1 00:00:00,000 --> 00:00:03,346 [MUSIC PLAYING] 2 00:00:07,387 --> 00:00:08,720 JESSICA HARROP: Hi, I'm Jessica. 3 00:00:08,720 --> 00:00:10,930 And today, I'm going to talk about her reaction I 4 00:00:10,930 --> 00:00:15,170 like to call Midas' Magic. 5 00:00:15,170 --> 00:00:18,460 And before I get started, let's watch the reaction in action 6 00:00:18,460 --> 00:00:21,528 with the help of Dr. Bassam Shakashiri. 7 00:00:21,528 --> 00:00:26,310 And here he is. 8 00:00:26,310 --> 00:00:29,220 He's actually the president of the American Chemical Society. 9 00:00:29,220 --> 00:00:33,690 And his motto is, "Science is fun." 10 00:00:33,690 --> 00:00:34,860 Here he is at MIT. 11 00:00:34,860 --> 00:00:36,660 And let's see what he has to show us. 12 00:00:36,660 --> 00:00:37,910 BASSAM SHAKASHIRI: Watch this. 13 00:00:37,910 --> 00:00:40,250 Here i take this clear and colorless liquid. 14 00:00:40,250 --> 00:00:44,232 And I put some of it in the beaker, about 100 milliliters. 15 00:00:44,232 --> 00:00:45,940 How do I know it's about 100 milliliters? 16 00:00:45,940 --> 00:00:47,365 AUDIENCE: It says so. 17 00:00:47,365 --> 00:00:49,490 BASSAM SHAKASHIRI: I'm reading the markers on here, 18 00:00:49,490 --> 00:00:50,610 on the beaker. 19 00:00:50,610 --> 00:00:53,086 And I take about 100 millimeters of a different 20 00:00:53,086 --> 00:00:54,210 clear and colorless liquid. 21 00:00:54,210 --> 00:00:55,380 But you don't know that it's different. 22 00:00:55,380 --> 00:00:56,562 They look the same, right? 23 00:00:56,562 --> 00:00:57,270 And look at this. 24 00:00:57,270 --> 00:00:58,260 Look what's going to happen now. 25 00:00:58,260 --> 00:00:59,162 AUDIENCE: Ooh. 26 00:00:59,162 --> 00:01:01,155 AUDIENCE: It's yellow. 27 00:01:01,155 --> 00:01:02,530 BASSAM SHAKASHIRI: Isn't that one 28 00:01:02,530 --> 00:01:04,700 of the most fascinating observations you make? 29 00:01:04,700 --> 00:01:06,850 You take two clear, colorless liquids. 30 00:01:06,850 --> 00:01:09,940 You mix them together, and you get a yellow substance 31 00:01:09,940 --> 00:01:12,440 that is insoluble in water. 32 00:01:12,440 --> 00:01:14,530 This is lead iodide. 33 00:01:14,530 --> 00:01:16,370 I mixed potassium iodide solution 34 00:01:16,370 --> 00:01:17,944 with lead nitrate solution. 35 00:01:17,944 --> 00:01:20,110 So the magician never tells you how the trick works. 36 00:01:20,110 --> 00:01:23,090 But in science, we like to know what's going on. 37 00:01:23,090 --> 00:01:24,590 JESSICA HARROP: So what is going on? 38 00:01:24,590 --> 00:01:26,050 Let's break it down. 39 00:01:26,050 --> 00:01:30,130 Dr. Shakashiri started with two clear, colorless liquids. 40 00:01:30,130 --> 00:01:36,560 He had about 100 milliliters of lead nitrate. 41 00:01:39,309 --> 00:01:40,100 And that's aqueous. 42 00:01:40,100 --> 00:01:42,010 That's in solution. 43 00:01:42,010 --> 00:01:49,870 And about 100 milliliters of potassium iodide, also 44 00:01:49,870 --> 00:01:54,700 aqueous, and when he mixed those together, 45 00:01:54,700 --> 00:01:57,950 he got a yellow precipitate. 46 00:01:57,950 --> 00:01:59,430 Let's color that in yellow. 47 00:02:03,350 --> 00:02:05,240 A precipitate is a solid. 48 00:02:05,240 --> 00:02:08,395 So how do we know what this yellow solid is? 49 00:02:08,395 --> 00:02:09,770 Well, this is the reaction that's 50 00:02:09,770 --> 00:02:11,560 called a double displacement reaction. 51 00:02:14,900 --> 00:02:18,350 And in this kind of reaction, the cation and anion pairs 52 00:02:18,350 --> 00:02:19,800 switch places. 53 00:02:19,800 --> 00:02:21,840 So what exactly does that mean? 54 00:02:21,840 --> 00:02:24,860 I'm going to use some colors to help me out. 55 00:02:24,860 --> 00:02:30,350 So we've got cations and anions in each of these compounds. 56 00:02:30,350 --> 00:02:32,790 The cations have positive charge. 57 00:02:32,790 --> 00:02:39,050 So in this case, it's lead, which has a 2+ charge 58 00:02:39,050 --> 00:02:45,740 and nitrate, NO3-. 59 00:02:45,740 --> 00:02:51,230 You need two of those to have a neutral compound. 60 00:02:51,230 --> 00:02:58,100 Our other compound, over here, has potassium, which has a +1. 61 00:02:58,100 --> 00:03:04,850 And our anion is iodide, which is -1. 62 00:03:04,850 --> 00:03:09,950 When these two solutions are mixed, we've got lead, 63 00:03:09,950 --> 00:03:10,770 which is our +2. 64 00:03:13,760 --> 00:03:16,245 And it's going to react with iodide. 65 00:03:21,410 --> 00:03:25,040 We need two of them to make it a neutral compound. 66 00:03:25,040 --> 00:03:33,780 And potassium nitrate, and we just need one nitrate here. 67 00:03:33,780 --> 00:03:38,317 So our cations and anions all switched places. 68 00:03:38,317 --> 00:03:40,650 We're going to need to balance this equation let's throw 69 00:03:40,650 --> 00:03:44,400 some twos there and there. 70 00:03:44,400 --> 00:03:47,190 So how can we predict which one of these two compounds 71 00:03:47,190 --> 00:03:49,290 is the yellow precipitate? 72 00:03:49,290 --> 00:03:52,560 Hundreds of years ago, chemists mixed ions together. 73 00:03:52,560 --> 00:03:56,490 And they came up with solubility tables, just like this one. 74 00:03:56,490 --> 00:03:57,990 Now this chart basically shows us 75 00:03:57,990 --> 00:04:01,020 when these two ions, an ion from this column and this column 76 00:04:01,020 --> 00:04:03,240 are mixed together, is their product, 77 00:04:03,240 --> 00:04:06,810 a compound that they form, soluble or insoluble in water? 78 00:04:06,810 --> 00:04:08,230 If it's soluble in water, there's 79 00:04:08,230 --> 00:04:10,620 an aq for aqueous on the chart. 80 00:04:10,620 --> 00:04:13,770 And if it's insoluble in water, there's an s for solid. 81 00:04:13,770 --> 00:04:19,680 So our two compounds that we want to look at our lead iodide 82 00:04:19,680 --> 00:04:22,329 and potassium nitrate. 83 00:04:25,280 --> 00:04:26,930 So let's take a look. 84 00:04:26,930 --> 00:04:29,330 Potassium nitrate-- we've got potassium 85 00:04:29,330 --> 00:04:32,000 down here at the bottom. 86 00:04:32,000 --> 00:04:36,210 We've got nitrate here at the top. 87 00:04:36,210 --> 00:04:42,710 When mixed together, aqueous solution, soluble in water. 88 00:04:42,710 --> 00:04:46,910 So it's more likely that our lead iodide would 89 00:04:46,910 --> 00:04:48,200 be the yellow precipitate. 90 00:04:48,200 --> 00:04:50,160 But let's see if that's true. 91 00:04:50,160 --> 00:04:55,145 Lead mixed with iodide-- 92 00:04:57,780 --> 00:04:59,290 voila. 93 00:04:59,290 --> 00:05:02,130 It's a solid. 94 00:05:02,130 --> 00:05:04,440 So to recap, solubility tables help 95 00:05:04,440 --> 00:05:07,770 chemists predict whether or not a precipitate will form 96 00:05:07,770 --> 00:05:09,840 when two solutions are mixed. 97 00:05:09,840 --> 00:05:17,280 So going back to our equation here, the lead iodide-- 98 00:05:17,280 --> 00:05:21,480 this is the yellow precipitate. 99 00:05:21,480 --> 00:05:23,310 It's a solid. 100 00:05:23,310 --> 00:05:27,780 And the potassium nitrate is aqueous. 101 00:05:27,780 --> 00:05:29,520 And even though I didn't paint my nails 102 00:05:29,520 --> 00:05:32,460 with this particular pigment, lead iodide, 103 00:05:32,460 --> 00:05:34,290 creating nail polish colors is one 104 00:05:34,290 --> 00:05:37,270 of the many different things that chemists can do. 105 00:05:37,270 --> 00:05:37,900 So there we go. 106 00:05:37,900 --> 00:05:39,660 I hope you enjoyed Midas' Magic. 107 00:05:39,660 --> 00:05:41,020 And I will see you next time. 108 00:05:41,020 --> 00:05:44,370 [MUSIC PLAYING]