WEBVTT 00:00:00.000 --> 00:00:03.346 align:middle line:90% [MUSIC PLAYING] 00:00:03.346 --> 00:00:07.387 align:middle line:90% 00:00:07.387 --> 00:00:08.720 align:middle line:90% JESSICA HARROP: Hi, I'm Jessica. 00:00:08.720 --> 00:00:10.930 align:middle line:84% And today, I'm going to talk about her reaction I 00:00:10.930 --> 00:00:15.170 align:middle line:90% like to call Midas' Magic. 00:00:15.170 --> 00:00:18.460 align:middle line:84% And before I get started, let's watch the reaction in action 00:00:18.460 --> 00:00:21.528 align:middle line:84% with the help of Dr. Bassam Shakashiri. 00:00:21.528 --> 00:00:26.310 align:middle line:90% And here he is. 00:00:26.310 --> 00:00:29.220 align:middle line:84% He's actually the president of the American Chemical Society. 00:00:29.220 --> 00:00:33.690 align:middle line:84% And his motto is, "Science is fun." 00:00:33.690 --> 00:00:34.860 align:middle line:90% Here he is at MIT. 00:00:34.860 --> 00:00:36.660 align:middle line:84% And let's see what he has to show us. 00:00:36.660 --> 00:00:37.910 align:middle line:90% BASSAM SHAKASHIRI: Watch this. 00:00:37.910 --> 00:00:40.250 align:middle line:84% Here i take this clear and colorless liquid. 00:00:40.250 --> 00:00:44.232 align:middle line:84% And I put some of it in the beaker, about 100 milliliters. 00:00:44.232 --> 00:00:45.940 align:middle line:84% How do I know it's about 100 milliliters? 00:00:45.940 --> 00:00:47.365 align:middle line:90% AUDIENCE: It says so. 00:00:47.365 --> 00:00:49.490 align:middle line:84% BASSAM SHAKASHIRI: I'm reading the markers on here, 00:00:49.490 --> 00:00:50.610 align:middle line:90% on the beaker. 00:00:50.610 --> 00:00:53.086 align:middle line:84% And I take about 100 millimeters of a different 00:00:53.086 --> 00:00:54.210 align:middle line:90% clear and colorless liquid. 00:00:54.210 --> 00:00:55.380 align:middle line:84% But you don't know that it's different. 00:00:55.380 --> 00:00:56.562 align:middle line:90% They look the same, right? 00:00:56.562 --> 00:00:57.270 align:middle line:90% And look at this. 00:00:57.270 --> 00:00:58.260 align:middle line:90% Look what's going to happen now. 00:00:58.260 --> 00:00:59.162 align:middle line:90% AUDIENCE: Ooh. 00:00:59.162 --> 00:01:01.155 align:middle line:90% AUDIENCE: It's yellow. 00:01:01.155 --> 00:01:02.530 align:middle line:84% BASSAM SHAKASHIRI: Isn't that one 00:01:02.530 --> 00:01:04.700 align:middle line:84% of the most fascinating observations you make? 00:01:04.700 --> 00:01:06.850 align:middle line:84% You take two clear, colorless liquids. 00:01:06.850 --> 00:01:09.940 align:middle line:84% You mix them together, and you get a yellow substance 00:01:09.940 --> 00:01:12.440 align:middle line:90% that is insoluble in water. 00:01:12.440 --> 00:01:14.530 align:middle line:90% This is lead iodide. 00:01:14.530 --> 00:01:16.370 align:middle line:84% I mixed potassium iodide solution 00:01:16.370 --> 00:01:17.944 align:middle line:90% with lead nitrate solution. 00:01:17.944 --> 00:01:20.110 align:middle line:84% So the magician never tells you how the trick works. 00:01:20.110 --> 00:01:23.090 align:middle line:84% But in science, we like to know what's going on. 00:01:23.090 --> 00:01:24.590 align:middle line:84% JESSICA HARROP: So what is going on? 00:01:24.590 --> 00:01:26.050 align:middle line:90% Let's break it down. 00:01:26.050 --> 00:01:30.130 align:middle line:84% Dr. Shakashiri started with two clear, colorless liquids. 00:01:30.130 --> 00:01:36.560 align:middle line:84% He had about 100 milliliters of lead nitrate. 00:01:36.560 --> 00:01:39.309 align:middle line:90% 00:01:39.309 --> 00:01:40.100 align:middle line:90% And that's aqueous. 00:01:40.100 --> 00:01:42.010 align:middle line:90% That's in solution. 00:01:42.010 --> 00:01:49.870 align:middle line:84% And about 100 milliliters of potassium iodide, also 00:01:49.870 --> 00:01:54.700 align:middle line:84% aqueous, and when he mixed those together, 00:01:54.700 --> 00:01:57.950 align:middle line:90% he got a yellow precipitate. 00:01:57.950 --> 00:01:59.430 align:middle line:90% Let's color that in yellow. 00:01:59.430 --> 00:02:03.350 align:middle line:90% 00:02:03.350 --> 00:02:05.240 align:middle line:90% A precipitate is a solid. 00:02:05.240 --> 00:02:08.395 align:middle line:84% So how do we know what this yellow solid is? 00:02:08.395 --> 00:02:09.770 align:middle line:84% Well, this is the reaction that's 00:02:09.770 --> 00:02:11.560 align:middle line:84% called a double displacement reaction. 00:02:11.560 --> 00:02:14.900 align:middle line:90% 00:02:14.900 --> 00:02:18.350 align:middle line:84% And in this kind of reaction, the cation and anion pairs 00:02:18.350 --> 00:02:19.800 align:middle line:90% switch places. 00:02:19.800 --> 00:02:21.840 align:middle line:90% So what exactly does that mean? 00:02:21.840 --> 00:02:24.860 align:middle line:84% I'm going to use some colors to help me out. 00:02:24.860 --> 00:02:30.350 align:middle line:84% So we've got cations and anions in each of these compounds. 00:02:30.350 --> 00:02:32.790 align:middle line:84% The cations have positive charge. 00:02:32.790 --> 00:02:39.050 align:middle line:84% So in this case, it's lead, which has a 2+ charge 00:02:39.050 --> 00:02:45.740 align:middle line:90% and nitrate, NO3-. 00:02:45.740 --> 00:02:51.230 align:middle line:84% You need two of those to have a neutral compound. 00:02:51.230 --> 00:02:58.100 align:middle line:84% Our other compound, over here, has potassium, which has a +1. 00:02:58.100 --> 00:03:04.850 align:middle line:84% And our anion is iodide, which is -1. 00:03:04.850 --> 00:03:09.950 align:middle line:84% When these two solutions are mixed, we've got lead, 00:03:09.950 --> 00:03:10.770 align:middle line:90% which is our +2. 00:03:10.770 --> 00:03:13.760 align:middle line:90% 00:03:13.760 --> 00:03:16.245 align:middle line:84% And it's going to react with iodide. 00:03:16.245 --> 00:03:21.410 align:middle line:90% 00:03:21.410 --> 00:03:25.040 align:middle line:84% We need two of them to make it a neutral compound. 00:03:25.040 --> 00:03:33.780 align:middle line:84% And potassium nitrate, and we just need one nitrate here. 00:03:33.780 --> 00:03:38.317 align:middle line:84% So our cations and anions all switched places. 00:03:38.317 --> 00:03:40.650 align:middle line:84% We're going to need to balance this equation let's throw 00:03:40.650 --> 00:03:44.400 align:middle line:90% some twos there and there. 00:03:44.400 --> 00:03:47.190 align:middle line:84% So how can we predict which one of these two compounds 00:03:47.190 --> 00:03:49.290 align:middle line:90% is the yellow precipitate? 00:03:49.290 --> 00:03:52.560 align:middle line:84% Hundreds of years ago, chemists mixed ions together. 00:03:52.560 --> 00:03:56.490 align:middle line:84% And they came up with solubility tables, just like this one. 00:03:56.490 --> 00:03:57.990 align:middle line:84% Now this chart basically shows us 00:03:57.990 --> 00:04:01.020 align:middle line:84% when these two ions, an ion from this column and this column 00:04:01.020 --> 00:04:03.240 align:middle line:84% are mixed together, is their product, 00:04:03.240 --> 00:04:06.810 align:middle line:84% a compound that they form, soluble or insoluble in water? 00:04:06.810 --> 00:04:08.230 align:middle line:84% If it's soluble in water, there's 00:04:08.230 --> 00:04:10.620 align:middle line:90% an aq for aqueous on the chart. 00:04:10.620 --> 00:04:13.770 align:middle line:84% And if it's insoluble in water, there's an s for solid. 00:04:13.770 --> 00:04:19.680 align:middle line:84% So our two compounds that we want to look at our lead iodide 00:04:19.680 --> 00:04:22.329 align:middle line:90% and potassium nitrate. 00:04:22.329 --> 00:04:25.280 align:middle line:90% 00:04:25.280 --> 00:04:26.930 align:middle line:90% So let's take a look. 00:04:26.930 --> 00:04:29.330 align:middle line:84% Potassium nitrate-- we've got potassium 00:04:29.330 --> 00:04:32.000 align:middle line:90% down here at the bottom. 00:04:32.000 --> 00:04:36.210 align:middle line:84% We've got nitrate here at the top. 00:04:36.210 --> 00:04:42.710 align:middle line:84% When mixed together, aqueous solution, soluble in water. 00:04:42.710 --> 00:04:46.910 align:middle line:84% So it's more likely that our lead iodide would 00:04:46.910 --> 00:04:48.200 align:middle line:90% be the yellow precipitate. 00:04:48.200 --> 00:04:50.160 align:middle line:90% But let's see if that's true. 00:04:50.160 --> 00:04:55.145 align:middle line:90% Lead mixed with iodide-- 00:04:55.145 --> 00:04:57.780 align:middle line:90% 00:04:57.780 --> 00:04:59.290 align:middle line:90% voila. 00:04:59.290 --> 00:05:02.130 align:middle line:90% It's a solid. 00:05:02.130 --> 00:05:04.440 align:middle line:84% So to recap, solubility tables help 00:05:04.440 --> 00:05:07.770 align:middle line:84% chemists predict whether or not a precipitate will form 00:05:07.770 --> 00:05:09.840 align:middle line:90% when two solutions are mixed. 00:05:09.840 --> 00:05:17.280 align:middle line:84% So going back to our equation here, the lead iodide-- 00:05:17.280 --> 00:05:21.480 align:middle line:90% this is the yellow precipitate. 00:05:21.480 --> 00:05:23.310 align:middle line:90% It's a solid. 00:05:23.310 --> 00:05:27.780 align:middle line:84% And the potassium nitrate is aqueous. 00:05:27.780 --> 00:05:29.520 align:middle line:84% And even though I didn't paint my nails 00:05:29.520 --> 00:05:32.460 align:middle line:84% with this particular pigment, lead iodide, 00:05:32.460 --> 00:05:34.290 align:middle line:84% creating nail polish colors is one 00:05:34.290 --> 00:05:37.270 align:middle line:84% of the many different things that chemists can do. 00:05:37.270 --> 00:05:37.900 align:middle line:90% So there we go. 00:05:37.900 --> 00:05:39.660 align:middle line:90% I hope you enjoyed Midas' Magic. 00:05:39.660 --> 00:05:41.020 align:middle line:90% And I will see you next time. 00:05:41.020 --> 00:05:44.370 align:middle line:90% [MUSIC PLAYING] 00:05:44.370 --> 00:06:10.310 align:middle line:90%