 00:10:17,984 --> 00:10:20,219 here's a picture of it. 185 00:10:20,219 --> 00:10:21,621 There's a picture of it. 186 00:10:21,621 --> 00:10:23,289 So there's sugar molecules there. 187 00:10:23,289 --> 00:10:26,826 Now they start in a crystal of sugar-- 188 00:10:26,826 --> 00:10:30,296 you pour your sugar in, a teaspoon of sugar. 189 00:10:30,296 --> 00:10:34,266 And it's in a solid, but then it goes off, 190 00:10:34,266 --> 00:10:36,836 and it breaks away into the water. 191 00:10:36,836 --> 00:10:39,672 And those little ones are the water molecules. 192 00:10:39,672 --> 00:10:40,306 Why? 193 00:10:40,306 --> 00:10:44,010 Because the water was bonding to itself. 194 00:10:44,010 --> 00:10:45,911 The water has dipoles-- 195 00:10:45,911 --> 00:10:46,545 dipole-dipole. 196 00:10:46,545 --> 00:10:47,113 Remember that? 197 00:10:47,113 --> 00:10:54,320 The water has hydrogen bonds, but the sugar does, too. 198 00:10:54,320 --> 00:10:55,688 The sugar does, too. 199 00:10:55,688 --> 00:10:58,691 And so the water sees this crystal of sugar, 200 00:10:58,691 --> 00:11:00,426 and it says well, hang on. 201 00:11:00,426 --> 00:11:04,897 If you come out, we could bond together in much the same way 202 00:11:04,897 --> 00:11:06,699 that we're already bonding with each other. 203 00:11:06,699 --> 00:11:09,201 The water molecules are already bonding with hydrogen dipole. 204 00:11:09,201 --> 00:11:12,338 The sugar is like, well I've got hydrogen. I've got dipole. 205 00:11:12,338 --> 00:11:16,809 And so it can break off, and it doesn't cost that much energy. 206 00:11:16,809 --> 00:11:20,780 In fact, it gains energy by doing this. 207 00:11:20,780 --> 00:11:21,681 They can gain. 208 00:11:21,681 --> 00:11:27,453 And so this can actually be a lower energy state overall. 209 00:11:27,453 --> 00:11:35,428 Now that's because of something that many of you 210 00:11:35,428 --> 00:11:40,933 have probably heard, and now we can put some bonding to it, 211 00:11:40,933 --> 00:11:45,838 but it's because like dissolves like. 212 00:11:45,838 --> 00:11:47,373 Oh yeah. 213 00:11:47,373 --> 00:11:48,340 That's technical. 214 00:11:51,143 --> 00:11:53,846 That's technical because now we know what like means. 215 00:11:53,846 --> 00:11:56,615 Like means a type of body. 216 00:11:56,615 --> 00:11:58,417 like means a type of-- 217 00:11:58,417 --> 00:11:59,719 It's like water. 218 00:11:59,719 --> 00:12:02,088 It has hydrogen bonding potential. 219 00:12:02,088 --> 00:12:06,158 Therefore, it's able to dissolve in the water. 220 00:12:09,028 --> 00:12:13,232 So water has-- well, what does water have? 221 00:12:13,232 --> 00:12:17,336 It's got dipoles, so it can do dipole-dipole stuff. 222 00:12:17,336 --> 00:12:19,171 It's got h-bonds. 223 00:12:19,171 --> 00:12:22,675 Oh, everything has London. 224 00:12:22,675 --> 00:12:26,112 Everything has London. 225 00:12:26,112 --> 00:12:27,580 So if you've got those ingredients, 226 00:12:27,580 --> 00:12:29,782 if you've got that ability, if you've got 227 00:12:29,782 --> 00:12:32,218 those likes, then you might be able to dissolve. 228 00:12:36,422 --> 00:12:45,197 Well, this is called a polar solvent 229 00:12:45,197 --> 00:12:48,167 because the molecules that make it up are polar. 230 00:12:50,736 --> 00:12:51,871 They've got dipole. 231 00:12:51,871 --> 00:12:55,107 Actually, and so we're very interested in understanding 232 00:12:55,107 --> 00:12:57,243 how things mix with other things and why 233 00:12:57,243 --> 00:12:59,378 they mix with other things. 234 00:12:59,378 --> 00:13:02,348 Let's take a look at another example. 235 00:13:02,348 --> 00:13:03,549 So here we have ethanol. 236 00:13:03,549 --> 00:13:05,417 I keep on bringing up ethanol. 237 00:13:05,417 --> 00:13:08,420 There might be some served, and if you're 21 or over, 238 00:13:08,420 --> 00:13:09,922 you can have some. 239 00:13:09,922 --> 00:13:13,025 Otherwise, it's illegal. 240 00:13:13,025 --> 00:13:15,161 Ethanol up there at the top. 241 00:13:15,161 --> 00:13:18,531 Thank goodness, you will say, at your Thanksgiving table, 242 00:13:18,531 --> 00:13:21,000 it is not methoxymethane. 243 00:13:21,000 --> 00:13:24,103 And because if it were, it would be the same chemical formula, 244 00:13:24,103 --> 00:13:25,337 but the oh-- 245 00:13:25,337 --> 00:13:27,406 the o would be in the middle of the two cs 246 00:13:27,406 --> 00:13:29,575 with the ch3s on the end, and you wouldn't 247 00:13:29,575 --> 00:13:30,743 be able to hydrogen bond it. 248 00:13:30,743 --> 00:13:32,678 It would all just be vapor. 249 00:13:32,678 --> 00:13:34,180 It'd be vapor. 250 00:13:34,180 --> 00:13:37,283 No, but it's ethanol because it has hydrogen bonding 251 00:13:37,283 --> 00:13:37,950 capabilities. 252 00:13:37,950 --> 00:13:39,952 But look at what happens if it's heptanol. 253 00:13:39,952 --> 00:13:42,822 So all I've done now is I've taken the same end group, 254 00:13:42,822 --> 00:13:48,093 and I've given it more of a carbon chain. 255 00:13:48,093 --> 00:13:50,796 How is that going to affect how it dissolves? 256 00:13:50,796 --> 00:13:52,398 Given what we just talked about that 257 00:13:52,398 --> 00:13:57,203 like dissolve-- they both have hydrogen bond potential. 258 00:13:57,203 --> 00:14:00,372 They both have hy-- but look, more and more of it, 259 00:14:00,372 --> 00:14:03,375 as you go from ethanol to heptanol, more and more 260 00:14:03,375 --> 00:14:05,678 and more of it is something else. 261 00:14:05,678 --> 00:14:09,348 It's only London. 262 00:14:09,348 --> 00:14:12,384 So what's going to happen now if I put this into water? 263 00:14:12,384 --> 00:14:14,887 Well, we can see this going series. 264 00:14:14,887 --> 00:14:19,091 Here's methanol, ethanol, propanol, butanol, pentanol, 265 00:14:19,091 --> 00:14:19,892 hexanol. 266 00:14:19,892 --> 00:14:22,061 Heptanol is down at the bottom, and there's 267 00:14:22,061 --> 00:14:24,697 the water solubility. 268 00:14:24,697 --> 00:14:25,998 We've got to write that down-- 269 00:14:25,998 --> 00:14:27,099 solubility. 270 00:14:31,370 --> 00:14:35,741 So solubility is kind of what it sounds like-- 271 00:14:35,741 --> 00:14:40,379 the ability for a solute-- 272 00:14:40,379 --> 00:14:42,081 that's the thing we're dissolving-- 273 00:14:45,117 --> 00:14:52,358 to dissolve in a solvent. 274 00:14:52,358 --> 00:14:56,228 That's the thing we're trying to dissolve it into. 275 00:14:56,228 --> 00:14:58,697 That's the solubility. 276 00:14:58,697 --> 00:15:00,966 And we'll be talking about the maximum solubility 277 00:15:00,966 --> 00:15:03,535 in just a few minutes, which is what we usually-- 278 00:15:03,535 --> 00:15:04,837 what's the solubility? 279 00:15:04,837 --> 00:15:07,640 We often mean the maximum. 280 00:15:07,640 --> 00:15:09,174 Well, that's what's listed here-- 281 00:15:09,174 --> 00:15:09,675 the maximum. 282 00:15:12,544 --> 00:15:14,480 Methanol, ethanol miscible. 283 00:15:14,480 --> 00:15:17,783 So you can put as much as you want, and it'll always 284 00:15:17,783 --> 00:15:20,085 keep mixing in with the water. 285 00:15:20,085 --> 00:15:23,522 But now look, once you get to butanol, pentanol, hexanol, 286 00:15:23,522 --> 00:15:25,724 it starts going down. 287 00:15:25,724 --> 00:15:29,028 You can't mix as much as you want. 288 00:15:29,028 --> 00:15:30,829 In fact, it's less and less and less, 289 00:15:30,829 --> 00:15:35,668 and the reason we now know is because of what I just said. 290 00:15:35,668 --> 00:15:39,872 As you go down, the hydrogen bond and dipole-dipole 291 00:15:39,872 --> 00:15:41,807 becomes less important because you've 292 00:15:41,807 --> 00:15:46,478 got more and more of the molecule that's only London. 293 00:15:46,478 --> 00:15:51,183 And so it's less like the water environment, the bonding 294 00:15:51,183 --> 00:15:55,788 environment that the water liked with itself. 295 00:15:55,788 --> 00:15:59,058 And so it has more trouble dissolving 296 00:15:59,058 --> 00:16:01,026 and being energetically favorable 297 00:16:01,026 --> 00:16:02,594 isolated by those water monitors. 298 00:16:02,594 --> 00:16:06,131 By the way, does anybody know the origin of the word proof, 299 00:16:06,131 --> 00:16:08,600 speaking of ethanol? 300 00:16:08,600 --> 00:16:13,739 If you buy a bottle of ethanol at the supermarket-- 301 00:16:13,739 --> 00:16:16,976 so there's gin or vodka or whatever, 302 00:16:16,976 --> 00:16:19,645 and it says it's something percent alcohol-- 303 00:16:19,645 --> 00:16:22,314 20% alcohol, 40 proof. 304 00:16:22,314 --> 00:16:23,983 Does anybody know where that comes from? 305 00:16:23,983 --> 00:16:25,351 It's this. 306 00:16:25,351 --> 00:16:27,586 It's just-- but what they did, they 307 00:16:27,586 --> 00:16:30,756 didn't know if you were making good alcohol back in the time. 308 00:16:30,756 --> 00:16:33,058 And they said, well, I don't have 309 00:16:33,058 --> 00:16:35,861 all these detailed abilities to measure and quantify it, 310 00:16:35,861 --> 00:16:38,931 so I was going to light it on fire. 311 00:16:38,931 --> 00:16:41,033 That is exactly what-- 312 00:16:41,033 --> 00:16:42,835 is this a good bottle of gin? 313 00:16:42,835 --> 00:16:43,635 I don't know. 314 00:16:43,635 --> 00:16:44,870 Let's light it on fire. 315 00:16:47,406 --> 00:16:48,807 That's what they did. 316 00:16:48,807 --> 00:16:54,046 And it turns out that if ethanol and water are at 50/50 mixture 317 00:16:54,046 --> 00:16:57,349 or more, it will light on fire. 318 00:16:57,349 --> 00:16:59,318 Don't try that, please. 319 00:16:59,318 --> 00:17:01,487 Don't do these experiments. 320 00:17:01,487 --> 00:17:06,191 But so that meant is this a good bottle of gin? 321 00:17:06,191 --> 00:17:09,862 Well if it's 50/50, I'm going to say it's a good bottle of gin. 322 00:17:09,862 --> 00:17:11,096 So let's light it on fire. 323 00:17:11,096 --> 00:17:12,464 Oh, it lit on fire. 324 00:17:12,464 --> 00:17:16,468 That's 100% proof that it's good. 325 00:17:16,468 --> 00:17:18,137 That is true. 326 00:17:18,137 --> 00:17:21,807 That is the origin of the word proof. 327 00:17:21,807 --> 00:17:25,844 It is proof that it's mixed well, and it's good stuff. 328 00:17:29,882 --> 00:17:33,952 Dissolution-- dissolution-- well, what else 329 00:17:33,952 --> 00:17:36,121 can we try to dissolve? 330 00:17:36,121 --> 00:17:37,589 We're dissolving alcohol. 331 00:17:37,589 --> 00:17:38,791 We're going down to heptanol. 332 00:17:38,791 --> 00:17:42,194 We're lucky it's not methoxymethane. 333 00:17:42,194 --> 00:17:44,163 We talked about sugar. 334 00:17:44,163 --> 00:17:47,332 So we've got to have a framework, by the way. 335 00:17:47,332 --> 00:17:50,402 Solubility-- the ability for a solute to dissolve. 336 00:17:50,402 --> 00:17:53,305 And now, there's a context here, right? 337 00:17:53,305 --> 00:17:55,774 Let's suppose I'm dissolving sugar. 338 00:17:55,774 --> 00:18:01,713 So sugar-- how are we going to write this dissolving down? 339 00:18:01,713 --> 00:18:11,824 Well, sugar is c12h22o11, and if we put it in water, we could 340 00:18:11,824 --> 00:18:14,960 we could formally write the whole thing out. 341 00:18:14,960 --> 00:18:15,861 We can write it out. 342 00:18:15,861 --> 00:18:23,469 We can say I'm going to add water to it, 343 00:18:23,469 --> 00:18:26,205 and that's going to go to-- 344 00:18:26,205 --> 00:18:32,377 it's going to go to c12h22o11 plus more water. 345 00:18:32,377 --> 00:18:36,548 But there's something very important that I'm leaving out, 346 00:18:36,548 --> 00:18:38,050 and when you think about dissolution, 347 00:18:38,050 --> 00:18:40,486 you've got to keep track. 348 00:18:40,486 --> 00:18:41,386 What was it? 349 00:18:41,386 --> 00:18:42,721 Was it a solid? 350 00:18:42,721 --> 00:18:43,622 Was it a liquid? 351 00:18:43,622 --> 00:18:47,126 Or was it something dissolved in a liquid? 352 00:18:47,126 --> 00:18:50,362 So this started as a solid, so we put an s there. 353 00:18:50,362 --> 00:18:52,064 This started as a liquid. 354 00:18:52,064 --> 00:18:55,801 This is the dissolved thing, so we put an aq. 355 00:18:55,801 --> 00:18:58,036 And the aq means aqueous. 356 00:18:58,036 --> 00:18:59,671 It is in an aqueous solution. 357 00:18:59,671 --> 00:19:01,373 It is a dissolved molecule. 358 00:19:04,476 --> 00:19:05,978 And so here, this is a liquid. 359 00:19:05,978 --> 00:19:11,583 Now the other thing that happens is-- well, 360 00:19:11,583 --> 00:19:15,254 the h2o is kind of there. 361 00:19:15,254 --> 00:19:16,622 It's all over the place. 362 00:19:16,622 --> 00:19:20,292 It's that solvent, and so we often 363 00:19:20,292 --> 00:19:24,630 leave it out because it's everywhere on both sides. 364 00:19:24,630 --> 00:19:26,431 And so often, what you'll see, and we'll 365 00:19:26,431 --> 00:19:29,801 write more of these coming, is that you might write 366 00:19:29,801 --> 00:19:34,306 a dissolution of sugar as this. 367 00:19:34,306 --> 00:19:39,378 Solid, and it just goes to something that is dissolved. 368 00:19:44,917 --> 00:19:47,486 And you know that what happened there is sometimes 369 00:19:47,486 --> 00:19:49,321 you'll also see it like this. 370 00:19:49,321 --> 00:19:50,622 What did you do on the arrow? 371 00:19:50,622 --> 00:19:52,591 I added water. 372 00:19:52,591 --> 00:19:55,827 That's what the arrow did. 373 00:19:55,827 --> 00:19:59,598 We're just getting comfortable with writing these dissolution 374 00:19:59,598 --> 00:20:00,732 reactions. 375 00:20:00,732 --> 00:20:02,034 Now what else can I dissolve? 376 00:20:02,034 --> 00:20:06,271 Well here's another good example-- 377 00:20:06,271 --> 00:20:10,008 vitamin A. There's some vitamins you can have as much 378 00:20:10,008 --> 00:20:11,543 as you want, pretty much. 379 00:20:11,543 --> 00:20:12,177 Why? 380 00:20:12,177 --> 00:20:14,913 Because they're water-soluble. 381 00:20:14,913 --> 00:20:16,682 And other vitamins are fat-soluble. 382 00:20:16,682 --> 00:20:21,353 That means they don't like water as 383 00:20:21,353 --> 00:20:27,693 much as they like the hydrophobic molecules 384 00:20:27,693 --> 00:20:28,760 of fat cells. 385 00:20:28,760 --> 00:20:31,830 And so they go into fatty tissue, 386 00:20:31,830 --> 00:20:34,499 where they don't come out. 387 00:20:34,499 --> 00:20:38,804 That's why you not have unlimited amounts of vitamin 388 00:20:38,804 --> 00:20:41,440 A. That's not good for you. 389 00:20:41,440 --> 00:20:44,076 But vitamin C-- no problem. 390 00:20:44,076 --> 00:20:48,647 No problem, because it's going to dissolve in water. 391 00:20:48,647 --> 00:20:51,250 And so your body can take in and get rid of as much of it 392 00:20:51,250 --> 00:20:51,750 as you want. 393 00:20:51,750 --> 00:20:53,885 But if it's dissolved in fat cells, 394 00:20:53,885 --> 00:20:54,953 that's a different thing. 395 00:20:54,953 --> 00:20:57,055 So vitamin A, vitamin C-- and you 396 00:20:57,055 --> 00:20:59,124 can see it right there from the chemistry. 397 00:20:59,124 --> 00:20:59,658 This is it. 398 00:20:59,658 --> 00:21:02,261 Look at all those oh groups in vitamin c. 399 00:21:02,261 --> 00:21:03,362 Look at that. 400 00:21:03,362 --> 00:21:06,265 Oh, that's going to love hydrogen bonding, 401 00:21:06,265 --> 00:21:09,301 and on vitamin A, you've just got the one all the way down 402 00:21:09,301 --> 00:21:11,103 there at the bottom. 403 00:21:11,103 --> 00:21:13,372 It's hydrophobic. 404 00:21:13,372 --> 00:21:16,074 By the way, in this class, we do not 405 00:21:16,074 --> 00:21:17,843 say the words hydrophobic interaction 406 00:21:17,843 --> 00:21:19,411 because that doesn't make sense. 407 00:21:19,411 --> 00:21:23,415 There is no such thing as a hydrophobic interaction. 408 00:21:23,415 --> 00:21:28,687 No, hydrophobic interaction is misused. 409 00:21:28,687 --> 00:21:31,490 What it really means is that something that's hydrophobic 410 00:21:31,490 --> 00:21:33,925 likes itself more-- 411 00:21:33,925 --> 00:21:36,395 being together with itself-- more than it 412 00:21:36,395 --> 00:21:40,098 likes being in the water, or something hydrophilic. 413 00:21:40,098 --> 00:21:43,502 That's what is meant, but there's no actual interaction 414 00:21:43,502 --> 00:21:45,537 there. 415 00:21:45,537 --> 00:21:48,573 Hydrophobic, hydrophilic. 416 00:21:48,573 --> 00:21:51,877 Well, those are other things you can think about dissolving. 417 00:21:51,877 --> 00:21:56,048 You can also dissolve salt, and this is what 418 00:21:56,048 --> 00:21:59,017 we're going to use as examples. 419 00:21:59,017 --> 00:22:01,019 And this is a picture of a salt crystal. 420 00:22:01,019 --> 00:22:04,489 So we show the sugar, and here's salt. Now, 421 00:22:04,489 --> 00:22:05,824 so the thing about salt-- 422 00:22:05,824 --> 00:22:06,591 where's my sugar? 423 00:22:06,591 --> 00:22:10,862 There's the sugar, and let's put salt underneath it. 424 00:22:10,862 --> 00:22:14,566 The thing about salt, which is really 425 00:22:14,566 --> 00:22:18,737 just a general term for when you have an ionic solid that 426 00:22:18,737 --> 00:22:22,341 can be made from a mixture of acids and bases and dissolves 427 00:22:22,341 --> 00:22:26,345 oftentimes a little bit, at least in water. 428 00:22:26,345 --> 00:22:32,851 So a salt or an ionic solid-- 429 00:22:32,851 --> 00:22:33,852 let's say for now-- 430 00:22:37,422 --> 00:22:41,593 this gives something different, because this breaks apart 431 00:22:41,593 --> 00:22:51,570 into positive and negative ions that they contain. 432 00:22:51,570 --> 00:22:55,140 So in the case of sodium and chlorine-- sodium chloride-- 433 00:22:55,140 --> 00:22:56,675 well, that's going to dissociate. 434 00:22:56,675 --> 00:23:00,979 If you pour salt in water, then here's the reaction for that. 435 00:23:00,979 --> 00:23:03,515 You've got sodium chloride solid. 436 00:23:03,515 --> 00:23:06,017 We put it in water. 437 00:23:06,017 --> 00:23:07,285 That's going to go into ions. 438 00:23:14,893 --> 00:23:18,130 So I put that in water, and it's different in the sense 439 00:23:18,130 --> 00:23:21,299 that it doesn't break down into the molecules that 440 00:23:21,299 --> 00:23:22,968 made up the sugar. 441 00:23:22,968 --> 00:23:24,603 It has a particle of sugar that's 442 00:23:24,603 --> 00:23:27,172 got millions and millions of molecules in it. 443 00:23:27,172 --> 00:23:28,640 Now they dissociate. 444 00:23:28,640 --> 00:23:31,443 That's what the aq means. 445 00:23:31,443 --> 00:23:32,477 Those are neutral. 446 00:23:32,477 --> 00:23:36,648 Here, it's a solid, but you can understand this 447 00:23:36,648 --> 00:23:38,316 from looking at it and thinking about it. 448 00:23:38,316 --> 00:23:41,520 Look at the way those water molecules are oriented. 449 00:23:41,520 --> 00:23:45,791 They're pointing to the cl with their positivity, 450 00:23:45,791 --> 00:23:47,259 with positive charge. 451 00:23:47,259 --> 00:23:50,395 And they're pointing to the sodium with the negative, 452 00:23:50,395 --> 00:23:53,865 and that's how they find happiness in water-- 453 00:23:53,865 --> 00:23:58,236 because they're ions, and water can be either way. 454 00:23:58,236 --> 00:24:00,272 It can point its dipole in either-- 455 00:24:00,272 --> 00:24:01,506 and so it can actually bond. 456 00:24:01,506 --> 00:24:03,775 Remember, the hydrogen has got a little positive charge 457 00:24:03,775 --> 00:24:06,344 because the oxygen took it. 458 00:24:06,344 --> 00:24:08,547 And so that's what the-- it has a dipole, 459 00:24:08,547 --> 00:24:11,082 and that's able to turn around and bond 460 00:24:11,082 --> 00:24:12,951 and be happy with each of these ions. 461 00:24:12,951 --> 00:24:14,486 That's why salt dissolves-- 462 00:24:17,722 --> 00:24:20,358 because it can find a happy place. 463 00:24:20,358 --> 00:24:22,694 Other reasons exist outside of this class, 464 00:24:22,694 --> 00:24:27,232 like entropy, thermodynamics. 465 00:24:27,232 --> 00:24:29,701 But this is how we're going to picture it as energetically 466 00:24:29,701 --> 00:24:30,268 happy. 467 00:24:30,268 --> 00:24:31,470 It can become happy. 468 00:24:35,340 --> 00:24:37,108 So we've dissolved some things. 469 00:24:37,108 --> 00:24:39,544 We've got to start thinking about the thing 470 00:24:39,544 --> 00:24:43,915 that I mentioned before, which is how much can I dissolve? 471 00:24:43,915 --> 00:24:45,650 How much can I dissolve? 472 00:24:45,650 --> 00:24:50,789 And in that, it gets into this table here. 473 00:24:50,789 --> 00:24:51,423 There it is. 474 00:24:51,423 --> 00:24:53,258 So that's how much. 475 00:24:53,258 --> 00:24:58,263 And you see it's listed there as moles per 100 grams. 476 00:24:58,263 --> 00:25:00,031 And so that's one way to write it. 477 00:25:00,031 --> 00:25:02,667 You could write it as-- 478 00:25:02,667 --> 00:25:14,279 it's often the max solubility is often what we're interested in. 479 00:25:14,279 --> 00:25:18,984 And you could write it in moles per 100 grams. 480 00:25:18,984 --> 00:25:23,088 You could write it in moles per liter. 481 00:25:23,088 --> 00:25:26,258 Well that's something that we've already learned. 482 00:25:26,258 --> 00:25:30,595 That's m form last Friday, the molarity. 483 00:25:30,595 --> 00:25:33,698 Or it could be in grams. 484 00:25:33,698 --> 00:25:36,401 Sometimes you'll see it in grams per liter. 485 00:25:36,401 --> 00:25:40,639 So don't get bogged down by the units. 486 00:25:40,639 --> 00:25:47,412 It's just how much of this stuff were you able to dissolve? 487 00:25:47,412 --> 00:25:49,180 If we look at sugar-- 488 00:25:49,180 --> 00:25:50,982 here's sugar, here's salt-- 489 00:25:50,982 --> 00:25:52,284 how much sugar can dissolve? 490 00:25:59,524 --> 00:26:00,792 I'm not going to cram it in. 491 00:26:03,595 --> 00:26:13,872 So for sugar, the max is 1,800, so I'm 492 00:26:13,872 --> 00:26:16,007 going to do both those units-- 493 00:26:16,007 --> 00:26:18,777 1,800 grams per liter. 494 00:26:18,777 --> 00:26:24,082 And if you convert that, it's 5.26 moles per liter. 495 00:26:24,082 --> 00:26:27,886 That's how much sugar you can dissolve in water. 496 00:26:27,886 --> 00:26:29,721 By the way, I did a quick calculation, 497 00:26:29,721 --> 00:26:33,959 and that's 429 teaspoons. 498 00:26:33,959 --> 00:26:36,528 That's 429 teaspoons. 499 00:26:36,528 --> 00:26:38,430 I don't know what everybody is saying-- 500 00:26:38,430 --> 00:26:40,765 Coke has so much sugar. 501 00:26:40,765 --> 00:26:45,704 Coke's got only 26 teaspoons per liter. 502 00:26:45,704 --> 00:26:49,040 You could put a lot more in, if they wanted. 503 00:26:49,040 --> 00:26:50,275 I'll go the other way. 504 00:26:50,275 --> 00:26:55,780 I challenge them to go near the solubility limit. 505 00:26:55,780 --> 00:26:57,949 They're not even close. 506 00:26:57,949 --> 00:27:00,752 Too much sugar. 507 00:27:00,752 --> 00:27:07,459 So salt-- you can also look at salt. For salt, what is it? 508 00:27:07,459 --> 00:27:12,497 Salt is 359 grams per liter, and then that's it. 509 00:27:12,497 --> 00:27:15,233 That's 6.14. 510 00:27:15,233 --> 00:27:15,800 This is nacl. 511 00:27:20,772 --> 00:27:23,942 It's interesting-- if you compare sodium chloride with 512 00:27:23,942 --> 00:27:26,177 sodium bromide-- 513 00:27:26,177 --> 00:27:35,487 so if you look at sodium bromide, it's going to be 8.9. 514 00:27:35,487 --> 00:27:39,524 And sodium fluoride there's only going to be 1. 515 00:27:42,160 --> 00:27:43,294 Why? 516 00:27:43,294 --> 00:27:46,464 Because it comes right down to the picture. 517 00:27:46,464 --> 00:27:49,334 I've got to make these happier. 518 00:27:49,334 --> 00:27:50,835 I've got to make them happier. 519 00:27:50,835 --> 00:27:53,571 If you've got the ions there, and the water likes it, 520 00:27:53,571 --> 00:27:56,875 but what if they really didn't have a strong ionic bond 521 00:27:56,875 --> 00:27:58,009 to start with? 522 00:27:58,009 --> 00:28:00,979 You can imagine you might be able to get to a higher 523 00:28:00,979 --> 00:28:02,580 amount of dissociation. 524 00:28:02,580 --> 00:28:05,917 Or what if they had a very strong ionic bond? 525 00:28:05,917 --> 00:28:07,519 You might imagine that less of it-- 526 00:28:07,519 --> 00:28:10,021 you've got a lower maximum solubility. 527 00:28:10,021 --> 00:28:12,991 So it all kind of goes together with the things 528 00:28:12,991 --> 00:28:13,792 that we've learned. 529 00:28:18,029 --> 00:28:20,598 But what we're really talking about 530 00:28:20,598 --> 00:28:22,967 is what I need to tell you about next. 531 00:28:22,967 --> 00:28:28,473 And that is this idea that we've reached a dynamic equilibrium. 532 00:28:28,473 --> 00:28:30,842 We've reached a dynamic equilibrium. 533 00:28:30,842 --> 00:28:32,610 So what does that mean? 534 00:28:32,610 --> 00:28:35,113 Well, if it's unsaturated-- 535 00:28:35,113 --> 00:28:39,584 so if it's unsaturated, I'm way before this limit. 536 00:28:39,584 --> 00:28:43,455 This is salt. That's the limit max. 537 00:28:43,455 --> 00:28:46,024 Max. 538 00:28:46,024 --> 00:28:48,893 What does it mean? 539 00:28:48,893 --> 00:28:51,429 What does it mean to be below it? 540 00:28:51,429 --> 00:28:54,032 Well, what does it mean to even have reached the maximum 541 00:28:54,032 --> 00:28:54,532 itself? 542 00:28:57,102 --> 00:29:00,505 What it means is not that things aren't dissolving. 543 00:29:00,505 --> 00:29:04,542 What it means is that things are reforming, recrystallizing 544 00:29:04,542 --> 00:29:07,679 at the same rate that they're dissolving. 545 00:29:07,679 --> 00:29:11,850 That's what the maximum means, and that's an equilibrium. 546 00:29:11,850 --> 00:29:13,752 And that's why we're going to talk about next. 547 00:29:13,752 --> 00:29:16,421 So if it's unsaturated, there's a nice little molecular 548 00:29:16,421 --> 00:29:17,055 picture. 549 00:29:17,055 --> 00:29:19,824 There's the thing you're dissolving, and look at them. 550 00:29:19,824 --> 00:29:22,460 They're going away into solution. 551 00:29:22,460 --> 00:29:24,729 Maybe it's salt breaking up into ions. 552 00:29:24,729 --> 00:29:26,731 Maybe it's sugar. 553 00:29:26,731 --> 00:29:28,967 They're going into solution and finding a happy place 554 00:29:28,967 --> 00:29:29,701 around the water. 555 00:29:29,701 --> 00:29:31,870 But once in a while, one of them comes back. 556 00:29:31,870 --> 00:29:34,405 You see that little particle there coming back. 557 00:29:34,405 --> 00:29:35,774 That happens. 558 00:29:35,774 --> 00:29:39,344 But much more, they're dissolving. 559 00:29:39,344 --> 00:29:43,948 Then, you reach this point of saturation where it cannot-- 560 00:29:43,948 --> 00:29:46,417 where it's going to recrystallize, 561 00:29:46,417 --> 00:29:49,521 reform the solid at the same rate that you dissolve. 562 00:29:49,521 --> 00:29:55,627 And that's the place where you can't dissolve anymore. 563 00:29:55,627 --> 00:29:57,862 So what's really happening is that you 564 00:29:57,862 --> 00:30:04,969 have a solute plus a solvent, and it's not going one way 565 00:30:04,969 --> 00:30:08,072 as we've been writing it down. 566 00:30:08,072 --> 00:30:09,674 It's going both ways. 567 00:30:09,674 --> 00:30:13,244 So it's actually the solute plus the solvent goes like this. 568 00:30:13,244 --> 00:30:14,813 That is what we've been talking about. 569 00:30:14,813 --> 00:30:19,717 That's dissolution, and that's the predominant mechanism 570 00:30:19,717 --> 00:30:22,620 on the left before you've saturated. 571 00:30:22,620 --> 00:30:26,124 But see, and that goes to some solution. 572 00:30:26,124 --> 00:30:28,193 But see, you can also precipitate. 573 00:30:36,167 --> 00:30:39,337 Precipitation. 574 00:30:39,337 --> 00:30:42,874 And so at the saturated solution, you have-- 575 00:30:42,874 --> 00:30:49,280 if it's saturated, then that's another way of saying we've 576 00:30:49,280 --> 00:30:59,290 reached the max possible concentration of the solute. 577 00:30:59,290 --> 00:31:05,363 Remember, the little brackets means concentration, molarity. 578 00:31:05,363 --> 00:31:08,499 It means that these rates-- 579 00:31:08,499 --> 00:31:10,368 thinking back to Friday-- 580 00:31:10,368 --> 00:31:12,403 are the same. 581 00:31:12,403 --> 00:31:15,340 It means these rates are the same. 582 00:31:15,340 --> 00:31:18,076 This is a dynamic equilibrium. 583 00:31:18,076 --> 00:31:21,479 And so that's what we need now the tools to talk about. 584 00:31:21,479 --> 00:31:25,516 And so we're going to talk about three things-- 585 00:31:25,516 --> 00:31:30,188 the reaction quotient, the equilibrium constant k, 586 00:31:30,188 --> 00:31:33,791 chemical equilibrium, and then the solubility product. 587 00:31:33,791 --> 00:31:36,294 Now if you think about-- 588 00:31:36,294 --> 00:31:38,363 I just said this is like the forward reaction is 589 00:31:38,363 --> 00:31:40,665 going in the same-- 590 00:31:40,665 --> 00:31:43,301 it's happening in the same rate as the reverse. 591 00:31:43,301 --> 00:31:47,972 And so if you think about this as like a graph 592 00:31:47,972 --> 00:31:50,808 of concentrations-- 593 00:31:50,808 --> 00:31:56,648 so I'll just put here concentrations and time-- 594 00:31:56,648 --> 00:31:58,783 then maybe I have started-- 595 00:31:58,783 --> 00:32:04,422 I've put my salt. I pour a teaspoon of salt in water, 596 00:32:04,422 --> 00:32:09,227 and the salt is dissolving. 597 00:32:09,227 --> 00:32:11,629 So it's going into the products. 598 00:32:11,629 --> 00:32:14,165 It starts out at zero in solution, 599 00:32:14,165 --> 00:32:17,602 and then it becomes products. 600 00:32:22,473 --> 00:32:26,577 At the same time, maybe I've started it up here, 601 00:32:26,577 --> 00:32:27,779 and these are the reactants-- 602 00:32:27,779 --> 00:32:30,214 Gesundheit-- that look like this-- 603 00:32:30,214 --> 00:32:32,517 Gesundheit-- and those would be the reactants. 604 00:32:35,353 --> 00:32:37,956 So the concentrations of these things-- 605 00:32:37,956 --> 00:32:41,292 at a certain point, they're changing. 606 00:32:41,292 --> 00:32:44,929 And then, at a certain point, they're not changing. 607 00:32:44,929 --> 00:32:48,232 But they're still reactions happening back and forth 608 00:32:48,232 --> 00:32:49,167 like I just showed you. 609 00:32:49,167 --> 00:32:52,570 It's a dynamic equilibrium. 610 00:32:52,570 --> 00:32:56,207 Now what we do is we write down for some arbitrary reaction-- 611 00:32:56,207 --> 00:32:59,644 aa plus, so let's go back to this one. 612 00:32:59,644 --> 00:33:02,714 But now, we're going to write it going both ways-- 613 00:33:02,714 --> 00:33:05,950 cc plus dd. 614 00:33:05,950 --> 00:33:08,486 You can define the reaction quotient q-- 615 00:33:08,486 --> 00:33:10,154 that's the first thing-- 616 00:33:10,154 --> 00:33:15,193 as the concentrations c of the products-- 617 00:33:15,193 --> 00:33:25,703 c to the c, d to the d, over a to the a, b to the b. 618 00:33:25,703 --> 00:33:30,341 Please do not confuse this with the rates. 619 00:33:30,341 --> 00:33:30,842 Yeah. 620 00:33:30,842 --> 00:33:33,478 I've been talking about the rates being equal. 621 00:33:33,478 --> 00:33:35,179 That's not from the rates. 622 00:33:35,179 --> 00:33:39,250 Remember, the exponents of the rate law 623 00:33:39,250 --> 00:33:43,688 come from experimental measurements. 624 00:33:43,688 --> 00:33:47,058 The reaction quotient comes from the stoichiometric 625 00:33:47,058 --> 00:33:49,861 coefficients. 626 00:33:49,861 --> 00:33:50,862 Why? 627 00:33:50,862 --> 00:33:55,933 These exponents here have to do literally with probabilities 628 00:33:55,933 --> 00:33:59,137 of reaction, of reacting. 629 00:33:59,137 --> 00:34:03,875 It has to do with the fact that if I've got two of c, 630 00:34:03,875 --> 00:34:08,780 then you multiply the amount of c times another amount of c 631 00:34:08,780 --> 00:34:10,281 in the same volume. 632 00:34:10,281 --> 00:34:12,683 It has to do with probabilities of reacting. 633 00:34:12,683 --> 00:34:14,418 That's where you get those exponents, 634 00:34:14,418 --> 00:34:17,655 and they're directly from the stoichiometric coefficients. 635 00:34:17,655 --> 00:34:21,125 They do not need to be experimentally measured. 636 00:34:21,125 --> 00:34:24,128 Once you have this, you have the reaction quotient. 637 00:34:26,764 --> 00:34:29,500 Now, why is this useful, this reaction quotient? 638 00:34:29,500 --> 00:34:34,338 Well, it's useful because there is a very special place where 639 00:34:34,338 --> 00:34:39,543 now it doesn't change anymore. 640 00:34:39,543 --> 00:34:41,212 These concentrations aren't changing. 641 00:34:41,212 --> 00:34:43,915 Reactions are still happening, but the concentrations 642 00:34:43,915 --> 00:34:46,551 aren't changing-- no change. 643 00:34:49,821 --> 00:34:52,723 If there is no change, then-- 644 00:34:52,723 --> 00:34:55,927 Gesundheit-- then q isn't changing because it's just 645 00:34:55,927 --> 00:34:58,463 a ratio of concentrations. 646 00:34:58,463 --> 00:35:03,034 It's a ratio of concentrations equal to this whole thing, not 647 00:35:03,034 --> 00:35:05,870 just the top line. 648 00:35:05,870 --> 00:35:11,509 The reaction quotient is related to the concentrations. 649 00:35:11,509 --> 00:35:13,010 So if the concentration zone changes 650 00:35:13,010 --> 00:35:16,214 even if reactions are happening still, it's a constant. 651 00:35:16,214 --> 00:35:21,919 So at this point, q equals a constant, 652 00:35:21,919 --> 00:35:25,123 and that is an equilibrium constant. 653 00:35:25,123 --> 00:35:26,023 So we'll call it keq. 654 00:35:30,094 --> 00:35:32,130 It's a dynamic equilibrium. 655 00:35:32,130 --> 00:35:36,868 k represents a dynamic equilibrium. 656 00:35:36,868 --> 00:35:42,707 And what's really useful about k is that for a given reaction, 657 00:35:42,707 --> 00:35:44,509 k is a constant. 658 00:35:44,509 --> 00:35:45,643 I just said it. 659 00:35:45,643 --> 00:35:47,478 But it doesn't matter-- if we're-- 660 00:35:47,478 --> 00:35:49,680 it depends on temperature. 661 00:35:49,680 --> 00:35:53,084 But if I keep the temperature fixed, k won't change. 662 00:35:53,084 --> 00:35:55,620 It's a constant. 663 00:35:55,620 --> 00:36:01,292 It's the constant that tells me where equilibrium is. 664 00:36:01,292 --> 00:36:03,494 It's the constant that tells me where equilibrium is. 665 00:36:07,064 --> 00:36:10,268 Now there's one more thing that we've got to write down-- 666 00:36:10,268 --> 00:36:11,536 that third one there. 667 00:36:11,536 --> 00:36:12,703 I'm going to put it on here. 668 00:36:19,110 --> 00:36:20,778 So k is an equilibrium constant. 669 00:36:20,778 --> 00:36:22,246 That's a general constant. 670 00:36:22,246 --> 00:36:24,515 But now, I'm going to turn my attention 671 00:36:24,515 --> 00:36:27,118 from any old reaction-- 672 00:36:27,118 --> 00:36:30,121 my k is actually very general concept for equilibrium. 673 00:36:30,121 --> 00:36:35,026 We are in this class going to use it for solubility. 674 00:36:35,026 --> 00:36:37,495 That's how we are using the equilibrium constant. 675 00:36:40,298 --> 00:36:51,909 And so the ksp is the solubility product, 676 00:36:51,909 --> 00:36:55,980 and it's an equilibrium constant. 677 00:36:55,980 --> 00:37:11,562 Equilibrium constant that is related to solubility. 678 00:37:11,562 --> 00:37:17,802 It is literally the product of solubilities in equilibrium. 679 00:37:17,802 --> 00:37:19,170 That is literally what it means. 680 00:37:19,170 --> 00:37:21,672 So we're going to do some examples to see that. 681 00:37:21,672 --> 00:37:26,177 It's an equilibrium-- so it's a constant of equilibrium. 682 00:37:26,177 --> 00:37:27,645 And it's called-- Gesundheit-- it's 683 00:37:27,645 --> 00:37:29,580 called the solubility product, because it's 684 00:37:29,580 --> 00:37:35,353 related to the equilibrium of dissolving something, 685 00:37:35,353 --> 00:37:39,523 dissolving some solute in a solvent. 686 00:37:39,523 --> 00:37:42,827 Now we're going to do examples with salts. 687 00:37:42,827 --> 00:37:44,862 So we're going to be dissolving salts and talking 688 00:37:44,862 --> 00:37:49,634 about equilibrium constants in that dissolution, 689 00:37:49,634 --> 00:37:51,936 otherwise known as the solubility product. 690 00:37:51,936 --> 00:37:54,605 It's just an equilibrium constant. 691 00:37:54,605 --> 00:37:55,806 There are many. 692 00:37:55,806 --> 00:37:57,608 This is the one we're going to care about, 693 00:37:57,608 --> 00:37:58,609 and we're going to do it for salts. 694 00:37:58,609 --> 00:38:00,278 And so one of the things you've got to-- 695 00:38:00,278 --> 00:38:03,681 so nacl-- that was kind of easy. 696 00:38:03,681 --> 00:38:08,886 That became a cation and an anion in solution. 697 00:38:08,886 --> 00:38:11,389 But salts can be made of many, many different types 698 00:38:11,389 --> 00:38:15,359 of cations, and there's lists that go on and on and on. 699 00:38:15,359 --> 00:38:18,396 Here are some, and they get named. 700 00:38:18,396 --> 00:38:20,531 So here's some of the anions. 701 00:38:20,531 --> 00:38:24,001 Oh, chlorine-- we just did that one. 702 00:38:24,001 --> 00:38:27,872 Bromine-- you can also have a carbonate. 703 00:38:27,872 --> 00:38:30,374 You could have chromates, hydroxides, oxalates, 704 00:38:30,374 --> 00:38:35,613 sulfates, sulfides, and the list goes on and on and on. 705 00:38:35,613 --> 00:38:37,348 There are many, many of these. 706 00:38:37,348 --> 00:38:38,949 They don't have to be a single atom. 707 00:38:38,949 --> 00:38:43,721 It can be a part of a salt that breaks off and has 708 00:38:43,721 --> 00:38:44,555 a negative charge. 709 00:38:44,555 --> 00:38:47,758 That's an anion, and here are some of the cations-- 710 00:38:47,758 --> 00:38:50,828 sodium, potassium, calcium. 711 00:38:50,828 --> 00:38:52,163 And you know about these things. 712 00:38:52,163 --> 00:38:56,067 We've been talking about these things. 713 00:38:56,067 --> 00:39:00,037 And you know if it's sodium, then you know it's only going 714 00:39:00,037 --> 00:39:02,707 to lose-- it's only going to be na+. 715 00:39:02,707 --> 00:39:07,812 It doesn't have a second weakly-bonded electron to lose. 716 00:39:07,812 --> 00:39:09,780 So it's really only going to be na+. 717 00:39:09,780 --> 00:39:10,915 But then you get-- 718 00:39:10,915 --> 00:39:13,751 and calcium is going to be calcium 2+. 719 00:39:13,751 --> 00:39:15,386 It's got two, magnesium two. 720 00:39:15,386 --> 00:39:20,524 And then transition metals are a little more complicated. 721 00:39:20,524 --> 00:39:22,693 They can be a little more complicated. 722 00:39:22,693 --> 00:39:24,362 Iron can be 2+ or 3+. 723 00:39:24,362 --> 00:39:29,433 It depends, and on and on and on for those. 724 00:39:29,433 --> 00:39:31,869 And so we'll do a few examples. 725 00:39:31,869 --> 00:39:32,870 We'll do a few examples. 726 00:39:35,673 --> 00:39:37,842 We'll get into the mood. 727 00:39:37,842 --> 00:39:40,411 And I want to do it-- first, I'm going to do an example that's 728 00:39:40,411 --> 00:39:42,146 actually a classic example, because it 729 00:39:42,146 --> 00:39:45,182 doesn't dissolve very well, but it's silver chloride. 730 00:39:45,182 --> 00:39:47,385 Now sodium chloride is-- 731 00:39:47,385 --> 00:39:52,823 sodium chloride goes all the way to the point where it basically 732 00:39:52,823 --> 00:39:54,392 dissolves so well. 733 00:39:56,994 --> 00:39:58,763 So you can imagine the equilibrium 734 00:39:58,763 --> 00:40:01,799 for sodium chloride goes way to the right. 735 00:40:01,799 --> 00:40:04,368 But for silver chloride, it's different. 736 00:40:04,368 --> 00:40:05,870 For silver chloride, it's different. 737 00:40:05,870 --> 00:40:08,339 So we're going to look at this curve. 738 00:40:08,339 --> 00:40:09,640 And I'll talk about this curve. 739 00:40:09,640 --> 00:40:10,207 Don't worry. 740 00:40:10,207 --> 00:40:11,575 We're coming to it. 741 00:40:11,575 --> 00:40:12,810 We are coming to it. 742 00:40:12,810 --> 00:40:16,514 Let me start in the middle again. 743 00:40:16,514 --> 00:40:19,216 Because what the equilibrium constant 744 00:40:19,216 --> 00:40:22,286 does, given the definition that I have just hidden, 745 00:40:22,286 --> 00:40:28,025 unfortunately, is it allows us to go back and forth. 746 00:40:28,025 --> 00:40:30,227 If I know the equilibrium constant, 747 00:40:30,227 --> 00:40:36,000 then I can get how much one of these ions is soluble. 748 00:40:36,000 --> 00:40:39,103 I can get the maximum solubility of it. 749 00:40:39,103 --> 00:40:41,372 So let's take an example. 750 00:40:41,372 --> 00:40:42,807 So here's a question. 751 00:40:42,807 --> 00:40:58,856 How much agcl dissolves in 1 liter of water? 752 00:40:58,856 --> 00:41:01,025 That's such a good question. 753 00:41:01,025 --> 00:41:02,359 I don't know. 754 00:41:02,359 --> 00:41:05,629 But I do know that the solubility product 755 00:41:05,629 --> 00:41:08,199 that this equilibrium constant for sodium chloride 756 00:41:08,199 --> 00:41:14,038 is 1.7 times 10 to the minus 10th. 757 00:41:14,038 --> 00:41:19,710 Now if I write down the dissolution reaction, 758 00:41:19,710 --> 00:41:24,949 sodium chloride solid is going to go to-- 759 00:41:27,618 --> 00:41:32,590 sorry, sodium silver-- silver plus in solution. 760 00:41:32,590 --> 00:41:36,594 So we put the aqueous plus chlorine minus in solution. 761 00:41:39,763 --> 00:41:41,799 And it is going to go back and forth. 762 00:41:45,803 --> 00:41:49,707 And so the ksp for this is going to equal-- 763 00:41:49,707 --> 00:41:52,643 I'm going to go with the equation that I wrote down-- 764 00:41:52,643 --> 00:41:56,547 the concentration of silver to the 1 times the concentration 765 00:41:56,547 --> 00:41:58,482 of chlorine minus-- these are ions-- 766 00:41:58,482 --> 00:42:01,719 divided by the concentration of silver chloride solid. 767 00:42:06,223 --> 00:42:07,391 Now we get to another thing. 768 00:42:07,391 --> 00:42:11,395 Remember, I got rid of water, because water is everywhere. 769 00:42:11,395 --> 00:42:12,963 It's the solvent. 770 00:42:12,963 --> 00:42:16,867 So you don't need to put it into these equilibrium calculations. 771 00:42:16,867 --> 00:42:22,006 Well, it's the same thing with the solid. 772 00:42:22,006 --> 00:42:25,209 So if I think about this a little bit, 773 00:42:25,209 --> 00:42:29,780 this equilibrium is between dissolved. 774 00:42:29,780 --> 00:42:35,853 It's between the ions that are dissolving. 775 00:42:35,853 --> 00:42:39,523 But there from this reaction, from the way 776 00:42:39,523 --> 00:42:45,162 it's written there, I've got a solid form of silver chloride. 777 00:42:45,162 --> 00:42:50,067 So this is not-- so this is the concentration of solid silver 778 00:42:50,067 --> 00:42:52,903 chloride in the solid. 779 00:42:52,903 --> 00:42:54,972 This is just a constant. 780 00:42:54,972 --> 00:42:56,707 That's not going to change. 781 00:42:56,707 --> 00:42:57,841 That's not going to change. 782 00:42:57,841 --> 00:43:01,412 Common misunderstanding. 783 00:43:01,412 --> 00:43:02,279 It doesn't change. 784 00:43:02,279 --> 00:43:05,316 So we get rid of it, because it gets folded into the constant. 785 00:43:05,316 --> 00:43:07,418 That's always the same. 786 00:43:07,418 --> 00:43:10,788 The concentration of this is always the same. 787 00:43:10,788 --> 00:43:12,156 And so we get rid of it. 788 00:43:12,156 --> 00:43:18,295 So now we have the ksp is equal to, in this case, 789 00:43:18,295 --> 00:43:22,266 ag+ times cl-. 790 00:43:22,266 --> 00:43:24,301 Talk about solubility product. 791 00:43:24,301 --> 00:43:26,537 Solubilities concentrate. 792 00:43:26,537 --> 00:43:29,373 The solubility is-- when I add this in, 793 00:43:29,373 --> 00:43:31,508 it reaches some equilibrium where they're 794 00:43:31,508 --> 00:43:33,444 dissolving and reforming. 795 00:43:33,444 --> 00:43:36,547 I wanted to know at what point that is, what concentrations 796 00:43:36,547 --> 00:43:37,982 is that going to be. 797 00:43:37,982 --> 00:43:41,385 This is them. 798 00:43:41,385 --> 00:43:43,454 So solubility product-- right there. 799 00:43:49,426 --> 00:43:53,030 I used the definition of equilibrium constant. 800 00:43:53,030 --> 00:43:56,667 And now I can use this reaction. 801 00:43:56,667 --> 00:44:00,804 I can use this reaction because the stoichiometric coefficients 802 00:44:00,804 --> 00:44:02,406 tell me-- 803 00:44:02,406 --> 00:44:05,075 they tell me both what the exponents there are-- 804 00:44:05,075 --> 00:44:09,113 1-- but they also tell me the relative molar amounts 805 00:44:09,113 --> 00:44:09,980 of these things. 806 00:44:09,980 --> 00:44:12,549 It's the same. 807 00:44:12,549 --> 00:44:17,521 So if x equals the concentration of silver plus, 808 00:44:17,521 --> 00:44:26,964 then it must also equal the concentration of cl minus. 809 00:44:26,964 --> 00:44:28,799 If you just let x equal the concentration, 810 00:44:28,799 --> 00:44:30,034 that comes from the reaction. 811 00:44:30,034 --> 00:44:33,037 1 in front of silver, 1 in front of chlorine. 812 00:44:33,037 --> 00:44:35,706 And so that means now that you can solve it 813 00:44:35,706 --> 00:44:46,250 because x squared is equal to 1.7 times 10 to the minus 10th, 814 00:44:46,250 --> 00:44:56,694 and x equals 1.3 times 10 to the minus fifth, m, 815 00:44:56,694 --> 00:45:00,164 and that equals these concentrations. 816 00:45:00,164 --> 00:45:02,032 That equals the concentration of silver plus. 817 00:45:02,032 --> 00:45:04,334 So that is how much, in equilibrium-- this 818 00:45:04,334 --> 00:45:05,703 is an equilibrium constant-- that 819 00:45:05,703 --> 00:45:12,476 is how much you will get of these ions dissolved in water. 820 00:45:12,476 --> 00:45:20,217 Now there is a nice way to set this up that is often 821 00:45:20,217 --> 00:45:21,485 taught in high school. 822 00:45:21,485 --> 00:45:22,219 I like it. 823 00:45:22,219 --> 00:45:25,189 I think it's a good way to keep track. 824 00:45:25,189 --> 00:45:28,292 And so if you were wanting to keep track, 825 00:45:28,292 --> 00:45:33,731 and you like tables, there's something called the ICE table. 826 00:45:33,731 --> 00:45:38,535 And in this case, it's a little bit boring, but as you'll see, 827 00:45:38,535 --> 00:45:43,874 it can actually wind up being pretty useful, 828 00:45:43,874 --> 00:45:46,176 especially when we add other ions, which 829 00:45:46,176 --> 00:45:49,580 are going to do soon. 830 00:45:49,580 --> 00:45:54,752 So ICE is initial change equilibrium. 831 00:45:54,752 --> 00:45:57,421 Initial change equilibrium. 832 00:45:57,421 --> 00:46:00,124 It's just a way of keeping track of what I just did, 833 00:46:00,124 --> 00:46:07,698 because I started with some amount of solid, 834 00:46:07,698 --> 00:46:09,399 and I had zero. 835 00:46:09,399 --> 00:46:10,501 I put it into water. 836 00:46:10,501 --> 00:46:17,875 I had zero, but then I added 1.3 times 10 to the minus fifth, 837 00:46:17,875 --> 00:46:22,212 and I added 1.3 times 10 to the minus fifth. 838 00:46:22,212 --> 00:46:28,852 And so my equilibrium is a little less, a little less 839 00:46:28,852 --> 00:46:31,622 solid. 840 00:46:31,622 --> 00:46:33,991 And over here, it's just these numbers. 841 00:46:37,728 --> 00:46:43,700 That was indeed boring, but have no fear. 842 00:46:43,700 --> 00:46:46,203 It becomes helpful. 843 00:46:46,203 --> 00:46:48,572 It becomes helpful because what we're going to do next-- 844 00:46:48,572 --> 00:46:49,807 not right now-- 845 00:46:49,807 --> 00:46:52,709 but on Wednesday, what we're going to do 846 00:46:52,709 --> 00:46:56,747 is we're going to mess with this equilibrium. 847 00:46:56,747 --> 00:46:59,082 Oh, equilibrium, I'm going to throw you off. 848 00:46:59,082 --> 00:47:00,551 And equilibrium is saying, no you're 849 00:47:00,551 --> 00:47:05,389 not, because I'm equilibrium, and I will always be found. 850 00:47:05,389 --> 00:47:08,725 And that's called Le Chatelier's Principle, and what that does 851 00:47:08,725 --> 00:47:10,527 is it allows us to really go back, 852 00:47:10,527 --> 00:47:15,632 and we get to actually add a bunch of chlorine ions to this, 853 00:47:15,632 --> 00:47:19,069 and we're going to see what happens to this balance. 854 00:47:19,069 --> 00:47:21,505 It will find equilibrium. 855 00:47:21,505 --> 00:47:24,274 And we have the tools now to know how to find it. 856 00:47:24,274 --> 00:47:26,476 That's that green curve there. 857 00:47:26,476 --> 00:47:28,178 This is what we're going to work with. 858 00:47:28,178 --> 00:47:29,813 There's the concentration of chlorine. 859 00:47:33,083 --> 00:47:35,586 There's a concentration of silver in ions. 860 00:47:35,586 --> 00:47:38,355 You see the dissolved chlorine on the x-axis, dissolved silver 861 00:47:38,355 --> 00:47:38,922 on the y-axis. 862 00:47:38,922 --> 00:47:39,923 And look at that. 863 00:47:39,923 --> 00:47:44,094 I've got that point b there that is 864 00:47:44,094 --> 00:47:46,463 where these things have found equilibrium 865 00:47:46,463 --> 00:47:48,966 when it's not messed with. 866 00:47:48,966 --> 00:47:52,436 Now the thing is, if you were a reaction happening, 867 00:47:52,436 --> 00:47:54,705 and you hadn't gotten to equilibrium yet-- 868 00:47:54,705 --> 00:47:57,507 so I hadn't added much silver chloride-- 869 00:47:57,507 --> 00:48:01,078 if that was the case, then you might be at point d. 870 00:48:01,078 --> 00:48:04,281 Notice that the reaction quotient, q, is less 871 00:48:04,281 --> 00:48:07,718 than the equilibrium constant. 872 00:48:07,718 --> 00:48:08,719 q is less. 873 00:48:08,719 --> 00:48:10,420 That means it's going to be driven 874 00:48:10,420 --> 00:48:13,190 to dissolve more than it precipitates until it 875 00:48:13,190 --> 00:48:16,526 gets to point B on this curve. 876 00:48:16,526 --> 00:48:21,665 You could also be way, way out with a much higher q point, e, 877 00:48:21,665 --> 00:48:24,201 and you know it has to find equilibrium. 878 00:48:24,201 --> 00:48:25,802 It's going to find equilibrium, which 879 00:48:25,802 --> 00:48:27,604 is what we just calculated. 880 00:48:27,604 --> 00:48:29,439 Those are the concentrations of equilibrium. 881 00:48:29,439 --> 00:48:31,541 It has to get back to point B. It's going to do it 882 00:48:31,541 --> 00:48:34,678 by precipitating out solid. 883 00:48:34,678 --> 00:48:35,779 It's gone too far. 884 00:48:38,815 --> 00:48:41,885 But you can see that equilibrium can also be had 885 00:48:41,885 --> 00:48:42,886 and will be had. 886 00:48:42,886 --> 00:48:44,621 It shall be had. 887 00:48:44,621 --> 00:48:47,991 Because k never changes if you fix the temperature. 888 00:48:47,991 --> 00:48:50,060 k is the same. 889 00:48:50,060 --> 00:48:52,195 So I can mess with this in other ways. 890 00:48:52,195 --> 00:48:54,498 I can go and add a whole bunch of chlorine, 891 00:48:54,498 --> 00:48:57,267 and it will come back down onto that green curve. 892 00:48:57,267 --> 00:48:59,169 It will come back down onto that green curve, 893 00:48:59,169 --> 00:49:01,171 which is the curve that guarantees 894 00:49:01,171 --> 00:49:03,140 k is the same constant. 895 00:49:03,140 --> 00:49:05,542 That's what that green curve is. 896 00:49:05,542 --> 00:49:08,545 And there's one last point I'm going to make today, 897 00:49:08,545 --> 00:49:10,714 and that is units. 898 00:49:10,714 --> 00:49:17,020 Units of k depend-- 899 00:49:17,020 --> 00:49:18,722 it was like the rate law. 900 00:49:18,722 --> 00:49:26,363 It depends on the reaction. 901 00:49:26,363 --> 00:49:30,767 Look, a concentration is a concentration. 902 00:49:30,767 --> 00:49:32,369 That was deep. 903 00:49:32,369 --> 00:49:36,139 Units are capital M moles per liter. 904 00:49:36,139 --> 00:49:39,209 But that means that k-- 905 00:49:39,209 --> 00:49:42,980 k is two of those multiplied together. 906 00:49:42,980 --> 00:49:50,320 So in this case, k has units of m squared. 907 00:49:50,320 --> 00:49:53,290 It must, or it wouldn't work. 908 00:49:53,290 --> 00:49:54,891 k can have units of m cubed. 909 00:49:57,494 --> 00:49:59,429 We will pick up here on Wednesday, 910 00:49:59,429 --> 00:50:03,600 and we'll cover more of this, more examples 911 00:50:03,600 --> 00:50:06,503 before we move on to acids and bases.