WEBVTT 00:00:06.606 --> 00:00:08.639 Acids and bases are everywhere. 00:00:08.639 --> 00:00:10.215 They're used to make foods, 00:00:10.215 --> 00:00:11.540 soaps and detergents, 00:00:11.540 --> 00:00:12.316 fertilizers, 00:00:12.316 --> 00:00:13.485 explosives, 00:00:13.485 --> 00:00:14.200 dyes, 00:00:14.200 --> 00:00:14.650 plastics, 00:00:14.650 --> 00:00:15.312 pesticides, 00:00:15.312 --> 00:00:16.545 even paper. 00:00:16.545 --> 00:00:18.212 Our stomachs are very acidic. 00:00:18.212 --> 00:00:20.038 Our blood is slightly basic. 00:00:20.038 --> 00:00:22.907 Our proteins are made up of amino acids, 00:00:22.907 --> 00:00:24.623 and the letters in our genetic code, 00:00:24.623 --> 00:00:26.828 those As, Ts, Cs, and Gs, 00:00:26.828 --> 00:00:28.649 are all bases. 00:00:28.649 --> 00:00:29.508 You were probably taught 00:00:29.508 --> 00:00:30.864 how acids and bases behave 00:00:30.864 --> 00:00:32.450 on the molecular level. 00:00:32.450 --> 00:00:34.129 You were probably never taught 00:00:34.129 --> 00:00:35.247 that a long time ago, 00:00:35.247 --> 00:00:37.305 like ancient Greek ago, 00:00:37.305 --> 00:00:39.673 before anyone knew about atoms or molecules, 00:00:39.673 --> 00:00:41.212 acids and bases were defined 00:00:41.212 --> 00:00:43.008 by how they behaved. 00:00:43.008 --> 00:00:46.460 Acids tasted sour and corroded metal. 00:00:46.460 --> 00:00:48.120 Bases felt slippery 00:00:48.120 --> 00:00:50.934 and could somehow counteract acids. 00:00:52.395 --> 00:00:54.599 When molecules dissolved in water interact, 00:00:54.599 --> 00:00:56.540 they are exchanging two main currencies 00:00:56.540 --> 00:00:58.198 with their surroundings: 00:00:58.198 --> 00:01:01.035 protons, also known as hydrogen ions, 00:01:01.035 --> 00:01:02.448 and electrons. 00:01:02.448 --> 00:01:05.339 Depending on how a molecule is composed or shaped, 00:01:05.339 --> 00:01:07.537 it may be willing to donate or accept 00:01:07.537 --> 00:01:09.118 either protons or electrons 00:01:09.118 --> 00:01:11.331 with some other community member. 00:01:11.331 --> 00:01:14.427 And some molecules are far more aggressive than others 00:01:14.427 --> 00:01:17.873 when it comes to donating or accepting either currency. 00:01:17.873 --> 00:01:19.955 Remember that protons are positively charged 00:01:19.955 --> 00:01:22.280 and electrons are negatively charged. 00:01:22.280 --> 00:01:24.980 So, if a molecule is willing to give up a proton, 00:01:24.980 --> 00:01:26.230 that's not too different 00:01:26.230 --> 00:01:28.745 from it being willing to accept an electron -- 00:01:28.745 --> 00:01:31.980 either way it's becoming more negatively charged. 00:01:31.980 --> 00:01:34.489 Other molecules are willing to accept a proton 00:01:34.489 --> 00:01:36.327 or give up an electron. 00:01:36.327 --> 00:01:38.649 These are becoming more positively charged. 00:01:38.649 --> 00:01:41.040 Some substances are so aggressive 00:01:41.040 --> 00:01:42.572 about donating their protons 00:01:42.572 --> 00:01:43.782 that when they get a chance, 00:01:43.782 --> 00:01:45.620 all of the molecules in a sample 00:01:45.620 --> 00:01:46.994 will dump a proton, 00:01:46.994 --> 00:01:48.288 sometimes more than one, 00:01:48.288 --> 00:01:50.285 to the surrounding water molecules. 00:01:50.285 --> 00:01:53.120 We call these strong acids. 00:01:53.120 --> 00:01:54.837 Meanwhile, some compounds are so ready 00:01:54.837 --> 00:01:56.117 to accept a proton 00:01:56.117 --> 00:01:57.369 that they won't wait around, 00:01:57.369 --> 00:01:59.009 they'll just rip one off water, 00:01:59.009 --> 00:02:00.535 which usually has two protons 00:02:00.535 --> 00:02:03.143 but is generous enough to hang out with just one. 00:02:03.143 --> 00:02:05.513 We call these strong bases. 00:02:05.513 --> 00:02:08.303 Other acids and bases are not so strong. 00:02:08.303 --> 00:02:11.313 They may donate just a few of their protons to water 00:02:11.313 --> 00:02:13.642 or accept just a few protons from water, 00:02:13.642 --> 00:02:16.708 but most of their molecules stay exactly the same. 00:02:16.708 --> 00:02:18.412 If left alone in water, 00:02:18.412 --> 00:02:20.243 they'll reach some equilibrium point 00:02:20.243 --> 00:02:22.073 where maybe only one out of a hundred 00:02:22.073 --> 00:02:23.906 or one out of ten thousand of their molecules 00:02:23.906 --> 00:02:26.455 has exchanged currency with water. 00:02:26.455 --> 00:02:27.577 As you might guess, 00:02:27.577 --> 00:02:30.159 we label these acids and bases weak, 00:02:30.159 --> 00:02:31.451 but in the common sense of the word, 00:02:31.451 --> 00:02:32.747 they're not weak. 00:02:32.747 --> 00:02:34.372 The vinegar in your salad dressing 00:02:34.372 --> 00:02:36.124 that you can smell from across the room, 00:02:36.124 --> 00:02:38.207 that is a weak acid. 00:02:38.207 --> 00:02:39.427 The ammonia you spray on glass 00:02:39.427 --> 00:02:40.553 for a streak-free shine, 00:02:40.553 --> 00:02:42.420 that is a weak base. 00:02:42.420 --> 00:02:45.058 So, it doesn't take much to be an active player 00:02:45.058 --> 00:02:46.938 in the chemical economy. 00:02:47.676 --> 00:02:50.349 Most acid-base chemistry takes place in water, 00:02:50.349 --> 00:02:53.068 which can act as either an acid or a base, 00:02:53.068 --> 00:02:54.996 accepting deposits and enabling withdrawals 00:02:54.996 --> 00:02:57.823 like a 24-hour molecular ATM. 00:02:57.823 --> 00:03:00.084 And when a proton-deposit customer, 00:03:00.084 --> 00:03:01.159 that's an acid, 00:03:01.159 --> 00:03:03.530 and a proton-withdrawal customer, 00:03:03.530 --> 00:03:04.340 the base, 00:03:04.340 --> 00:03:05.721 shop at the same time, 00:03:05.721 --> 00:03:07.503 their net effect on water's account 00:03:07.503 --> 00:03:09.087 may cancel out, 00:03:09.087 --> 00:03:11.737 and we call this neutralization. 00:03:11.737 --> 00:03:13.682 Now, certain molecules can behave 00:03:13.682 --> 00:03:15.889 as acids or bases without water, 00:03:15.889 --> 00:03:17.469 but that's another story. 00:03:17.469 --> 00:03:19.139 Let's end by saluting water 00:03:19.139 --> 00:03:20.890 as the resilient and fair banker 00:03:20.890 --> 00:03:22.718 for acids and bases. 00:03:22.718 --> 00:03:24.020 It's always open for business, 00:03:24.020 --> 00:03:25.222 doesn't charge interest, 00:03:25.222 --> 00:03:27.522 and will never foreclose on your molecules, 00:03:27.522 --> 00:03:30.463 which is more than I can say for [bleep]. 00:03:30.816 --> 00:03:31.941 Waah-waah.