WEBVTT 00:00:00.000 --> 00:00:01.400 00:00:01.400 --> 00:00:10.833 Alright, we’re going to start this first Camtasia of Chapter 15, by talking about definitions of acids and bases. Acids and bases are 00:00:10.833 --> 00:00:14.799 things that have been known about for hundreds, if not thousands, of years. Um, 00:00:14.800 --> 00:00:19.833 there were lots of different compounds that people discovered over time that 00:00:19.833 --> 00:00:24.899 they, ah, put in these different classifications. And originally acids 00:00:24.900 --> 00:00:32.433 and bases were just defined based on some of the basic properties that they had. For instance, 00:00:32.433 --> 00:00:41.033 acids were things that would taste sour, OK? Um, they didn’t know what it was that made it taste sour, but they knew that it tasted sour. 00:00:41.033 --> 00:00:50.099 Um, they would react with certain metals, not all metals, but would react with SOME metals to make hydrogen gas, 00:00:50.100 --> 00:00:58.700 which you have seen before. Alright. Um, 00:00:58.700 --> 00:01:06.600 one of the things about, ah, acids, or bases, is that they would react with certain compounds and change their color. And one of the 00:01:06.600 --> 00:01:12.633 first things that was really used as a test was litmus, it’s from a fungus, um, 00:01:12.633 --> 00:01:18.666 but what it would do, an acid would turn litmus to a red color. OK, so 00:01:18.666 --> 00:01:24.299 these were different things that they noticed that all these compounds had in common. Um, bases 00:01:24.300 --> 00:01:33.466 would be things that would taste bitter, OK, they didn’t have a particular reaction with metals that they did, um, but they would 00:01:33.466 --> 00:01:42.632 feel slippery or soapy, turns out that’s a reaction with your skin, um, but it would, feel slippery or soapy, um, when you touched it. 00:01:42.633 --> 00:01:51.599 And they also would change the color of litmus, they would turn litmus, um, into a blue color. OK, so over the years, 00:01:51.600 --> 00:01:59.566 there were MANY, MANY, different compounds, that when they were discovered or tested, um, it would taste sour. OK, and so when they, 00:01:59.566 --> 00:02:02.166 well, they would add it to some of the metal, and …HUH, it might make a 00:02:02.166 --> 00:02:04.799 little bit of hydrogen gas. But it would definitely change the color of the litmus. 00:02:04.800 --> 00:02:11.800 If there’s something that they would, you know, feel that it was kind of soapy or slippery they’d taste it and it tastes bitter, they’d test against 00:02:11.800 --> 00:02:17.433 litmus and it turned litmus blue, and so lots and lots of different compounds that they were able to separate in to 00:02:17.433 --> 00:02:21.899 acids or bases based on these properties, but over the years as they started to 00:02:21.900 --> 00:02:26.400 look at, you know, what was in these different compounds, there didn’t 00:02:26.400 --> 00:02:33.233 seem to be anything really…that stood out. That made something acidic or basic. Um, the one other 00:02:33.233 --> 00:02:43.733 thing about the acids and bases is that if you combine them, um, they would combine to make salt water. Uh, 00:02:43.733 --> 00:02:48.999 so they would make a salt, and water if it was an aqueous solution, um, 00:02:49.000 --> 00:02:54.300 and when you had the salt you really didn’t have your acidic or basic properties anymore; it was no longer 00:02:54.300 --> 00:03:00.100 sour, it was no longer bitter, it didn’t really feel soapy any more, it didn’t react with metals. Um, and so 00:03:00.100 --> 00:03:11.233 essentially, this was neutralization. OK? They essentially cancelled each other out and we got this salt water, OK? So, they were known about 00:03:11.233 --> 00:03:19.166 for … MANY, MANY years, but they didn’t really know WHY they behaved that way, and there were lots and lots of different reasons 00:03:19.166 --> 00:03:25.666 that were thrown out, um, some stuck around more than others. OK? 00:03:25.666 --> 00:03:32.199 One of the first ones that really made...sense, in hind sight, um, was proposed 00:03:32.200 --> 00:03:41.800 by a guy by the name of Arrhenius, um, this is the same guy who had the Arrhenius Equation that you learned for the 00:03:41.800 --> 00:03:50.333 kinetics chapter. Um, and Arrhenius, what he was doing was he was working on his PhD thesis in the 1880’s. 00:03:50.333 --> 00:03:57.966 And, (sigh) he was looking at acids and bases, and one of the things that … again, he was trying to 00:03:57.966 --> 00:04:05.632 figure out what was going on. Um, and so to figure out what was going on, um, he actually was looking at… 00:04:05.633 --> 00:04:11.499 conductivity of solutions. OK? Annnd, it’s been a while since we’ve done conductivity, so we are going to 00:04:11.500 --> 00:04:17.733 look at a couple of videos real quick to remind ourselves of conductivity of solutions. Alriight. 00:04:17.733 --> 00:04:25.766 So... "Well, we’ve gotta demonstrate that, I think is the best thing to do. So, what I have here, 00:04:25.766 --> 00:04:39.866 is ah, just some water, I’ll put that there, and more water. Then I have this awesome testing machine, which is, ah, lethal in the wrong hands, 00:04:39.866 --> 00:04:46.066 I’ll plug this in here, and there is a light bulb on the bottom as you can see, which will be 00:04:46.066 --> 00:04:51.032 on the top in a minute, and there’s a couple of electrodes sticking out the top. But if something connects the electrodes the light bulb 00:04:51.033 --> 00:04:56.033 lights, OK? So obviously a piece of metal conducts electricity very well, the electrons fly through it and the 00:04:56.033 --> 00:05:01.166 light bulb lights up. Now, how about water? Is that an electrical conductor? Oh, … 00:05:01.166 --> 00:05:07.132 some people,….no, it’s not distilled (inaudible) with that, aaaaah, some people say yes, some people 00:05:07.133 --> 00:05:14.466 say no. Whadya think? Welll, not enough to light up the light bulb. 00:05:14.466 --> 00:05:21.832 But if I was having a bath in there, and somebody threw this in I’d be dead.OK? There is enough 00:05:21.833 --> 00:05:29.299 electrical current passing through there to zap a person but not enough to light up a 20-watt light bulb or whatever this is, so, not a whole lotta 00:05:29.300 --> 00:05:36.533 current travels through. In a light bulb like this, you might have an ampere of current, to light it up nice and bright. In the bath tub it 00:05:36.533 --> 00:05:41.666 only takes milliamps to go through your body to kill you. OK, so, distilled water or 00:05:41.666 --> 00:05:46.832 just plain tap water, not much conductivity. Now, what is it that carries charge? 00:05:46.833 --> 00:05:50.699 In the case of, of, this thing it’s electrons being transferred through the 00:05:50.700 --> 00:05:54.600 spatula, and the electrons are mobile in the metal so they are what carry charge. 00:05:54.600 --> 00:06:04.433 But what if we have something in solution-like some sodium chloride, common table salt, safety sealed. 00:06:04.433 --> 00:06:17.499 So let’s put some salt in here. Stir it up a little bit, now this is dissolving, and my claim is that this is turning into ions, but, ah, the only way we could 00:06:17.500 --> 00:06:25.666 know that there are ions in there would be to show that the solution has some electrical conductivity. And you can see that, of course it, 00:06:25.666 --> 00:06:32.799 does. So, what’s happening here? It’s the ions now in the solution that are carrying the charge. Positive and negative charges; positive 00:06:32.800 --> 00:06:38.766 sodium ions, negative chloride ions, those are the things that are carrying the charge from one electrode to the other and completing the 00:06:38.766 --> 00:06:45.732 circuit. In ordinary water there are not sufficient number of ions – there are some ions but not a sufficient number to, ah, to 00:06:45.733 --> 00:06:54.199 see that, ah, enough current would be, um, carried to light up this thing. Light up this bulb. Now, does it mean that when we dissolve 00:06:54.200 --> 00:07:01.066 something it necessarily conducts electricity? Well, here’s some sugar. So I’ll throw some sugar in, 00:07:01.066 --> 00:07:09.099 stir that around. You know that sugar is fairly soluble in water. I put about the same amount of sugar in there 00:07:09.100 --> 00:07:15.900 that I had, ah, sodium chloride in the other one. So let’s see what happens. Zippo! So just 00:07:15.900 --> 00:07:22.100 because something dissolves in water does not mean that it has separated into ions. The sodium chloride does, 00:07:22.100 --> 00:07:28.066 the sugar doesn’t but yet it’s still soluble so there’s two different things going on in there. This part of the way 00:07:28.066 --> 00:07:35.699 tells how you can really kill someone, you throw sodium chloride in the water first and then throw the toaster in bath tub. 00:07:35.700 --> 00:07:39.133 One of my favorite shows is called, “Mythbusters,” I just, I laugh my head off when they do 00:07:39.133 --> 00:07:42.599 things, and they, they demonstrated this, and they threw sodium chloride in 00:07:42.600 --> 00:07:48.566 and threw their dummy in and yes, he got electrocuted more than if there was no sodium chloride in. Somebody have a question? 00:07:48.566 --> 00:07:59.666 (student in background) Well, your body has salt on it, that’s true just not enough. If you put more in you get more conductivity and … 00:07:59.666 --> 00:08:06.099 the guy’s even deader.” Alright. So that pretty much just demonstrates the idea of conductivity. 00:08:06.100 --> 00:08:11.000 And as he said when we have ions present in solution, then, um, the 00:08:11.000 --> 00:08:16.266 light bulb lights up. When there weren’t ions present in solution, like with the, um, 00:08:16.266 --> 00:08:21.566 the, ah, sugar, then there was no conductivity. Now, he just 00:08:21.566 --> 00:08:30.932 did salt and sugar, we’re gonna look at a couple of other solutions, I think, if it goes, there we go. There we go. Um, so 00:08:30.933 --> 00:08:38.166 this has a variety of different things. Same type of idea, he has a probe 00:08:38.166 --> 00:08:45.399 (TAP WATER), little bit of lighting up, you can actually see that one, you couldn’t see it on the other one. 00:08:45.400 --> 00:08:58.000 (DISTILLED WATER, huh, what? SALT WATER, one teaspoon per cup.) Nice and bright. 00:08:58.000 --> 00:09:05.433 (HYDROCHLORIC ACID), HCl here, nice and bright. 00:09:05.433 --> 00:09:12.866 (SODIUM HYDROXIDE, just as concentrated) Nice and bright. (SUGAR WATER), here’s our sugar again. 00:09:12.866 --> 00:09:26.032 (SWEET), Vinegar (VINEGAR, a weak acid), lights up, not quite as much as the HCl did before. (ETHANOL, a dissociative 00:09:26.033 --> 00:09:44.633 that doesn’t associate – don’t try this at home, BARIUM SULFATE, it’s insoluble. Nooo conductivity here!) Alright, 00:09:44.633 --> 00:09:56.999 dorky looking guy. Alright, um, so, the point there, though was that um, some solutions conduct, some don’t. And, what was 00:09:57.000 --> 00:10:01.833 known about a lot of the acids at the time was that they had formulas of molecular compounds. 00:10:01.833 --> 00:10:06.666 So we have things like, ah, HCl, where it’s known that hydrogen bonds 00:10:06.666 --> 00:10:17.332 to chlorine. Um, and that we have things like acidic acid – CH3COOH, ok? So, a lot of the 00:10:17.333 --> 00:10:23.666 acids were known to be, um, molecular compounds. OK? 00:10:23.666 --> 00:10:29.466 And it was assumed that if you have molecular compounds, something like sugar, um, that when you put it in, 00:10:29.466 --> 00:10:35.266 water, it is not going to split up into ions, ‘cause it is a molecule. If you have salt, something 00:10:35.266 --> 00:10:44.532 like Sodium Chloride, and you put it into sugar, OK? Um, you’re going to get your individual ions. OK? Because it 00:10:44.533 --> 00:10:51.999 is ionic. Now, this was the excepted reasoning. What Arrhenius said, though, was he said, “You know what? When I put acids in water, whether 00:10:52.000 --> 00:11:00.166 it’s a strong acid or a weak acid, I get things lighting up.” And so, what he said was that even though acids are molecular compounds, 00:11:00.166 --> 00:11:12.466 they can ionize. OK? Um, helps if I spell it right. They can ionize. They can create ions in solution. And so what that 00:11:12.466 --> 00:11:17.632 means is that something has to come off, and what he figured out was, 00:11:17.633 --> 00:11:22.799 well, all of them have some hydrogen floating around that is able to fall off. 00:11:22.800 --> 00:11:34.133 And so Arrhenius said that acids are things which increase the concentration of H plus in solution, bases are 00:11:34.133 --> 00:11:42.766 things which increase the concentration of hydroxides in solution. OK? Now, this was a very bold statement 00:11:42.766 --> 00:11:52.832 back in the 1880’s, when he made it. Um, his PhD committee, um, that you present your research to, that say “yay or nay,” 00:11:52.833 --> 00:11:57.733 um, did not agree with it, he almost failed. If he had we probably 00:11:57.733 --> 00:12:02.633 wouldn’t have had our Arrhenius Equation. (laughs so inaudible word) named after him. 00:12:02.633 --> 00:12:10.966 It was only through some political maneuvering that he was able to pass, um, and it turns out he was right. OK, acids are things that 00:12:10.966 --> 00:12:17.666 increase the concentration of H plus, bases are things that increase the concentration of hydroxide, um, but this was a very radical 00:12:17.666 --> 00:12:23.566 idea at the time, Ok? Now one of the things we talk about acids and bases, um, lot of times we are dealing with water. 00:12:23.566 --> 00:12:33.666 So, when we have an H plus in water, OK, we have a bare proton, floating around in water, and water has all 00:12:33.666 --> 00:12:40.632 those lone pair electrons on the oxygen, OK? And so what is going to happen is that, in water, they are 00:12:40.633 --> 00:12:46.933 going to make, um, a coordinate covalent bond, and they are going to make 00:12:46.933 --> 00:12:53.266 H3O plus, which is our hydronium ion, OK? So technically, when we are dealing 00:12:53.266 --> 00:12:59.366 with acids in aqueous solution-which is where we see them most of the time-um, what we get is not 00:12:59.366 --> 00:13:06.132 an increase in the concentration of H plus, what we get is an increase in the concentration of hydronium ion. OK? Um, 00:13:06.133 --> 00:13:15.999 but, ah, just some terminology to be aware of, OK, because sometimes we’ll write our acids as H plus, sometimes we’ll write them as 00:13:16.000 --> 00:13:25.433 H3O plus. Sometimes we will call them a proton, because H plus is just a bare proton floating around, or a hydrogen 00:13:25.433 --> 00:13:29.666 ion, not as often but we could, sometimes we’ll call it hydronium. 00:13:29.666 --> 00:13:33.932 So the terms are used interchangeably, sometimes you’ll see H plus people call hydronium, 00:13:33.933 --> 00:13:43.133 sometimes you’ll see H3O plus people call it protons, they use the terms and, um, symbols interchangeably. OK. But that is 00:13:43.133 --> 00:13:51.866 our acid; we increase the H plus in solution, our base increase is hydroxide, according to Arrhenius. OK? This is a 00:13:51.866 --> 00:13:55.699 really, really great definition of acid-base. It’s what we usually 00:13:55.700 --> 00:13:59.566 use to start out when we’re teaching it, um, but there are a couple of problems. 00:13:59.566 --> 00:14:14.232 OK? First of all, you have to be in water. If you’re not in water, it doesn’t really work very well. OK. The second one is you have to 00:14:14.233 --> 00:14:22.799 have both H plus and hydroxide, when you’re not in water you’ve often don’t have hydroxide, OK? 00:14:22.800 --> 00:14:38.066 Um, and so there are some things that we … um, describe as acids and bases which um, …may or may not work, OK, using Arrhenius’s 00:14:38.066 --> 00:14:45.699 definition. So to illustrate that, quickie little video here, um, what we have is a flask that 00:14:45.700 --> 00:14:53.333 has ammonium, and then, ah, a Q-tip that has some HCl, OK? Now, 00:14:53.333 --> 00:15:05.399 HCl we know is an acid, ammonia we know is a base, OK? Um, we kind of put the two right by each other and we are getting ammonium 00:15:05.400 --> 00:15:17.533 chloride, which is a salt, so we’re even doing a neutralization. Um, but if we think about the reaction between, um, 00:15:17.533 --> 00:15:36.233 HCl gas and NH3 gas, what we wind up getting is NH4Cl solid. 00:15:36.233 --> 00:15:40.599 No H plus floating around in solution to increase its concentration, definitely no 00:15:40.600 --> 00:15:45.000 hydroxide floating around in solution to increase its concentration. So even though we have something 00:15:45.000 --> 00:15:54.200 that we know is an acid and something that we know is a base, and they’re coming together to make salt, a neutralization like we said acids and 00:15:54.200 --> 00:16:02.033 bases do, um, according to the Arrhenius definition, um, we can’t classify this as an acid-base reaction. OK? So there had to be 00:16:02.033 --> 00:16:14.899 other ways of describing it. Um, the next best way of describing it was proposed in 1923 by a pair of guys, one named 00:16:14.900 --> 00:16:21.133 Bronsted, the other named Lowry; um, they were not working together, they published their definitions 00:16:21.133 --> 00:16:27.766 within a couple months of each other, and so this has just become the Bronsted-Lowry definition. And so what these two guys did, 00:16:27.766 --> 00:16:36.899 was they said, “Well, you know what? We don’t want to use both H plus AND hydroxide, um, so we’re just going to focus 00:16:36.900 --> 00:16:45.700 on the H plus.” OK? And so what they did was they looked at the reaction, if I have an acid and a base, OK, they come together 00:16:45.700 --> 00:16:53.966 and make water. And so, they said, “OK, we’re gonna say that our H pluses are acid, what is the base doing 00:16:53.966 --> 00:17:01.832 in relation to the H plus?” And they figured out that what it’s doing is it is picking up an H plus, OK? And so they said 00:17:01.833 --> 00:17:16.866 that an acid is something that donates a proton and base is therefore something that accepts the proton. OK. Um, 00:17:16.866 --> 00:17:23.199 all of the previous definitions of acid and base that Arrhenius gave still worked. 00:17:23.200 --> 00:17:29.533 OK, so if you think about it, ah, if we have HCl, OK, and we put it in water, 00:17:29.533 --> 00:17:40.366 OK, HCl we said is an acid. OK? It’s going to make hydronium ion and chloride ion, OK? And so HCl still 00:17:40.366 --> 00:17:48.399 functions as an acid. It is donating a proton, what it’s donating it to here in this case is water, and so water is going to function as a base. 00:17:48.400 --> 00:18:00.366 Um, something like ammonia, OK? Um, when we put it in water, we get ammonium ion and hydroxide, OK? 00:18:00.366 --> 00:18:05.932 It’s the hydroxide here that, um, allowed Arrhenius to call it a 00:18:05.933 --> 00:18:11.499 base-ammonia base. Um, in this case though, for the Bronsted-Lowry, what is 00:18:11.500 --> 00:18:21.333 happening is it is picking up a proton from the water. OK? That’s what gives us our NH4 plus and what we have left over is 00:18:21.333 --> 00:18:26.066 the hydroxide, OK, so things that were acids according to the Arrhenius 00:18:26.066 --> 00:18:30.799 definition are still acids, things that were bases according to the Arrhenius definition, 00:18:30.800 --> 00:18:39.233 um, are still bases, the one thing that is different now though, is that I can do something like my gas phase reaction, OK? I can have 00:18:39.233 --> 00:18:55.899 HCl and NH3, OK? And they can still function as an acid and a base. So the HCl donates, so it is an acid, um, the NH3 accepts, so it is a 00:18:55.900 --> 00:19:03.366 base, OK? And I make my NH4 plus ion and my chloride ion, which come together 00:19:03.366 --> 00:19:10.866 to make the ammonium chloride salt. OK? So. It was a much more, ah, 00:19:10.866 --> 00:19:18.666 generic definition. Um, it applied to things that didn’t have hydroxides floating around in solution, and it also 00:19:18.666 --> 00:19:23.132 got rid of, um, the need for water. So we have gas phase 00:19:23.133 --> 00:19:27.599 things now, this definition works really, really good in organic solvents where we don’t have any 00:19:27.600 --> 00:19:35.566 water present. And so, it’s a much more generic definition of acid-base than the Arrhenius was. OK? We have 00:19:35.566 --> 00:19:46.666 couple of results from this, though. Um, one of the things is we have some species that can act as an acid or base. Here with the water, 00:19:46.666 --> 00:19:49.832 um, when the water was combined with the HCl it functioned as a base. When the 00:19:49.833 --> 00:19:52.999 water was combined with the ammonia it functioned as an acid. OK? 00:19:53.000 --> 00:20:05.233 That is what is known as an amphoteric species. OK? It is something that 00:20:05.233 --> 00:20:16.799 can act as an acid or a base, depending on what is put in it. OK? 00:20:16.800 --> 00:20:30.333 So the best example of that is our water, OK? Other things are polyprotic acids, that have lost 00:20:30.333 --> 00:20:48.466 at least one but not all, of their protons, OK? So for example, if I have 00:20:48.466 --> 00:20:57.666 bicarbonate, HCO3 minus, OK? It lost one, but it hasn’t lost both, OK? So what it can do 00:20:57.666 --> 00:21:09.799 is it can pick up that proton, so it can accept a proton to make H2CO3. If it accepts a proton um, then it is acting 00:21:09.800 --> 00:21:25.433 as a base. OK? But it also has this H plus here, that it can get rid of – so it can donate a proton and act as an acid to make CO3 with a negative 00:21:25.433 --> 00:21:31.933 2 charge. OK. So. Amphoteric species. Water is one of the great examples, but also these polyprotic acids that 00:21:31.933 --> 00:21:38.866 have lost AT LEAST ONE, so it can get it back and act as a base, BUT NOT ALL, so it can lose more and act as an acid 00:21:38.866 --> 00:21:52.599 um, of the protons. OK? That is one result. Another result of, um, our, ah, Bronsted-Lowry definition, is that 00:21:52.600 --> 00:22:07.066 we have are called conjugate acid-base pairs. OK? Um, one of the 00:22:07.066 --> 00:22:15.866 things that maybe you noticed when we were looking at the definitions, um, I have an acid and a base; OK? I have an acid and a base, alright? 00:22:15.866 --> 00:22:24.066 Um, every time that we have a reaction, we always have a reaction between an acid and an a base, ‘cause something has to donate, 00:22:24.066 --> 00:22:33.332 something has to accept. OK? The other thing, though, about our acid-base reactions we figured out in the last chapter, a lot of 00:22:33.333 --> 00:22:41.433 our reactions are technically reversible, OK? Um, sometimes the reverse reaction isn’t very favorable, but our reactions 00:22:41.433 --> 00:22:46.933 are reversible. OK? And so, um, 00:22:46.933 --> 00:23:01.999 we start out with an acid-base, and if we’re gonna reverse our reaction, then the proton is going 00:23:02.000 --> 00:23:18.366 BACK, and so our products are also an acid and a base. Alright? So, if we 00:23:18.366 --> 00:23:31.466 look at one of these reactions, OK, if we look at, say the, um, ammonia reacting with the water, OK? Um, we said that we 00:23:31.466 --> 00:23:43.166 made ammonium ion and we made hydroxide, OK? Um, actually I’m gonna do this on the next page. Alright, so, um, our 00:23:43.166 --> 00:23:55.632 ammonia and our water going to make ammonium ion and hydroxide. So we said, in the forward reaction, what happened was that 00:23:55.633 --> 00:24:07.499 the water donated a proton to the, um, ammonia, and so the water donates it acts as an acid; the ammonia accepts 00:24:07.500 --> 00:24:16.633 so it acts as a base. OK? However, if I’m going to do the reverse reaction, OK, I have to 00:24:16.633 --> 00:24:24.599 give that proton back, so now NH4 plus is donating a proton, so IT acts as an acid; 00:24:24.600 --> 00:24:29.766 the hydroxide accepts, so it acts as a base, alright? So, on the 00:24:29.766 --> 00:24:34.932 reactant side we have an acid and a base, on the products side we have an acid and a base. 00:24:34.933 --> 00:24:48.299 OK? If I pair up my base on my reactive side with my acid on the product side, um, I have NH3 and NH4 00:24:48.300 --> 00:25:00.833 plus, OK? One is a base, one is an acid, the only difference between the two is an H plus. OK? If I look at the other pair, I have a water 00:25:00.833 --> 00:25:13.633 that’s an acid, I have a hydroxide that is a base. OK? Again, one is a reactant, one is a product, one is an acid, one is a base, um, and again if I 00:25:13.633 --> 00:25:22.899 look at the two, the only difference is that there’s just that one H plus that’s going back and forth, OK? And so these are my conjugate 00:25:22.900 --> 00:25:34.433 acid-base pairs that I get from the Bronsted- Lowry definition: one of them is the NH3 00:25:34.433 --> 00:25:41.899 -NH4 plus, the other pair is the water and the hydroxide. And so one of the things that we get from the Bronsted-Lowry definition 00:25:41.900 --> 00:25:53.266 is we get these conjugate acid-base pairs in all of our reactions. OK? So, as example, gonna put a couple of these in here, 00:25:53.266 --> 00:26:02.366 what I want you to do is identify what are the conjugate acid-base pairs in these two reactions. So which one is the acid, 00:26:02.366 --> 00:26:11.032 which one is the base? (Sound effect) oops, if I write it right…HCO3 minus…which one is the acid, which one is the base, on 00:26:11.033 --> 00:26:22.633 each side, and what is the acid-base pairs? OK? So, take 00:26:22.633 --> 00:26:37.966 a couple minutes here, and do that, and when you’re done, start it back up and we’ll go over it. (Sigh) Alright. 00:26:37.966 --> 00:26:43.832 So, the first one: carbonate and water make bicarbonate and hydroxide, OK? 00:26:43.833 --> 00:26:49.733 It helps to pick one of the compounds, um, and then look and see how it changes on the other side. 00:26:49.733 --> 00:26:56.733 So if I start out with CO3 here, OK, I have CO3; the other side the thing that has carbon 00:26:56.733 --> 00:27:05.266 is HCO3. So what I do, this starts out without hydrogen, it gets hydrogen, so that means we must be accepting, 00:27:05.266 --> 00:27:17.366 ‘cause it picked something up, so that means it acts as a base and my water acts as an acid because it is giving it up. OK? On the other 00:27:17.366 --> 00:27:25.566 side, um, what I have, ah, here I have the hydrogen, I need to get rid of it to 00:27:25.566 --> 00:27:33.332 go back to the other side. So I need to give this one up. So I’m donating, and so this is my acid; 00:27:33.333 --> 00:27:40.299 hydroxide, maybe obviously, is going to be my base, OK? Um, so one pair 00:27:40.300 --> 00:27:53.466 is carbonate and bicarbonate, the other pair is again water and hydroxide, OK? Alright, second reaction. 00:27:53.466 --> 00:27:59.232 I have acetate and nitrous acid. Um, going to make acetic 00:27:59.233 --> 00:28:10.033 acid and nitrite. OK? So again, I’m gonna look and see which things are similar; I have C2H3O2 HC2H3O2, so that is going to be one of my pairs. 00:28:10.033 --> 00:28:14.766 Don't know which one is the acid or the base yet, but they only 00:28:14.766 --> 00:28:19.532 differ by a proton, so I know that that is one of my pairs, and then the other one that 00:28:19.533 --> 00:28:28.733 has nitrogen is going to be my other pair. OK, so those are my pairs, which one is the acid, which one is the base? This one starts out without a 00:28:28.733 --> 00:28:36.966 hydrogen, winds up with a hydrogen, so this one is accepting so it’s my base. My nitrous acid is my acid, it is donating. 00:28:36.966 --> 00:28:42.399 On the reverse side, um, that needs to lose this hydrogen, so this is 00:28:42.400 --> 00:28:47.833 the acid, the nitrite is going to be my base because it’s going to pick up that hydrogen. 00:28:47.833 --> 00:29:00.866 OK? So this is my Bronsted-Lowry definition of an acid and a base. OK? And again, more generic, it covers a LOT more situations, OK. 00:29:00.866 --> 00:29:13.032 I have one more definition of an acid and a base, OK, and that is the Lewis acid and base definition. OK? 00:29:13.033 --> 00:29:29.933 Now, this one is going to be the most generic. OK? And it rises in situations where we need to get rid of the hydrogen as well. 00:29:29.933 --> 00:29:37.999 Alright, (sigh) an example of this. Um, if I have a metal oxide, OK, sodium oxide; 00:29:38.000 --> 00:29:51.033 metal oxides are known to be basic. OK. Um, non-metal oxides, like SO3 here, are acidic, OK. 00:29:51.033 --> 00:29:59.733 where we get things like our acid rain, we have nitrous oxides and sulfur oxides, um, these are acidic oxides, OK. 00:29:59.733 --> 00:30:06.866 So I have something that I know is a basic oxide, if I put it in water I get a base. Something that I know is an acidic oxide, if I 00:30:06.866 --> 00:30:19.299 put it in water I get an acid. If I take these two and add them together, what I get is, I get 00:30:19.300 --> 00:30:28.366 sodium sulfate, which is neutral. OK? So again, take a base and an acid and I’ve combined them together to get a neutral salt. 00:30:28.366 --> 00:30:35.366 This is your classic acid-base reaction, but I don’t have any hydrogens. OK? Um, 00:30:35.366 --> 00:30:43.599 so I can’t use the Arrhenius Equation, I can’t use the Bronsted-Lowry definition, how am I going to define this as an acid or a base? OK. 00:30:43.600 --> 00:30:54.233 This is where Lewis came in. OK? Lewis. You have learned about Lewis when we talked about Lewis structures back in 1061. 00:30:54.233 --> 00:31:02.633 Gilbert N. Lewis is the dude who came up with Lewis structures, and so, when we’re doing Lewis structures 00:31:02.633 --> 00:31:07.966 we were looking at valence electrons, and where those valence electrons were, OK? And 00:31:07.966 --> 00:31:23.766 so this is what he did with the acid-base reaction, was he looked at electrons. OK? So, again, 00:31:23.766 --> 00:31:36.299 looking at our generic acid, OK, um, and our generic base, OK. Here we’re going to actually draw the Lewis structure of a hydroxide, OK. 00:31:36.300 --> 00:31:49.033 Um, but what is going on in terms of our electrons when we are doing an acid-base reaction? What Lewis figured out was that the electrons 00:31:49.033 --> 00:31:56.633 were going from the hydroxide to the H plus to create this coordinate covalent bond. 00:31:56.633 --> 00:32:14.199 OK, and so what he said was that an acid is something that accepts electrons, OK, a base is therefore going to be something that donates 00:32:14.200 --> 00:32:37.733 electrons. OK. So an acid either has to have or can make – AH – empty orbitals in order to pick up those electrons. 00:32:37.733 --> 00:32:48.533 A base has to have lone pair electrons in order to donate them. OK? And so this now becomes our 00:32:48.533 --> 00:32:57.433 most GENERIC definition, OK? An acid is something that can accept electrons, a base is something that can donate electrons. 00:32:57.433 --> 00:33:06.633 So with our Sodium Oxide and our Sulfur Trioxide, OK. What we have, if we get rid of the sodium because that’s just floating around, 00:33:06.633 --> 00:33:26.133 is we have oxide with a negative two charge, um, that is our base, OK. And we’re combining it with Sulfur Trioxide. OK. 00:33:26.133 --> 00:33:33.766 Right now the Sulfur Trioxide does not have, um, really an empty orbital, but what it can do is, 00:33:33.766 --> 00:33:42.199 it can pick up those pair of electrons and when it does that, um, it can rearrange – OK, it can dump ‘em out, sulfur can have an expanded 00:33:42.200 --> 00:33:50.666 octet. Um, and what we get is we get the sulfate ion, OK? Um, 00:33:50.666 --> 00:34:00.766 so. This is…the sulfur functions as our acid 00:34:00.766 --> 00:34:05.899 because it can accept the lone pair electrons, um, the oxide is our base. OK? Again, 00:34:05.900 --> 00:34:12.400 this is a real GENERIC definition, the most generic definition that we have acids and bases. 00:34:12.400 --> 00:34:18.933 Um, we don’t use it most of the time, a lot of times we do have our H pluses floating around, and it’s easier to think about 00:34:18.933 --> 00:34:26.899 the H pluses and where they’re going. Um, the Lewis definition is often used, um, 00:34:26.900 --> 00:34:43.065 with complex ions. OK. Complex ions are metal ions that have things stuck on ‘em, like, water, 00:34:43.065 --> 00:35:00.632 ammonia, cyanide, things like that, OK? Um, so, for example, ah, if we had silver ion combining with NH3 00:35:00.633 --> 00:35:16.266 we can make, um, AgNH3 two plus, OK. Or I could take something like Boron Hydroxide and 00:35:16.266 --> 00:35:28.499 add water to it, and in doing that get Boron with four Hydroxides and H plus. Alright? 00:35:28.500 --> 00:35:37.933 So, um, in both of these cases, using the Lewis definition, what is going to be our acid? What is going to be our base? 00:35:37.933 --> 00:35:50.766 Alright? So, what is going to be our acid, what is going to be our base? We need to think about electrons. OK. Silver ion? Probably doesn’t have 00:35:50.766 --> 00:35:58.132 a whole lot of electrons, OK? Ammonia, though, NH3, there are lone pair electrons on that nitrogen, 00:35:58.133 --> 00:36:09.633 OK, so those lone pair electrons can attack, so… our NH3 DONATES electrons, so it is a base; 00:36:09.633 --> 00:36:22.633 silver ACCEPTS electrons, and so it is going to be an acid. OK? With my boron hydroxide, if you think about it, boron we said before, 00:36:22.633 --> 00:36:29.666 likes to have three things stuck to it and it has this empty p orbital on it. My 00:36:29.666 --> 00:36:36.699 water has two lone pair electrons that can go fill that empty p orbital, to create the fourth 00:36:36.700 --> 00:36:49.166 bond. So, my boron ACCEPTS lone pair electrons so it is going to be an acid, the water DONATES so it is going to be a base. OK, 00:36:49.166 --> 00:36:55.099 and after it donates one of the hydrogens just falls off and that’s our extra hydrogen floating around here. Alright. 00:36:55.100 --> 00:37:00.400 So those are our three definitions of acids and bases. Um, 00:37:00.400 --> 00:37:05.700 the Arrhenius definition, an acid is something that increases the concentration of H plus 00:37:05.700 --> 00:37:14.666 in water; a base increases the hydroxide concentration. Um, works really well in water, but pretty much just in water. 00:37:14.666 --> 00:37:25.532 Um, the Arrhenius definition we have, um, our acids that donate protons, our bases that accept protons and for 00:37:25.533 --> 00:37:33.133 those we have our conjugate acid-base pairs that we have to worry about, and our amphiprotic species; their most generic definition is the 00:37:33.133 --> 00:37:42.133 Lewis acid and base definition that looks at the electrons. Um, acids accept lone pair electrons, bases donate lone pair electrons. 00:37:42.133 --> 00:37:51.066 Alright? And so those are our definitions of acids and bases.