1 00:00:16,015 --> 00:00:16,282 Thank you for that. 2 00:00:16,282 --> 00:00:18,785 Happy Monday after Thanksgiving. 3 00:00:18,785 --> 00:00:22,322 I hope you guys had a good break. 4 00:00:22,322 --> 00:00:28,361 We are back in action here on acids and bases, 5 00:00:28,361 --> 00:00:31,331 second lecture on acid and bases. 6 00:00:31,331 --> 00:00:35,902 Before we get into that, there's a celebration 7 00:00:35,902 --> 00:00:37,437 happening on Friday. 8 00:00:37,437 --> 00:00:38,972 You know that's why we're all feeling 9 00:00:38,972 --> 00:00:40,907 like a little extra goodness right now. 10 00:00:40,907 --> 00:00:44,411 Because we know there's a third midterm coming up Friday 11 00:00:44,411 --> 00:00:45,712 in this class, right? 12 00:00:45,712 --> 00:00:47,647 And that's nothing but excitement. 13 00:00:47,647 --> 00:00:48,882 Here's a concept map 14 00:00:48,882 --> 00:00:51,116 that I made for exam 3. 15 00:00:51,117 --> 00:00:54,220 This helps you sort of see the kinds of problems, 16 00:00:54,220 --> 00:00:57,223 right, that you could get, the topics that we've covered, 17 00:00:57,223 --> 00:01:00,093 and how it's all flowed and connected together, all right? 18 00:01:00,093 --> 00:01:01,294 So here are the quizzes. 19 00:01:01,294 --> 00:01:04,297 There's the optional one. 20 00:01:04,297 --> 00:01:06,699 Oh, you could still do it. 21 00:01:06,699 --> 00:01:11,670 So please, if you want to do the 8.5 and get that graded-- 22 00:01:11,670 --> 00:01:13,673 and then if it's higher than your lowest quiz, 23 00:01:13,673 --> 00:01:15,408 we'll swap it in for that. 24 00:01:15,408 --> 00:01:17,510 And you still get to drop one-- 25 00:01:17,510 --> 00:01:21,648 please do that and hand it in by tomorrow's recitation. 26 00:01:21,648 --> 00:01:22,382 There's that one. 27 00:01:22,382 --> 00:01:25,551 There's quiz-- there's the other two quizzes. 28 00:01:25,551 --> 00:01:29,521 And here are the psets, and the goody bags. 29 00:01:29,521 --> 00:01:31,825 All of this is the kinds of problems-- 30 00:01:31,825 --> 00:01:36,128 this has the practice problems and the topics 31 00:01:36,128 --> 00:01:39,365 that we want you to know about for Friday. 32 00:01:39,999 --> 00:01:43,803 Oh, and also, on Wednesday, instead 33 00:01:43,803 --> 00:01:47,907 of introducing a new topic that you won't be tested on, 34 00:01:47,907 --> 00:01:50,477 I'd prefer just to talk about these topics. 35 00:01:50,477 --> 00:01:52,312 So that's what I'm going to do on Wednesday. 36 00:01:52,312 --> 00:01:56,783 And we'll do some additional problems and kind of review. 37 00:01:56,783 --> 00:02:01,020 OK, but we still got to get through the rest of acids 38 00:02:01,020 --> 00:02:02,689 and bases. 39 00:02:02,689 --> 00:02:06,626 Now this is where we left off. 40 00:02:06,626 --> 00:02:09,929 This way of thinking about acids and bases 41 00:02:09,929 --> 00:02:12,565 is where we left off on Wednesday, all right? 42 00:02:13,433 --> 00:02:17,003 And this is the Arrhenius-- oh, Svante. 43 00:02:17,003 --> 00:02:19,873 Oh, Svante-- he was the first-- remember, 44 00:02:19,873 --> 00:02:21,808 [INAUDIBLE] over thousands of years would say, 45 00:02:21,808 --> 00:02:23,276 this is bitter. 46 00:02:23,276 --> 00:02:24,310 Put it in that category. 47 00:02:24,310 --> 00:02:25,311 This is sour. 48 00:02:25,311 --> 00:02:27,079 Mmm, right? 49 00:02:27,079 --> 00:02:28,581 Acid-- no, base. 50 00:02:28,581 --> 00:02:29,082 Acid. 51 00:02:29,082 --> 00:02:32,519 And there are ways that people categorized acids and bases 52 00:02:32,519 --> 00:02:34,320 for a long time. 53 00:02:34,320 --> 00:02:37,490 But nobody really started to try to understand them 54 00:02:37,490 --> 00:02:40,994 at the atomic scale until Svante came along and said, look, 55 00:02:40,994 --> 00:02:45,732 it's all about the H+ and the OH-, right? 56 00:02:45,732 --> 00:02:48,768 So acids-- and this is what we talked about on Wednesday. 57 00:02:48,768 --> 00:02:54,507 Acids are donating H+ ions, protons, into solution, 58 00:02:54,507 --> 00:02:55,308 into water. 59 00:02:55,308 --> 00:02:59,245 And bases are donating OH-, adding more of those types 60 00:02:59,245 --> 00:03:00,547 of ions into the water. 61 00:03:00,547 --> 00:03:05,852 And that's what makes them have the properties they have, OK? 62 00:03:05,852 --> 00:03:09,088 Now, so if you have-- 63 00:03:09,088 --> 00:03:10,023 so let's see. 64 00:03:10,023 --> 00:03:13,226 So H-- I'm going to just write this one on the board. 65 00:03:13,226 --> 00:03:15,495 Because we're going to talk about these two reactions-- 66 00:03:15,495 --> 00:03:17,630 plus H2O-- 67 00:03:17,630 --> 00:03:23,303 and remember, the water is just a kind of spectator there. 68 00:03:23,303 --> 00:03:24,003 It's a liquid. 69 00:03:24,003 --> 00:03:24,837 It's everywhere. 70 00:03:24,837 --> 00:03:26,439 It's the thing you're dissolving in. 71 00:03:26,439 --> 00:03:27,941 It's the solvent. 72 00:03:27,941 --> 00:03:29,442 That's the water. 73 00:03:29,442 --> 00:03:32,712 So you don't include it in these-- 74 00:03:32,712 --> 00:03:35,180 if it's just the liquid that you're dissolving something, 75 00:03:35,180 --> 00:03:38,384 it's not what you include in things like equilibrium 76 00:03:38,384 --> 00:03:41,487 constant expressions. 77 00:03:41,487 --> 00:03:43,122 OK, so that's going to be-- 78 00:03:43,122 --> 00:03:45,525 oh, but these guys, these are dissolved in the liquid, 79 00:03:45,525 --> 00:03:46,025 all right? 80 00:03:46,025 --> 00:03:47,427 These are the ions-- 81 00:03:47,427 --> 00:03:48,228 plus CL-. 82 00:03:53,600 --> 00:03:57,637 OK, now in this particular case, you 83 00:03:57,637 --> 00:04:01,074 can write the equilibrium constant, right? 84 00:04:01,074 --> 00:04:02,542 And that's the acid. 85 00:04:02,542 --> 00:04:05,545 It's also [INAUDIBLE] the acid dissociation constant. 86 00:04:05,545 --> 00:04:08,281 Remember, we had the solubility product constant. 87 00:04:08,281 --> 00:04:10,950 And we also can write the Ka, right? 88 00:04:10,950 --> 00:04:14,053 So Ka for this would be-- 89 00:04:14,053 --> 00:04:18,992 following our normal K equilibrium constant procedure, 90 00:04:18,992 --> 00:04:21,894 it would look something like this, right? 91 00:04:21,894 --> 00:04:25,298 Now here's the thing-- 92 00:04:25,298 --> 00:04:30,236 for this particular reaction of-- 93 00:04:30,236 --> 00:04:34,907 for this particular dissociation of HCl, of this acid-- 94 00:04:34,907 --> 00:04:37,409 and remember, it's an acid because it's giving us H+. 95 00:04:37,409 --> 00:04:40,713 Oh, H+ doesn't stay H+. 96 00:04:40,713 --> 00:04:42,915 Remember, that's also what we talked about Wednesday. 97 00:04:42,915 --> 00:04:46,119 H+ is actually H3O+. 98 00:04:46,119 --> 00:04:48,921 But the H+ is not stable in pure water. 99 00:04:48,921 --> 00:04:51,724 But sometimes-- actually, very often-- you'll see it-- 100 00:04:51,724 --> 00:04:54,927 in textbooks as well-- you'll see it just written as H+. 101 00:04:54,927 --> 00:04:57,697 But we know that it's the same thing. 102 00:04:57,697 --> 00:05:02,035 H3O-- if it's in water, it's H3O+, right, OK, so don't let-- 103 00:05:02,035 --> 00:05:04,737 but this is something like 10 to the sixth. 104 00:05:04,737 --> 00:05:07,540 That's huge. 105 00:05:07,540 --> 00:05:11,010 That equilibrium is so far over. 106 00:05:11,010 --> 00:05:16,082 That equilibrium is so far over given this enormous equilibrium 107 00:05:16,082 --> 00:05:20,286 constant, that we often will say that this reaction has 108 00:05:20,286 --> 00:05:21,487 gone to completion. 109 00:05:25,224 --> 00:05:28,027 Now we know that it's not infinite. 110 00:05:28,027 --> 00:05:31,331 So it hasn't-- technically there's still a little arrow 111 00:05:31,331 --> 00:05:34,367 going that way, all right? 112 00:05:34,367 --> 00:05:41,140 But-- and so, but since it's so much almost to completion, 113 00:05:41,140 --> 00:05:44,043 you'll often also see it written with just one arrow, all right? 114 00:05:44,043 --> 00:05:45,345 So I wanted to make that clear. 115 00:05:45,345 --> 00:05:47,447 But we know that it's an equilibrium. 116 00:05:47,447 --> 00:05:48,981 This has found an equilibrium. 117 00:05:48,981 --> 00:05:51,351 So there's still a little bit happening the other way, 118 00:05:51,351 --> 00:05:53,386 but just so little, all right? 119 00:05:53,386 --> 00:05:56,956 So you'll often see that going to completion. 120 00:05:56,956 --> 00:06:02,228 OK, good-- getting us back into the mood. 121 00:06:02,228 --> 00:06:09,168 Now for the base, we can have NaOH-- 122 00:06:09,168 --> 00:06:10,403 let's do that one-- 123 00:06:10,403 --> 00:06:20,113 plus H2O goes to Na+ in solution plus OH-. 124 00:06:20,113 --> 00:06:22,548 And this is the Arrhenius acid-base definition-- 125 00:06:22,548 --> 00:06:23,816 gesundheit. 126 00:06:23,816 --> 00:06:30,690 And you could write a similar expression for the base, Na+, 127 00:06:30,690 --> 00:06:33,058 OH-. 128 00:06:33,058 --> 00:06:35,261 And that's going to go over NaOH. 129 00:06:35,261 --> 00:06:42,835 Now this is also very large. 130 00:06:42,835 --> 00:06:44,871 Now these are both strong. 131 00:06:44,871 --> 00:06:47,507 And we're going to come back to this at the end of the lecture. 132 00:06:47,507 --> 00:06:49,742 I want to talk about what makes an acid or a base 133 00:06:49,742 --> 00:06:51,344 strong or weak. 134 00:06:51,344 --> 00:06:52,945 These are both strong. 135 00:06:52,945 --> 00:06:55,415 And just as a little preview to where we're getting, 136 00:06:55,415 --> 00:06:57,683 that's because they dissociate so much. 137 00:06:57,683 --> 00:07:01,220 So this also has a very high Kb-- 138 00:07:01,220 --> 00:07:03,523 Kb, because we're talking about a base-- 139 00:07:03,523 --> 00:07:06,192 Kb, Ka, Kb, right? 140 00:07:06,192 --> 00:07:09,395 Oh, but some people don't like these large exponents, 141 00:07:09,395 --> 00:07:13,299 these large or small 10 to the minus 5th, 10 to the positive 142 00:07:13,299 --> 00:07:14,033 fifth. 143 00:07:14,033 --> 00:07:16,536 And so we take the log. 144 00:07:16,536 --> 00:07:18,371 You can take the log of these. 145 00:07:18,371 --> 00:07:24,544 And then you'll get, like, a pKb, right, or pKb, 146 00:07:24,544 --> 00:07:26,946 which is the power of that. 147 00:07:26,946 --> 00:07:34,954 So log of Kb would be low, right, would be low. 148 00:07:34,954 --> 00:07:36,355 If this is going to be high, then 149 00:07:36,355 --> 00:07:38,591 minus the log of the power of that is going to be low. 150 00:07:38,591 --> 00:07:44,397 So you can talk about pKb, Kb, Ka, pKa. 151 00:07:44,397 --> 00:07:47,667 It's all just thinking about these equilibrium constants. 152 00:07:47,667 --> 00:07:51,671 And we'll come back to this in a second. 153 00:07:51,671 --> 00:07:53,606 If I had a question for you-- 154 00:07:53,606 --> 00:07:57,643 if I said, OK, how would you use this-- 155 00:07:57,643 --> 00:08:01,280 if I said that I've got point-- 156 00:08:01,280 --> 00:08:02,849 I'm going to give you a problem now-- 157 00:08:02,849 --> 00:08:12,258 0.05 moles per liter of NaOH, and I asked you, what's the pH, 158 00:08:12,258 --> 00:08:14,760 well, you can do it now, all right? 159 00:08:14,760 --> 00:08:15,294 Why? 160 00:08:15,294 --> 00:08:20,500 Because I've just told you it's a almost fully dissociated 161 00:08:20,500 --> 00:08:21,501 base. 162 00:08:21,501 --> 00:08:25,571 So the equilibrium constant for that dissociation of that base 163 00:08:25,571 --> 00:08:26,606 is very, very high. 164 00:08:26,606 --> 00:08:29,675 It means it lies very far over to the right. 165 00:08:29,675 --> 00:08:32,010 So basically, what does that mean? 166 00:08:32,010 --> 00:08:34,780 If I've got 0.05 moles per liter starting out, 167 00:08:34,780 --> 00:08:35,780 it's mostly dissociated. 168 00:08:35,780 --> 00:08:36,782 [SNEEZE] 169 00:08:36,782 --> 00:08:38,284 Gesundheit. 170 00:08:38,284 --> 00:08:44,991 So I've got 0.05 moles per liter of Na+ and OH-, all right? 171 00:08:44,991 --> 00:08:47,693 OK, but the OH- is what matters. 172 00:08:47,693 --> 00:08:53,866 So full dissociation-- oh, we're going to do this because I want 173 00:08:53,866 --> 00:08:55,835 to be precise here-- 174 00:08:55,835 --> 00:08:57,169 put that in quotes. 175 00:08:57,169 --> 00:09:02,775 It's almost full-- means that I have 0.05 moles per liter 176 00:09:02,775 --> 00:09:04,510 of OH--- 177 00:09:04,510 --> 00:09:06,312 by the way, and Na+. 178 00:09:06,312 --> 00:09:09,048 But Na+ is a spectator in terms of the pH. 179 00:09:09,048 --> 00:09:12,084 It's not going to change the pH, right, the Na+? 180 00:09:12,084 --> 00:09:14,453 Oh, but the OH will, all right? 181 00:09:14,453 --> 00:09:17,690 And so now we go back to these Ks. 182 00:09:17,690 --> 00:09:21,460 We know-- right, we know-- 183 00:09:21,460 --> 00:09:24,263 that the equilibrium constant of pure water is equal 184 00:09:24,263 --> 00:09:31,971 to the concentration of H+ in solution, which is H3O+, 185 00:09:31,971 --> 00:09:36,108 times OH-, and that that's equal to 10 to the minus 14th, 186 00:09:36,108 --> 00:09:36,609 all right? 187 00:09:36,609 --> 00:09:42,048 That's another thing that we talked about on Wednesday. 188 00:09:42,048 --> 00:09:44,150 So if that's true, if the-- 189 00:09:44,150 --> 00:09:48,120 which it is at 25 C-- the equilibrium constant for water, 190 00:09:48,120 --> 00:09:48,788 which is-- 191 00:09:48,788 --> 00:09:51,090 remember, water can be either one. 192 00:09:51,090 --> 00:09:52,290 It's this times this. 193 00:09:52,290 --> 00:09:53,826 And we know what this is. 194 00:09:53,826 --> 00:09:56,862 Now you know what that is, all right? 195 00:09:56,862 --> 00:09:58,397 And if you know what H+-- 196 00:09:58,397 --> 00:10:02,134 if the concentration of H+ is known, then the pH-- 197 00:10:02,134 --> 00:10:04,904 power of-- the p is the minus lower-- 198 00:10:04,904 --> 00:10:08,341 the pH of that is something you can calculate. 199 00:10:08,341 --> 00:10:16,515 And so the pH winds up, here, being 12.7, all rigth? 200 00:10:16,515 --> 00:10:19,952 And that's the kind of thing that you can have fun with. 201 00:10:19,952 --> 00:10:25,691 You dissolve some base, and you can measure a pH, or a pOH, 202 00:10:25,691 --> 00:10:26,759 if you wanted-- 203 00:10:26,759 --> 00:10:30,262 all stuff we talked about last week. 204 00:10:30,262 --> 00:10:31,764 OK, but now we move on. 205 00:10:31,764 --> 00:10:36,936 And now we're going to introduce the next definition of acids 206 00:10:36,936 --> 00:10:40,506 and bases by first talking about what happens when you mix them 207 00:10:40,506 --> 00:10:42,341 together, all right? 208 00:10:42,341 --> 00:10:44,710 These are not mixing together yet. 209 00:10:44,710 --> 00:10:47,313 They're just-- a base dissolves in water. 210 00:10:47,313 --> 00:10:49,649 An acid dissolves in water. 211 00:10:49,649 --> 00:10:55,087 But what if I had an acid and a base, and I mix them together. 212 00:10:55,087 --> 00:11:04,764 OK, well, so if I did that, then I would have HCl plus NaOH. 213 00:11:04,764 --> 00:11:06,999 Now I'm just going to-- 214 00:11:06,999 --> 00:11:08,434 I'm not going to include the water. 215 00:11:08,434 --> 00:11:11,103 It's there on the left, and it's going to be there on the right. 216 00:11:11,103 --> 00:11:13,339 I'm just going to write all these ions down that happen, 217 00:11:13,339 --> 00:11:13,606 right? 218 00:11:13,606 --> 00:11:14,707 So you're going to get-- 219 00:11:14,707 --> 00:11:16,342 oh, you're going to get H+-- 220 00:11:16,342 --> 00:11:19,445 oh, we know it's H3O+-- 221 00:11:19,445 --> 00:11:26,786 plus Cl- plus Na+. 222 00:11:26,786 --> 00:11:29,121 OK, these are all dissolved in water. 223 00:11:29,121 --> 00:11:33,726 I'm emphasizing that with the little aqueous subscripts. 224 00:11:33,726 --> 00:11:35,828 And you can see what's going to happen now, right? 225 00:11:35,828 --> 00:11:37,897 So if I have these there, well, look at this. 226 00:11:37,897 --> 00:11:41,233 The Na+ and the Cl-, boy, do-- 227 00:11:41,233 --> 00:11:43,069 they see each other, and they're like, well, 228 00:11:43,069 --> 00:11:47,940 maybe we could form some salt. Maybe we could form some salt. 229 00:11:47,940 --> 00:11:51,177 And then the OH and the H, and those form water. 230 00:11:51,177 --> 00:11:56,348 And so you can get H2O plus NaCl. 231 00:11:56,348 --> 00:11:59,518 And so what happens is what's written there, 232 00:11:59,518 --> 00:12:04,657 is that when you mix an acid with a base, you will get water 233 00:12:04,657 --> 00:12:06,092 and some salt. Now remember, salt 234 00:12:06,092 --> 00:12:12,398 is a general term, all right, for these cations and anions, 235 00:12:12,398 --> 00:12:13,999 right, coming together in a solid. 236 00:12:13,999 --> 00:12:18,070 So OK, now here's the thing though, all right? 237 00:12:18,070 --> 00:12:21,507 So this was the acid and I'm writing this explicitly. 238 00:12:21,507 --> 00:12:24,243 Because you'll see-- and this was the base. 239 00:12:26,912 --> 00:12:28,848 Because what is neutralization? 240 00:12:28,848 --> 00:12:32,451 Well, you think about it in terms of pH. 241 00:12:32,451 --> 00:12:35,888 I had something with maybe a low pH, or maybe a high pH, 242 00:12:35,888 --> 00:12:39,158 and I want it to become neutral. 243 00:12:39,158 --> 00:12:42,061 Neutral would be-- if I'm in pure water, 244 00:12:42,061 --> 00:12:44,163 Kw is 10 to the minus 14th. 245 00:12:44,163 --> 00:12:48,200 Neutral would be-- it's the same acid and base ratio. 246 00:12:48,200 --> 00:12:51,804 So these are each 10 to the minus seventh, pH 7, 247 00:12:51,804 --> 00:12:53,539 neutral, all right? 248 00:12:53,539 --> 00:12:58,544 There's no excess of protons or OH-, all right? 249 00:12:58,544 --> 00:13:00,279 So if there's no excess, it's neutral. 250 00:13:00,279 --> 00:13:05,451 So neutralization is basically the act of making it neutral. 251 00:13:05,451 --> 00:13:07,486 So I had something that gave a lot of H+. 252 00:13:07,486 --> 00:13:11,223 And now I got something that gives me a lot of OH-. 253 00:13:11,223 --> 00:13:15,060 If I have the same amount of them, all right-- 254 00:13:15,060 --> 00:13:18,631 so they're equivalent-- then you can make it neutral. 255 00:13:18,631 --> 00:13:21,801 That's neutralization, OK? 256 00:13:21,801 --> 00:13:24,804 But see, the thing is I can take HCl, 257 00:13:24,804 --> 00:13:29,041 and I can mix Windex, or ammonia, with it 258 00:13:29,041 --> 00:13:32,278 and neutralize it. 259 00:13:32,278 --> 00:13:34,046 And back then, they were like, but that 260 00:13:34,046 --> 00:13:36,081 doesn't make any sense. 261 00:13:36,081 --> 00:13:39,618 But first of all, because we don't have Windex yet. 262 00:13:39,618 --> 00:13:44,723 But second of all, because Windex doesn't have any OH-. 263 00:13:44,723 --> 00:13:46,425 Gesundheit. 264 00:13:46,425 --> 00:13:49,261 And so that got them really thinking, all right? 265 00:13:49,261 --> 00:13:50,930 So if I take-- so let's take NH3. 266 00:13:54,033 --> 00:13:55,401 So if I take NH3-- 267 00:13:55,401 --> 00:13:57,036 dah. 268 00:13:57,036 --> 00:14:04,143 If I take NH3 and I go like this, NH3 plus HCl-- 269 00:14:04,143 --> 00:14:05,344 now this is not-- 270 00:14:05,344 --> 00:14:09,448 I'm not writing the liquid dissociation of the thing. 271 00:14:09,448 --> 00:14:12,451 I'm mixing it, acid and something else 272 00:14:12,451 --> 00:14:13,686 that I know neutralizes it. 273 00:14:13,686 --> 00:14:15,421 And in fact, what ends up happening 274 00:14:15,421 --> 00:14:17,423 is you get-- gesundheit. 275 00:14:17,423 --> 00:14:18,958 You get this. 276 00:14:22,127 --> 00:14:29,401 And so what we know is that this is neutralizing. 277 00:14:29,401 --> 00:14:33,305 It's taking-- what's happening in this reaction? 278 00:14:33,305 --> 00:14:36,141 What's actually happening? 279 00:14:36,141 --> 00:14:37,710 What did the-- what did that base 280 00:14:37,710 --> 00:14:42,548 do effectively to neutralize HCl? 281 00:14:42,548 --> 00:14:47,286 What it did is it took H+ from the solution. 282 00:14:47,286 --> 00:14:49,889 That's what it did, all right? 283 00:14:49,889 --> 00:14:56,295 So NH3-- in this reaction, NH3 takes. 284 00:14:56,295 --> 00:15:01,267 It takes H+ from the solution. 285 00:15:03,936 --> 00:15:07,973 That's exactly-- HCl was like, I want to make it acidic-- 286 00:15:07,973 --> 00:15:09,708 H+, H+, H+. 287 00:15:09,708 --> 00:15:12,578 And NH3 is like, no, give me the H+. 288 00:15:12,578 --> 00:15:13,445 You cannot make this. 289 00:15:13,445 --> 00:15:15,414 I'm neutralizing you. 290 00:15:15,414 --> 00:15:18,284 I'm taking your H+ back. 291 00:15:18,284 --> 00:15:20,419 If it takes that, then that's neutralizing. 292 00:15:20,419 --> 00:15:28,694 That's going to neutralize the HCl as well. 293 00:15:28,694 --> 00:15:29,828 But see, we have a problem. 294 00:15:29,828 --> 00:15:36,435 Because this is not an OH-donating molecule. 295 00:15:36,435 --> 00:15:37,703 But it still neutralizes. 296 00:15:37,703 --> 00:15:39,932 And so we need a broader definition. 297 00:15:39,939 --> 00:15:40,973 And that came from-- 298 00:15:40,973 --> 00:15:43,008 that came from Bronsted and Lowry. 299 00:15:43,008 --> 00:15:46,512 And so this is another way of thinking, 300 00:15:46,512 --> 00:15:50,249 a more general way of thinking of acids and bases-- 301 00:15:53,385 --> 00:15:56,989 more general and more correct, because the Arrhenius 302 00:15:56,989 --> 00:16:01,994 definition does not cover classes of molecules 303 00:16:01,994 --> 00:16:05,798 that could be a base. 304 00:16:05,798 --> 00:16:10,102 And so in this way, in the Bronsted-Lowry definition-- 305 00:16:10,102 --> 00:16:12,671 in the Bronsted-Lowry definition-- 306 00:16:12,671 --> 00:16:15,040 it's all about the proton. 307 00:16:15,040 --> 00:16:17,509 So let me write that down here. 308 00:16:17,509 --> 00:16:28,420 So in Bronstein and Lowry, their definition is that acid-- 309 00:16:28,420 --> 00:16:32,891 and he did it by looking at acid-base neutralization 310 00:16:32,891 --> 00:16:34,526 reactions like I just described. 311 00:16:34,526 --> 00:16:39,164 Acid-base neutralization-- I'm not going to write it, 312 00:16:39,164 --> 00:16:40,232 because there's no room-- 313 00:16:40,232 --> 00:16:46,672 reactions is all about the proton transfer. 314 00:16:50,209 --> 00:16:54,880 These are proton transfer reactions. 315 00:16:54,880 --> 00:16:58,717 This is how they saw acids and bases, as exchanging a proton. 316 00:16:58,717 --> 00:17:03,522 Taking it or giving it, that's what it's about, all right? 317 00:17:03,522 --> 00:17:06,458 And so in our sort of general-- 318 00:17:06,458 --> 00:17:10,929 you know, in the general HA lingo that we introduced, 319 00:17:10,929 --> 00:17:21,339 you would have HA plus B. And that's going to go to BH+ plus 320 00:17:21,339 --> 00:17:21,839 A-. 321 00:17:24,843 --> 00:17:28,847 That's an acid-base reaction. 322 00:17:28,847 --> 00:17:34,286 And so you can see that these are-- this is a proton donor. 323 00:17:34,286 --> 00:17:36,955 This is a proton donor. 324 00:17:36,955 --> 00:17:39,191 And this is an acceptor. 325 00:17:42,261 --> 00:17:47,499 It's a donor, H+ donor, H+ acceptor. 326 00:17:47,499 --> 00:17:49,935 That defines them, according to Bronsted and Lowry, 327 00:17:49,935 --> 00:17:53,138 as acids and bases. 328 00:17:53,138 --> 00:17:55,340 OK. 329 00:17:55,340 --> 00:17:57,142 OK, well we can also-- 330 00:17:57,142 --> 00:17:58,377 OK, so now let's see. 331 00:17:58,377 --> 00:18:00,145 Let's now go back. 332 00:18:00,145 --> 00:18:03,549 That's a broader definition. 333 00:18:03,549 --> 00:18:07,453 Let's now go back to the ammonia, OK? 334 00:18:07,453 --> 00:18:09,988 And what I want to do now is, instead of mixing it 335 00:18:09,988 --> 00:18:13,559 with an acid to think about whether it trades a proton, 336 00:18:13,559 --> 00:18:15,694 I want to just dissolve it in water. 337 00:18:15,694 --> 00:18:18,630 So now we know it's a base, OK? 338 00:18:18,630 --> 00:18:19,364 So what happens? 339 00:18:19,364 --> 00:18:25,971 So if I dissolve NH3 in H2O-- 340 00:18:25,971 --> 00:18:29,374 I want to point something out here, that if I do this, 341 00:18:29,374 --> 00:18:37,116 and I get NH4+ plus OH-, that's the-- 342 00:18:37,116 --> 00:18:39,051 now I'm taking a base. 343 00:18:39,051 --> 00:18:40,486 So there we had-- 344 00:18:40,486 --> 00:18:41,520 there's the acid. 345 00:18:41,520 --> 00:18:43,021 Here's the base. 346 00:18:43,021 --> 00:18:44,389 That's the Arrhenius base. 347 00:18:44,389 --> 00:18:49,261 But now I'm taking a Bronsted-Lowry base, right? 348 00:18:49,261 --> 00:18:51,296 It took an H+. 349 00:18:51,296 --> 00:18:56,068 Well, that means that this is a base. 350 00:18:56,068 --> 00:19:02,574 But look, this-- OK, this gave a proton. 351 00:19:02,574 --> 00:19:07,146 So this must be an acid according to Bronsted-- 352 00:19:07,146 --> 00:19:09,248 according to Bronsted and Lowry. 353 00:19:09,248 --> 00:19:12,851 And similarly, over here, we know 354 00:19:12,851 --> 00:19:14,820 that this is going to give one. 355 00:19:14,820 --> 00:19:16,522 And I'm going to write that in a second. 356 00:19:16,522 --> 00:19:18,690 And this would love to accept one. 357 00:19:18,690 --> 00:19:20,159 So that's a base, right? 358 00:19:20,159 --> 00:19:21,760 And remember, we have a name for this. 359 00:19:21,760 --> 00:19:24,563 In the same reaction, we have a name for this. 360 00:19:24,563 --> 00:19:30,035 This would be the conjugate, all right? 361 00:19:32,971 --> 00:19:34,072 Those are conjugates. 362 00:19:34,072 --> 00:19:41,013 That's why I'm writing those, all right? 363 00:19:41,013 --> 00:19:46,185 So there's a conjugate base-acid, conjugate acid-base. 364 00:19:46,185 --> 00:19:49,221 Now we have a Bronsted-Lowry understanding 365 00:19:49,221 --> 00:19:51,723 of what conjugate acid-base means. 366 00:19:51,723 --> 00:19:55,294 It's just a proton transfer, all right? 367 00:19:55,294 --> 00:19:57,996 It's just a proton transfer. 368 00:19:57,996 --> 00:20:00,933 Now notice I could take this-- so I've taken this base, 369 00:20:00,933 --> 00:20:06,638 and I've put it into a solution of water. 370 00:20:06,638 --> 00:20:09,441 I could take this acid and do the same thing. 371 00:20:09,441 --> 00:20:13,545 So if I do that, I've got NH4+. 372 00:20:13,545 --> 00:20:16,748 And I'm going to put that in water now, OK? 373 00:20:16,748 --> 00:20:18,750 So I've taken this out. 374 00:20:18,750 --> 00:20:21,220 And now I'm putting that acid into water. 375 00:20:21,220 --> 00:20:23,689 And if I do that, look at what happens. 376 00:20:23,689 --> 00:20:28,627 I get NH3 plus H3O+. 377 00:20:31,964 --> 00:20:34,199 Notice what happened. 378 00:20:34,199 --> 00:20:37,836 Well, I've switched acid. 379 00:20:37,836 --> 00:20:39,071 That's my acid. 380 00:20:39,071 --> 00:20:44,710 But this took the proton, so it must be a base, right? 381 00:20:44,710 --> 00:20:47,145 And over here I've got the base. 382 00:20:47,145 --> 00:20:49,781 And this must be an acid. 383 00:20:49,781 --> 00:20:53,986 Proton transfer, that's what's happening here-- 384 00:20:53,986 --> 00:20:56,455 conjugates. 385 00:20:56,455 --> 00:20:59,992 I took the base, and I got an acid. 386 00:20:59,992 --> 00:21:03,195 So this tells us that water-- 387 00:21:03,195 --> 00:21:05,163 and it tells us what we said on Wednesday. 388 00:21:05,163 --> 00:21:07,299 Water can be both. 389 00:21:07,299 --> 00:21:09,601 Notice water is an acid in the one hand 390 00:21:09,601 --> 00:21:10,902 and a base on the other. 391 00:21:10,902 --> 00:21:12,137 That makes it amphoteric. 392 00:21:14,673 --> 00:21:20,212 So H2O can be both. 393 00:21:20,212 --> 00:21:22,147 It can take or give protons. 394 00:21:22,147 --> 00:21:23,782 And so it is amphoteric. 395 00:21:28,787 --> 00:21:32,291 Just for fun, if you take the conjugate-- you know, 396 00:21:32,291 --> 00:21:35,494 if you take any acid-base pair, and they're conjugates, 397 00:21:35,494 --> 00:21:39,331 you can also write out the Ka's and Kb's, all right? 398 00:21:39,331 --> 00:21:49,941 And so if I take a conjugate acid and base, 399 00:21:49,941 --> 00:21:54,279 well, you know that you could write Ka, all right? 400 00:21:54,279 --> 00:21:56,548 OK, so let's write the acid dissociation again. 401 00:21:56,548 --> 00:21:58,517 So for that one, here it is. 402 00:21:58,517 --> 00:22:03,555 Ka is NH-- is H3O+. 403 00:22:03,555 --> 00:22:09,328 OK, I'm going to take the bottom one, H3O+, times NH3, right, 404 00:22:09,328 --> 00:22:12,431 concentrations, divided by NH4+. 405 00:22:16,301 --> 00:22:18,303 But if I took the base dissociation 406 00:22:18,303 --> 00:22:20,372 constant from the conjugate-- 407 00:22:20,372 --> 00:22:22,574 I'm taking the conjugates now, right-- 408 00:22:22,574 --> 00:22:24,910 then I would get that it's-- 409 00:22:24,910 --> 00:22:34,986 OK, it's OH- and NH4+ divided by NH3. 410 00:22:38,523 --> 00:22:40,859 Like I'm saying, just for fun, you can now look at this. 411 00:22:40,859 --> 00:22:44,196 You go, Ka times Kb-- 412 00:22:44,196 --> 00:22:45,297 Ka times Kb. 413 00:22:45,297 --> 00:22:59,678 That's reassuring that Ka times Kb is equal to H3O+ times OH-. 414 00:22:59,678 --> 00:23:04,649 And I mean concentrations, which is Kw. 415 00:23:04,649 --> 00:23:10,789 That is fun, for the Bronsted-Lowry acid-base 416 00:23:10,789 --> 00:23:12,124 conjugate. 417 00:23:12,124 --> 00:23:15,260 NH4+, NH3, right? 418 00:23:15,260 --> 00:23:17,295 OK. 419 00:23:17,295 --> 00:23:20,999 OK, that's Bronsted-Lowry Lowry acids and bases. 420 00:23:20,999 --> 00:23:23,101 Here's a little recap. 421 00:23:23,101 --> 00:23:24,035 Here's a little recap. 422 00:23:24,035 --> 00:23:26,271 I'm not going to read through this in detail, 423 00:23:26,271 --> 00:23:27,572 but I just wanted to give you-- 424 00:23:27,572 --> 00:23:29,141 OK, what have we done so far? 425 00:23:29,141 --> 00:23:31,076 We've talked about amphoteric. 426 00:23:31,076 --> 00:23:33,111 We've talked about conjugate acids and bases. 427 00:23:33,111 --> 00:23:36,948 These are now written in the Bronsted-Lowry form, right? 428 00:23:36,948 --> 00:23:39,518 They accept or give a proton. 429 00:23:39,518 --> 00:23:43,422 We've talked about the conjugate acid-base pair, what I just 430 00:23:43,422 --> 00:23:46,224 drew an example of right there, neutralization 431 00:23:46,224 --> 00:23:49,394 reactions, and salt. OK, good. 432 00:23:49,394 --> 00:23:52,297 These are some concepts that we have covered that I 433 00:23:52,297 --> 00:23:54,166 would like you to know about. 434 00:23:54,166 --> 00:23:56,935 Now but there's a few more concepts 435 00:23:56,935 --> 00:23:58,670 that we have to come back to-- 436 00:23:58,670 --> 00:24:00,872 a few more concepts that we have to come back to. 437 00:24:00,872 --> 00:24:02,941 And it has to do with what I started with. 438 00:24:02,941 --> 00:24:07,078 In the beginning, I said, you know, these Ks are huge. 439 00:24:07,078 --> 00:24:10,982 So the equilibrium-- if an equilibrium constant lies-- 440 00:24:10,982 --> 00:24:15,687 is very large, then you know you're mostly making product, 441 00:24:15,687 --> 00:24:16,421 right? 442 00:24:16,421 --> 00:24:19,424 And so it's essentially to completion. 443 00:24:19,424 --> 00:24:23,328 And I also mentioned that those are strong, 444 00:24:23,328 --> 00:24:26,131 strong acids, strong bases-- 445 00:24:26,131 --> 00:24:28,266 strong acids, strong bases. 446 00:24:28,266 --> 00:24:33,872 Why is an acid or base strong or weak? 447 00:24:33,872 --> 00:24:37,609 That's what I want to talk about next, all right? 448 00:24:37,609 --> 00:24:39,978 And actually, there are-- 449 00:24:39,978 --> 00:24:44,149 there really aren't that many strong acids or strong bases. 450 00:24:44,149 --> 00:24:47,686 In fact, they're mostly here. 451 00:24:47,686 --> 00:24:50,789 These are really, pretty much most of them. 452 00:24:50,789 --> 00:24:52,557 Minor [INAUDIBLE] I don't want to go into. 453 00:24:52,557 --> 00:24:53,625 But these are really-- 454 00:24:53,625 --> 00:24:56,328 if you think about the general category of strong acids, 455 00:24:56,328 --> 00:24:58,930 strong bases, this is it. 456 00:24:58,930 --> 00:25:00,832 Why? 457 00:25:00,832 --> 00:25:02,801 Why is that? 458 00:25:02,801 --> 00:25:05,437 Well, it has to do with what we've been talking about, 459 00:25:05,437 --> 00:25:06,037 all right? 460 00:25:06,037 --> 00:25:07,806 So those are strong acids. 461 00:25:07,806 --> 00:25:08,740 Those are strong bases. 462 00:25:11,309 --> 00:25:15,013 It has to do with dissociation. 463 00:25:15,013 --> 00:25:17,215 It has to do with dissociation. 464 00:25:17,215 --> 00:25:25,156 So if I take HCl and I put it in water, 465 00:25:25,156 --> 00:25:28,093 it almost completely dissociates. 466 00:25:28,093 --> 00:25:31,096 That's why it's a strong acid. 467 00:25:31,096 --> 00:25:35,500 Now there's confusion around this. 468 00:25:35,500 --> 00:25:36,635 And I want to make that-- 469 00:25:36,635 --> 00:25:37,936 I want to make it very clear. 470 00:25:37,936 --> 00:25:39,704 There is a big distinction I want to make. 471 00:25:44,042 --> 00:25:47,712 Because if something is a weak acid, 472 00:25:47,712 --> 00:25:51,883 meaning it's not one of these, what that means is it 473 00:25:51,883 --> 00:25:54,219 doesn't dissociate very much. 474 00:25:54,219 --> 00:25:55,153 That's what it means. 475 00:25:55,153 --> 00:25:58,924 It doesn't have anything to do with concentration, all right? 476 00:25:58,924 --> 00:26:00,492 So let's take a weak acid. 477 00:26:00,492 --> 00:26:02,160 Let's take vinegar, all right? 478 00:26:02,160 --> 00:26:04,696 So if I take a weak acid-- 479 00:26:07,332 --> 00:26:08,833 we see vinegar as CH3COOH. 480 00:26:13,338 --> 00:26:15,540 You know what's nice about writing them out this way? 481 00:26:15,540 --> 00:26:17,342 You say, why didn't you put the H in there, 482 00:26:17,342 --> 00:26:22,480 and make it CH4, and CO2, or put the two Cs together? 483 00:26:22,480 --> 00:26:24,683 Oftentimes you'll see molecules written out this way, 484 00:26:24,683 --> 00:26:26,952 because this tells us a little bit 485 00:26:26,952 --> 00:26:28,620 of a hint about connectivity. 486 00:26:28,620 --> 00:26:31,556 And for acids and bases, it's actually useful. 487 00:26:31,556 --> 00:26:33,224 Because you see the H there? 488 00:26:33,224 --> 00:26:34,993 That's the one that's going to trade. 489 00:26:34,993 --> 00:26:38,363 That's the Bronsted-Lowry transfer H, all right? 490 00:26:38,363 --> 00:26:39,998 So often, for acids and bases, you'll 491 00:26:39,998 --> 00:26:42,601 see that written out in this way. 492 00:26:42,601 --> 00:26:44,869 Makes it easier to think about. 493 00:26:44,869 --> 00:26:50,542 And if I mix this into water, then what do I get? 494 00:26:50,542 --> 00:26:52,410 Well, I'm going to get H3O-- 495 00:26:52,410 --> 00:26:54,012 I'm going to write this down here-- 496 00:26:54,012 --> 00:26:57,916 H3O+-- that's an acid, right-- 497 00:26:57,916 --> 00:27:00,251 plus CH3COO-. 498 00:27:03,989 --> 00:27:06,691 There's the H that came off-- 499 00:27:06,691 --> 00:27:08,093 proton transfer. 500 00:27:08,093 --> 00:27:12,397 So why is it weak? 501 00:27:12,397 --> 00:27:18,169 Well, it's weak because here, the acid equilibrium constant 502 00:27:18,169 --> 00:27:22,574 is something like 10 to the minus fifth. 503 00:27:22,574 --> 00:27:30,582 So even if I have a lot, you do even if I had like 1 mole per 504 00:27:30,582 --> 00:27:35,220 liter of this stuff in solution, it wouldn't-- 505 00:27:35,220 --> 00:27:36,888 most of it wouldn't dissolve. 506 00:27:36,888 --> 00:27:39,791 In fact, much less than a percent of vinegar actually 507 00:27:39,791 --> 00:27:44,195 gives me H3O+, all right? 508 00:27:44,195 --> 00:27:47,332 But you think, oh, just add more vinegar. 509 00:27:47,332 --> 00:27:48,500 No. 510 00:27:48,500 --> 00:27:53,238 No, because we're talking about concentrations, right? 511 00:27:53,238 --> 00:27:56,374 It's the concentration in that water. 512 00:27:56,374 --> 00:27:58,143 I'm locked into that by this. 513 00:27:58,143 --> 00:27:59,678 This is an equilibrium constant. 514 00:27:59,678 --> 00:28:01,346 And it's talking about the concentration 515 00:28:01,346 --> 00:28:02,781 that I get in the water. 516 00:28:05,283 --> 00:28:06,284 I'm stuck. 517 00:28:06,284 --> 00:28:10,755 I can't be-- that's how much you dissociate, right? 518 00:28:10,755 --> 00:28:13,458 That's how much you associate as a concentration. 519 00:28:16,027 --> 00:28:19,264 So it's more acidic than water for sure, all right? 520 00:28:19,264 --> 00:28:22,300 It's 100 times more acidic than water, all right, 521 00:28:22,300 --> 00:28:24,335 10 to the minus fifth. 522 00:28:24,335 --> 00:28:27,439 But it's never going to be a strong acid, because I don't 523 00:28:27,439 --> 00:28:30,075 give very much of the protons. 524 00:28:30,075 --> 00:28:32,577 So this is the key that I want to make clear. 525 00:28:32,577 --> 00:28:34,646 This is the key, OK? 526 00:28:34,646 --> 00:28:37,315 It's very important. 527 00:28:37,315 --> 00:28:41,486 It gets its own board. 528 00:28:41,486 --> 00:28:44,489 The strength of an acid, OK? 529 00:28:44,489 --> 00:28:59,971 So acid concentration is not equal to acid strength. 530 00:29:03,742 --> 00:29:05,310 More, and more, and more vinegar-- no. 531 00:29:07,846 --> 00:29:10,849 It doesn't matter, because it's about association. 532 00:29:10,849 --> 00:29:13,785 See, this is about-- 533 00:29:13,785 --> 00:29:18,123 this is a function of the solubility. 534 00:29:18,123 --> 00:29:20,291 So how much can I get in there? 535 00:29:20,291 --> 00:29:22,694 We talked about all that a lot already. 536 00:29:22,694 --> 00:29:27,265 That's a different thing, solubility, the Ksp. 537 00:29:27,265 --> 00:29:28,600 How much of this can I dissolve? 538 00:29:28,600 --> 00:29:30,101 Great. 539 00:29:30,101 --> 00:29:35,340 I can dissolve a lot of vinegar in water. 540 00:29:35,340 --> 00:29:37,408 And it doesn't crash out, right? 541 00:29:37,408 --> 00:29:38,476 That's wonderful. 542 00:29:38,476 --> 00:29:41,379 Doesn't make it a strong acid. 543 00:29:41,379 --> 00:29:53,458 This is about dissociation, all right? 544 00:29:53,458 --> 00:30:00,999 And so if you think about what makes an acid a strong acid-- 545 00:30:00,999 --> 00:30:03,935 or for that-- or a weak acid, or what the relative strengths 546 00:30:03,935 --> 00:30:06,871 of acids are-- and the same holds for bases, 547 00:30:06,871 --> 00:30:08,139 just the other way around-- 548 00:30:08,139 --> 00:30:15,246 it has to do with how easy it is to take that H off or add it 549 00:30:15,246 --> 00:30:16,848 on, right? 550 00:30:16,848 --> 00:30:19,884 That's what it has to do with. 551 00:30:19,884 --> 00:30:22,320 And so if you look at-- for example, 552 00:30:22,320 --> 00:30:29,194 if you look at just a little series, all right-- 553 00:30:29,194 --> 00:30:34,032 if you look at a series there, even the strong acids 554 00:30:34,032 --> 00:30:36,968 have differences. 555 00:30:36,968 --> 00:30:37,769 They're all strong. 556 00:30:37,769 --> 00:30:39,971 They go mostly to completion. 557 00:30:39,971 --> 00:30:42,040 But if you think about it in terms of what we just 558 00:30:42,040 --> 00:30:49,848 talked about, the acid strength is 559 00:30:49,848 --> 00:30:57,622 going to go roughly often opposite trend 560 00:30:57,622 --> 00:30:59,090 as bond strength. 561 00:31:05,263 --> 00:31:13,238 That's of the proton transfer of the H, all right? 562 00:31:13,238 --> 00:31:14,706 There is an H-- 563 00:31:14,706 --> 00:31:17,375 HCl, HBr, HI. 564 00:31:17,375 --> 00:31:22,146 Which will be the strongest acid of those three, right? 565 00:31:22,146 --> 00:31:23,848 Well, we now know. 566 00:31:23,848 --> 00:31:35,126 This must be the strongest, right? 567 00:31:35,126 --> 00:31:39,530 Opposite-- because this is going to be easier 568 00:31:39,530 --> 00:31:41,633 to get the hydrogens off in solution. 569 00:31:44,335 --> 00:31:48,439 And you can think about the weak acids in the same exact way. 570 00:31:48,439 --> 00:31:49,941 These are the strong acids. 571 00:31:49,941 --> 00:31:51,442 This holds for all-- 572 00:31:51,442 --> 00:31:53,244 you know, it's a proton transfer. 573 00:31:53,244 --> 00:31:56,748 It's all about the strength of the proton. 574 00:31:56,748 --> 00:31:59,751 Neutralization is a proton transfer. 575 00:31:59,751 --> 00:32:02,053 Whether you make an acid strong or how strong it is 576 00:32:02,053 --> 00:32:04,322 depends on how many of those protons go into solution. 577 00:32:06,991 --> 00:32:08,793 And so you can look up charts like this. 578 00:32:08,793 --> 00:32:10,295 And I love looking at this stuff, 579 00:32:10,295 --> 00:32:12,764 because it makes you think about the chemistry, all right? 580 00:32:12,764 --> 00:32:13,731 So here you go. 581 00:32:13,731 --> 00:32:19,103 You've got, OK, acid, different acids, molecular formula, 582 00:32:19,103 --> 00:32:21,205 all right, structural formula, conjugate-- 583 00:32:21,205 --> 00:32:24,609 notice they're putting that H there in blue. 584 00:32:24,609 --> 00:32:26,544 Oh, that's so helpful. 585 00:32:26,544 --> 00:32:29,147 And you just look at the blue H, and you think about it 586 00:32:29,147 --> 00:32:32,417 as dissociating, just like Bronsten and Lowry did. 587 00:32:32,417 --> 00:32:34,085 You think about that as coming off. 588 00:32:34,085 --> 00:32:37,622 And then you think about the conjugate base, all right, 589 00:32:37,622 --> 00:32:38,957 that's formed on the other side. 590 00:32:38,957 --> 00:32:40,358 And then you go over here, and you 591 00:32:40,358 --> 00:32:44,996 think, oh, this tells me how much it's coming up, how often. 592 00:32:44,996 --> 00:32:49,300 This tells me the equilibrium of putting this into solution. 593 00:32:49,300 --> 00:32:50,301 You say, this is-- 594 00:32:50,301 --> 00:32:53,538 which one of these is going to be weaker or stronger, 595 00:32:53,538 --> 00:32:55,106 all right? 596 00:32:55,106 --> 00:32:59,544 Well, and what does that mean about the bond strength itself? 597 00:32:59,544 --> 00:33:01,846 What does that mean about how easy it is to dissociate? 598 00:33:01,846 --> 00:33:02,647 We now know. 599 00:33:02,647 --> 00:33:04,983 And we can think about that, and understand that. 600 00:33:04,983 --> 00:33:09,253 These are not-- these may look similar, 601 00:33:09,253 --> 00:33:12,991 these Hs attached to carbon or oxygen. What's the difference? 602 00:33:12,991 --> 00:33:16,294 Big difference when you put them in water. 603 00:33:16,294 --> 00:33:18,596 A lot more or a lot less might come off. 604 00:33:18,596 --> 00:33:21,899 Changing the acid strength-- the more that comes off, 605 00:33:21,899 --> 00:33:27,572 the more the dissociation is to the right, all right? 606 00:33:27,572 --> 00:33:31,042 Oh, and the lower, right, the higher 607 00:33:31,042 --> 00:33:32,810 this number, because the equilibrium moves 608 00:33:32,810 --> 00:33:34,846 over to the right, all right? 609 00:33:34,846 --> 00:33:38,783 And the less that comes off, the lower this equilibrium constant 610 00:33:38,783 --> 00:33:40,885 is, Ka, right-- 611 00:33:40,885 --> 00:33:42,353 the lower it is. 612 00:33:42,353 --> 00:33:43,721 The higher the pK-- 613 00:33:43,721 --> 00:33:46,457 we don't like these small, tiny numbers. 614 00:33:46,457 --> 00:33:49,260 You take a minus log, and you talk about pKs. 615 00:33:49,260 --> 00:33:51,996 That's fine, all right? 616 00:33:51,996 --> 00:33:54,332 OK, good. 617 00:33:54,332 --> 00:33:57,068 This is the kind of fundamental understanding 618 00:33:57,068 --> 00:34:00,104 of acids and bases that I want you guys to have. 619 00:34:00,104 --> 00:34:03,508 And so if we go back to neutralization, 620 00:34:03,508 --> 00:34:06,677 now you say, well, OK, this makes sense, right? 621 00:34:06,677 --> 00:34:08,279 We had a strong acid and a strong base. 622 00:34:08,279 --> 00:34:10,581 If you had them equivalent, you'd get a pH of 7. 623 00:34:10,581 --> 00:34:12,650 Now you know, if you had a strong acid, weak base, 624 00:34:12,650 --> 00:34:15,119 weak acid, strong base, it's going to-- 625 00:34:15,119 --> 00:34:18,422 this is fairly self-explanatory, less than 7 or greater than 7. 626 00:34:18,422 --> 00:34:21,525 And now you know also, if it's a weak acid and a weak base, 627 00:34:21,525 --> 00:34:23,494 and you're neutralizing these together, 628 00:34:23,494 --> 00:34:25,696 it would depend on the Ka and Kb. 629 00:34:25,696 --> 00:34:28,599 Because it depends on how many of those ions 630 00:34:28,599 --> 00:34:31,101 you put in solution or can take out. 631 00:34:31,101 --> 00:34:35,039 And that's given by the Ka and Kb, OK? 632 00:34:35,039 --> 00:34:35,840 Good. 633 00:34:35,840 --> 00:34:36,706 Good. 634 00:34:36,706 --> 00:34:39,377 So we could answer questions-- we're now 635 00:34:39,377 --> 00:34:40,844 armed to answer questions. 636 00:34:40,844 --> 00:34:42,914 And like I said, I want to answer-- 637 00:34:42,914 --> 00:34:44,782 we're going to do some problems on Wednesday. 638 00:34:44,782 --> 00:34:47,217 We'll talk about the topics that are going to be on exam 3. 639 00:34:49,754 --> 00:34:51,355 But we can answer questions like this. 640 00:34:51,355 --> 00:34:53,424 Here we are talking about acids and bases. 641 00:34:53,424 --> 00:34:56,860 What if I mix a bunch of them together, 642 00:34:56,860 --> 00:34:58,162 and they've got different Ka's? 643 00:34:58,162 --> 00:35:02,033 So think about this, what if I mix all of these together? 644 00:35:02,033 --> 00:35:04,969 Can I get my pH, right? 645 00:35:04,969 --> 00:35:05,870 So here's a question. 646 00:35:05,870 --> 00:35:10,241 You have 1 mole per liter of HCN with that acid 647 00:35:10,241 --> 00:35:13,478 dissociation constant and 5 moles per liter of HNO2 648 00:35:13,478 --> 00:35:14,645 with that one. 649 00:35:14,645 --> 00:35:18,049 What's-- OK, you write that dissociation reactions 650 00:35:18,049 --> 00:35:19,684 and calculate the pH of the solution. 651 00:35:22,520 --> 00:35:24,288 That's a good question, right? 652 00:35:24,288 --> 00:35:25,189 So let's see. 653 00:35:25,189 --> 00:35:27,191 Now how would I answer it? 654 00:35:27,191 --> 00:35:31,829 Well, oh, Bronsted-Lowry, don't want to erase you, 655 00:35:31,829 --> 00:35:34,165 but I have to. 656 00:35:34,165 --> 00:35:35,299 I have no choice. 657 00:35:38,102 --> 00:35:39,337 So let's answer that question. 658 00:35:41,973 --> 00:35:43,841 The way that we think about this, 659 00:35:43,841 --> 00:35:45,576 it's telling us what to do. 660 00:35:45,576 --> 00:35:48,880 Write the dissociation reactions for each species. 661 00:35:48,880 --> 00:35:50,515 OK, so I'm going to write it down. 662 00:35:50,515 --> 00:35:51,482 So I have HCN. 663 00:35:51,482 --> 00:36:01,826 HCN, right, is going to go to H+ plus CN-. 664 00:36:01,826 --> 00:36:06,430 Now Ka, for this, is equal to H+-- 665 00:36:06,430 --> 00:36:09,567 oh boy, did I drop my subscripts-- times 666 00:36:09,567 --> 00:36:18,609 CN- divided by HCN concentrations. 667 00:36:18,609 --> 00:36:22,146 But we're back to solubility product days, right? 668 00:36:22,146 --> 00:36:24,081 This is an equilibrium. 669 00:36:24,081 --> 00:36:26,217 And so it's going both ways. 670 00:36:26,217 --> 00:36:29,287 But you know from the coefficients here-- 671 00:36:29,287 --> 00:36:31,389 all right, you know from those coefficients 672 00:36:31,389 --> 00:36:35,760 that if I dissociate x amount of this, then that's how much 673 00:36:35,760 --> 00:36:40,198 of this and this that I make, all right? 674 00:36:40,198 --> 00:36:43,234 So now I know, right, that-- 675 00:36:43,234 --> 00:36:47,038 well, OK-- Ka times-- 676 00:36:47,038 --> 00:36:48,439 if I just bring this over there-- 677 00:36:48,439 --> 00:36:54,045 HCN is equal to x squared, where x-- 678 00:36:54,045 --> 00:36:57,548 let's let x equal concentration of H+, 679 00:36:57,548 --> 00:37:00,952 which equals the concentration of CN-. 680 00:37:00,952 --> 00:37:05,723 Been there, done that, right, from the solubility product 681 00:37:05,723 --> 00:37:08,226 problems that we've done. 682 00:37:08,226 --> 00:37:12,830 And so you can get, from this, that the concentration of H+, 683 00:37:12,830 --> 00:37:21,806 which is also H3O+, is equal to 2.5 times 10 to the minus 5 684 00:37:21,806 --> 00:37:23,107 moles per liter. 685 00:37:23,107 --> 00:37:23,841 Good. 686 00:37:23,841 --> 00:37:24,342 OK. 687 00:37:24,342 --> 00:37:26,310 But you can keep going. 688 00:37:26,310 --> 00:37:31,949 And I'm not going to do all the math. 689 00:37:31,949 --> 00:37:39,023 But you could go through the same exercise with HNO2. 690 00:37:39,023 --> 00:37:44,462 So for HNO2, you get that the concentration 691 00:37:44,462 --> 00:37:47,498 of these ions that you get from that dissociation 692 00:37:47,498 --> 00:37:53,804 is around 2 times 10 to the minus 3 moles per liter. 693 00:37:53,804 --> 00:37:58,709 And by the way, maybe I got less than 10 694 00:37:58,709 --> 00:38:02,013 to the minus seventh out of these things-- 695 00:38:02,013 --> 00:38:02,813 maybe. 696 00:38:02,813 --> 00:38:07,585 Maybe if I did, then, if I did, then I'd 697 00:38:07,585 --> 00:38:12,156 also need to take into account pure water, right? 698 00:38:12,156 --> 00:38:18,863 So from pure water, we know, if you just had water by itself, 699 00:38:18,863 --> 00:38:21,399 then you'd have, the concentration 700 00:38:21,399 --> 00:38:28,773 here is 10 to the minus seventh moles per liter. 701 00:38:28,773 --> 00:38:30,574 But now you just look at this, and you say, 702 00:38:30,574 --> 00:38:31,475 OK, I got my answer. 703 00:38:31,475 --> 00:38:36,047 Because everything's a lot lower than this one thing. 704 00:38:36,047 --> 00:38:38,482 So this is going to dominate. 705 00:38:38,482 --> 00:38:39,417 I mix it all together. 706 00:38:39,417 --> 00:38:41,152 But you see, it doesn't matter. 707 00:38:41,152 --> 00:38:45,756 The other things aren't able to disassociate nearly as many H+ 708 00:38:45,756 --> 00:38:46,324 ions-- 709 00:38:46,324 --> 00:38:47,458 they're just not able to-- 710 00:38:47,458 --> 00:38:50,294 as HNO2. 711 00:38:50,294 --> 00:38:52,129 So this dominates. 712 00:38:52,129 --> 00:38:53,964 And you can just calculate the pH from this. 713 00:38:53,964 --> 00:38:56,400 So you're going to get, like, two, three digits down 714 00:38:56,400 --> 00:38:56,967 some effect. 715 00:38:56,967 --> 00:38:58,836 But it's OK, right? 716 00:38:58,836 --> 00:39:00,871 From this, you can get the pH. 717 00:39:00,871 --> 00:39:10,648 And the pH is equal to 1.35. 718 00:39:10,648 --> 00:39:15,052 The total contribution of H+ ions in that solution is 719 00:39:15,052 --> 00:39:19,690 roughly given by this contribution here, OK? 720 00:39:19,690 --> 00:39:23,260 Might not have been, but it was in that case. 721 00:39:23,260 --> 00:39:25,930 OK, how about this one? 722 00:39:25,930 --> 00:39:31,302 So here's another-- OK, so we could take another example. 723 00:39:31,302 --> 00:39:34,605 Let's stay over here. 724 00:39:34,605 --> 00:39:38,042 OK, so in this example, I'm barely giving you 725 00:39:38,042 --> 00:39:40,077 anything here, it seems like. 726 00:39:40,077 --> 00:39:41,946 But I give you enough. 727 00:39:41,946 --> 00:39:45,816 I've got a 0.2 moles per liter solution of a weak acid. 728 00:39:45,816 --> 00:39:48,986 And it's 9.4% dissociated. 729 00:39:48,986 --> 00:39:51,522 That's the key. 730 00:39:51,522 --> 00:39:52,123 That's the key. 731 00:39:52,123 --> 00:39:55,393 Because remember, this is-- now we've learned 732 00:39:55,393 --> 00:39:56,627 the Bronsted-Lowry definition. 733 00:39:56,627 --> 00:40:01,399 It's all about H+ in or coming out. 734 00:40:01,399 --> 00:40:03,868 That's what-- there it is. 735 00:40:03,868 --> 00:40:06,804 Now I erase it though. 736 00:40:06,804 --> 00:40:07,938 It's all about the H+. 737 00:40:07,938 --> 00:40:13,177 So if I know 9.4% dissociated, I know something 738 00:40:13,177 --> 00:40:16,881 about what kind of acid that is, right? 739 00:40:16,881 --> 00:40:25,423 So if I have, now, HA plus H2O, and that goes to H3O+-- 740 00:40:25,423 --> 00:40:32,863 I've switched back-- plus A-, then how much dissociated? 741 00:40:32,863 --> 00:40:38,536 Well, 0.2 moles per liter times 0.094, right? 742 00:40:38,536 --> 00:40:43,374 So 0.094, that's the percent-- 743 00:40:43,374 --> 00:40:43,941 is that right? 744 00:40:43,941 --> 00:40:49,647 Yes, 9.4%-- times 0.2 moles per liter. 745 00:40:49,647 --> 00:40:57,788 And that equals 0.019-ish, right? 746 00:40:57,788 --> 00:41:00,724 That's how much HA-- 747 00:41:00,724 --> 00:41:03,594 HA-- dissociated. 748 00:41:07,665 --> 00:41:09,767 But if I know that, and I know my reaction, 749 00:41:09,767 --> 00:41:12,837 and I got the stoichiometric coefficients from the reaction, 750 00:41:12,837 --> 00:41:18,342 then I also know how much H3O+ and A- formed. 751 00:41:18,342 --> 00:41:24,081 If that much dissociated, then that much formed, right? 752 00:41:24,081 --> 00:41:25,483 Because they're-- right? 753 00:41:25,483 --> 00:41:26,417 That's the reaction. 754 00:41:26,417 --> 00:41:27,985 Those are the coefficients. 755 00:41:27,985 --> 00:41:29,386 And so I can get it all. 756 00:41:29,386 --> 00:41:35,359 And I can calculate Ka, which equals 2 times 10 to the minus 757 00:41:35,359 --> 00:41:37,828 third. 758 00:41:37,828 --> 00:41:39,630 I didn't give the pH. 759 00:41:39,630 --> 00:41:42,766 All I gave you was how much of it dissociated. 760 00:41:42,766 --> 00:41:44,435 I didn't even tell you what acid it was. 761 00:41:44,435 --> 00:41:49,440 But that's OK, because we now know that this is what counts. 762 00:41:49,440 --> 00:41:53,577 This dissociation, how many of these Hs per liter, 763 00:41:53,577 --> 00:41:57,147 how many of those go into solution is what matters. 764 00:41:57,147 --> 00:41:59,717 OK, now there's another thing that I want to talk about. 765 00:41:59,717 --> 00:42:00,885 And we'll do some more-- 766 00:42:00,885 --> 00:42:03,187 you know, a little bit more, like I 767 00:42:03,187 --> 00:42:05,189 said, problems on Wednesday. 768 00:42:05,189 --> 00:42:07,525 There's just one more thing I want you to know about 769 00:42:07,525 --> 00:42:09,860 related to acids and bases, and that 770 00:42:09,860 --> 00:42:13,898 is that you can have more than one. 771 00:42:13,898 --> 00:42:17,501 All these examples, if you go back to this list, 772 00:42:17,501 --> 00:42:22,406 those all had one hydrogen that was ever going to leave, 773 00:42:22,406 --> 00:42:23,207 let's say. 774 00:42:23,207 --> 00:42:24,975 I mean, OK, ever-- maybe if you went up 775 00:42:24,975 --> 00:42:27,278 to the middle of the sun or something, you'd get those. 776 00:42:27,278 --> 00:42:29,446 But this is-- you know, in normal conditions, 777 00:42:29,446 --> 00:42:31,782 these are the ones that are going to leave, and no more. 778 00:42:31,782 --> 00:42:36,020 But you can have molecules like phosphoric acid where-- 779 00:42:36,020 --> 00:42:38,055 look at all those protons. 780 00:42:38,055 --> 00:42:39,890 So here's acetic acid. 781 00:42:39,890 --> 00:42:41,525 That's the one that's willing to leave. 782 00:42:41,525 --> 00:42:42,126 Those are not. 783 00:42:42,126 --> 00:42:43,327 They're on the carbon. 784 00:42:43,327 --> 00:42:44,728 Way too hard to get them off. 785 00:42:44,728 --> 00:42:48,666 This one-- OK, in solution, sure, to a certain extent. 786 00:42:48,666 --> 00:42:52,703 In phosphoric acid, I've got three hydrogens. 787 00:42:52,703 --> 00:42:55,472 And so that's called a multiprotic acid. 788 00:42:55,472 --> 00:42:56,106 Why? 789 00:42:56,106 --> 00:42:58,642 Because protic-- proton-- 790 00:42:58,642 --> 00:43:01,812 how many protons, right? 791 00:43:01,812 --> 00:43:05,316 It could be monoprotic, like the ones we've talked about, 792 00:43:05,316 --> 00:43:09,553 or it could be multiprotic, like phosphoric acid. 793 00:43:09,553 --> 00:43:12,222 And so if you think about this the way 794 00:43:12,222 --> 00:43:16,226 we now think about acids and bases, 795 00:43:16,226 --> 00:43:19,597 we think about an acid as a dissociation, right, 796 00:43:19,597 --> 00:43:22,366 with some dissociation equilibrium constant. 797 00:43:25,970 --> 00:43:28,639 And so if you think about phosphoric acid, H3PO4-- 798 00:43:31,375 --> 00:43:35,579 oh, let's put the water in, H2O, liquid. 799 00:43:38,082 --> 00:43:45,789 And that goes to H2PO4- plus H3O+. 800 00:43:45,789 --> 00:43:49,293 Well the Ka for this one is-- 801 00:43:49,293 --> 00:43:52,630 so if I put the Ka's in here, this one 802 00:43:52,630 --> 00:43:58,602 is 7.5 times 10 to the minus 3. 803 00:43:58,602 --> 00:44:01,005 But see, what happens is, now, this one 804 00:44:01,005 --> 00:44:02,973 has two more hydrogens that could come off. 805 00:44:02,973 --> 00:44:05,609 So you could write those dissociation reactions as well. 806 00:44:05,609 --> 00:44:13,651 So H2PO4-, if you put that in solution, which it is, 807 00:44:13,651 --> 00:44:19,690 then that could give you HPO4 2-, all right? 808 00:44:19,690 --> 00:44:24,628 H2, H-- it's a proton transfer. 809 00:44:24,628 --> 00:44:28,298 Minus, 2-, all right-- 810 00:44:28,298 --> 00:44:29,166 plus H3O+. 811 00:44:31,935 --> 00:44:38,142 And there's one more, plus one more. 812 00:44:38,142 --> 00:44:41,545 This dissociation constant is much, much smaller, 813 00:44:41,545 --> 00:44:46,817 6.2 times 10 to the minus 8. 814 00:44:46,817 --> 00:44:54,291 And the third one is 4.2 times 10 to the minus 13th. 815 00:44:54,291 --> 00:44:56,727 So they're smaller, but they happen. 816 00:44:56,727 --> 00:44:58,228 And that's important. 817 00:44:58,228 --> 00:44:59,463 And it can be very important. 818 00:44:59,463 --> 00:45:00,831 It depends on the molecule. 819 00:45:00,831 --> 00:45:04,968 But in this case, it's not just the parent, that acid there 820 00:45:04,968 --> 00:45:05,936 that's losing a proton. 821 00:45:05,936 --> 00:45:09,006 But then, this one can also lose a proton. 822 00:45:09,006 --> 00:45:11,308 It can also be an acid. 823 00:45:11,308 --> 00:45:14,712 It just has an equilibrium that's not as far over. 824 00:45:14,712 --> 00:45:19,883 So it's not going to give as many H+ into solution, OK? 825 00:45:19,883 --> 00:45:21,685 It's important to know about. 826 00:45:21,685 --> 00:45:24,154 Then finally, the last thing I want you to know, 827 00:45:24,154 --> 00:45:27,191 you will not be tested on this, but it's important. 828 00:45:27,191 --> 00:45:29,626 Because here's where we are. 829 00:45:29,626 --> 00:45:30,627 Here's where we are. 830 00:45:30,627 --> 00:45:35,999 Arrhenius said, right before Thanksgiving, 831 00:45:35,999 --> 00:45:39,636 it's all about the H+ and the OH-. 832 00:45:39,636 --> 00:45:43,073 That got us really far, got us through Thanksgiving. 833 00:45:43,073 --> 00:45:45,943 But then today, we're like, no, it's got to be more general. 834 00:45:45,943 --> 00:45:48,812 It's just proton transfer. 835 00:45:48,812 --> 00:45:52,349 No, don't tell me about OH-. 836 00:45:52,349 --> 00:45:54,852 It's just proton transfer. 837 00:45:54,852 --> 00:45:58,122 And so then comes Lewis. 838 00:45:58,122 --> 00:45:59,256 Oh, we know Lewis. 839 00:45:59,256 --> 00:46:00,991 We've already talked a lot about Lewis. 840 00:46:00,991 --> 00:46:05,529 Lewis said, why are you guys all obsessed about protons? 841 00:46:05,529 --> 00:46:09,433 And he said it in just that way. 842 00:46:09,433 --> 00:46:11,869 An acid is much more general even than that. 843 00:46:11,869 --> 00:46:14,905 An acid is any species, anything that 844 00:46:14,905 --> 00:46:16,607 except a pair of electrons. 845 00:46:16,607 --> 00:46:20,177 Remember, Lewis was all about those electrons and the octets. 846 00:46:20,177 --> 00:46:24,848 And a base is any species that can donate a pair of electrons. 847 00:46:24,848 --> 00:46:29,419 So Lewis correctly took a much more general view 848 00:46:29,419 --> 00:46:31,155 and said, no, acids and bases are not 849 00:46:31,155 --> 00:46:32,723 even about proton transfer. 850 00:46:32,723 --> 00:46:36,326 They're about electron transfer. 851 00:46:36,326 --> 00:46:39,062 And again, I'm not going to test you on Lewis, acids, and bases, 852 00:46:39,062 --> 00:46:40,864 but I wanted you to have that full picture. 853 00:46:40,864 --> 00:46:44,134 That means, by the way, aluminum 3+-- 854 00:46:44,134 --> 00:46:46,537 take an aluminum atom, make it 3+. 855 00:46:46,537 --> 00:46:49,540 It wants electrons. 856 00:46:49,540 --> 00:46:51,675 It's an acid. 857 00:46:51,675 --> 00:46:54,645 It's an acid, all right? 858 00:46:54,645 --> 00:46:56,880 Doesn't have a prot-- it wants electrons though. 859 00:46:56,880 --> 00:46:58,982 That makes it an acid according to Lewis. 860 00:46:58,982 --> 00:47:02,986 So that concludes acids and bases. 861 00:47:02,986 --> 00:47:06,056 And I'll see you guys on Wednesday.