1 00:00:00,000 --> 00:00:06,825 [MUSIC PLAYING] 2 00:00:06,825 --> 00:00:08,700 JESSICA HARROP: Hi, I'm Jessica and today I'm 3 00:00:08,700 --> 00:00:11,340 going to talk to you about a chemical demonstration I like 4 00:00:11,340 --> 00:00:13,890 to call colorful indicators. 5 00:00:16,650 --> 00:00:18,540 Indicators show us what we normally 6 00:00:18,540 --> 00:00:21,840 wouldn't be able to see, from the canary in the coal mine 7 00:00:21,840 --> 00:00:24,420 to a paint that changes color with temperature 8 00:00:24,420 --> 00:00:27,510 to the acid base indicators we'll be seeing today. 9 00:00:27,510 --> 00:00:31,190 And chemist Dr. Bassam Shakhashiri here he is-- 10 00:00:31,190 --> 00:00:33,630 is going to be showing us the demo. 11 00:00:33,630 --> 00:00:36,090 He's the president of the American Chemical Society 12 00:00:36,090 --> 00:00:38,530 and performing this demo right here at MIT. 13 00:00:38,530 --> 00:00:39,030 [WHOOSH] 14 00:00:39,030 --> 00:00:40,863 BASSAM SHAKHASHIRI: Now what I'm going to do 15 00:00:40,863 --> 00:00:43,890 is an experiment using another form of carbon dioxide. 16 00:00:43,890 --> 00:00:45,480 It's called dry ice. 17 00:00:45,480 --> 00:00:48,390 Dry ice is solid carbon dioxide. 18 00:00:48,390 --> 00:00:50,950 And you'll notice I'm putting what on? 19 00:00:50,950 --> 00:00:52,225 AUDIENCE: Gloves. 20 00:00:52,225 --> 00:00:54,060 BASSAM SHAKHASHIRI: Putting gloves. 21 00:00:54,060 --> 00:00:56,280 And I'm going to open this bucket 22 00:00:56,280 --> 00:01:02,740 and pick up three chunks of carbon dioxide solid. 23 00:01:02,740 --> 00:01:05,650 This is solid carbon dioxide. 24 00:01:05,650 --> 00:01:10,280 Its temperature is minus 78 degrees Celsius. 25 00:01:10,280 --> 00:01:12,050 It's very cold. 26 00:01:12,050 --> 00:01:14,960 Dry ice changes from being a solid to a gas by a process we 27 00:01:14,960 --> 00:01:16,857 call sublimation. 28 00:01:16,857 --> 00:01:19,190 Sublimation is happening right now, but we can't see it. 29 00:01:19,190 --> 00:01:21,090 How come we can't see it? 30 00:01:21,090 --> 00:01:24,067 Because carbon dioxide as gas is what? 31 00:01:24,067 --> 00:01:24,900 AUDIENCE: Invisible. 32 00:01:24,900 --> 00:01:25,680 BASSAM SHAKHASHIRI: It's invisible. 33 00:01:25,680 --> 00:01:26,610 It has no color. 34 00:01:26,610 --> 00:01:29,040 So sublimation is happening right now. 35 00:01:29,040 --> 00:01:30,820 We can't see it. 36 00:01:30,820 --> 00:01:33,270 And I'm going to put those three back in here 37 00:01:33,270 --> 00:01:35,910 and ask you to focus your attention on what you 38 00:01:35,910 --> 00:01:37,519 see between my two hands here. 39 00:01:37,519 --> 00:01:39,060 What do you see between my two hands? 40 00:01:39,060 --> 00:01:41,580 In order to sharpen your powers of observation 41 00:01:41,580 --> 00:01:44,910 and develop the skills of reporting these observations, 42 00:01:44,910 --> 00:01:49,420 I ask you to pretend to be the play by play radio announcer, 43 00:01:49,420 --> 00:01:52,260 describing to someone who was not with us what's going on. 44 00:01:52,260 --> 00:01:54,212 Not the TV announcer, that person 45 00:01:54,212 --> 00:01:55,920 has got it made because the picture tells 46 00:01:55,920 --> 00:01:57,070 almost everything. 47 00:01:57,070 --> 00:01:59,242 So, there are how many cylinders? 48 00:01:59,242 --> 00:02:00,159 AUDIENCE: Six. 49 00:02:00,159 --> 00:02:02,700 BASSAM SHAKHASHIRI: And what do you see inside the cylinders? 50 00:02:02,700 --> 00:02:03,870 AUDIENCE: Colored liquid. 51 00:02:03,870 --> 00:02:05,369 BASSAM SHAKHASHIRI: Colored liquids. 52 00:02:05,369 --> 00:02:07,060 OK, I'm listening to you on the radio. 53 00:02:07,060 --> 00:02:10,259 And what I hear you say is that there are six cylinders. 54 00:02:10,259 --> 00:02:12,150 And they have in them colored liquids. 55 00:02:12,150 --> 00:02:12,990 Come on. 56 00:02:12,990 --> 00:02:15,190 Your brain learned a lot more information 57 00:02:15,190 --> 00:02:17,240 than those two statements, right? 58 00:02:17,240 --> 00:02:17,850 Right? 59 00:02:17,850 --> 00:02:19,520 So they're about this big, you said. 60 00:02:19,520 --> 00:02:21,810 I can see you on the radio saying it's about this big, 61 00:02:21,810 --> 00:02:22,410 right? 62 00:02:22,410 --> 00:02:24,120 You've got to do better than this, OK? 63 00:02:24,120 --> 00:02:27,030 Are they 100 milliliters in size? 64 00:02:27,030 --> 00:02:29,340 Are they 10 milliliters in size? 65 00:02:29,340 --> 00:02:30,940 Are they somewhere in between? 66 00:02:30,940 --> 00:02:31,440 Yes. 67 00:02:31,440 --> 00:02:33,690 We put a bracket on it when we estimate in science. 68 00:02:33,690 --> 00:02:34,650 We put a bracket on it. 69 00:02:34,650 --> 00:02:35,490 All right. 70 00:02:35,490 --> 00:02:37,830 And they have, yes, colored liquids. 71 00:02:37,830 --> 00:02:40,900 How do you know they're liquids? 72 00:02:40,900 --> 00:02:41,770 They could be gels. 73 00:02:41,770 --> 00:02:42,610 How do we find out? 74 00:02:46,770 --> 00:02:48,020 We shake them up a little bit. 75 00:02:48,020 --> 00:02:50,750 Because we know from experience, it's a keyword, 76 00:02:50,750 --> 00:02:54,560 we learn things-- a brain learns things, so we use them, right? 77 00:02:54,560 --> 00:02:56,600 So they're liquids. 78 00:02:56,600 --> 00:02:59,240 So I'm going to take chunks of dry ice 79 00:02:59,240 --> 00:03:02,630 and put them in the cylinders in a very special way. 80 00:03:02,630 --> 00:03:08,916 And when I get done, you tell me what the special way is. 81 00:03:08,916 --> 00:03:11,840 AUDIENCE: It's blowing out. 82 00:03:11,840 --> 00:03:15,170 BASSAM SHAKHASHIRI: What's blowing out? 83 00:03:15,170 --> 00:03:16,982 You see any bubbles? 84 00:03:16,982 --> 00:03:20,571 What kind of bubbles are those? 85 00:03:20,571 --> 00:03:22,455 AUDIENCE: Blue. 86 00:03:22,455 --> 00:03:23,868 Green. 87 00:03:23,868 --> 00:03:25,889 Green. 88 00:03:25,889 --> 00:03:26,930 BASSAM SHAKHASHIRI: What? 89 00:03:26,930 --> 00:03:28,370 You want to know what's in there? 90 00:03:28,370 --> 00:03:29,744 You already know what's in there. 91 00:03:29,744 --> 00:03:31,910 Dry ice, I put the dry ice in there. 92 00:03:31,910 --> 00:03:33,780 What did I put the dry ice into? 93 00:03:33,780 --> 00:03:36,500 Into two cylinders that have colored liquids in them, right? 94 00:03:36,500 --> 00:03:38,510 And I put the dry ice in every other cylinder. 95 00:03:38,510 --> 00:03:40,460 I didn't put it in every cylinder, right? 96 00:03:40,460 --> 00:03:43,600 Every other cylinder, leaving one for comparison purposes. 97 00:03:43,600 --> 00:03:47,540 So these are dyes that change color when the pH of the liquid 98 00:03:47,540 --> 00:03:48,050 changes. 99 00:03:48,050 --> 00:03:48,750 [WHOOSH] 100 00:03:48,750 --> 00:03:49,010 JESSICA HARROP: All right. 101 00:03:49,010 --> 00:03:50,070 So let's break down. 102 00:03:50,070 --> 00:03:52,560 What's happening in these cylinders. 103 00:03:52,560 --> 00:03:53,500 There's six of them. 104 00:03:57,720 --> 00:03:59,490 And each set is a different color 105 00:03:59,490 --> 00:04:03,610 because they're different acid base indicators inside them. 106 00:04:03,610 --> 00:04:06,510 So this set starts out blue. 107 00:04:06,510 --> 00:04:09,360 This one starts out pink. 108 00:04:09,360 --> 00:04:13,530 And the final one is purple. 109 00:04:13,530 --> 00:04:17,589 And every cylinder contains a few drops of sodium hydroxide, 110 00:04:17,589 --> 00:04:19,529 which is a base. 111 00:04:19,529 --> 00:04:26,140 NaOH, sodium hydroxide, and it's a base. 112 00:04:26,140 --> 00:04:27,630 So let's start with the basics. 113 00:04:27,630 --> 00:04:29,790 What is an acid and a base? 114 00:04:29,790 --> 00:04:32,160 One definition is that acids are compounds 115 00:04:32,160 --> 00:04:39,260 that donate a hydrogen ion or H plus to another compound. 116 00:04:39,260 --> 00:04:43,260 And the compound that accepts that hydrogen ion is a base. 117 00:04:43,260 --> 00:04:45,780 So acids are hydrogen ion donors. 118 00:04:45,780 --> 00:04:48,840 And bases are hydrogen ion acceptors. 119 00:04:48,840 --> 00:04:50,160 Here's some examples. 120 00:04:50,160 --> 00:04:52,080 Sodium hydroxide is a base. 121 00:04:52,080 --> 00:04:53,910 It's used to make soap. 122 00:04:53,910 --> 00:05:00,020 And acetic acid, which looks like this, 123 00:05:00,020 --> 00:05:02,370 it makes vinegar sour. 124 00:05:02,370 --> 00:05:04,970 All right, so let's look back at our cylinders here. 125 00:05:04,970 --> 00:05:07,830 This first set of cylinders contains the indicator 126 00:05:07,830 --> 00:05:09,560 bromothymol blue. 127 00:05:09,560 --> 00:05:12,180 Let's take a look at the spectrum. 128 00:05:12,180 --> 00:05:14,960 All right, so let's take a look at bromothymol blue, 129 00:05:14,960 --> 00:05:17,870 the indicator in the first set of cylinders. 130 00:05:17,870 --> 00:05:19,880 As you can see here, there's a scale of numbers. 131 00:05:19,880 --> 00:05:21,620 This is a pH scale. 132 00:05:21,620 --> 00:05:23,840 The higher the number, the more basic the solution. 133 00:05:23,840 --> 00:05:25,910 The lower the number, the more acidic. 134 00:05:25,910 --> 00:05:27,920 So our solution started off basic. 135 00:05:27,920 --> 00:05:28,550 It was blue. 136 00:05:28,550 --> 00:05:31,250 It had sodium hydroxide in it. 137 00:05:31,250 --> 00:05:34,100 And this is what the chemical structure of the molecule 138 00:05:34,100 --> 00:05:36,740 looks like when it's blue. 139 00:05:36,740 --> 00:05:38,270 The chemical bonds in the molecule 140 00:05:38,270 --> 00:05:40,580 are absorbing colors of the visible spectrum that 141 00:05:40,580 --> 00:05:41,940 are not blue. 142 00:05:41,940 --> 00:05:46,270 So blue is reflected back to our eyes. 143 00:05:46,270 --> 00:05:49,630 Now, if our compound picks up a hydrogen ion which 144 00:05:49,630 --> 00:05:54,130 it would if you added an acid to it, the molecule changes color. 145 00:05:54,130 --> 00:05:57,460 Now it absorbs blue and reflects yellow. 146 00:05:57,460 --> 00:06:00,070 Since the colors depend on the structure of the molecule, 147 00:06:00,070 --> 00:06:02,110 a chemist could reprogram the molecule 148 00:06:02,110 --> 00:06:04,420 to switch its color at other pHs, 149 00:06:04,420 --> 00:06:07,000 other numbers on this scale. 150 00:06:07,000 --> 00:06:09,190 That's useful depending on the kind of reactions 151 00:06:09,190 --> 00:06:10,890 she may want to study. 152 00:06:10,890 --> 00:06:13,570 Now, nature experiments with color all the time. 153 00:06:13,570 --> 00:06:16,300 Animals use color to avoid predators, attract mates, 154 00:06:16,300 --> 00:06:17,890 scare off enemies, etc. 155 00:06:17,890 --> 00:06:18,502 [WHOOSH] 156 00:06:18,502 --> 00:06:19,960 All right, so now let's take a look 157 00:06:19,960 --> 00:06:22,270 at what's happening in the second set of cylinders 158 00:06:22,270 --> 00:06:23,680 that started off pink. 159 00:06:23,680 --> 00:06:24,420 [WHOOSH] 160 00:06:24,420 --> 00:06:27,490 The indicator in there is phenolphthalein. 161 00:06:27,490 --> 00:06:29,830 The same thing is happening with our bromothymol blue, 162 00:06:29,830 --> 00:06:33,700 but this time when the solution is basic, it's pink. 163 00:06:33,700 --> 00:06:36,235 And when it's acidic, it's colorless. 164 00:06:36,235 --> 00:06:37,450 [WHOOSH] 165 00:06:37,450 --> 00:06:40,030 But why does adding dry ice change the solution 166 00:06:40,030 --> 00:06:42,100 from basic to acidic? 167 00:06:42,100 --> 00:06:44,830 Well, dry ice is solid carbon dioxide. 168 00:06:44,830 --> 00:06:46,570 When you add it to water, it bubbles. 169 00:06:46,570 --> 00:06:49,540 And part of every bubble of carbon dioxide dissolves. 170 00:06:49,540 --> 00:06:51,854 When it does, it forms carbonic acid. 171 00:06:51,854 --> 00:06:53,020 Let's look at that equation. 172 00:06:57,620 --> 00:07:00,480 So there's more and more carbonic acid in the water. 173 00:07:00,480 --> 00:07:03,230 And this acid reacts with the sodium hydroxide 174 00:07:03,230 --> 00:07:04,550 until there's none left. 175 00:07:04,550 --> 00:07:06,050 So the solution becomes acidic. 176 00:07:13,010 --> 00:07:16,820 So we saw our bromothymol blue turning from blue to yellow 177 00:07:16,820 --> 00:07:19,960 as the solution became more acidic. 178 00:07:19,960 --> 00:07:23,840 And we saw our phenolphthalein turn from pink to colorless 179 00:07:23,840 --> 00:07:25,352 as it became more acidic. 180 00:07:25,352 --> 00:07:26,810 Now, let's watch again what happens 181 00:07:26,810 --> 00:07:28,730 in the final set of cylinders. 182 00:07:28,730 --> 00:07:29,230 [WHOOSH] 183 00:07:29,230 --> 00:07:30,480 BASSAM SHAKHASHIRI: All right. 184 00:07:30,480 --> 00:07:35,000 So now I ask you to focus your attention on this cylinder. 185 00:07:35,000 --> 00:07:37,510 Actually, you can focus your attention 186 00:07:37,510 --> 00:07:39,660 on anything you want to, OK? 187 00:07:39,660 --> 00:07:41,810 You can even not pay attention if you want to. 188 00:07:41,810 --> 00:07:44,040 We live in a free country. 189 00:07:44,040 --> 00:07:46,560 But if you want to follow the experiment with me, 190 00:07:46,560 --> 00:07:48,630 I want you to focus your attention on this one 191 00:07:48,630 --> 00:07:50,910 and tell me, count them out, how many different color 192 00:07:50,910 --> 00:07:54,516 changes you see as I drop the dry ice in there. 193 00:08:01,810 --> 00:08:04,160 I'm listening to you on the radio. 194 00:08:04,160 --> 00:08:05,290 One. 195 00:08:05,290 --> 00:08:06,032 Wow, I heard wow. 196 00:08:06,032 --> 00:08:07,240 What kind of a count is that? 197 00:08:10,610 --> 00:08:12,260 Three so far. 198 00:08:12,260 --> 00:08:13,940 Three different color changes. 199 00:08:13,940 --> 00:08:17,340 But you know, I'm listening to you on the radio. 200 00:08:17,340 --> 00:08:19,340 You want me to appreciate what you're seeing, 201 00:08:19,340 --> 00:08:21,870 so what were the color changes that you saw? 202 00:08:21,870 --> 00:08:23,570 Why couldn't you say those, right? 203 00:08:23,570 --> 00:08:26,690 You see how we have to help our brain make 204 00:08:26,690 --> 00:08:29,600 the right observations and make the right reporting. 205 00:08:29,600 --> 00:08:30,362 [WHOOSH] 206 00:08:30,362 --> 00:08:32,570 JESSICA HARROP: OK, so in the final set of cylinders, 207 00:08:32,570 --> 00:08:35,990 Dr. Shakhashiri has a mixture of indicators. 208 00:08:35,990 --> 00:08:37,520 This created the color changes that 209 00:08:37,520 --> 00:08:41,059 occurred as the solution became more and more acidic. 210 00:08:41,059 --> 00:08:45,190 There were three changes that we saw. 211 00:08:45,190 --> 00:08:52,165 It went from purple to blue to green to yellow. 212 00:08:52,165 --> 00:08:52,790 [MUSIC PLAYING] 213 00:08:52,790 --> 00:08:54,206 All right, that's it for me today. 214 00:08:54,206 --> 00:08:56,200 I'll see you next time.