1 00:00:16,015 --> 00:00:17,384 We're going to pick up 2 00:00:17,384 --> 00:00:20,387 where we left off on Monday. 3 00:00:20,387 --> 00:00:23,289 And where we left off was we were dissolving stuff. 4 00:00:23,289 --> 00:00:26,459 We talked about how things dissolve. 5 00:00:26,459 --> 00:00:28,361 Why does something dissolve maybe 6 00:00:28,361 --> 00:00:29,996 in this solvent versus that? 7 00:00:29,996 --> 00:00:31,131 And how does it dissolve? 8 00:00:31,131 --> 00:00:32,131 And what makes them-- 9 00:00:32,131 --> 00:00:34,300 and then we say, well, what if we had something 10 00:00:34,300 --> 00:00:36,336 and we wanted it to dissolve all the way until it 11 00:00:36,336 --> 00:00:37,470 couldn't dissolve anymore? 12 00:00:37,470 --> 00:00:41,641 Well, that's called saturation, right? 13 00:00:41,641 --> 00:00:42,776 And we talked about that. 14 00:00:42,776 --> 00:00:46,312 We talked about how if you had a general reaction, maybe 15 00:00:46,312 --> 00:00:52,619 we had something like this, aA plus bB 16 00:00:52,619 --> 00:00:56,099 goes to and comes back from 17 00:00:56,099 --> 00:01:01,161 cC plus dD, then this reaction 18 00:01:01,161 --> 00:01:03,063 can happen in both ways, right? 19 00:01:03,063 --> 00:01:07,934 And so the general concept that we called a reaction quotient, 20 00:01:07,934 --> 00:01:13,039 reaction Q, is equal to-- 21 00:01:13,039 --> 00:01:16,443 remember, it's equal to the concentrations 22 00:01:16,443 --> 00:01:20,646 raised to those stoichiometric coefficients. 23 00:01:20,646 --> 00:01:25,318 And it's the products over the reactants. 24 00:01:25,318 --> 00:01:26,719 OK, so that's what we-- 25 00:01:26,719 --> 00:01:33,226 now then, we say, well OK, that's 26 00:01:33,226 --> 00:01:36,963 a thing that has to do with maybe-- 27 00:01:36,963 --> 00:01:38,598 where's that reaction going? 28 00:01:38,598 --> 00:01:40,633 What's dominating it? 29 00:01:40,633 --> 00:01:43,970 And remember, these are the stoichiometric coefficients, 30 00:01:43,970 --> 00:01:47,240 and they're related to literally the probability 31 00:01:47,240 --> 00:01:49,576 that that reaction can happen. 32 00:01:49,576 --> 00:01:52,979 OK, and so if you want an intuitive 33 00:01:52,979 --> 00:01:56,015 reason for the exponents, you can think about this as, well, 34 00:01:56,015 --> 00:01:59,252 if these all have to get close enough in a given volume 35 00:01:59,252 --> 00:02:04,357 to react, then that's where those exponents come from. 36 00:02:04,357 --> 00:02:06,192 But unlike the rate law-- 37 00:02:06,192 --> 00:02:08,495 and I said this Monday, and I'm saying it again today-- 38 00:02:08,495 --> 00:02:10,896 they are not things that are experimentally measured. 39 00:02:10,896 --> 00:02:15,268 Instead, they just come from the reaction itself, OK? 40 00:02:15,268 --> 00:02:18,771 So we're just getting back into the right mood here. 41 00:02:18,771 --> 00:02:20,173 But then we said, well, but look. 42 00:02:20,173 --> 00:02:21,508 OK, this thing is reacting. 43 00:02:21,508 --> 00:02:23,009 It's going back and forth, whatever. 44 00:02:23,009 --> 00:02:26,880 But what about once it reaches equilibrium, 45 00:02:26,880 --> 00:02:28,047 all right, equilibrium? 46 00:02:28,047 --> 00:02:31,284 And when it reaches equilibrium, it's the same thing, 47 00:02:31,284 --> 00:02:38,291 but we call it Keq, in equilibrium, 48 00:02:38,291 --> 00:02:41,761 eq'm, equilibrium, right? 49 00:02:41,761 --> 00:02:46,031 So that reaction quotient has a very specific value, 50 00:02:46,031 --> 00:02:52,338 a constant, a constant, once this way is happening 51 00:02:52,338 --> 00:02:55,241 in the same amount as that way. 52 00:02:55,241 --> 00:02:58,711 Right, that's the saturation point. 53 00:02:58,711 --> 00:03:00,480 Well, if you're dissolving something, 54 00:03:00,480 --> 00:03:03,550 that's the saturation point. 55 00:03:03,550 --> 00:03:06,252 OK, so it's where the precipitation-- remember, 56 00:03:06,252 --> 00:03:09,289 we wrote this as dissolution and precipitation 57 00:03:09,289 --> 00:03:11,024 when we were putting stuff in solution. 58 00:03:11,024 --> 00:03:12,959 And that's where we got to. 59 00:03:12,959 --> 00:03:15,562 And we went a little bit further, 60 00:03:15,562 --> 00:03:17,263 and we had a specific example. 61 00:03:17,263 --> 00:03:18,898 And that's where I want to start today, 62 00:03:18,898 --> 00:03:21,234 and that's silver chloride. 63 00:03:21,234 --> 00:03:22,468 OK, so here we go. 64 00:03:22,468 --> 00:03:25,171 So we have silver chloride. 65 00:03:25,171 --> 00:03:29,909 And if I write this all out for silver chloride, I've got AgCl. 66 00:03:29,909 --> 00:03:32,745 And I've got a little pinch of it, 67 00:03:32,745 --> 00:03:34,480 like a little speck of silver chloride. 68 00:03:34,480 --> 00:03:36,382 And I'm putting it into a beaker. 69 00:03:36,382 --> 00:03:41,321 So it starts out as a solid, and I add some water to it. 70 00:03:41,321 --> 00:03:44,457 And the water is l, because it's everywhere. 71 00:03:44,457 --> 00:03:45,124 It's the liquid. 72 00:03:45,124 --> 00:03:46,459 It's the solvent. 73 00:03:46,459 --> 00:03:49,529 OK, it's the liquid that I'm dissolving it in. 74 00:03:49,529 --> 00:03:52,131 And we say, well OK, that's going to go like this. 75 00:03:52,131 --> 00:03:56,936 So that reaction, it's going to give us silver ions-- 76 00:03:56,936 --> 00:04:00,273 remember salts, we did salts-- 77 00:04:00,273 --> 00:04:08,014 and chlorine ions, and back to some more water. 78 00:04:08,014 --> 00:04:09,782 OK, that's H2O. 79 00:04:09,782 --> 00:04:13,386 Now, the aq means aqueous. 80 00:04:13,386 --> 00:04:16,289 Because it's a salt, right, these 81 00:04:16,289 --> 00:04:19,358 are now dissolved ions, because it's a salt. 82 00:04:19,358 --> 00:04:20,893 So we write them like that. 83 00:04:20,893 --> 00:04:23,997 And we know we got water everywhere. 84 00:04:23,997 --> 00:04:28,568 So oftentimes, we leave the water out. 85 00:04:28,568 --> 00:04:30,403 Oftentimes we don't really write the water, 86 00:04:30,403 --> 00:04:31,971 because it's on both sides. 87 00:04:31,971 --> 00:04:36,909 And anyway, the water is just surrounding stuff. 88 00:04:36,909 --> 00:04:39,712 It's not necessarily being consumed. 89 00:04:39,712 --> 00:04:42,982 The concentration of the water isn't changing. 90 00:04:42,982 --> 00:04:45,852 The water is the water in the liquid phase. 91 00:04:45,852 --> 00:04:48,888 Well, OK, then we went even further and said, 92 00:04:48,888 --> 00:04:53,860 well, if you write a Keq for this, then 93 00:04:53,860 --> 00:04:57,430 that would look something like the concentration of silver 94 00:04:57,430 --> 00:05:03,236 plus in solution times the concentration of chlorine 95 00:05:03,236 --> 00:05:05,738 minus in solution. 96 00:05:05,738 --> 00:05:09,008 And that would be divided by the concentration 97 00:05:09,008 --> 00:05:12,679 of silver chloride as a solid. 98 00:05:12,679 --> 00:05:14,947 And then we said-- 99 00:05:14,947 --> 00:05:17,082 but hold on. 100 00:05:17,082 --> 00:05:19,118 But hold on. 101 00:05:19,118 --> 00:05:22,188 In the solid phase, the concentration 102 00:05:22,188 --> 00:05:23,523 isn't changing, right? 103 00:05:23,523 --> 00:05:27,193 As a solid, the concentration of silver chloride 104 00:05:27,193 --> 00:05:28,061 is silver chloride. 105 00:05:28,061 --> 00:05:29,796 It's a constant. 106 00:05:29,796 --> 00:05:34,067 And so then we said, well OK, if this is a constant, 107 00:05:34,067 --> 00:05:35,835 this is a constant. 108 00:05:38,938 --> 00:05:45,244 Then we can also absorb it into the equilibrium constant. 109 00:05:45,244 --> 00:05:47,013 And I somewhat confusingly wrote it 110 00:05:47,013 --> 00:05:51,851 as Ksp in both this form and the form 111 00:05:51,851 --> 00:05:53,853 that we know and love for Ksp, which 112 00:05:53,853 --> 00:05:57,890 is simply literally the solubilities of these times 113 00:05:57,890 --> 00:05:59,192 each other. 114 00:05:59,192 --> 00:06:01,260 Right, and that is Ksp. 115 00:06:01,260 --> 00:06:03,096 So I wanted just to clarify this, 116 00:06:03,096 --> 00:06:06,833 because a student asked a very good question, which is, 117 00:06:06,833 --> 00:06:08,468 which is it? 118 00:06:08,468 --> 00:06:11,170 Is this in Ksp or is this in Keq? 119 00:06:11,170 --> 00:06:17,009 Well, the big full picture for Keq, you'd write it all in. 120 00:06:17,009 --> 00:06:25,184 But the solubility product is focusing in on the dissolution 121 00:06:25,184 --> 00:06:27,120 of these ions. 122 00:06:27,120 --> 00:06:30,022 And so you wrap this into the equilibrium constant, 123 00:06:30,022 --> 00:06:31,491 because it's another constant. 124 00:06:31,491 --> 00:06:33,126 So that's the solubility product. 125 00:06:33,126 --> 00:06:35,161 And that's where we got to on Monday. 126 00:06:35,161 --> 00:06:39,665 The solubility product is a special equilibrium constant, 127 00:06:39,665 --> 00:06:44,837 where what we're talking about is-- 128 00:06:44,837 --> 00:06:47,306 what are the concentrations when you've 129 00:06:47,306 --> 00:06:52,044 reached saturation of this dissolution precipitation 130 00:06:52,044 --> 00:06:53,846 reaction, OK? 131 00:06:53,846 --> 00:06:55,615 That's the solubility product. 132 00:06:55,615 --> 00:06:57,283 That's Ksp. 133 00:06:57,283 --> 00:06:59,852 So you wrap this in, and you get Ksp. 134 00:07:02,555 --> 00:07:04,123 You can think about it as, well, maybe 135 00:07:04,123 --> 00:07:08,728 you could have called this some Ksp in a pre-Ksp. 136 00:07:08,728 --> 00:07:10,396 And then you wrap this in, and then it's 137 00:07:10,396 --> 00:07:12,965 still just [INAUDIBLE],, because it's still just a constant 138 00:07:12,965 --> 00:07:14,367 representing this reaction. 139 00:07:14,367 --> 00:07:16,302 OK, I just wanted to make this super clear, 140 00:07:16,302 --> 00:07:19,672 because this part leads to confusion often, 141 00:07:19,672 --> 00:07:22,241 that this gets left out, because it's constant. 142 00:07:22,241 --> 00:07:23,543 It doesn't change. 143 00:07:23,543 --> 00:07:25,244 OK, good. 144 00:07:25,244 --> 00:07:29,582 Now we get to that, because this is a constant. 145 00:07:29,582 --> 00:07:31,784 OK, so what does that mean? 146 00:07:31,784 --> 00:07:35,621 Well, it means that if I dissolve this thing in water, 147 00:07:35,621 --> 00:07:42,028 then the equilibrium, the equilibrium is a fixed number. 148 00:07:42,028 --> 00:07:44,063 This equilibrium product is fixed. 149 00:07:44,063 --> 00:07:46,199 And that has a very important meaning. 150 00:07:46,199 --> 00:07:47,567 It's the green curve. 151 00:07:47,567 --> 00:07:50,069 You see, it says equilibrium. 152 00:07:50,069 --> 00:07:54,340 And so what that means is that if I'm at point B, well, there 153 00:07:54,340 --> 00:07:55,041 I go. 154 00:07:55,041 --> 00:07:58,144 I've got my-- we said Ksp. 155 00:07:58,144 --> 00:08:08,588 Ksp for this one equals, what was it, 1.7 times 10 156 00:08:08,588 --> 00:08:11,057 to the minus 10th. 157 00:08:11,057 --> 00:08:13,693 Units are coming. 158 00:08:13,693 --> 00:08:24,737 And so that's the Ksp for silver chloride and H20. 159 00:08:24,737 --> 00:08:30,877 Oh, and you have to say at some temperature. 160 00:08:30,877 --> 00:08:33,246 It will depend on temperature. 161 00:08:33,246 --> 00:08:37,415 You often will just be at room temperature, 25C, for example. 162 00:08:37,415 --> 00:08:40,019 So often these get quoted just at room temperature. 163 00:08:42,889 --> 00:08:46,292 OK, so once I know that, then I know that that's equilibrium 164 00:08:46,292 --> 00:08:47,660 no matter what, right? 165 00:08:47,660 --> 00:08:48,895 And so that means that if-- 166 00:08:48,895 --> 00:08:50,029 and then we solve this. 167 00:08:50,029 --> 00:08:54,901 You said, well OK, if I dissolve silver chloride, 168 00:08:54,901 --> 00:08:59,672 and I had nothing else, then the Ksp 169 00:08:59,672 --> 00:09:03,910 would equal the concentration of silver 170 00:09:03,910 --> 00:09:08,614 times the concentration of chlorine ions. 171 00:09:08,614 --> 00:09:09,782 But those are equal. 172 00:09:09,782 --> 00:09:11,284 And so we let each one of them be x, 173 00:09:11,284 --> 00:09:13,119 then it's equal to x squared. 174 00:09:13,119 --> 00:09:18,524 And so we know that the concentration of each of them 175 00:09:18,524 --> 00:09:22,528 is 10 to the minus-- 176 00:09:22,528 --> 00:09:23,930 let me write it exactly-- 177 00:09:23,930 --> 00:09:26,599 1.3 times 10 to the minus fifth. 178 00:09:26,599 --> 00:09:28,467 Now, it's a concentration, so you 179 00:09:28,467 --> 00:09:32,805 know that it's got to be capital M, moles per liter. 180 00:09:32,805 --> 00:09:35,241 And since that's the case, since that's 181 00:09:35,241 --> 00:09:38,210 where you know what it is, then now you can back up. 182 00:09:38,210 --> 00:09:41,013 Because this is the concentration of Ag ions 183 00:09:41,013 --> 00:09:43,549 and it's also the concentration of chlorine ions, 184 00:09:43,549 --> 00:09:46,652 then you know that the units of Ksp 185 00:09:46,652 --> 00:09:49,088 must be M squared, all right? 186 00:09:52,091 --> 00:10:01,100 Units in this case, moles per liter squared. 187 00:10:01,100 --> 00:10:04,303 Must be, because otherwise the concentration isn't right, 188 00:10:04,303 --> 00:10:06,772 the units of concentration. 189 00:10:06,772 --> 00:10:08,641 OK, now we're going to play with this. 190 00:10:08,641 --> 00:10:12,311 OK, so I'm at B. I'm at point B. You see that? 191 00:10:12,311 --> 00:10:13,379 There I am. 192 00:10:13,379 --> 00:10:15,581 And I've got my concentration of chlorine, 193 00:10:15,581 --> 00:10:16,882 concentration of silver. 194 00:10:16,882 --> 00:10:18,517 And I'm here. 195 00:10:18,517 --> 00:10:21,654 And so that's 1.3 times 10 to the minus fifth. 196 00:10:21,654 --> 00:10:25,191 OK, now if I didn't have as much, 197 00:10:25,191 --> 00:10:29,862 if I weren't at the saturation point, then I could add more. 198 00:10:29,862 --> 00:10:31,364 I'd be here. 199 00:10:31,364 --> 00:10:33,933 And I could add more solid silver chloride. 200 00:10:33,933 --> 00:10:39,438 And eventually, I'd reach this equilibrium. 201 00:10:39,438 --> 00:10:42,308 But if I added more than that, so now I'm 202 00:10:42,308 --> 00:10:46,979 adding way more than I can, then it's just going to be a solid. 203 00:10:46,979 --> 00:10:48,848 And that's kind of boring. 204 00:10:48,848 --> 00:10:50,750 So now I'm up here. 205 00:10:50,750 --> 00:10:52,785 But maybe I add ions in. 206 00:10:52,785 --> 00:10:53,719 So these are the ions. 207 00:10:53,719 --> 00:10:55,287 So maybe I add a whole bunch of ions. 208 00:10:55,287 --> 00:10:56,922 Well, they're just going to precipitate. 209 00:10:56,922 --> 00:10:58,924 I can't be here and be in equilibrium. 210 00:10:58,924 --> 00:11:00,693 That's the point of the green curve. 211 00:11:00,693 --> 00:11:03,029 This K doesn't change. 212 00:11:03,029 --> 00:11:08,200 This K is this K. That's what the green curve is. 213 00:11:08,200 --> 00:11:11,270 It is that being constant. 214 00:11:11,270 --> 00:11:12,171 That's very important. 215 00:11:12,171 --> 00:11:13,205 That is equilibrium. 216 00:11:13,205 --> 00:11:19,578 Now, there is a way though to move around on it, 217 00:11:19,578 --> 00:11:21,914 because if I did, imagine now-- 218 00:11:21,914 --> 00:11:24,950 look at point C. Imagine now that I've 219 00:11:24,950 --> 00:11:28,988 found some source of chlorine ions 220 00:11:28,988 --> 00:11:33,659 and I add a whole bunch of them, right, a whole bunch of them 221 00:11:33,659 --> 00:11:35,094 into the solution. 222 00:11:35,094 --> 00:11:37,129 I don't want to add silver and chlorine together. 223 00:11:37,129 --> 00:11:39,065 I just add chlorine. 224 00:11:39,065 --> 00:11:40,766 Well, you can see what's going to happen. 225 00:11:40,766 --> 00:11:42,802 I have to get to equilibrium. 226 00:11:42,802 --> 00:11:46,639 And so in order to stay in equilibrium for silver chloride 227 00:11:46,639 --> 00:11:50,643 in solution, then I must lower my concentration of silver, 228 00:11:50,643 --> 00:11:53,813 because I added all this chlorine. 229 00:11:53,813 --> 00:11:55,915 The only way to do that is to eat up 230 00:11:55,915 --> 00:11:58,250 some silver and precipitate. 231 00:11:58,250 --> 00:11:59,685 That's the only way to do that. 232 00:11:59,685 --> 00:12:01,387 And that has a name. 233 00:12:01,387 --> 00:12:03,289 And that's what I want to talk about next. 234 00:12:03,289 --> 00:12:05,725 That is called the common ion effect. 235 00:12:09,695 --> 00:12:12,665 Now, this is an example. 236 00:12:12,665 --> 00:12:16,902 This is an example of a broader principle 237 00:12:16,902 --> 00:12:22,041 which I mentioned Monday, which is Le Chatelier's principle. 238 00:12:22,041 --> 00:12:22,541 OK. 239 00:12:27,646 --> 00:12:39,191 And that is that position of equilibrium will move. 240 00:12:39,191 --> 00:12:43,629 It's still equilibrium, but it's moving on that green curve 241 00:12:43,629 --> 00:12:45,064 to counteract change. 242 00:12:50,069 --> 00:12:54,974 This is a very general principle. 243 00:12:54,974 --> 00:12:58,978 It applies to many, many things, not just concentrations. 244 00:12:58,978 --> 00:13:01,814 It applies to changes in pressure and other changes 245 00:13:01,814 --> 00:13:02,915 that you make in a system. 246 00:13:02,915 --> 00:13:04,750 Here we care about concentration. 247 00:13:04,750 --> 00:13:07,186 And in this particular case, we're 248 00:13:07,186 --> 00:13:08,721 going to see it for what happens when 249 00:13:08,721 --> 00:13:14,426 you add ions of one particular type and not the other. 250 00:13:14,426 --> 00:13:18,130 That's the common ion effect, but it's a very general effect, 251 00:13:18,130 --> 00:13:20,232 that it resists the change. 252 00:13:20,232 --> 00:13:23,435 Now, let's see how that works. 253 00:13:26,772 --> 00:13:29,141 If I want a source of ions, let's say 254 00:13:29,141 --> 00:13:31,544 I want a source of chlorine, one way 255 00:13:31,544 --> 00:13:34,847 would be to add a whole bunch of sodium chloride. 256 00:13:34,847 --> 00:13:38,784 So let's suppose that I have-- 257 00:13:38,784 --> 00:13:46,859 OK, so as an example, I'm going to add to this nice equilibrium 258 00:13:46,859 --> 00:13:49,695 that I reached here-- so I'm at point B, OK? 259 00:13:49,695 --> 00:14:00,506 And I'm going to add 0.1 moles per liter of sodium chloride. 260 00:14:00,506 --> 00:14:06,045 And this nearly-- and so we're going to say it does-- 261 00:14:06,045 --> 00:14:10,649 it nearly fully disassociates. 262 00:14:10,649 --> 00:14:13,185 And we'll be talking about that later today. 263 00:14:13,185 --> 00:14:22,661 And so that means that NaCl basically goes to Na+ plus Cl-, 264 00:14:22,661 --> 00:14:23,829 both in solution. 265 00:14:23,829 --> 00:14:32,071 So if I put 0.1 moles per liter of sodium chloride 266 00:14:32,071 --> 00:14:35,674 into this container of the silver chloride, 267 00:14:35,674 --> 00:14:37,476 I'm basically going to get 0.1, because 268 00:14:37,476 --> 00:14:38,844 of the stoichiometric coefficient 269 00:14:38,844 --> 00:14:41,847 here, 1, 1, 1, right? 270 00:14:41,847 --> 00:14:43,649 So if I put 0.1 moles per liter of this, 271 00:14:43,649 --> 00:14:46,852 I'm going to have 0.1 moles per liter of chlorine ions 272 00:14:46,852 --> 00:14:49,822 that I just dumped into the container. 273 00:14:49,822 --> 00:14:53,859 But the sodium is not going to do anything. 274 00:14:53,859 --> 00:14:55,294 But look at the chlorine. 275 00:14:55,294 --> 00:14:59,398 That's going to mess with my equilibrium. 276 00:14:59,398 --> 00:15:01,267 But K is a constant. 277 00:15:01,267 --> 00:15:03,102 So let's see what happens. 278 00:15:03,102 --> 00:15:05,170 We can do it visually. 279 00:15:05,170 --> 00:15:08,340 But we can also do it back when we use the ICE table, right? 280 00:15:08,340 --> 00:15:12,745 So now we're going to go ICE again, AgCl. 281 00:15:12,745 --> 00:15:15,648 And here's Ag+. 282 00:15:18,183 --> 00:15:20,219 And here's Cl-. 283 00:15:20,219 --> 00:15:21,887 So now I've added the-- 284 00:15:21,887 --> 00:15:25,057 OK, so my initial is that this is solid. 285 00:15:25,057 --> 00:15:29,361 And remember, this is the solid that I'm putting in there. 286 00:15:29,361 --> 00:15:33,632 And then my initial is that I started 287 00:15:33,632 --> 00:15:35,434 in that nice equilibrium at point B. 288 00:15:35,434 --> 00:15:39,204 So I've got 1.3 times 10 to the minus fifth. 289 00:15:39,204 --> 00:15:40,873 And over here, I've got the same. 290 00:15:44,343 --> 00:15:47,146 But now the change, now the change. 291 00:15:49,648 --> 00:15:55,220 OK, so we're going to add some chlorine ions, 0.1. 292 00:15:55,220 --> 00:15:57,723 So I've added 0.1 moles per liter of chlorine ions 293 00:15:57,723 --> 00:16:00,726 from the salt, from sodium chloride. 294 00:16:00,726 --> 00:16:05,364 Yeah, but now some of that is going to react, 295 00:16:05,364 --> 00:16:08,167 because I just said, Le Chatelier's principle 296 00:16:08,167 --> 00:16:11,637 tells me that now it's got to counter that. 297 00:16:11,637 --> 00:16:13,572 And you can see it right here too. 298 00:16:13,572 --> 00:16:15,774 I'm adding a whole bunch of chlorine. 299 00:16:15,774 --> 00:16:17,042 Look at how far I'm going out. 300 00:16:17,042 --> 00:16:22,781 0.1, that's literally all the way out to here. 301 00:16:22,781 --> 00:16:25,951 And so the amount of silver has got to go down. 302 00:16:25,951 --> 00:16:28,220 And what's going to happen is it's 303 00:16:28,220 --> 00:16:31,590 going to consume some of the silver and form precipitate 304 00:16:31,590 --> 00:16:34,026 to counter all this addition. 305 00:16:34,026 --> 00:16:37,496 It's going to run the reaction the other way. 306 00:16:37,496 --> 00:16:42,067 So it's going to lose a little bit there from the 0.1. 307 00:16:42,067 --> 00:16:44,803 That's going to react with the silver ions. 308 00:16:44,803 --> 00:16:49,241 So that's going to also lose, and this is going to gain. 309 00:16:49,241 --> 00:16:50,809 That's how much that's going to gain. 310 00:16:50,809 --> 00:16:52,211 So those are the variables, right? 311 00:16:52,211 --> 00:16:54,013 This is the ICE table. 312 00:16:54,013 --> 00:16:55,914 That's how much it's going to lo-- 313 00:16:55,914 --> 00:16:58,951 these are going to react to give me some precipitate. 314 00:16:58,951 --> 00:17:06,425 And so the equilibrium is more solid forms. 315 00:17:06,425 --> 00:17:10,061 That's not a good E. More solid forms. 316 00:17:10,061 --> 00:17:16,734 And over here, it's 1.3 times 10 to the minus fifth minus x. 317 00:17:16,734 --> 00:17:21,306 And over here, it's 0.1 minus x. 318 00:17:21,306 --> 00:17:23,976 That's the equilibrium condition. 319 00:17:23,976 --> 00:17:25,644 I've added in a common ion. 320 00:17:25,644 --> 00:17:28,380 This is the common ion effect. 321 00:17:28,380 --> 00:17:35,054 Yeah, so now if you do the math, then what happens? 322 00:17:35,054 --> 00:17:39,625 Well again, Ksp is the same. 323 00:17:39,625 --> 00:17:40,993 It's the equilibrium constant. 324 00:17:40,993 --> 00:17:41,994 So it's the constant. 325 00:17:41,994 --> 00:17:44,997 So that is going to be the same value. 326 00:17:44,997 --> 00:17:50,669 It's going to be 1.7 times 10 to the minus 10th. 327 00:17:50,669 --> 00:17:54,306 But you see, Ksp is also equal to the concentration 328 00:17:54,306 --> 00:17:57,776 in equilibrium of the silver ions times the concentration 329 00:17:57,776 --> 00:17:58,911 of the chlorine ions. 330 00:17:58,911 --> 00:18:05,050 So it's going to be 0.1 minus x times 1.3 times 10 331 00:18:05,050 --> 00:18:07,453 to the fifth minus x. 332 00:18:10,022 --> 00:18:14,026 And then we don't like doing all this math, and so we simplify. 333 00:18:14,026 --> 00:18:17,229 Then we can simplify, because look, 334 00:18:17,229 --> 00:18:21,600 you started with silver ions in a very small concentration. 335 00:18:21,600 --> 00:18:25,037 You can't take away something you don't have. 336 00:18:25,037 --> 00:18:30,209 And so x has got to be somehow this or less, right? 337 00:18:30,209 --> 00:18:32,144 And so x is a small number. 338 00:18:32,144 --> 00:18:35,314 And this is a really big number in comparison. 339 00:18:35,314 --> 00:18:39,151 And so we like simplifying our lives, right? 340 00:18:39,151 --> 00:18:42,488 And so we like saying that that's like 0.1. 341 00:18:42,488 --> 00:18:43,455 We know that. 342 00:18:43,455 --> 00:18:46,024 That'll make the math a lot easier. 343 00:18:46,024 --> 00:18:48,026 It'll make the math easier. 344 00:18:48,026 --> 00:18:58,770 And so now we can say that this is equal to 0.1 times 1.3 times 345 00:18:58,770 --> 00:19:01,940 10 to the minus fifth minus x. 346 00:19:01,940 --> 00:19:06,712 And then we get that x equals 1.7 times 10 347 00:19:06,712 --> 00:19:08,747 to the minus ninth. 348 00:19:08,747 --> 00:19:10,649 That is the common ion effect. 349 00:19:10,649 --> 00:19:12,985 What I've done, I've taken this thing in equilibrium, 350 00:19:12,985 --> 00:19:14,286 and I've added one of the ions. 351 00:19:18,123 --> 00:19:20,492 And it changes the solubility. 352 00:19:20,492 --> 00:19:23,195 Remember, the solubility is what we care about. 353 00:19:23,195 --> 00:19:27,766 That's what the solubility constant helps us determine. 354 00:19:27,766 --> 00:19:32,938 And I've literally just changed it by orders of magnitude, 355 00:19:32,938 --> 00:19:36,041 because now the amount that this-- 356 00:19:36,041 --> 00:19:38,443 so this thing precipitates like crazy. 357 00:19:38,443 --> 00:19:41,914 I added in a little bit of some other salt that 358 00:19:41,914 --> 00:19:42,748 had chlorine ions. 359 00:19:42,748 --> 00:19:46,618 And all of a sudden, silver chloride precipitates out. 360 00:19:46,618 --> 00:19:47,719 So here's a video of this. 361 00:19:47,719 --> 00:19:48,453 This is kind of cool. 362 00:19:48,453 --> 00:19:49,054 So watch. 363 00:19:49,054 --> 00:19:51,690 This is an equilibrium container. 364 00:19:51,690 --> 00:19:54,893 And what I'm adding is salt. And look at that. 365 00:19:54,893 --> 00:19:55,460 What is that? 366 00:19:55,460 --> 00:19:58,730 That's silver chloride precipitate, right, 367 00:19:58,730 --> 00:20:01,300 because the thing has to reach equilibrium. 368 00:20:01,300 --> 00:20:03,969 And so in order to do so, what you do 369 00:20:03,969 --> 00:20:06,471 is you suppress the solubility. 370 00:20:06,471 --> 00:20:10,175 Literally, by adding chlorine, the common ion effect, 371 00:20:10,175 --> 00:20:13,745 you suppress the solubility of the silver chloride. 372 00:20:13,745 --> 00:20:16,148 It's pretty cool stuff. 373 00:20:16,148 --> 00:20:17,382 That is the common ion effect. 374 00:20:17,382 --> 00:20:19,718 Now, why does this matter? 375 00:20:19,718 --> 00:20:21,420 Let me give you one-- no, I'll get to why 376 00:20:21,420 --> 00:20:22,554 this matters in a second. 377 00:20:22,554 --> 00:20:24,122 One more question. 378 00:20:24,122 --> 00:20:27,292 Now without even doing the math, check this one out. 379 00:20:27,292 --> 00:20:29,695 This is cool. 380 00:20:29,695 --> 00:20:34,266 Without even doing the math, I can take barium sulfate, 381 00:20:34,266 --> 00:20:39,137 and from the common ion effect-- so barium sulfate is 382 00:20:39,137 --> 00:20:39,771 going to go. 383 00:20:39,771 --> 00:20:41,106 So what does that one look like? 384 00:20:41,106 --> 00:20:49,248 Well, it's going to go to Ba 2+ plus SO4 2-, both in solution, 385 00:20:49,248 --> 00:20:50,349 in solution. 386 00:20:50,349 --> 00:20:53,385 Dissolved ions, this is a solid. 387 00:20:53,385 --> 00:20:57,189 Now, here's the question. 388 00:20:57,189 --> 00:21:00,325 Which of the following will be required in the least amount 389 00:21:00,325 --> 00:21:05,130 to dissolve the same amount of BaSO4? 390 00:21:05,130 --> 00:21:07,266 I don't need any constants or math. 391 00:21:07,266 --> 00:21:11,136 I can use this same principle, because if I had some 0.1 392 00:21:11,136 --> 00:21:15,040 molar or 0.01 moles per liter of either of these, 393 00:21:15,040 --> 00:21:16,575 what are they doing? 394 00:21:16,575 --> 00:21:19,611 They're serving up ions, right? 395 00:21:22,281 --> 00:21:24,149 In the one case, you're serving up-- 396 00:21:24,149 --> 00:21:28,320 so in case A, you're going to give me-- 397 00:21:28,320 --> 00:21:29,421 what do I have there? 398 00:21:29,421 --> 00:21:33,358 H2SO4, so let's do A first. 399 00:21:33,358 --> 00:21:41,400 H2SO4 is going to give me a whole bunch of H+ but also SO4 400 00:21:41,400 --> 00:21:42,567 2-. 401 00:21:42,567 --> 00:21:48,206 And in case B, you have BaCl-- 402 00:21:48,206 --> 00:21:51,910 OK, so you have BaCl2. 403 00:21:51,910 --> 00:21:55,447 And if I put that in, I've got this in water, right? 404 00:21:55,447 --> 00:21:57,482 But if this dissolves in water a little bit, 405 00:21:57,482 --> 00:22:02,654 then it's going to serve up some Ba 2+ plus 2Cl-. 406 00:22:05,791 --> 00:22:09,494 Either way, now you know what's going to happen, 407 00:22:09,494 --> 00:22:12,964 because if I'm trying to dissolve something 408 00:22:12,964 --> 00:22:17,102 and I add any of the ions that it's dissolving 409 00:22:17,102 --> 00:22:19,638 into from some external source, it's 410 00:22:19,638 --> 00:22:21,973 going to drive it this way. 411 00:22:21,973 --> 00:22:25,310 It's going to precipitate. 412 00:22:25,310 --> 00:22:27,579 So the answer has to be just water. 413 00:22:27,579 --> 00:22:31,049 Stick with pure water in this case. 414 00:22:31,049 --> 00:22:33,318 Otherwise you're going to have more trouble dissolving, 415 00:22:33,318 --> 00:22:34,686 just like we just showed. 416 00:22:34,686 --> 00:22:36,988 You're going to have more trouble dissolving, not less. 417 00:22:36,988 --> 00:22:38,190 That's the common ion effect. 418 00:22:40,992 --> 00:22:44,062 OK, so now why does this matter? 419 00:22:44,062 --> 00:22:46,365 Why does this matter? 420 00:22:46,365 --> 00:22:48,433 We go back to the pteropod. 421 00:22:48,433 --> 00:22:50,102 And by the way, I didn't have this link, 422 00:22:50,102 --> 00:22:52,804 and I should have when I showed you the-- 423 00:22:52,804 --> 00:22:54,706 and this is your goody bag, et cetera. 424 00:22:54,706 --> 00:22:56,308 There's some really nice articles 425 00:22:56,308 --> 00:22:58,643 here that you can find related to these experiments 426 00:22:58,643 --> 00:23:01,513 and other things about ocean acidity in case 427 00:23:01,513 --> 00:23:03,348 you're interested. 428 00:23:03,348 --> 00:23:06,785 But see, what I did was that this was my 429 00:23:06,785 --> 00:23:08,320 why this matters on Monday. 430 00:23:08,320 --> 00:23:11,690 And I wanted to tell you about the goody bag and about 431 00:23:11,690 --> 00:23:16,595 how things dissolve, because Monday was about dissolving 432 00:23:16,595 --> 00:23:19,030 and finding a saturation point. 433 00:23:19,030 --> 00:23:22,167 Now we can get to the next place, which is, 434 00:23:22,167 --> 00:23:25,971 why does that matter for the pteropod's shell? 435 00:23:25,971 --> 00:23:29,307 What is the chemistry that matters there? 436 00:23:29,307 --> 00:23:32,778 OK, so I made the ocean a little more acidic. 437 00:23:32,778 --> 00:23:34,012 Why does that matter? 438 00:23:34,012 --> 00:23:36,415 But you see, now we're armed with the knowledge we 439 00:23:36,415 --> 00:23:37,849 need to answer that question. 440 00:23:37,849 --> 00:23:38,850 Now we're armed with it. 441 00:23:38,850 --> 00:23:42,120 All we need to do, as always with everything in life, 442 00:23:42,120 --> 00:23:43,822 is look at the chemistry. 443 00:23:43,822 --> 00:23:45,490 That's it. 444 00:23:45,490 --> 00:23:48,226 Say that at the Thanksgiving table. 445 00:23:48,226 --> 00:23:50,095 You'll be very popular. 446 00:23:50,095 --> 00:23:53,565 We said CO2 plus H2O. 447 00:23:53,565 --> 00:24:01,606 This goes-- oh, find some equilibrium to H2CO3. 448 00:24:01,606 --> 00:24:03,308 Now, this is called carbonic acid. 449 00:24:09,047 --> 00:24:10,582 This is called carbonic acid. 450 00:24:10,582 --> 00:24:12,317 There's the pteropod up there. 451 00:24:12,317 --> 00:24:14,453 And there's the reaction that's really relevant 452 00:24:14,453 --> 00:24:16,788 that you'll see from the ones we're about to write down. 453 00:24:16,788 --> 00:24:18,056 Why? 454 00:24:18,056 --> 00:24:22,260 Because the thing is that, what happens to carbonic acid? 455 00:24:22,260 --> 00:24:28,400 Well, carbonic acid also goes through a dissolution reaction. 456 00:24:28,400 --> 00:24:32,204 So this is CO2 dissolving in water. 457 00:24:32,204 --> 00:24:36,741 So carbonic acid goes like this. 458 00:24:36,741 --> 00:24:42,914 OK, it goes into HCO3- plus H+. 459 00:24:46,685 --> 00:24:48,286 Now, here's the thing. 460 00:24:48,286 --> 00:24:50,388 OK, what is the shell made of? 461 00:24:50,388 --> 00:24:57,395 Well, the shell that's dissolving, the core material 462 00:24:57,395 --> 00:24:59,064 is calcium carbonate. 463 00:24:59,064 --> 00:25:02,167 So that's CaCO3. 464 00:25:02,167 --> 00:25:03,301 That's the shell. 465 00:25:03,301 --> 00:25:07,606 And the shell also has an equilibrium reaction 466 00:25:07,606 --> 00:25:08,974 that happens. 467 00:25:08,974 --> 00:25:13,945 The shell of a sea creature is in dynamic equilibrium 468 00:25:13,945 --> 00:25:15,514 with the ocean. 469 00:25:15,514 --> 00:25:17,082 And so it's going like this. 470 00:25:17,082 --> 00:25:27,359 It's going to, well, OK, Ca2+ and CO3 2-. 471 00:25:27,359 --> 00:25:30,328 OK, but the thing is, it has an equilibrium constant. 472 00:25:30,328 --> 00:25:33,598 All these have equilibrium constants. 473 00:25:33,598 --> 00:25:37,502 So for example, for this one, the Ksp, 474 00:25:37,502 --> 00:25:39,237 the solubility product constant-- 475 00:25:39,237 --> 00:25:40,438 because this is a solid. 476 00:25:40,438 --> 00:25:43,508 This is the solid shell, solid, going 477 00:25:43,508 --> 00:25:45,076 to ions in aqueous solution. 478 00:25:47,812 --> 00:25:52,183 So the Ksp for that is somewhere around 5 times 10 479 00:25:52,183 --> 00:25:55,987 to the minus ninth, 5 times 10 to the minus ninth. 480 00:25:55,987 --> 00:25:57,122 Yeah, but here's the thing. 481 00:25:57,122 --> 00:25:59,391 We just went through this. 482 00:25:59,391 --> 00:26:03,061 If I consume one of these or change the concentration of one 483 00:26:03,061 --> 00:26:06,731 of these and not the other-- 484 00:26:06,731 --> 00:26:07,566 we just did this. 485 00:26:07,566 --> 00:26:09,367 If I could change the concentration, 486 00:26:09,367 --> 00:26:14,005 if I consume any of these, then I might drive the reaction-- 487 00:26:14,005 --> 00:26:15,740 consume or produce. 488 00:26:15,740 --> 00:26:18,543 If I change any of these independently, 489 00:26:18,543 --> 00:26:21,813 I'm going to drive the reaction, because that's 490 00:26:21,813 --> 00:26:25,817 how we keep to our K. That's what Le Chatelier's 491 00:26:25,817 --> 00:26:27,352 principle tells us. 492 00:26:27,352 --> 00:26:36,661 And so what ends up happening is you've got the extra H+ ions. 493 00:26:36,661 --> 00:26:38,663 So these are ions in solution. 494 00:26:38,663 --> 00:26:39,698 Where did they come from? 495 00:26:39,698 --> 00:26:43,168 They came from the CO2 giving us carbonic acid, 496 00:26:43,168 --> 00:26:44,936 which then gave us H+. 497 00:26:44,936 --> 00:26:46,871 Those are what I'm talking about. 498 00:26:46,871 --> 00:26:54,012 Well, they react with the CO3 2-. 499 00:26:57,616 --> 00:27:03,288 This lowers the CO3 2- concentration near the shell-- 500 00:27:03,288 --> 00:27:03,989 [STUDENT SNEEZES] 501 00:27:03,989 --> 00:27:04,689 --right? 502 00:27:04,689 --> 00:27:05,290 Gesundheit. 503 00:27:05,290 --> 00:27:07,926 And if I lower this, because I've taken some of this now 504 00:27:07,926 --> 00:27:11,262 and I've reacted it, so now I've got less of it. 505 00:27:11,262 --> 00:27:13,765 And because of what we just saw, if I've got less of this, 506 00:27:13,765 --> 00:27:17,135 you're going to drive this way, which is going 507 00:27:17,135 --> 00:27:20,839 to dissolve more of the shell. 508 00:27:20,839 --> 00:27:22,374 That's why this works. 509 00:27:22,374 --> 00:27:25,777 Well, that's why this happens. 510 00:27:25,777 --> 00:27:29,581 Works sounds like a positive thing. 511 00:27:29,581 --> 00:27:37,489 So this lowers the concentration of CO3 2-, 512 00:27:37,489 --> 00:27:44,796 and that drives more dissolution. 513 00:27:44,796 --> 00:27:46,231 That is what's happening. 514 00:27:46,231 --> 00:27:48,967 And we now can understand it in terms of the concepts 515 00:27:48,967 --> 00:27:51,936 that we've just learned. 516 00:27:51,936 --> 00:27:53,872 Historically, I mentioned 50 million years. 517 00:27:53,872 --> 00:27:56,341 Actually, by some accounts, it's 300 million. 518 00:27:56,341 --> 00:28:00,178 It depends on which studies you read. 519 00:28:00,178 --> 00:28:03,615 But for at least 50 and maybe as much as 300 million years, 520 00:28:03,615 --> 00:28:08,620 the ocean has had a pH of 8.18. 521 00:28:08,620 --> 00:28:12,157 Now, where's the-- oh. 522 00:28:12,157 --> 00:28:23,234 So let's just say last, oh, 50 to 300 millionish years, 523 00:28:23,234 --> 00:28:29,974 the ocean pH was 8.18. 524 00:28:29,974 --> 00:28:36,915 And today, it's 8.07. 525 00:28:36,915 --> 00:28:45,023 And the prediction is that in 2100, it will be 7.8. 526 00:28:45,023 --> 00:28:47,325 Now, as we will see in a little bit-- 527 00:28:47,325 --> 00:28:49,094 and you say, what's pH? 528 00:28:49,094 --> 00:28:50,662 And many of you probably already know, 529 00:28:50,662 --> 00:28:53,064 but I will tell you what it is in a little bit. 530 00:28:53,064 --> 00:28:55,700 But because this is a logarithmic thing, 531 00:28:55,700 --> 00:28:57,969 this is a lot, right? 532 00:28:57,969 --> 00:29:00,638 Today the ocean is 25% more acidic 533 00:29:00,638 --> 00:29:03,441 than it's been in 300 millionish years. 534 00:29:03,441 --> 00:29:08,246 And in 2100, it will be 126% more acidic. 535 00:29:08,246 --> 00:29:14,786 That's why they use 7.8 in the experiments of the pteropods. 536 00:29:14,786 --> 00:29:18,256 OK, right. 537 00:29:18,256 --> 00:29:20,458 Why does this happen? 538 00:29:20,458 --> 00:29:22,660 Why is this molecule an acid? 539 00:29:22,660 --> 00:29:25,497 We're talking about acidification of oceans. 540 00:29:25,497 --> 00:29:27,165 Why is this an acid in the first place? 541 00:29:27,165 --> 00:29:28,666 What does it mean to be an acid? 542 00:29:28,666 --> 00:29:30,702 And that is the next topic. 543 00:29:30,702 --> 00:29:33,404 That is what I want to talk about next. 544 00:29:33,404 --> 00:29:35,507 What is an acid? 545 00:29:35,507 --> 00:29:41,045 And an acid is something that is very specific. 546 00:29:41,045 --> 00:29:44,549 It has a very definite meaning to it. 547 00:29:44,549 --> 00:29:47,118 And I want to talk about that today, 548 00:29:47,118 --> 00:29:50,021 and then we'll continue after the break. 549 00:29:50,021 --> 00:29:55,460 So this molecule, carbonic acid, is called 550 00:29:55,460 --> 00:29:58,997 an acid because of that proton. 551 00:29:58,997 --> 00:30:01,299 And you could feel it. 552 00:30:01,299 --> 00:30:03,434 You could feel it in this whole thing. 553 00:30:03,434 --> 00:30:09,174 The proton is the thing that caused the problem, right? 554 00:30:09,174 --> 00:30:13,411 An acid, this is an acid because of the proton. 555 00:30:13,411 --> 00:30:19,851 So an acid, it's a dissolution reaction, dissolution. 556 00:30:19,851 --> 00:30:21,319 It's what we've been talking about. 557 00:30:21,319 --> 00:30:28,092 It's a dissolution reaction that gives an H+. 558 00:30:31,496 --> 00:30:40,405 Now if I think about it as a generic case, generic acid A, 559 00:30:40,405 --> 00:30:44,375 then the reaction looks something like this. 560 00:30:44,375 --> 00:30:47,278 I'm going to call out the acid and the proton 561 00:30:47,278 --> 00:30:50,281 that it gives separately. 562 00:30:50,281 --> 00:30:52,083 OK, so this is HA. 563 00:30:52,083 --> 00:30:55,353 So we do this because it highlights that it's an acid, 564 00:30:55,353 --> 00:30:58,790 H+ in solution-- 565 00:30:58,790 --> 00:31:04,295 and these can all be in solution-- plus A- in solution. 566 00:31:04,295 --> 00:31:07,932 All right, H+, A-. 567 00:31:07,932 --> 00:31:10,201 Right, so I've taken a proton off. 568 00:31:10,201 --> 00:31:12,003 You see it's right there. 569 00:31:12,003 --> 00:31:18,710 That's HA, HA, where A is HCO3 and H is H. And then 570 00:31:18,710 --> 00:31:20,311 what I've done is I've transferred 571 00:31:20,311 --> 00:31:21,646 the proton into solution. 572 00:31:21,646 --> 00:31:22,914 That's an acid. 573 00:31:22,914 --> 00:31:30,021 Now the thing is, you will see a lot of places and people 574 00:31:30,021 --> 00:31:30,989 writing H+. 575 00:31:30,989 --> 00:31:34,459 And we will do that too, because so many textbooks use H+. 576 00:31:34,459 --> 00:31:41,132 But what I want you to know is that H+ is never a thing. 577 00:31:41,132 --> 00:31:42,634 We just write it that way. 578 00:31:42,634 --> 00:31:45,937 H+ is not stable in water. 579 00:31:45,937 --> 00:31:49,307 So the proper-- ah! 580 00:31:49,307 --> 00:31:54,646 The proper way to write this general reaction would be HA 581 00:31:54,646 --> 00:31:59,217 plus H2O is going to go to-- and now I'm going to write 582 00:31:59,217 --> 00:32:02,186 the full, so the full goes both ways-- 583 00:32:02,186 --> 00:32:06,391 is going to go to H3O+ plus A-. 584 00:32:06,391 --> 00:32:07,225 [STUDENT SNEEZES] 585 00:32:07,225 --> 00:32:09,360 Gesundheit. 586 00:32:09,360 --> 00:32:12,931 This is what happens, because H+ is not stable in water. 587 00:32:12,931 --> 00:32:15,566 But you will see H+ written all over the place. 588 00:32:15,566 --> 00:32:20,705 When you see H+, and if it's in water, know that it's H3O+. 589 00:32:20,705 --> 00:32:23,041 That is what is stable. 590 00:32:23,041 --> 00:32:26,244 OK, H+ in water is not. 591 00:32:26,244 --> 00:32:27,679 Now, there's something here that's 592 00:32:27,679 --> 00:32:29,914 important in terms of terminology. 593 00:32:29,914 --> 00:32:33,384 And that is that these are-- notice that these are related. 594 00:32:33,384 --> 00:32:37,355 The HA and the A- seem very related. 595 00:32:37,355 --> 00:32:41,526 And the H2O and the H3O+ seem very related. 596 00:32:41,526 --> 00:32:45,296 Well, they are, because a proton is the only difference 597 00:32:45,296 --> 00:32:46,698 between them. 598 00:32:46,698 --> 00:32:50,201 And so those are called conjugate pairs. 599 00:32:50,201 --> 00:32:52,570 Conjugate, related, conjugate pairs. 600 00:32:56,441 --> 00:33:01,045 OK, those are called conjugate pairs. 601 00:33:01,045 --> 00:33:04,983 Now, back in the day, there was a lot of interest. 602 00:33:04,983 --> 00:33:10,021 People knew about these kind of liquids, mostly liquids, 603 00:33:10,021 --> 00:33:11,622 for a long time. 604 00:33:11,622 --> 00:33:15,026 And there was a lot of experimentation before this. 605 00:33:15,026 --> 00:33:18,262 Let's see, well, there's these general classes of materials. 606 00:33:18,262 --> 00:33:20,698 We're going to call them A and B. Well, 607 00:33:20,698 --> 00:33:23,568 A seems to always taste kind of sour. 608 00:33:23,568 --> 00:33:25,370 B is bitter. 609 00:33:25,370 --> 00:33:28,106 A reacts with carbonates to make CO2. 610 00:33:28,106 --> 00:33:32,010 B reacts with fats and soap to make soaps. 611 00:33:32,010 --> 00:33:32,944 One reacts with metals. 612 00:33:32,944 --> 00:33:33,711 The other doesn't. 613 00:33:33,711 --> 00:33:35,380 And by the way, if we mix them together, 614 00:33:35,380 --> 00:33:37,949 we seem to always get salt and water. 615 00:33:37,949 --> 00:33:41,519 This had been going on for centuries, this investigation 616 00:33:41,519 --> 00:33:46,357 into properties of acids and bases. 617 00:33:46,357 --> 00:33:47,792 But who was it that came along? 618 00:33:47,792 --> 00:33:50,194 Who was it that came along? 619 00:33:50,194 --> 00:33:52,397 Svante! 620 00:33:52,397 --> 00:33:54,932 Is there anything you can't do, Svante? 621 00:33:54,932 --> 00:33:57,468 I ask you again. 622 00:33:57,468 --> 00:34:02,540 In the late 1800s, it was Svante to the rescue who 623 00:34:02,540 --> 00:34:05,476 first proposed that what is happening here 624 00:34:05,476 --> 00:34:07,945 is a dissolution reaction. 625 00:34:07,945 --> 00:34:10,614 That is what an acid or a base is. 626 00:34:10,614 --> 00:34:14,018 It is that on the one hand, you're given an H+, 627 00:34:14,018 --> 00:34:17,088 which is what I just said. 628 00:34:17,088 --> 00:34:22,226 But on the other hand, for a base you're given a OH-. 629 00:34:22,226 --> 00:34:24,195 And it was Svante Arrhenius who first 630 00:34:24,195 --> 00:34:27,398 put that down and first conceived of acids and ba-- 631 00:34:27,398 --> 00:34:28,866 are we snapping? 632 00:34:28,866 --> 00:34:30,400 Are we quiet snapping for Svante? 633 00:34:30,400 --> 00:34:31,235 I love it. 634 00:34:31,235 --> 00:34:32,737 I've just recently learned what that 635 00:34:32,737 --> 00:34:36,040 means, which makes me happy. 636 00:34:36,040 --> 00:34:38,109 Quiet snapping. 637 00:34:38,109 --> 00:34:40,043 It's instead of clapping. 638 00:34:40,043 --> 00:34:42,813 But you don't make noise, but you still want to give props. 639 00:34:42,813 --> 00:34:44,047 I got it. 640 00:34:44,047 --> 00:34:44,849 I'm there. 641 00:34:44,849 --> 00:34:45,917 I'm right there. 642 00:34:45,917 --> 00:34:47,885 Now, OK. 643 00:34:47,885 --> 00:34:49,286 OK, now here's the thing. 644 00:34:49,286 --> 00:34:50,254 So we'll talk about it. 645 00:34:50,254 --> 00:34:55,960 So Arrhenius says bases give OH ions in solution, and oh, 646 00:34:55,960 --> 00:34:56,994 acids give H+. 647 00:34:56,994 --> 00:35:00,531 But we know that that's H3O+. 648 00:35:00,531 --> 00:35:01,599 OK, we know that. 649 00:35:04,302 --> 00:35:07,872 Yeah, but the thing is there's disillusion reactions. 650 00:35:07,872 --> 00:35:11,209 These things lead to really small concentrations. 651 00:35:11,209 --> 00:35:12,810 And so Soren Sorensen. 652 00:35:15,379 --> 00:35:16,481 That is a beer bottle. 653 00:35:16,481 --> 00:35:20,585 By the way, his research was funded by a beer company, 654 00:35:20,585 --> 00:35:23,888 and it was all about the taste of beer. 655 00:35:23,888 --> 00:35:27,592 He called it looking at proteins, 656 00:35:27,592 --> 00:35:29,360 but it was about beer. 657 00:35:29,360 --> 00:35:30,795 And what he realized, he said, I've 658 00:35:30,795 --> 00:35:33,598 been doing all these dissolution reactions of ions. 659 00:35:33,598 --> 00:35:34,832 I think Arrhenius was right. 660 00:35:34,832 --> 00:35:37,168 Ions are really important, and we're 661 00:35:37,168 --> 00:35:38,736 trying to measure these things. 662 00:35:38,736 --> 00:35:42,039 But I'm sick of all these zeros. 663 00:35:42,039 --> 00:35:47,512 I don't like writing 0.0001 or whatever all the time. 664 00:35:47,512 --> 00:35:52,316 And oh, look at that, 1.3 times 10 to the minus fifth. 665 00:35:52,316 --> 00:35:54,785 That's not efficient. 666 00:35:54,785 --> 00:35:57,488 And so what Sorensen did is he talked 667 00:35:57,488 --> 00:36:00,558 about how you've got the power. 668 00:36:00,558 --> 00:36:02,226 Now, what do I mean by power? 669 00:36:02,226 --> 00:36:04,028 So many things, right? 670 00:36:04,028 --> 00:36:10,835 But if I look at H+, OK, H3O+, and I say it-- 671 00:36:10,835 --> 00:36:17,808 let's suppose the concentration is 0.00, oh boy, 00001, 672 00:36:17,808 --> 00:36:19,343 that's 10 to the minus 7. 673 00:36:22,380 --> 00:36:24,615 But Sorensen wasn't happy with that. 674 00:36:24,615 --> 00:36:25,683 You simplified it. 675 00:36:25,683 --> 00:36:28,019 Wait, two, four-- no, it's not. 676 00:36:28,019 --> 00:36:32,089 OK, maybe it is now. 677 00:36:32,089 --> 00:36:33,658 He said, well, 10 to the minus seventh 678 00:36:33,658 --> 00:36:38,129 is still four characters I got to write, four. 679 00:36:38,129 --> 00:36:41,632 So he went to the math department at his place 680 00:36:41,632 --> 00:36:44,435 and he said, what else can be-- 681 00:36:44,435 --> 00:36:47,271 I want to talk about the power of these ions. 682 00:36:47,271 --> 00:36:51,142 And they're like, power, well, that's the logarithm. 683 00:36:51,142 --> 00:36:54,612 And so if you take the log, it's the power 684 00:36:54,612 --> 00:37:00,952 of hydrogen. Power of hydrogen is the pH. 685 00:37:00,952 --> 00:37:02,453 And that's simply minus the log. 686 00:37:02,453 --> 00:37:04,789 They didn't want negative numbers either. 687 00:37:04,789 --> 00:37:07,491 Oh, but you can have negative pH. 688 00:37:07,491 --> 00:37:09,393 You can. 689 00:37:09,393 --> 00:37:09,894 Why? 690 00:37:09,894 --> 00:37:14,699 Because this is the definition of pH. 691 00:37:14,699 --> 00:37:19,337 Or you could do pOH, if you're going with Arrhenius. 692 00:37:19,337 --> 00:37:22,573 So the power of hydrogen is the pH. 693 00:37:22,573 --> 00:37:28,379 The pOH would be minus log of the concentration of OH-. 694 00:37:28,379 --> 00:37:29,013 That's the pOH. 695 00:37:29,013 --> 00:37:32,750 But pH is the one that we most often 696 00:37:32,750 --> 00:37:36,621 see to describe whether something is acidic or basic. 697 00:37:39,123 --> 00:37:42,793 And so now you see, well, OK, well, this is a pH. 698 00:37:42,793 --> 00:37:43,794 Now this is easy, right? 699 00:37:43,794 --> 00:37:45,496 It's a pH of 7. 700 00:37:45,496 --> 00:37:50,034 And if the concentration were 0.1, it would be a pH of 1, 701 00:37:50,034 --> 00:37:53,504 minus log, the power of hydrogen, 702 00:37:53,504 --> 00:37:57,508 the log, literally the log. 703 00:37:57,508 --> 00:37:59,944 OK, now if you look at scales of pH, 704 00:37:59,944 --> 00:38:02,780 and it's a really fun thing to do, then 705 00:38:02,780 --> 00:38:05,549 what you find is that usually, almost always actually, 706 00:38:05,549 --> 00:38:07,685 you'll see the scale ranging from 0 to 14. 707 00:38:07,685 --> 00:38:10,388 That's what Sorensen originally decided. 708 00:38:10,388 --> 00:38:12,657 I'm going to talk about these ions in solution. 709 00:38:12,657 --> 00:38:14,325 I don't want to write it out every time. 710 00:38:14,325 --> 00:38:16,093 I'm just going to have a simple scale. 711 00:38:16,093 --> 00:38:18,696 We'll take the minus log, and there you go. 712 00:38:18,696 --> 00:38:21,565 Yeah, but you can see that if the concentration is 713 00:38:21,565 --> 00:38:24,502 more than one here, then you could have negative pHs. 714 00:38:24,502 --> 00:38:27,738 There's nothing special about zero here. 715 00:38:27,738 --> 00:38:30,174 It just so happens that most things, 716 00:38:30,174 --> 00:38:32,143 certainly that he was playing with at the time, 717 00:38:32,143 --> 00:38:33,277 were in this scale. 718 00:38:33,277 --> 00:38:35,446 And here is a few things that we know. 719 00:38:35,446 --> 00:38:36,247 There it is, right? 720 00:38:36,247 --> 00:38:38,883 OK, don't play with that one, but play 721 00:38:38,883 --> 00:38:40,484 with lemon juice, vinegar. 722 00:38:40,484 --> 00:38:41,719 By the way, vinegar-- 723 00:38:41,719 --> 00:38:44,722 OK, wine is around 3 and 1/2. 724 00:38:44,722 --> 00:38:45,923 Vinegar is around 2. 725 00:38:49,060 --> 00:38:53,164 The word vinegar is [NON-ENGLISH SPEECH].. 726 00:38:53,164 --> 00:38:55,266 It's eager wine. 727 00:38:55,266 --> 00:38:56,367 That's it, right? 728 00:38:56,367 --> 00:39:00,204 But it's because of the acidity, the acidity. 729 00:39:00,204 --> 00:39:01,272 Well, it's more than that. 730 00:39:01,272 --> 00:39:08,045 But it's the acidity is changing by orders of magnitude, power. 731 00:39:08,045 --> 00:39:10,581 And then you can go back and you see, but OK, there's coffee. 732 00:39:10,581 --> 00:39:12,049 I like that a lot. 733 00:39:12,049 --> 00:39:15,152 And blood. 734 00:39:15,152 --> 00:39:20,291 By the way, by the way, talk about ocean acidity, 735 00:39:20,291 --> 00:39:23,461 blood has a very narrow range of pH. 736 00:39:23,461 --> 00:39:27,331 And if you change the pH of your blood by more than 0.2, 737 00:39:27,331 --> 00:39:29,934 it is very likely to lead to death. 738 00:39:29,934 --> 00:39:30,968 So just think about that. 739 00:39:30,968 --> 00:39:33,738 That's what we're doing to the ocean. 740 00:39:33,738 --> 00:39:36,974 OK, anyway, that was an aside. 741 00:39:36,974 --> 00:39:41,679 Seawater, oh, pH 8.07 currently and dropping. 742 00:39:41,679 --> 00:39:43,147 OK, baking soda, ammonia. 743 00:39:43,147 --> 00:39:48,786 So this is very powerful, no pun intended actually. 744 00:39:48,786 --> 00:39:51,822 Now, these are dissociation reactions. 745 00:39:51,822 --> 00:39:53,257 These are dissolution reactions. 746 00:39:53,257 --> 00:39:58,996 I'm taking an acid, and I'm dissociating it in water. 747 00:39:58,996 --> 00:40:02,566 And so you have the equilibrium constant for that dissociation, 748 00:40:02,566 --> 00:40:03,734 right? 749 00:40:03,734 --> 00:40:08,239 And so if you go back to that, that's 750 00:40:08,239 --> 00:40:10,007 still going to matter here. 751 00:40:10,007 --> 00:40:12,877 And that's going to be important in thinking 752 00:40:12,877 --> 00:40:16,614 about what an acid is. 753 00:40:16,614 --> 00:40:18,249 Because, again, why is this it? 754 00:40:18,249 --> 00:40:19,750 Well, because there's these protons. 755 00:40:19,750 --> 00:40:21,118 Well, how many of them are there? 756 00:40:21,118 --> 00:40:23,320 It depends on how it dissolved. 757 00:40:23,320 --> 00:40:26,757 Where did it find its equilibrium? 758 00:40:26,757 --> 00:40:30,394 And so for some of them, like I just wrote, 759 00:40:30,394 --> 00:40:36,333 we just talked about HCl plus H2O. 760 00:40:36,333 --> 00:40:43,107 That went to H3O+ plus Cl-. 761 00:40:43,107 --> 00:40:52,450 OK, now the thing is, if I had 0.1 moles per liter of HCl, 762 00:40:52,450 --> 00:40:58,689 then it's going to lead to a concentration of H3O+ of around 763 00:40:58,689 --> 00:41:03,961 0.1 moles per liter, because it's nearly full, 764 00:41:03,961 --> 00:41:09,099 nearly full dissociation. 765 00:41:09,099 --> 00:41:10,067 What do I mean by that? 766 00:41:10,067 --> 00:41:12,436 Well, I mean that-- yeah, OK, so you'll often 767 00:41:12,436 --> 00:41:16,106 see for an acid like that, one arrow. 768 00:41:16,106 --> 00:41:20,778 Well, we know that in reality, there's another arrow there. 769 00:41:20,778 --> 00:41:26,484 But see, here the acid dissociation constant is huge. 770 00:41:26,484 --> 00:41:30,020 So now we have a thing for the equilibrium 771 00:41:30,020 --> 00:41:33,457 of an acid, which forms by dissociating 772 00:41:33,457 --> 00:41:36,694 the acid into its ions. 773 00:41:36,694 --> 00:41:41,365 And this is-- well, in this case, it's 10 to the sixth. 774 00:41:41,365 --> 00:41:45,035 It's enormous, which means that the equilibrium lies very, 775 00:41:45,035 --> 00:41:46,737 very, very, very far over. 776 00:41:46,737 --> 00:41:48,539 And so oftentimes you'll see if it's 777 00:41:48,539 --> 00:41:52,510 going to strongly dissociate it, like sodium chloride did, 778 00:41:52,510 --> 00:41:54,879 then you'll sometimes see it written as just one arrow. 779 00:41:54,879 --> 00:41:59,350 But there's a little bit going back as well. 780 00:41:59,350 --> 00:42:01,785 That is another equilibrium constant. 781 00:42:01,785 --> 00:42:03,888 And we will talk about Ka a little later 782 00:42:03,888 --> 00:42:06,957 and probably pick up on it next week. 783 00:42:06,957 --> 00:42:09,727 OK, so near full dissociation. 784 00:42:09,727 --> 00:42:14,865 Now, the other thing that can happen that's important 785 00:42:14,865 --> 00:42:16,233 is water can do both. 786 00:42:19,403 --> 00:42:20,771 Let's see, where should I go? 787 00:42:20,771 --> 00:42:24,775 I'll go back over here. 788 00:42:24,775 --> 00:42:29,046 So water, see that picture there? 789 00:42:29,046 --> 00:42:30,614 They got it wrong, but it's OK. 790 00:42:30,614 --> 00:42:32,583 They got it right, because we all get along. 791 00:42:32,583 --> 00:42:35,052 If you want to put H+, fine. 792 00:42:35,052 --> 00:42:38,155 But you know that it's actually H3O+. 793 00:42:38,155 --> 00:42:41,058 OK, but you can put H+, no problem. 794 00:42:41,058 --> 00:42:44,461 OK, now there it is. 795 00:42:44,461 --> 00:42:47,898 And you can see that what water can do is it can do both. 796 00:42:47,898 --> 00:42:50,734 And that turns out to be extremely important. 797 00:42:50,734 --> 00:42:56,340 So if I take water and I mix it with water, 798 00:42:56,340 --> 00:43:09,687 ah ha, then you can get a combination of these ions, 799 00:43:09,687 --> 00:43:13,791 oh, plus a whole bunch of water. 800 00:43:13,791 --> 00:43:16,327 So this would be like dissociation. 801 00:43:16,327 --> 00:43:21,365 Now, the word for this, water can turn into either. 802 00:43:21,365 --> 00:43:23,233 It can be basic or acidic. 803 00:43:23,233 --> 00:43:28,405 It can deliver OH- or H3O+. 804 00:43:28,405 --> 00:43:32,409 That's called autoionization, and it also has a special word. 805 00:43:32,409 --> 00:43:38,782 Water is called amphoteric, amphoteric. 806 00:43:38,782 --> 00:43:47,057 Now, that means that the same thing can 807 00:43:47,057 --> 00:43:56,867 be both, both acid or a base. 808 00:43:56,867 --> 00:43:59,103 It can act as either. 809 00:43:59,103 --> 00:44:01,939 So if you take pure water-- 810 00:44:01,939 --> 00:44:03,440 so let's see. 811 00:44:03,440 --> 00:44:13,484 If I take pure water and [GROANS] and I look 812 00:44:13,484 --> 00:44:19,857 at the concentrations of these, so H3O+, 813 00:44:19,857 --> 00:44:21,291 it's all happening from the water. 814 00:44:21,291 --> 00:44:22,226 There's nothing in it. 815 00:44:22,226 --> 00:44:23,527 I didn't add anything to it. 816 00:44:23,527 --> 00:44:25,429 It's just pure water, H3O+. 817 00:44:25,429 --> 00:44:28,465 So that means that if that reaction happens, 818 00:44:28,465 --> 00:44:31,869 it's going to generate the same number. 819 00:44:31,869 --> 00:44:36,607 So the H3O+ would equal the concentration of the OH-. 820 00:44:36,607 --> 00:44:40,544 And in pure water, that is a value 821 00:44:40,544 --> 00:44:45,115 that is equal to 1 times 10 to the minus seventh moles 822 00:44:45,115 --> 00:44:54,158 per liter at 25C, at 25C. 823 00:44:54,158 --> 00:44:56,293 And so now we have yet another. 824 00:44:56,293 --> 00:44:58,429 That's neutral. 825 00:44:58,429 --> 00:45:02,700 You can understand that that's neutral, 826 00:45:02,700 --> 00:45:04,735 because you have the same-- 827 00:45:04,735 --> 00:45:10,007 if an acid is H+ or H3O+ in solution and a base is OH-, 828 00:45:10,007 --> 00:45:16,146 and I've made the same number, then the acidity and basicity 829 00:45:16,146 --> 00:45:17,414 are neutralizing one other. 830 00:45:17,414 --> 00:45:18,782 So that's neutral. 831 00:45:18,782 --> 00:45:23,821 And in fact, you can see that that pH is 7. 832 00:45:23,821 --> 00:45:27,624 Oh, and we can even write the equilibrium constant for water, 833 00:45:27,624 --> 00:45:35,999 which is going to be those guys, H3O+ times OH-, 834 00:45:35,999 --> 00:45:42,740 which is equal to 10 to the negative 14th, 835 00:45:42,740 --> 00:45:46,343 because that's the dissociation reaction for water. 836 00:45:46,343 --> 00:45:49,780 Water plus water goes to those ions in solution. 837 00:45:49,780 --> 00:45:53,050 We ignore the water, and then we're 838 00:45:53,050 --> 00:45:55,185 left with this same thing we've been 839 00:45:55,185 --> 00:45:58,288 doing, 10 to the minus 14th. 840 00:45:58,288 --> 00:46:00,991 Now, that takes us-- 841 00:46:00,991 --> 00:46:02,593 those are neutral. 842 00:46:02,593 --> 00:46:06,096 And so speaking of neutral, that's 843 00:46:06,096 --> 00:46:07,931 where we're going to go next. 844 00:46:07,931 --> 00:46:12,035 And I think what I want to do now is-- 845 00:46:12,035 --> 00:46:15,172 so we're going to go next into neutralizing things, 846 00:46:15,172 --> 00:46:17,107 so like if you add an acid to a base 847 00:46:17,107 --> 00:46:18,442 or if you add a base to an acid. 848 00:46:18,442 --> 00:46:22,346 And we already said on Monday, you get salt and water. 849 00:46:22,346 --> 00:46:26,617 But see, to understand that, you need a broader definition. 850 00:46:26,617 --> 00:46:30,187 Svante is amazing, but Svante missed something. 851 00:46:30,187 --> 00:46:33,924 And so we need a different definition of acids and bases 852 00:46:33,924 --> 00:46:35,192 that's more general. 853 00:46:35,192 --> 00:46:37,327 And that's what we're going to start with on Monday. 854 00:46:37,327 --> 00:46:41,298 But wait, because this is a great place for me 855 00:46:41,298 --> 00:46:44,601 to work on my arm. 856 00:46:44,601 --> 00:46:46,637 I got to hit-- 857 00:46:46,637 --> 00:46:50,541 OK, we're going to go all the way up there 858 00:46:50,541 --> 00:46:54,044 and all the way up there and right there 859 00:46:54,044 --> 00:46:59,483 and right there and, well, there and there and there. 860 00:46:59,483 --> 00:47:01,752 [YELLING] 861 00:47:01,752 --> 00:47:02,953 Oh, that was excitement. 862 00:47:02,953 --> 00:47:04,788 Let's go back there and there. 863 00:47:04,788 --> 00:47:07,658 Well, OK, and there. 864 00:47:07,658 --> 00:47:10,060 Oh, that was the same direction there. 865 00:47:10,060 --> 00:47:15,933 And there and there in the middle and there and there. 866 00:47:15,933 --> 00:47:24,842 Oh, that was there and there and there and there. 867 00:47:24,842 --> 00:47:28,512 You guys are seeing I need a stronger arm here. 868 00:47:28,512 --> 00:47:32,115 [GRUNTS] I can't really get too far. 869 00:47:32,115 --> 00:47:33,951 And [GRUNTS]. 870 00:47:36,687 --> 00:47:38,288 Oh, that side is all-- 871 00:47:38,288 --> 00:47:43,760 and there and there and there. 872 00:47:43,760 --> 00:47:48,098 And one more, I'm going deep. 873 00:47:48,098 --> 00:47:49,600 Have a great Thanksgiving, everyone. 874 00:47:49,600 --> 00:47:51,435 [APPLAUSE] 875 00:47:51,435 --> 00:47:53,437 See you guys on Monday.