WEBVTT 00:00:00.521 --> 00:00:03.781 There are a variety of different kinds of chemical reactions 00:00:03.781 --> 00:00:05.361 that we learn about. 00:00:05.361 --> 00:00:07.301 We know about acid-base reactions. 00:00:07.301 --> 00:00:10.681 You know about solubility and about how salts fall to the bottom 00:00:10.681 --> 00:00:12.361 and form precipitates. 00:00:12.361 --> 00:00:16.521 There's a category of reaction involving metals that's less familiar 00:00:16.521 --> 00:00:19.161 to folks, but actually is pretty darn important. 00:00:19.161 --> 00:00:21.620 It's the simple question of what happens when you throw 00:00:21.620 --> 00:00:23.621 metals into water. 00:00:23.621 --> 00:00:26.181 There are actually four different categories of this thing 00:00:26.181 --> 00:00:28.821 called a displacement reaction. 00:00:28.821 --> 00:00:31.961 A displacement reaction in which you throw metal into water 00:00:31.961 --> 00:00:34.301 will have the following results: 00:00:34.301 --> 00:00:39.501 The metal will be turned into a cation, the water will be turned 00:00:39.501 --> 00:00:45.321 into a base, a hydroxide, and then hydrogen gas will be evolved. 00:00:45.321 --> 00:00:47.641 And the most famous of those examples, 00:00:47.641 --> 00:00:51.681 throwing sodium and lithium into water makes a big explosion 00:00:51.681 --> 00:00:55.281 even in cold water and the solution turns pink from 00:00:55.281 --> 00:00:58.921 phenoltheline being in there because of the hydroxide ions 00:00:58.921 --> 00:01:02.621 and that explosion is hydrogen gas. 00:01:02.621 --> 00:01:05.781 As you move across the periodic table, you move from the most 00:01:05.781 --> 00:01:13.881 active metals like lithium and sodium to a second category of metal 00:01:13.881 --> 00:01:17.481 which is the alkali earth metals and those are the kinds of things 00:01:17.481 --> 00:01:21.923 than can react even in hot water, and then there's a whole suite 00:01:21.923 --> 00:01:25.443 of metals in the periodic table, transition metals, 00:01:25.443 --> 00:01:27.903 which dissolve in acid. 00:01:27.903 --> 00:01:29.503 You're all familiar with this. 00:01:29.503 --> 00:01:34.223 If you throw iron into water that is acidified you end up dissolving 00:01:34.223 --> 00:01:35.253 the iron away. 00:01:35.253 --> 00:01:37.663 Well we're going to do that experiment here, 00:01:37.663 --> 00:01:40.983 only we're going to use zinc as a transition metal and 00:01:40.983 --> 00:01:44.683 we're going to use zinc in particular because zinc finds a 00:01:44.683 --> 00:01:47.844 substantial amount of use in coins and I'm going to be 00:01:47.844 --> 00:01:50.944 showing you another demonstration in which you get to watch 00:01:50.944 --> 00:01:55.864 what happens when you pour hydrochloric acid onto a penny. 00:01:55.864 --> 00:01:57.544 It's kind of interesting. 00:01:57.544 --> 00:02:02.044 So let me go ahead and pour the acid in and you'll notice 00:02:02.044 --> 00:02:04.164 the foaming occurring. 00:02:04.164 --> 00:02:09.564 This foaming is from the evolution of hydrogen gas while 00:02:09.564 --> 00:02:16.263 the zinc metal is being oxidized to zinc ion and the solution 00:02:16.263 --> 00:02:18.264 is turning basic. 00:02:18.264 --> 00:02:22.964 Now, if I was to capture the evolving gas by putting a balloon 00:02:22.964 --> 00:02:28.284 over the top of it and then tie it off, I could light off that balloon 00:02:28.284 --> 00:02:31.764 and I would see a pop coming from the hydrogen gas 00:02:31.764 --> 00:02:33.464 that had evolved. 00:02:33.464 --> 00:02:35.884 So this is an examle of a displacement reaction and 00:02:35.884 --> 00:02:40.784 this is an example of a metal which is not so reactive 00:02:40.784 --> 00:02:45.204 that it dissolves in water, it is not so reactive that 00:02:45.204 --> 00:02:48.685 it dissolves in hot water, but is in that category where if you 00:02:48.685 --> 00:02:52.465 dump it into acid, in particular hydrochloric acid here, 00:02:52.465 --> 00:02:54.955 you'll be able to get it to dissolve away.