1 00:00:00,000 --> 00:00:15,080 [SQUEAKING] [RUSTLING] [CLICKING] 2 00:00:15,080 --> 00:00:17,400 JOHN DOLHUN: Good afternoon, everyone. 3 00:00:17,400 --> 00:00:22,460 Welcome to The Ellen Swallow Richards lab part two. 4 00:00:22,460 --> 00:00:24,920 There is-- the room will be a little bit more 5 00:00:24,920 --> 00:00:26,660 sparsely populated today. 6 00:00:26,660 --> 00:00:28,010 I wonder why. 7 00:00:28,010 --> 00:00:29,540 Lab reports are due, right? 8 00:00:32,479 --> 00:00:35,400 So we're going to get started. 9 00:00:35,400 --> 00:00:40,970 And I'm going to start off by talking about probably the most 10 00:00:40,970 --> 00:00:46,040 important parameter in measuring the health of the river, 11 00:00:46,040 --> 00:00:50,030 and that's the dissolved oxygen. So when 12 00:00:50,030 --> 00:00:54,080 we look at the dissolved oxygen concentrations 13 00:00:54,080 --> 00:00:58,820 out there, for a river to really be healthy, 14 00:00:58,820 --> 00:01:02,700 we're looking for something greater than probably about 8 15 00:01:02,700 --> 00:01:03,200 PPM. 16 00:01:13,520 --> 00:01:17,960 If the concentrations fall down to 5 or less, 17 00:01:17,960 --> 00:01:21,620 then you'll start to see the fish move around erratically, 18 00:01:21,620 --> 00:01:24,470 because they're trying to get their oxygen. 19 00:01:24,470 --> 00:01:33,950 So less than or equal to 5, and we have some stress 20 00:01:33,950 --> 00:01:36,200 placed on the aquatic life. 21 00:01:36,200 --> 00:01:38,630 If the dissolved oxygen concentration 22 00:01:38,630 --> 00:01:48,457 goes below 2, even for an hour or two, 23 00:01:48,457 --> 00:01:49,790 you're going to have fish kills. 24 00:01:57,070 --> 00:02:01,150 So let's take a moment to actually see 25 00:02:01,150 --> 00:02:04,030 how this oxygen gets into the water, 26 00:02:04,030 --> 00:02:06,920 and this is the big picture. 27 00:02:06,920 --> 00:02:11,350 So if you look at this, you've got two processes going on. 28 00:02:11,350 --> 00:02:14,860 You've got the oxygen coming in from the atmosphere, 29 00:02:14,860 --> 00:02:18,610 and it's diffusing into the water system. 30 00:02:18,610 --> 00:02:23,650 You also have down below, you've got aerobic biodegradation 31 00:02:23,650 --> 00:02:25,670 taking place. 32 00:02:25,670 --> 00:02:38,830 So we've got oxygen diffusing into the water, 33 00:02:38,830 --> 00:02:46,200 and then we've got aerobic biodegradation. 34 00:02:51,280 --> 00:02:57,070 These are the two main processes that are taking place, 35 00:02:57,070 --> 00:03:01,600 and both of these processes are going-- 36 00:03:01,600 --> 00:03:06,100 they have different kinetics, yet they're coupled together, 37 00:03:06,100 --> 00:03:10,720 coupled in the sense that if aerobic biodegradation uses up 38 00:03:10,720 --> 00:03:15,400 the oxygen, more oxygen will start to dissolve in. 39 00:03:15,400 --> 00:03:17,740 There's a transfer driving force that 40 00:03:17,740 --> 00:03:20,500 actually lets more oxygen dissolve into the water. 41 00:03:23,850 --> 00:03:29,630 The rate at which oxygen is dissolving 42 00:03:29,630 --> 00:03:34,280 is actually proportional to the deficit of oxygen 43 00:03:34,280 --> 00:03:35,600 that's in the river. 44 00:03:42,490 --> 00:03:50,750 And that deficit is equal to the equilibrium level 45 00:03:50,750 --> 00:03:55,250 that we would expect minus the actual level 46 00:03:55,250 --> 00:03:56,750 that we actually find. 47 00:04:06,340 --> 00:04:09,210 So the amounts of oxygen that we're talking about 48 00:04:09,210 --> 00:04:11,430 are very tiny. 49 00:04:11,430 --> 00:04:14,490 And there was a brilliant chemist 50 00:04:14,490 --> 00:04:29,750 by the name of William Henry, who actually, back in 1803, 51 00:04:29,750 --> 00:04:32,270 came out with Henry's Law. 52 00:04:39,510 --> 00:04:44,680 And what Henry's Law says is very simple. 53 00:04:44,680 --> 00:04:58,420 The solubility of a dissolved gas in a body of water 54 00:04:58,420 --> 00:05:01,480 is proportional to the partial pressure 55 00:05:01,480 --> 00:05:03,880 of that gas over the water. 56 00:05:08,350 --> 00:05:11,020 There's even a Henry's Law constant here, 57 00:05:11,020 --> 00:05:13,750 and there are tables of these. 58 00:05:13,750 --> 00:05:15,280 There are thousands of them. 59 00:05:15,280 --> 00:05:19,510 For every solvent, for every gas, for every temperature 60 00:05:19,510 --> 00:05:21,570 combination that you can think of, 61 00:05:21,570 --> 00:05:26,150 there is a Henry Law constant that you can plug in. 62 00:05:26,150 --> 00:05:29,330 Let's think about, what is the partial pressure 63 00:05:29,330 --> 00:05:32,190 of oxygen on any given day? 64 00:05:32,190 --> 00:05:33,380 How do we calculate that? 65 00:05:44,100 --> 00:05:45,150 Yes, yeah. 66 00:05:45,150 --> 00:05:45,810 Alec. 67 00:05:45,810 --> 00:05:47,580 AUDIENCE: So if you have total pressure, 68 00:05:47,580 --> 00:05:49,920 and then you know the makeup of the atmosphere. 69 00:05:49,920 --> 00:05:52,120 You can just break it down. 70 00:05:52,120 --> 00:05:54,200 So say your pressure is 1 atmosphere 71 00:05:54,200 --> 00:05:57,690 and you have 20% oxygen in the at-- that's not right. 72 00:05:57,690 --> 00:05:59,910 But 20% oxygen in the atmosphere, 73 00:05:59,910 --> 00:06:03,333 your oxygen would be contributing 0.20 atmospheres 74 00:06:03,333 --> 00:06:04,500 to the pressure [INAUDIBLE]. 75 00:06:04,500 --> 00:06:05,580 JOHN DOLHUN: Very good. 76 00:06:05,580 --> 00:06:06,960 Very good, Alec. 77 00:06:06,960 --> 00:06:12,340 So Alec said that you've got 20.9% oxygen in the atmosphere. 78 00:06:12,340 --> 00:06:15,630 So we can convert that to a decimal. 79 00:06:15,630 --> 00:06:18,240 Partial pressure of oxygen on any given day 80 00:06:18,240 --> 00:06:22,050 would be the percent of oxygen that's 81 00:06:22,050 --> 00:06:27,660 in the atmosphere times the atmospheric pressure 82 00:06:27,660 --> 00:06:34,620 on that particular day minus the pressure of the water vapor 83 00:06:34,620 --> 00:06:37,060 that we're talking about. 84 00:06:37,060 --> 00:06:42,375 So that gives us a handle on this. 85 00:06:42,375 --> 00:06:44,940 I want to show you probably the simplest 86 00:06:44,940 --> 00:06:47,550 example of Henry's Law. 87 00:06:47,550 --> 00:06:54,360 I brought a bottle of Coke here, and these are hard, right, 88 00:06:54,360 --> 00:06:55,830 because they pack them-- 89 00:06:55,830 --> 00:07:00,970 there's a head of carbon dioxide gas over the liquid. 90 00:07:00,970 --> 00:07:04,120 Now when I open this, I'm going to release the gas, 91 00:07:04,120 --> 00:07:07,770 so the partial pressure of CO2 over this liquid is gone. 92 00:07:07,770 --> 00:07:10,650 We should start to see bubbles coming out of the solution, 93 00:07:10,650 --> 00:07:12,459 right? 94 00:07:12,459 --> 00:07:14,040 [HISSING] 95 00:07:14,040 --> 00:07:20,700 Oh good, it's not an explosive one, so that's good. 96 00:07:20,700 --> 00:07:24,840 So there are the bubbles of the dissolved carbon dioxide 97 00:07:24,840 --> 00:07:26,970 gas starting to come out. 98 00:07:26,970 --> 00:07:31,050 And that's a simple example of Henry's Law. 99 00:07:31,050 --> 00:07:33,615 Can anybody think of a more complex example? 100 00:07:40,940 --> 00:07:45,480 Anybody a diver here? 101 00:07:45,480 --> 00:07:46,500 Kelly, you're a diver? 102 00:07:46,500 --> 00:07:48,167 AUDIENCE: Oh, no, I'm just [INAUDIBLE].. 103 00:07:48,167 --> 00:07:49,980 JOHN DOLHUN: OK. 104 00:07:49,980 --> 00:07:50,800 When you-- 105 00:07:50,800 --> 00:07:52,230 AUDIENCE: Yeah. 106 00:07:52,230 --> 00:07:53,440 It's like the bends, right? 107 00:07:53,440 --> 00:07:56,910 Because as you go down further, the pressure 108 00:07:56,910 --> 00:08:03,560 increases so that more nitrogen can dissolve in your blood, 109 00:08:03,560 --> 00:08:04,170 you said? 110 00:08:04,170 --> 00:08:05,460 JOHN DOLHUN: Yeah, very good. 111 00:08:05,460 --> 00:08:07,715 Yeah, so you've got gases in your blood. 112 00:08:07,715 --> 00:08:09,090 And when you go down, when you're 113 00:08:09,090 --> 00:08:12,310 diving down under a great pressure, 114 00:08:12,310 --> 00:08:17,590 when you start your ascent, all of those gas bubbles 115 00:08:17,590 --> 00:08:19,210 are going to come out. 116 00:08:19,210 --> 00:08:20,470 And they have to go somewhere. 117 00:08:20,470 --> 00:08:22,930 They could migrate anywhere in your body, 118 00:08:22,930 --> 00:08:26,090 and it could cause a rash. 119 00:08:26,090 --> 00:08:29,560 It could cause some type of joint pain. 120 00:08:29,560 --> 00:08:32,840 You could end up with paralysis, even death. 121 00:08:32,840 --> 00:08:37,510 So divers have to really, really time their ascent. 122 00:08:37,510 --> 00:08:39,039 That there's a name for that. 123 00:08:39,039 --> 00:08:40,690 Kelly said the bends. 124 00:08:40,690 --> 00:08:42,194 That's one of the names. 125 00:08:45,620 --> 00:08:50,615 It's also called DCS, Decompression Sickness. 126 00:09:02,410 --> 00:09:07,060 That's a great example of Henry's Law. 127 00:09:07,060 --> 00:09:12,370 What about if we think about temperature and dissolved 128 00:09:12,370 --> 00:09:13,840 oxygen? 129 00:09:13,840 --> 00:09:15,910 Let's actually take a look at that. 130 00:09:20,630 --> 00:09:25,100 Here is a graph of oxygen concentration and temperature. 131 00:09:25,100 --> 00:09:26,690 What stands out to you here? 132 00:09:36,710 --> 00:09:37,210 Sean? 133 00:09:37,210 --> 00:09:40,780 AUDIENCE: It decreases exponentially with temperature. 134 00:09:40,780 --> 00:09:42,820 JOHN DOLHUN: Yeah, as the water is warming up, 135 00:09:42,820 --> 00:09:46,580 look what's happening to the dissolved oxygen. 136 00:09:46,580 --> 00:09:48,486 Why do you think that's happening? 137 00:09:52,950 --> 00:09:59,040 And why, when the water is cold, can we hold so much oxygen 138 00:09:59,040 --> 00:10:02,180 in that cold water? 139 00:10:02,180 --> 00:10:02,930 Kelly. 140 00:10:02,930 --> 00:10:05,750 AUDIENCE: Is it because, as the temperature increases, 141 00:10:05,750 --> 00:10:08,245 the average kinetic energy of the molecules 142 00:10:08,245 --> 00:10:10,910 increases, and the distribution broadens, 143 00:10:10,910 --> 00:10:16,040 so more oxygen has the ability to escape? 144 00:10:16,040 --> 00:10:17,195 JOHN DOLHUN: Good, good. 145 00:10:17,195 --> 00:10:20,870 As the temperature increases, the kinetic energy of the water 146 00:10:20,870 --> 00:10:23,240 molecules is increasing, and they're 147 00:10:23,240 --> 00:10:26,360 starting-- think about when you boil water. 148 00:10:26,360 --> 00:10:28,790 Bam, they're bubbling out. 149 00:10:28,790 --> 00:10:31,400 That hydrogen bonding network is gone. 150 00:10:31,400 --> 00:10:34,910 All those intermolecular forces of attraction are gone. 151 00:10:34,910 --> 00:10:39,350 Now think about this side when the water gets really cold 152 00:10:39,350 --> 00:10:45,170 and you form this hydrogen bonding network. 153 00:10:45,170 --> 00:10:47,300 I mean, it expands, right? 154 00:10:47,300 --> 00:10:48,200 Pipes break. 155 00:10:48,200 --> 00:10:49,550 That's why our pipes break. 156 00:10:49,550 --> 00:10:52,775 It's because of the hydrogen bonding in the ice crystals 157 00:10:52,775 --> 00:10:54,410 when they expand out. 158 00:10:54,410 --> 00:10:58,150 But look at the crevices here in these things. 159 00:10:58,150 --> 00:11:01,580 So the oxygen molecules can swim in and out of those, 160 00:11:01,580 --> 00:11:04,880 and they can become weakly trapped and pinned in. 161 00:11:04,880 --> 00:11:09,700 And there you've got a dramatic increase 162 00:11:09,700 --> 00:11:15,020 in the amount of oxygen that can dissolve in the colder waters. 163 00:11:15,020 --> 00:11:20,960 The other thing to keep in mind about the water is the heat 164 00:11:20,960 --> 00:11:23,660 capacity of water is much greater 165 00:11:23,660 --> 00:11:26,090 than the heat capacity of air. 166 00:11:26,090 --> 00:11:28,700 It takes a lot more energy to change 167 00:11:28,700 --> 00:11:30,750 the temperature of water. 168 00:11:30,750 --> 00:11:32,625 I mean, you can-- 169 00:11:32,625 --> 00:11:34,890 I've gone out when it's 85 degrees, 170 00:11:34,890 --> 00:11:37,830 and I want to go for a swim across from my house. 171 00:11:37,830 --> 00:11:41,190 And I jump in, and it's only 67 in there. 172 00:11:41,190 --> 00:11:44,820 So the water hasn't caught up to the temperature of the air. 173 00:11:47,870 --> 00:11:54,270 Now there are a lot of different equations out there 174 00:11:54,270 --> 00:11:57,120 that actually would let us calculate 175 00:11:57,120 --> 00:12:02,430 the potential of a body of water to hold oxygen, theoretically, 176 00:12:02,430 --> 00:12:05,320 how much could be out there on a given day. 177 00:12:05,320 --> 00:12:07,860 And the more complex the equation, 178 00:12:07,860 --> 00:12:09,660 the better the results. 179 00:12:09,660 --> 00:12:12,840 I found a couple empirical, simple equations 180 00:12:12,840 --> 00:12:17,280 that give really good results, so I'm going to go with these. 181 00:12:17,280 --> 00:12:21,700 And they're all based on altitude and temperature. 182 00:12:21,700 --> 00:12:23,940 If you look at the equation, it's 183 00:12:23,940 --> 00:12:26,980 all about the atmospheric pressure, 184 00:12:26,980 --> 00:12:31,840 the water vapor pressure, and the temperature of the water, 185 00:12:31,840 --> 00:12:33,880 which is in Celsius. 186 00:12:33,880 --> 00:12:39,750 So if we look at that equation, if the pressure, 187 00:12:39,750 --> 00:12:43,150 the atmospheric pressure goes up, right, 188 00:12:43,150 --> 00:12:46,130 what happens to the dissolved oxygen concentration? 189 00:12:53,740 --> 00:12:56,110 If you're trying to calculate the saturated level 190 00:12:56,110 --> 00:13:00,070 of dissolved oxygen, and the pressure goes up, 191 00:13:00,070 --> 00:13:01,870 the atmospheric pressure, what happens 192 00:13:01,870 --> 00:13:03,370 to the DO concentration? 193 00:13:07,480 --> 00:13:11,140 I promise this is not a trick question. 194 00:13:11,140 --> 00:13:12,372 This is-- Alec. 195 00:13:12,372 --> 00:13:13,330 AUDIENCE: It increases. 196 00:13:13,330 --> 00:13:15,250 JOHN DOLHUN: It absolutely increases. 197 00:13:15,250 --> 00:13:16,150 Yeah. 198 00:13:16,150 --> 00:13:18,880 Now what happens if we have a high water vapor 199 00:13:18,880 --> 00:13:21,700 pressure that day? 200 00:13:21,700 --> 00:13:24,010 You might be on a mountaintop stream. 201 00:13:24,010 --> 00:13:25,730 Water vapor pressure is very high. 202 00:13:25,730 --> 00:13:26,890 What happens to the DO? 203 00:13:31,410 --> 00:13:31,910 Someone? 204 00:13:31,910 --> 00:13:32,840 AUDIENCE: Decreases. 205 00:13:32,840 --> 00:13:34,100 JOHN DOLHUN: Sam, decreases. 206 00:13:34,100 --> 00:13:35,870 Good. 207 00:13:35,870 --> 00:13:40,190 And the other situation, which if the river temperature is 208 00:13:40,190 --> 00:13:43,520 high, then it's intuitive, right? 209 00:13:43,520 --> 00:13:48,620 Your DO is going to be smaller. 210 00:13:48,620 --> 00:13:50,870 So that's how you use those equations. 211 00:13:50,870 --> 00:13:52,910 And then what you can do with the equation 212 00:13:52,910 --> 00:13:57,560 is you can calculate a thing called the percent saturation 213 00:13:57,560 --> 00:14:05,020 level, which is the actual DO that you get in the lab divided 214 00:14:05,020 --> 00:14:09,670 by the potential of water to hold oxygen 215 00:14:09,670 --> 00:14:12,520 based on the temperature and pressure above. 216 00:14:12,520 --> 00:14:14,350 And that saturated level is going 217 00:14:14,350 --> 00:14:18,910 to tell us a lot about the condition of the water. 218 00:14:18,910 --> 00:14:23,440 Usually-- I mean, you could have from 90% to 110%, 219 00:14:23,440 --> 00:14:24,400 something like that. 220 00:14:24,400 --> 00:14:25,540 That's normal. 221 00:14:25,540 --> 00:14:29,920 If you get to 120% or greater, that's 222 00:14:29,920 --> 00:14:32,950 a problem, because there are different diseases 223 00:14:32,950 --> 00:14:34,270 that the fish can-- 224 00:14:34,270 --> 00:14:37,955 they have an oxygen bubble disease fish can get 225 00:14:37,955 --> 00:14:40,146 if it becomes too saturated. 226 00:14:40,146 --> 00:14:44,800 So this is something that you'll do these calculations, 227 00:14:44,800 --> 00:14:48,580 and the TAs will carry a pH meter. 228 00:14:48,580 --> 00:14:51,040 They'll record the air temperature, 229 00:14:51,040 --> 00:14:54,670 the atmospheric pressure, the river water 230 00:14:54,670 --> 00:14:56,560 temperature each day you go down, 231 00:14:56,560 --> 00:14:58,930 and they'll put that on the whiteboard. 232 00:14:58,930 --> 00:15:04,450 Here is some simple data that will 233 00:15:04,450 --> 00:15:06,340 allow you to interpolate the water 234 00:15:06,340 --> 00:15:11,660 vapor pressures based on temperatures. 235 00:15:11,660 --> 00:15:13,490 And you can go in between these, and you'll 236 00:15:13,490 --> 00:15:15,410 get very good results. 237 00:15:15,410 --> 00:15:19,230 If you can't find it on here, you could use this equation. 238 00:15:19,230 --> 00:15:23,190 But the T here is the temperature of air, 239 00:15:23,190 --> 00:15:25,350 and it's in Kelvin. 240 00:15:25,350 --> 00:15:27,510 And back here, this is the temperature 241 00:15:27,510 --> 00:15:29,470 of the river in Celsius. 242 00:15:29,470 --> 00:15:33,200 So don't get confused with that. 243 00:15:33,200 --> 00:15:36,050 And now I'd like to spend a few minutes talking 244 00:15:36,050 --> 00:15:42,440 about the actual method that we're going to use in this lab. 245 00:15:42,440 --> 00:15:44,690 This method was actually discovered 246 00:15:44,690 --> 00:15:55,500 by a graduate student by the name of Winkler back in 1888. 247 00:15:55,500 --> 00:15:58,890 And the method has withstood time. 248 00:15:58,890 --> 00:16:03,000 What he did is he developed this series of oxidation reduction 249 00:16:03,000 --> 00:16:09,090 equations to actually measure the dissolved oxygen 250 00:16:09,090 --> 00:16:12,300 concentration in saltwater. 251 00:16:12,300 --> 00:16:15,360 And he came up with this series of equations. 252 00:16:15,360 --> 00:16:19,740 And it's been 130 years, and this is still here. 253 00:16:19,740 --> 00:16:23,550 Today they have the fancy dissolved oxygen meters, 254 00:16:23,550 --> 00:16:25,260 which we're not using, but you can just 255 00:16:25,260 --> 00:16:28,500 drop it in and get your DO. 256 00:16:28,500 --> 00:16:32,940 They used this method to calibrate those meters today. 257 00:16:32,940 --> 00:16:34,440 So you're using-- you're going to be 258 00:16:34,440 --> 00:16:36,660 doing the real chemistry here. 259 00:16:36,660 --> 00:16:41,740 The whole method is based on that if you've 260 00:16:41,740 --> 00:16:45,730 got oxygen in the water, iodide is 261 00:16:45,730 --> 00:16:48,850 going to get oxidized to iodine, and you're 262 00:16:48,850 --> 00:16:53,410 going to be able to titrate the iodine with sodium thiosulfate. 263 00:16:53,410 --> 00:16:59,150 So let's just go through the method just a little bit here. 264 00:16:59,150 --> 00:17:01,720 So we start with manganese sulfate, 265 00:17:01,720 --> 00:17:04,660 and we form a white precipitate. 266 00:17:04,660 --> 00:17:08,560 But if oxygen is present in the water, 267 00:17:08,560 --> 00:17:11,740 oxygen is an oxidizing agent here. 268 00:17:11,740 --> 00:17:16,150 It's going to oxidize this manganese hydroxide 269 00:17:16,150 --> 00:17:21,560 to this tetravalent manganic species. 270 00:17:21,560 --> 00:17:26,170 So you've got manganese over here, which is a plus 2, 271 00:17:26,170 --> 00:17:30,210 and over here, you've got a plus 4. 272 00:17:30,210 --> 00:17:31,140 There are a couple-- 273 00:17:31,140 --> 00:17:34,210 in the literature, there's some argument about this. 274 00:17:34,210 --> 00:17:38,070 Some people feel the species is a trivalent, 275 00:17:38,070 --> 00:17:40,780 and they're saying it's MnOH3. 276 00:17:43,350 --> 00:17:48,720 So on this side, you'd have a trivalent manganese species. 277 00:17:48,720 --> 00:17:52,720 Other people are saying no, it's MnO2. 278 00:17:52,720 --> 00:17:54,435 It's a hydrated form of mnO2. 279 00:17:57,900 --> 00:17:59,820 It's tetravalent. 280 00:17:59,820 --> 00:18:02,850 What I've done is I've combined both these 281 00:18:02,850 --> 00:18:07,290 to give you this manganic species here, which works. 282 00:18:07,290 --> 00:18:09,690 This is tetravalent. 283 00:18:09,690 --> 00:18:12,060 So notice that when you've formed this, 284 00:18:12,060 --> 00:18:15,330 this is like a brown flock. 285 00:18:15,330 --> 00:18:19,370 You've captured the oxygen at this point. 286 00:18:19,370 --> 00:18:24,290 Now you've got to dissolve that, so we add sulfuric acid 287 00:18:24,290 --> 00:18:27,290 to dissolve that brown precipitate. 288 00:18:27,290 --> 00:18:30,890 And then there's iodide in there. 289 00:18:30,890 --> 00:18:40,430 So this oxidized manganese will oxidize iodide to iodine. 290 00:18:40,430 --> 00:18:44,180 We can then detect it with sodium thiosulfate, 291 00:18:44,180 --> 00:18:49,250 and the iodine gets reduced back down to iodide. 292 00:18:49,250 --> 00:18:53,510 If you look at this, for every oxygen, every one oxygen, 293 00:18:53,510 --> 00:18:56,920 you make to manganic species. 294 00:18:56,920 --> 00:19:00,770 Each manganic species gives you one I2, 295 00:19:00,770 --> 00:19:04,580 and each I2 requires two thiosulfate. 296 00:19:04,580 --> 00:19:15,410 So that's a 4 to 1 ratio, thiosulfate to oxygen. 297 00:19:15,410 --> 00:19:18,580 So let's take a look at your first day, which 298 00:19:18,580 --> 00:19:23,290 is the standardization of the thiosulfate. 299 00:19:23,290 --> 00:19:26,470 We have to know exactly what the concentration of that 300 00:19:26,470 --> 00:19:31,380 is when we titrate the river water to actually get-- to home 301 00:19:31,380 --> 00:19:33,880 in on the exact concentration. 302 00:19:33,880 --> 00:19:38,830 So we're going to be using a primary standard, potassium 303 00:19:38,830 --> 00:19:39,330 biiodate. 304 00:19:47,660 --> 00:19:52,650 Does anybody know what the qualities of a primary standard 305 00:19:52,650 --> 00:19:53,150 are? 306 00:19:59,390 --> 00:20:01,190 When you pick a primary standard, 307 00:20:01,190 --> 00:20:02,330 it's pretty important. 308 00:20:02,330 --> 00:20:06,910 You want something that has certain properties. 309 00:20:06,910 --> 00:20:08,935 Anybody ever worked with a primary standard? 310 00:20:11,760 --> 00:20:14,490 No? 311 00:20:14,490 --> 00:20:19,305 OK, well, first thing, notice how big this is. 312 00:20:19,305 --> 00:20:22,020 It has a very high formula weight. 313 00:20:22,020 --> 00:20:24,585 So that's actually a good thing. 314 00:20:24,585 --> 00:20:28,820 Not all primary standards have that. 315 00:20:28,820 --> 00:20:30,650 When you mass it out, you're going 316 00:20:30,650 --> 00:20:33,530 to have less error on the balance because 317 00:20:33,530 --> 00:20:35,630 of the mass of this thing. 318 00:20:35,630 --> 00:20:40,190 Also, it has to be something that's pure. 319 00:20:40,190 --> 00:20:45,650 And this is like 99.9% pure. 320 00:20:45,650 --> 00:20:48,470 The other thing is you need something 321 00:20:48,470 --> 00:20:51,800 that does not have any water vapor attached, 322 00:20:51,800 --> 00:20:53,810 no attached water. 323 00:20:53,810 --> 00:20:56,300 The TAs put this in the oven. 324 00:20:56,300 --> 00:21:02,090 So no hydrated water. 325 00:21:05,520 --> 00:21:08,610 And then the final thing is, you want-- 326 00:21:08,610 --> 00:21:12,510 it should be stable at room temperature and when heated. 327 00:21:23,360 --> 00:21:25,640 And oftentimes we'll look at the cost, too. 328 00:21:25,640 --> 00:21:28,448 That's another factor that comes into play. 329 00:21:28,448 --> 00:21:29,990 But what you're going to do is you're 330 00:21:29,990 --> 00:21:34,950 going to weigh out 0.0818 grams of this. 331 00:21:34,950 --> 00:21:37,400 And if you divide by the molecular weight of that, 332 00:21:37,400 --> 00:21:39,200 you'll get moles. 333 00:21:39,200 --> 00:21:42,030 And you're going to make a 100-mil solution. 334 00:21:42,030 --> 00:21:45,170 So divide that by 0.1 liters, and you'll 335 00:21:45,170 --> 00:21:47,120 get your concentration. 336 00:21:47,120 --> 00:21:52,760 You're actually making up something like a 0.0021 molar 337 00:21:52,760 --> 00:21:57,060 solution of that standard. 338 00:21:57,060 --> 00:22:01,550 And then you're going to use that to standardize 339 00:22:01,550 --> 00:22:04,390 your thiosulfate. 340 00:22:04,390 --> 00:22:08,120 We're also going to be using starch in this reaction. 341 00:22:08,120 --> 00:22:11,020 So why do you think we need to use starch 342 00:22:11,020 --> 00:22:13,083 when we're titrating something? 343 00:22:17,820 --> 00:22:18,620 Alec. 344 00:22:18,620 --> 00:22:20,310 AUDIENCE: Starch reacts with iodide, 345 00:22:20,310 --> 00:22:23,460 and it creates the blue color so that when 346 00:22:23,460 --> 00:22:25,435 we react-- when we were titrating, 347 00:22:25,435 --> 00:22:26,670 it could turn really pale. 348 00:22:26,670 --> 00:22:27,030 JOHN DOLHUN: OK. 349 00:22:27,030 --> 00:22:29,655 AUDIENCE: So it was really hard to tell if it was clear or not. 350 00:22:29,655 --> 00:22:31,830 So I think the starch helps indicate whether or not 351 00:22:31,830 --> 00:22:34,020 you've gotten rid of all of the iodide. 352 00:22:34,020 --> 00:22:35,010 Iodide, yeah. 353 00:22:35,010 --> 00:22:35,760 JOHN DOLHUN: Good. 354 00:22:35,760 --> 00:22:36,070 Good. 355 00:22:36,070 --> 00:22:36,800 That's very good. 356 00:22:36,800 --> 00:22:40,860 So starch actually reacts with iodide and iodine, 357 00:22:40,860 --> 00:22:42,300 gives you that blue-black color. 358 00:22:42,300 --> 00:22:46,050 So if you're titrating something yellow to clear, 359 00:22:46,050 --> 00:22:49,270 sometimes it might be harder to see. 360 00:22:49,270 --> 00:22:54,370 So what Alec said was your solution 361 00:22:54,370 --> 00:22:58,650 actually reacts with starch. 362 00:22:58,650 --> 00:23:02,590 So I actually brought some of the solution in here, 363 00:23:02,590 --> 00:23:04,420 and I brought a piece of bread in. 364 00:23:04,420 --> 00:23:06,430 I don't know if this is going to work, 365 00:23:06,430 --> 00:23:10,300 but bread has starch in it, doesn't it? 366 00:23:10,300 --> 00:23:13,630 So I'm going to put someone on this bread. 367 00:23:13,630 --> 00:23:15,560 Wow. 368 00:23:15,560 --> 00:23:17,080 Look at that blue black. 369 00:23:17,080 --> 00:23:18,850 So something's going on here. 370 00:23:18,850 --> 00:23:21,720 It's reacting with the starch, right? 371 00:23:21,720 --> 00:23:24,390 Can I have a volunteer? 372 00:23:24,390 --> 00:23:27,730 Some brave person? 373 00:23:27,730 --> 00:23:29,740 I know you're all tired, but one of you. 374 00:23:29,740 --> 00:23:32,580 One of you, come up. 375 00:23:32,580 --> 00:23:34,170 Come on up, Maida. 376 00:23:34,170 --> 00:23:35,460 Maida, right? 377 00:23:38,210 --> 00:23:39,170 It's Maida, right? 378 00:23:39,170 --> 00:23:39,410 AUDIENCE: Yes. 379 00:23:39,410 --> 00:23:40,160 JOHN DOLHUN: OK. 380 00:23:40,160 --> 00:23:42,570 Maida, stand up front here. 381 00:23:42,570 --> 00:23:46,130 So what we're going to do is we're going to open this up. 382 00:23:46,130 --> 00:23:51,000 And put a pair of these on, Maida. 383 00:23:51,000 --> 00:23:58,340 And I'm going to let you hold this beaker 384 00:23:58,340 --> 00:24:00,650 and face your fellow students. 385 00:24:00,650 --> 00:24:03,230 And just hold it nice and-- 386 00:24:05,834 --> 00:24:07,380 and what we're going to do is we're 387 00:24:07,380 --> 00:24:09,330 going to add something to it. 388 00:24:09,330 --> 00:24:11,020 It's clear, right? 389 00:24:11,020 --> 00:24:14,920 OK, keep your eye on the beaker. 390 00:24:14,920 --> 00:24:16,590 Maida, don't drop but whatever you do. 391 00:24:16,590 --> 00:24:16,860 AUDIENCE: I won't drop it. 392 00:24:16,860 --> 00:24:17,527 JOHN DOLHUN: OK. 393 00:24:17,527 --> 00:24:18,350 [CHUCKLES] 394 00:24:22,630 --> 00:24:24,580 OK. 395 00:24:24,580 --> 00:24:26,617 So keep your eye on that beaker. 396 00:24:30,030 --> 00:24:31,770 Don't take your eyes off the beaker. 397 00:24:38,680 --> 00:24:40,395 Now what-- don't worry. 398 00:24:40,395 --> 00:24:41,860 Keep watching it, Maida. 399 00:24:41,860 --> 00:24:42,610 Don't get nervous. 400 00:24:42,610 --> 00:24:43,890 Oh! 401 00:24:43,890 --> 00:24:46,120 Now that's what I'm talking about. 402 00:24:46,120 --> 00:24:47,430 You see that? 403 00:24:47,430 --> 00:24:49,660 This is what we're talking about. 404 00:24:49,660 --> 00:24:51,450 And I mean, you're titrating. 405 00:24:51,450 --> 00:24:52,620 You can't see the end point. 406 00:24:52,620 --> 00:24:56,400 You put this in, now that last drop of titrant, 407 00:24:56,400 --> 00:24:58,410 it's going to turn it clear. 408 00:24:58,410 --> 00:25:00,725 You're going to be able to see your titration. 409 00:25:00,725 --> 00:25:03,030 And thank you very much, Maida. 410 00:25:08,800 --> 00:25:11,920 So what's going on with the starch? 411 00:25:11,920 --> 00:25:14,500 Let's take a look at this. 412 00:25:14,500 --> 00:25:20,170 Starch is made up of about 25% amylose, which 413 00:25:20,170 --> 00:25:23,050 is the linear helical form. 414 00:25:23,050 --> 00:25:28,920 And it also is made up about 75% of the branched amylopectin. 415 00:25:28,920 --> 00:25:34,455 What happens is we have iodine and iodide present 416 00:25:34,455 --> 00:25:39,520 in our solution, and when those two come together, 417 00:25:39,520 --> 00:25:44,590 they actually form this pentaiodide anion. 418 00:25:44,590 --> 00:25:50,980 So you've got some I2, some I minus. 419 00:25:50,980 --> 00:25:53,650 Remember, I2 is amber. 420 00:25:53,650 --> 00:25:55,600 I minus is clear. 421 00:25:55,600 --> 00:25:59,660 When you get these two together and they 422 00:25:59,660 --> 00:26:04,700 insert into this helix, the amylose helix of starch, 423 00:26:04,700 --> 00:26:09,560 and what amylose does is it forces the pentaiodide anion 424 00:26:09,560 --> 00:26:12,930 to go in linearly into that helix. 425 00:26:12,930 --> 00:26:16,390 Then the energy spacings change. 426 00:26:16,390 --> 00:26:19,350 So you've got-- the way the wavelength of light hits 427 00:26:19,350 --> 00:26:21,540 that, you're going to see blue black. 428 00:26:21,540 --> 00:26:25,140 It's all happening inside of the starch with the amylose. 429 00:26:25,140 --> 00:26:26,640 That's the key thing. 430 00:26:26,640 --> 00:26:28,210 There are different people-- 431 00:26:28,210 --> 00:26:32,280 some people still believe it's I3 minus. 432 00:26:32,280 --> 00:26:34,560 There's somebody else out there saying no, no, it's 433 00:26:34,560 --> 00:26:36,600 a polyiodide. 434 00:26:36,600 --> 00:26:40,170 There's always going to be some controversy in the-- 435 00:26:40,170 --> 00:26:42,270 but they're working on it. 436 00:26:42,270 --> 00:26:44,010 I like I5. 437 00:26:44,010 --> 00:26:50,310 And someone actually made an inorganic complex 438 00:26:50,310 --> 00:26:55,920 to make it look like starch, and they proved it was I5. 439 00:26:55,920 --> 00:26:57,720 But even after this paper came out, 440 00:26:57,720 --> 00:27:00,120 there's still a lot of controversy, so. 441 00:27:02,880 --> 00:27:07,687 So for your standardization, pretty simple. 442 00:27:07,687 --> 00:27:09,270 You're going to go through, and you're 443 00:27:09,270 --> 00:27:10,920 going to just follow these steps. 444 00:27:10,920 --> 00:27:14,250 The TAs will go through this with you, very simple. 445 00:27:14,250 --> 00:27:16,740 And you're going to start off with probably 446 00:27:16,740 --> 00:27:22,650 something like this, kind of like a reddish solution. 447 00:27:22,650 --> 00:27:29,520 And then you're going to start adding your thiosulfate. 448 00:27:29,520 --> 00:27:34,980 And gradually, your titrating the iodine in this solution 449 00:27:34,980 --> 00:27:36,780 to iodide. 450 00:27:36,780 --> 00:27:39,205 So here you've got a more yellow solution. 451 00:27:41,725 --> 00:27:46,780 What you want to do is you want to find a spot when it turns 452 00:27:46,780 --> 00:27:50,580 yellow to add your starch. 453 00:27:50,580 --> 00:27:54,540 And the starch has to be bubbly hot on the hot plate. 454 00:27:54,540 --> 00:27:59,150 And if you add it too early, there's 455 00:27:59,150 --> 00:28:00,920 so much iodine in there, it's going 456 00:28:00,920 --> 00:28:03,200 to destroy the starch complex. 457 00:28:03,200 --> 00:28:05,420 You won't get a reaction. 458 00:28:05,420 --> 00:28:10,365 But if you wait until it's so pale yellow, what happens, 459 00:28:10,365 --> 00:28:10,865 Thomas? 460 00:28:12,850 --> 00:28:13,850 AUDIENCE: It turns blue. 461 00:28:13,850 --> 00:28:15,990 It makes the complex successfully, 462 00:28:15,990 --> 00:28:17,670 it turns it dark blue. 463 00:28:17,670 --> 00:28:20,040 JOHN DOLHUN: It turns it dark blue. 464 00:28:20,040 --> 00:28:20,730 Yeah. 465 00:28:20,730 --> 00:28:23,087 But if you wait too long, right-- 466 00:28:23,087 --> 00:28:25,670 AUDIENCE: [? I ?] [? mean, ?] if you add too much, [INAUDIBLE] 467 00:28:25,670 --> 00:28:26,620 JOHN DOLHUN: Did you-- 468 00:28:26,620 --> 00:28:28,970 you had a reaction yesterday where your starch 469 00:28:28,970 --> 00:28:30,680 was an globules, right? 470 00:28:30,680 --> 00:28:31,550 Is that-- 471 00:28:31,550 --> 00:28:32,502 AUDIENCE: Oh yeah. 472 00:28:32,502 --> 00:28:35,862 It formed a film because we didn't keep it hot. 473 00:28:35,862 --> 00:28:37,820 JOHN DOLHUN: Oh, the starch was not hot enough. 474 00:28:37,820 --> 00:28:39,580 OK, that explains that. 475 00:28:39,580 --> 00:28:40,520 AUDIENCE: [INAUDIBLE] 476 00:28:40,520 --> 00:28:40,970 JOHN DOLHUN: Yeah. 477 00:28:40,970 --> 00:28:41,943 AUDIENCE: We put it in and stirred, 478 00:28:41,943 --> 00:28:44,900 and it made a bunch of little blue specks that [INAUDIBLE].. 479 00:28:44,900 --> 00:28:46,220 JOHN DOLHUN: Yes, yes. 480 00:28:46,220 --> 00:28:47,730 Yeah, I've seen that before. 481 00:28:47,730 --> 00:28:52,850 So you want to keep your starch hot, and just be patient. 482 00:28:52,850 --> 00:28:57,020 And then you just take a plastic pasture pipette, 483 00:28:57,020 --> 00:28:59,660 take a swig of it, shoot it in, and you 484 00:28:59,660 --> 00:29:01,610 should get your blue black. 485 00:29:01,610 --> 00:29:03,570 And then look. 486 00:29:03,570 --> 00:29:05,120 You've got your blue black. 487 00:29:05,120 --> 00:29:07,730 You put that last drop of thiosulfate in, 488 00:29:07,730 --> 00:29:10,440 and you've got your clear solution. 489 00:29:10,440 --> 00:29:12,440 So you turn around, and you're writing this down 490 00:29:12,440 --> 00:29:16,970 in your notebooks, right, and then you look back, 491 00:29:16,970 --> 00:29:19,460 but it's starting to turn blue black again. 492 00:29:19,460 --> 00:29:20,440 What should you do? 493 00:29:23,490 --> 00:29:24,350 What would you do? 494 00:29:28,840 --> 00:29:31,322 AUDIENCE: Add another drop of titrant. 495 00:29:31,322 --> 00:29:33,030 JOHN DOLHUN: Add another drop of titrant. 496 00:29:33,030 --> 00:29:35,070 That's what I would do, Thomas. 497 00:29:35,070 --> 00:29:36,200 But it's not correct. 498 00:29:36,200 --> 00:29:36,950 AUDIENCE: [LAUGHS] 499 00:29:36,950 --> 00:29:38,742 JOHN DOLHUN: But I would do the same thing. 500 00:29:38,742 --> 00:29:40,440 I would add another drop of titrant. 501 00:29:40,440 --> 00:29:41,930 AUDIENCE: Oh, what if it just turned blue by itself, 502 00:29:41,930 --> 00:29:43,555 [INAUDIBLE] and you're just [INAUDIBLE] 503 00:29:43,555 --> 00:29:46,410 JOHN DOLHUN: There's a side reaction going on in the air. 504 00:29:46,410 --> 00:29:48,510 When you get this clear, you've got 505 00:29:48,510 --> 00:29:51,250 all iodide present in there. 506 00:29:51,250 --> 00:29:52,290 But what happens is-- 507 00:29:55,180 --> 00:30:00,010 so you've got iodide there, but you also 508 00:30:00,010 --> 00:30:01,450 have oxygen in the air. 509 00:30:04,860 --> 00:30:15,090 And the oxygen is oxidizing the iodide to iodine, 510 00:30:15,090 --> 00:30:18,450 and we don't want this iodine coming from the air. 511 00:30:18,450 --> 00:30:20,610 We want it only from the river water, 512 00:30:20,610 --> 00:30:22,950 right, from the oxygen in the river. 513 00:30:22,950 --> 00:30:27,330 So this is a side reaction that can go on if you let it set. 514 00:30:27,330 --> 00:30:29,010 So just ignore it. 515 00:30:29,010 --> 00:30:35,670 Just take your end point, your final neutralization, 516 00:30:35,670 --> 00:30:38,040 and you're good. 517 00:30:38,040 --> 00:30:40,800 Take a look at the stoichiometry here. 518 00:30:40,800 --> 00:30:45,575 One biiodate make six I2. 519 00:30:45,575 --> 00:30:50,020 Each I2 reacts with two thiosulfate. 520 00:30:50,020 --> 00:30:55,715 So it's 12 to 1 thiosulfate to biiodate. 521 00:30:55,715 --> 00:30:57,090 What you're going to do is you're 522 00:30:57,090 --> 00:31:01,140 going to do three trials, and they all should agree to 523 00:31:01,140 --> 00:31:03,360 within 2% or 3%. 524 00:31:03,360 --> 00:31:06,780 If they don't, do an extra trial or two. 525 00:31:06,780 --> 00:31:08,880 And what you're going to do is you're 526 00:31:08,880 --> 00:31:11,730 going to find your mean, your standard deviation, 527 00:31:11,730 --> 00:31:14,370 and your confidence intervals and then give all 528 00:31:14,370 --> 00:31:16,530 that information to your TA. 529 00:31:16,530 --> 00:31:18,690 Yesterday the TAs did a beautiful job. 530 00:31:18,690 --> 00:31:21,690 They put everybody's on an Excel spreadsheet, 531 00:31:21,690 --> 00:31:23,650 had it all averaged out. 532 00:31:23,650 --> 00:31:26,020 They really did a good job yesterday. 533 00:31:26,020 --> 00:31:30,270 The students really homed in on the exact concentration 534 00:31:30,270 --> 00:31:32,690 of the thiosulfate. 535 00:31:32,690 --> 00:31:34,400 So it's pretty simple. 536 00:31:34,400 --> 00:31:37,460 You do your calculations right there in the lab. 537 00:31:37,460 --> 00:31:40,970 And then you have a choice of using the class average 538 00:31:40,970 --> 00:31:44,960 or using your own results for the dissolved oxygen that will 539 00:31:44,960 --> 00:31:46,340 take place on the next day. 540 00:31:51,620 --> 00:31:54,020 So collection of water samples. 541 00:31:54,020 --> 00:31:57,680 So you're going to be going to the river for day two. 542 00:31:57,680 --> 00:32:00,500 And we have these poles. 543 00:32:00,500 --> 00:32:06,160 If you have long arms, you'll take a short poll. 544 00:32:06,160 --> 00:32:08,690 If you're short and have short arms, 545 00:32:08,690 --> 00:32:10,490 then we have real long poles. 546 00:32:10,490 --> 00:32:12,770 They're like hockey sticks. 547 00:32:12,770 --> 00:32:18,980 So you get your stick, and what you do is you insert your-- 548 00:32:18,980 --> 00:32:22,830 your BOD bottle snaps into the clip that I've got inside. 549 00:32:22,830 --> 00:32:25,130 You take the stopper out, and then you 550 00:32:25,130 --> 00:32:26,900 go to the edge of the dock. 551 00:32:26,900 --> 00:32:32,150 Don't fall in, and don't push anybody, OK. 552 00:32:32,150 --> 00:32:36,080 Remember the cyanobacteria and all that out there. 553 00:32:36,080 --> 00:32:38,900 And take gloves with you, because when 554 00:32:38,900 --> 00:32:42,740 you put this under water, it's got to be completely submerged. 555 00:32:42,740 --> 00:32:44,780 You have to reach over the dock. 556 00:32:44,780 --> 00:32:47,060 You've got to stopper it underwater. 557 00:32:47,060 --> 00:32:49,910 So you've got to have gloves with you, all right. 558 00:32:49,910 --> 00:32:52,040 So I stoppered mine underwater. 559 00:32:52,040 --> 00:32:57,500 I bring it up, take it out, and then I look at the-- 560 00:32:57,500 --> 00:33:01,400 I take the bottle, and I do this test. 561 00:33:01,400 --> 00:33:03,410 I don't see any bubbles. 562 00:33:03,410 --> 00:33:05,070 That's a good sign. 563 00:33:05,070 --> 00:33:06,870 That means it's perfect. 564 00:33:06,870 --> 00:33:10,340 If you see bubbles, you've introduced more oxygen 565 00:33:10,340 --> 00:33:11,120 in there. 566 00:33:11,120 --> 00:33:14,030 Your DO concentrations are going to be too high. 567 00:33:14,030 --> 00:33:16,980 Pour it out, and restart again. 568 00:33:16,980 --> 00:33:19,980 OK, so that's the collection. 569 00:33:19,980 --> 00:33:22,850 Then you bring the stuff back to the lab, 570 00:33:22,850 --> 00:33:28,352 and you're going to treat the bottles in the lab. 571 00:33:28,352 --> 00:33:31,790 This here is wrong. 572 00:33:31,790 --> 00:33:35,450 You don't want to use these digital pipetters to treat 573 00:33:35,450 --> 00:33:39,250 the water, because you'll be introducing oxygen 574 00:33:39,250 --> 00:33:40,640 into those water bottles. 575 00:33:40,640 --> 00:33:45,440 What you're going to use is your 10-mL glass pipette. 576 00:33:45,440 --> 00:33:49,670 And what we're going to do here is 577 00:33:49,670 --> 00:33:53,300 each pair of students will have four bottles. 578 00:33:53,300 --> 00:33:54,620 So you're going to-- 579 00:33:54,620 --> 00:33:58,730 first, you're going to treat it with the manganese sulfate, 2 580 00:33:58,730 --> 00:34:00,140 mLs of manganese sulfate. 581 00:34:00,140 --> 00:34:03,710 That's the first reaction on that oxidation reduction 582 00:34:03,710 --> 00:34:05,600 Winkler series. 583 00:34:05,600 --> 00:34:07,790 And the way you do it is-- what I would do 584 00:34:07,790 --> 00:34:12,170 is I would take up 10 mils of manganese sulfate 585 00:34:12,170 --> 00:34:15,310 to prevent any airflow, any air. 586 00:34:15,310 --> 00:34:17,060 And then what you're going to do is you're 587 00:34:17,060 --> 00:34:19,010 going to take the stopper out. 588 00:34:19,010 --> 00:34:22,580 You're going to go just below the surface of the liquid 589 00:34:22,580 --> 00:34:24,679 and put in 2 mils. 590 00:34:24,679 --> 00:34:26,600 And then your partner can stopper it. 591 00:34:26,600 --> 00:34:27,679 You go to the next one. 592 00:34:27,679 --> 00:34:29,540 You do all four of them. 593 00:34:29,540 --> 00:34:33,500 The last 2 mils in here, shoot it into waste. 594 00:34:33,500 --> 00:34:37,219 And then do the same thing with the alkaline-iodide-azide 595 00:34:37,219 --> 00:34:40,040 reagent, 2 mils in each bottle. 596 00:34:40,040 --> 00:34:44,989 And you should look at the bottle at this point. 597 00:34:44,989 --> 00:34:46,730 After you add those reagents, there 598 00:34:46,730 --> 00:34:49,010 should not be any bubbles. 599 00:34:49,010 --> 00:34:52,460 If there's a bubble, it means you've introduced air, 600 00:34:52,460 --> 00:34:57,660 and your DO values will be higher by doing that. 601 00:34:57,660 --> 00:35:04,250 So once you've treated with these two steps here, you've 602 00:35:04,250 --> 00:35:06,560 essentially trapped the oxygen. You're 603 00:35:06,560 --> 00:35:10,080 going to have this brown flock like this. 604 00:35:10,080 --> 00:35:15,000 Now you just shake that a bit, and then you're 605 00:35:15,000 --> 00:35:18,930 going to dissolve it now by adding sulfuric acid, 28 606 00:35:18,930 --> 00:35:20,730 drops of sulfuric. 607 00:35:20,730 --> 00:35:23,670 Acid for the sulfuric, you don't go below the surface. 608 00:35:23,670 --> 00:35:27,330 You just open the lid, and you drip, drip it in. 609 00:35:27,330 --> 00:35:28,320 The acid is heavy. 610 00:35:28,320 --> 00:35:31,290 It's going to fall right to the bottom of the bottle. 611 00:35:31,290 --> 00:35:35,970 And now you should have a bubble in there. 612 00:35:35,970 --> 00:35:38,730 You will have a bubble after you add the sulfuric, 613 00:35:38,730 --> 00:35:41,260 and that's OK. 614 00:35:41,260 --> 00:35:45,120 So when you're done with this, you're ready to titrate. 615 00:35:45,120 --> 00:35:49,710 And we've got to-- we're supposed to titrate 200 mils. 616 00:35:49,710 --> 00:35:52,980 That's what you titrated when you did your standardization as 617 00:35:52,980 --> 00:35:54,650 well. 618 00:35:54,650 --> 00:36:00,460 But we've got to make up for the 4 mils 619 00:36:00,460 --> 00:36:03,370 that we added there in the beginning. 620 00:36:03,370 --> 00:36:05,700 We've displaced something there. 621 00:36:05,700 --> 00:36:11,160 So you want to titrate 200 mLs times-- 622 00:36:11,160 --> 00:36:18,000 you've got a 300 mL BOD bottle, and you've taken and added 623 00:36:18,000 --> 00:36:20,810 4 mLs of stuff to it. 624 00:36:20,810 --> 00:36:23,500 So if you do the math to make up for that, 625 00:36:23,500 --> 00:36:27,780 you really have to titrate 203 mLs. 626 00:36:27,780 --> 00:36:30,850 So there's a couple ways you could do this. 627 00:36:30,850 --> 00:36:36,980 You can use a 100-mL graduated cylinder, and the error on that 628 00:36:36,980 --> 00:36:39,950 is about plus or minus 0.5. 629 00:36:39,950 --> 00:36:44,280 You fill that up twice, put that in your container. 630 00:36:44,280 --> 00:36:49,410 The last 3 mils, you could use this for accuracy 631 00:36:49,410 --> 00:36:53,430 to get your last 3 mLs in, and then you're good. 632 00:36:53,430 --> 00:36:58,890 But you can also just titrate 200 mLs 633 00:36:58,890 --> 00:37:03,420 and then multiply your answer by a correction factor, which 634 00:37:03,420 --> 00:37:07,980 would be 203 over 200. 635 00:37:07,980 --> 00:37:19,100 And that will give you the same answer as titrating the 203. 636 00:37:19,100 --> 00:37:22,070 So the math is pretty simple here. 637 00:37:22,070 --> 00:37:25,220 You're converting the moles of your titrant 638 00:37:25,220 --> 00:37:28,910 to moles of oxygen, grams of oxygen. 639 00:37:28,910 --> 00:37:31,520 You divide by the liters. 640 00:37:31,520 --> 00:37:36,260 If you're doing 200 mLs, that's 0.2 liters. 641 00:37:36,260 --> 00:37:40,360 And then you get your milligrams per liter in PPM. 642 00:37:46,880 --> 00:37:50,960 I kept mentioning we're using the-- 643 00:37:50,960 --> 00:37:54,170 we've got to add this alkaline-azide solution. 644 00:37:54,170 --> 00:37:57,410 We're actually using the azide modification 645 00:37:57,410 --> 00:37:59,710 of the Winkler method. 646 00:37:59,710 --> 00:38:01,860 And what is that? 647 00:38:01,860 --> 00:38:09,280 Well, there are NOx gases in the atmosphere. 648 00:38:09,280 --> 00:38:12,940 What's the nastiest NOx gas that you can think of? 649 00:38:25,670 --> 00:38:27,780 I'll give you a hint. 650 00:38:27,780 --> 00:38:33,581 It's a big greenhouse gas, and it's not CO2. 651 00:38:33,581 --> 00:38:35,330 AUDIENCE: Ozone? 652 00:38:35,330 --> 00:38:38,270 JOHN DOLHUN: Ozone is a gas up there, yeah. 653 00:38:38,270 --> 00:38:40,610 But that protects us. 654 00:38:40,610 --> 00:38:45,550 Our ozone layer is a layer of protection. 655 00:38:45,550 --> 00:38:46,690 But what's-- yes. 656 00:38:46,690 --> 00:38:50,375 AUDIENCE: Is it NO2 or-- 657 00:38:50,375 --> 00:38:51,500 JOHN DOLHUN: The other way. 658 00:38:51,500 --> 00:38:52,310 AUDIENCE: Or N O? 659 00:38:52,310 --> 00:38:55,550 I know that [INAUDIBLE] 660 00:38:55,550 --> 00:38:59,410 JOHN DOLHUN: All right, please don't laugh at this. 661 00:38:59,410 --> 00:39:03,710 It's laughing gas, N2O. 662 00:39:03,710 --> 00:39:05,830 You're all-- I mean, the atmosphere 663 00:39:05,830 --> 00:39:08,220 is loaded with laughing gas. 664 00:39:08,220 --> 00:39:08,980 I know. 665 00:39:08,980 --> 00:39:11,440 Everybody's laughing now. 666 00:39:11,440 --> 00:39:12,640 It's great. 667 00:39:12,640 --> 00:39:15,430 Where does it come from, N2O? 668 00:39:15,430 --> 00:39:17,440 All the fertilizer. 669 00:39:17,440 --> 00:39:20,560 1% of all the fertilizer in the world 670 00:39:20,560 --> 00:39:23,290 goes up in the atmosphere as laughing gas. 671 00:39:23,290 --> 00:39:25,270 It's not from a dentist's office. 672 00:39:25,270 --> 00:39:26,550 It's from fertilizer. 673 00:39:26,550 --> 00:39:27,940 I know. 674 00:39:27,940 --> 00:39:29,770 I don't want to think about dentists. 675 00:39:29,770 --> 00:39:31,360 I was just at one yesterday. 676 00:39:31,360 --> 00:39:33,880 I don't like dentists. 677 00:39:33,880 --> 00:39:41,240 But every ton of laughing gas that's in the atmosphere. 678 00:39:41,240 --> 00:39:45,280 is like 300 tons of CO2. 679 00:39:45,280 --> 00:39:48,860 And it stays up there for over 100 years. 680 00:39:48,860 --> 00:39:51,350 And what does it do? 681 00:39:51,350 --> 00:39:59,000 Well, who said ozone back there? 682 00:39:59,000 --> 00:39:59,780 There you are. 683 00:39:59,780 --> 00:40:01,190 OK. 684 00:40:01,190 --> 00:40:05,120 Laughing gas reacts with ozone, and it 685 00:40:05,120 --> 00:40:07,590 forms dinitrogen dioxide. 686 00:40:10,500 --> 00:40:15,570 And this dinitrogen dioxide only lasts for about an hour. 687 00:40:15,570 --> 00:40:27,090 And immediately, the N2O2 reacts with air and water 688 00:40:27,090 --> 00:40:28,080 to form nitrites. 689 00:40:35,760 --> 00:40:41,110 And here we are talking about greenhouse gas in the world, 690 00:40:41,110 --> 00:40:44,730 and this is affecting our little tiny reaction in the Charles 691 00:40:44,730 --> 00:40:49,320 River experiment, because these nitrites, look what they do. 692 00:40:49,320 --> 00:40:53,280 They get in and oxidize iodide to iodine. 693 00:40:53,280 --> 00:40:55,590 And we don't want our iodine coming 694 00:40:55,590 --> 00:41:00,510 from some reaction from laughing gas, right, from nitrite. 695 00:41:00,510 --> 00:41:03,750 We want it coming from the oxygen in the river. 696 00:41:03,750 --> 00:41:06,870 So we add sodium azide. 697 00:41:06,870 --> 00:41:10,110 And that zaps the nitrites, convert them 698 00:41:10,110 --> 00:41:13,320 to harmless nitrogen and water. 699 00:41:13,320 --> 00:41:19,010 So that's the theory behind why we're 700 00:41:19,010 --> 00:41:20,990 using the azide modification. 701 00:41:20,990 --> 00:41:23,210 All that for these nitrites. 702 00:41:26,840 --> 00:41:33,290 So let's talk for a moment about pH, pH in natural waters. 703 00:41:33,290 --> 00:41:34,613 Let's see here. 704 00:41:34,613 --> 00:41:36,545 Pulling down some board, here. 705 00:41:40,420 --> 00:41:42,430 Who knows the definition of pH? 706 00:41:53,490 --> 00:41:56,185 Remember your chemical principles from a long time a-- 707 00:41:56,185 --> 00:41:56,685 Alec. 708 00:41:56,685 --> 00:41:59,760 AUDIENCE: I think it was log of concentration of hydrogen 709 00:41:59,760 --> 00:42:00,822 ions, [INAUDIBLE] ions. 710 00:42:00,822 --> 00:42:01,780 JOHN DOLHUN: Very good. 711 00:42:01,780 --> 00:42:04,590 The negative log of the concentration of the hydrogen 712 00:42:04,590 --> 00:42:05,716 ions. 713 00:42:05,716 --> 00:42:06,216 So pH. 714 00:42:12,990 --> 00:42:16,230 And I mean, you all know the pH scale is 0 to 14, 715 00:42:16,230 --> 00:42:19,020 and acid is less than 7. 716 00:42:19,020 --> 00:42:22,410 And I hope you know what color litmus paper changes, right, 717 00:42:22,410 --> 00:42:22,915 with pH. 718 00:42:25,680 --> 00:42:29,970 That was a question on a TV show with Regis Philbin, 719 00:42:29,970 --> 00:42:31,890 You Want to Be a Millionaire. 720 00:42:31,890 --> 00:42:36,290 A guy actually got up to the million dollar question. 721 00:42:36,290 --> 00:42:40,430 And I happened to turn it on just at that point, 722 00:42:40,430 --> 00:42:42,080 and they ask him, what color does 723 00:42:42,080 --> 00:42:45,470 litmus paper change in base? 724 00:42:45,470 --> 00:42:48,590 And the guy said, oh, I don't know, 725 00:42:48,590 --> 00:42:51,110 but can I call my lifeline? 726 00:42:51,110 --> 00:42:52,490 And they said yes. 727 00:42:52,490 --> 00:42:55,610 So he called this prestigious biologist 728 00:42:55,610 --> 00:42:58,790 at one of the California universities. 729 00:42:58,790 --> 00:43:00,770 And they said red. 730 00:43:00,770 --> 00:43:02,000 [LAUGHTER] 731 00:43:02,000 --> 00:43:06,514 And the guy answers red, and he loses the million dollars. 732 00:43:06,514 --> 00:43:09,860 Oh, I was beside myself. 733 00:43:09,860 --> 00:43:12,660 So if you remember anything, remember what color 734 00:43:12,660 --> 00:43:15,320 litmus paper is in acid. 735 00:43:15,320 --> 00:43:24,440 But in the river, the pH can go from 6.5 to 8.5. 736 00:43:24,440 --> 00:43:30,800 And the pH effects everything, from the solubility of metals-- 737 00:43:30,800 --> 00:43:34,385 if it gets too acidic out there in the river, 738 00:43:34,385 --> 00:43:40,740 the metals become more soluble, mercury, cadmium, arsenic, 739 00:43:40,740 --> 00:43:42,000 all those metals. 740 00:43:42,000 --> 00:43:45,300 So the fish uptake the metals, and we eat the fish. 741 00:43:45,300 --> 00:43:48,690 And with global warming, the acidity of the rivers 742 00:43:48,690 --> 00:43:54,210 is gradually drifting very slightly lower. 743 00:43:54,210 --> 00:43:57,390 It also affects the forms of phosphorous. 744 00:43:57,390 --> 00:44:02,310 So remember, you've got PO4 to the 3 minus. 745 00:44:02,310 --> 00:44:04,950 But if it's slightly acidic, you might 746 00:44:04,950 --> 00:44:12,810 have the hydrogen phosphate or the dihydrogen phosphate. 747 00:44:16,170 --> 00:44:20,750 Or you could end up with phosphoric acid, 748 00:44:20,750 --> 00:44:24,150 depending on how acidic it gets. 749 00:44:24,150 --> 00:44:26,891 What about photosynthesis and pH? 750 00:44:29,870 --> 00:44:34,570 Where are my biologists at, my resident bi-- 751 00:44:34,570 --> 00:44:36,790 there must be somebody in bio in here. 752 00:44:36,790 --> 00:44:39,160 Come on. 753 00:44:39,160 --> 00:44:41,230 Don't be afraid. 754 00:44:41,230 --> 00:44:42,400 Yes. 755 00:44:42,400 --> 00:44:43,750 There you are. 756 00:44:43,750 --> 00:44:47,446 What's the equation for photosynthesis? 757 00:44:47,446 --> 00:44:49,080 AUDIENCE: Water and carbon dioxide. 758 00:44:49,080 --> 00:44:50,080 JOHN DOLHUN: Good, good. 759 00:44:50,080 --> 00:44:52,150 Water and carbon dioxide. 760 00:44:52,150 --> 00:44:54,100 Let's just write that down for a moment. 761 00:44:57,950 --> 00:45:08,020 So CO2 plus water, little bit of sun. 762 00:45:08,020 --> 00:45:10,120 AUDIENCE: Oxygen and glucose. 763 00:45:10,120 --> 00:45:12,760 JOHN DOLHUN: Oxygen and sugars, good. 764 00:45:12,760 --> 00:45:14,610 So CH2O, n. 765 00:45:20,230 --> 00:45:25,000 So does the pH go up or down during photosynthesis? 766 00:45:29,060 --> 00:45:31,165 I mean, it's like a 50/50 chance. 767 00:45:36,630 --> 00:45:39,550 Sean, you want to answer, don't you? 768 00:45:39,550 --> 00:45:42,520 AUDIENCE: I would say the pH goes up. 769 00:45:42,520 --> 00:45:43,520 JOHN DOLHUN: It goes up? 770 00:45:43,520 --> 00:45:44,400 OK. 771 00:45:44,400 --> 00:45:45,180 Anyone else? 772 00:45:45,180 --> 00:45:45,975 Alec? 773 00:45:45,975 --> 00:45:47,100 AUDIENCE: It goes down? 774 00:45:47,100 --> 00:45:47,850 JOHN DOLHUN: It goes down? 775 00:45:47,850 --> 00:45:48,240 OK. 776 00:45:48,240 --> 00:45:48,780 [LAUGHTER] 777 00:45:48,780 --> 00:45:49,500 There you go. 778 00:45:49,500 --> 00:45:52,350 I told you it's like a 50/50, right? 779 00:45:52,350 --> 00:45:56,130 All right, let's do a little experiment with this. 780 00:45:58,680 --> 00:46:00,670 I'm going to pour myself a drink here. 781 00:46:04,380 --> 00:46:05,640 This is good stuff. 782 00:46:11,150 --> 00:46:12,830 It's not Gatorade, I can tell you that. 783 00:46:16,175 --> 00:46:21,020 This is a classic test in the medical profession, 784 00:46:21,020 --> 00:46:24,020 if you're going to medical school, for breath. 785 00:46:24,020 --> 00:46:28,160 And when I'm doing this, you cannot make me laugh. 786 00:46:28,160 --> 00:46:30,670 If you make me laugh, I'm dead, OK. 787 00:46:30,670 --> 00:46:31,730 Please. 788 00:46:31,730 --> 00:46:36,540 I'm going to play some music to relax myself here. 789 00:46:36,540 --> 00:46:40,820 Let me just-- let me see if we can get this on here. 790 00:46:40,820 --> 00:46:41,540 OK. 791 00:46:41,540 --> 00:46:42,250 There we go. 792 00:46:45,340 --> 00:46:47,460 So I'm breathing into this. 793 00:46:51,450 --> 00:46:55,350 We don't hear any music coming out. 794 00:46:55,350 --> 00:46:56,922 Going to-- 795 00:46:56,922 --> 00:47:01,190 [MUSIC PLAYING] 796 00:47:01,190 --> 00:47:01,750 There we go. 797 00:47:10,410 --> 00:47:12,030 You're making me laugh, Sean. 798 00:47:15,790 --> 00:47:18,130 I may have to have you come up and help me with this. 799 00:47:18,130 --> 00:47:22,090 [MUSIC PLAYING] 800 00:47:41,410 --> 00:47:43,073 I may not be OK. 801 00:47:43,073 --> 00:47:44,365 The color's supposed to change. 802 00:47:44,365 --> 00:47:48,122 [MUSIC PLAYING] 803 00:47:59,530 --> 00:48:00,680 There we are. 804 00:48:00,680 --> 00:48:02,980 Good? 805 00:48:02,980 --> 00:48:03,700 I'm OK. 806 00:48:07,460 --> 00:48:09,980 So what just happened? 807 00:48:12,888 --> 00:48:14,930 AUDIENCE: You blew carbon dioxide into the water. 808 00:48:14,930 --> 00:48:17,000 JOHN DOLHUN: I blew carbon dioxide in the water. 809 00:48:17,000 --> 00:48:25,764 So we've got CO2 plus water going to what? 810 00:48:29,480 --> 00:48:30,190 Yeah. 811 00:48:30,190 --> 00:48:31,190 AUDIENCE: Carbonic acid. 812 00:48:31,190 --> 00:48:32,315 JOHN DOLHUN: Carbonic acid. 813 00:48:32,315 --> 00:48:33,125 Good. 814 00:48:33,125 --> 00:48:41,150 H2CO3, which breaks down into H plus plus bicarbonate. 815 00:48:44,290 --> 00:48:49,850 Now photosynthesis needs carbon dioxide, right? 816 00:48:49,850 --> 00:48:52,620 So we take that out of the equation, 817 00:48:52,620 --> 00:48:57,630 which means we're also taking out the H plus. 818 00:48:57,630 --> 00:48:59,696 So does the pH go up or down? 819 00:48:59,696 --> 00:49:00,610 AUDIENCE: Up. 820 00:49:00,610 --> 00:49:01,800 JOHN DOLHUN: Alec? 821 00:49:01,800 --> 00:49:02,990 Up, up, up. 822 00:49:02,990 --> 00:49:03,650 OK? 823 00:49:03,650 --> 00:49:04,610 Good. 824 00:49:04,610 --> 00:49:07,980 And pollution and pH, same thing. 825 00:49:07,980 --> 00:49:11,480 If you've got pollution, you've got all this vegetation. 826 00:49:11,480 --> 00:49:15,140 So you've got photosynthesis, so the pH is going to be up. 827 00:49:17,880 --> 00:49:25,720 This is Lassen Lake, Volcanic National Park, pH 2, 2.0. 828 00:49:25,720 --> 00:49:29,070 You do not want to stick your foot into this lake. 829 00:49:29,070 --> 00:49:33,900 And then you've got some safety of the chemicals, which 830 00:49:33,900 --> 00:49:38,580 the most serious is the azide reagent, which 831 00:49:38,580 --> 00:49:41,100 it's a neurological toxin. 832 00:49:41,100 --> 00:49:44,620 And if you ingest it, it can cause death. 833 00:49:44,620 --> 00:49:47,910 So please be careful with that. 834 00:49:47,910 --> 00:49:50,850 Sulfuric acid, you know how bad that is. 835 00:49:50,850 --> 00:49:53,520 You don't want to get it in your respiratory system. 836 00:49:53,520 --> 00:49:57,930 And the manganese sulfate seems innocuous, 837 00:49:57,930 --> 00:50:01,110 but it attacks the central nervous system, 838 00:50:01,110 --> 00:50:03,730 targets blood and kidneys. 839 00:50:03,730 --> 00:50:05,250 So be careful with that. 840 00:50:05,250 --> 00:50:10,290 Sodium thiosulfate is a respiratory irritant, 841 00:50:10,290 --> 00:50:13,330 can cause breathing problems. 842 00:50:13,330 --> 00:50:17,100 So if you feel like you're having breathing issues, 843 00:50:17,100 --> 00:50:18,270 it could be that. 844 00:50:18,270 --> 00:50:21,150 Biiodate can burn your eyes. 845 00:50:21,150 --> 00:50:24,510 Very, very dangerous stuff around your eyes. 846 00:50:24,510 --> 00:50:28,030 So all of these things, you have to be careful with. 847 00:50:28,030 --> 00:50:28,560 OK. 848 00:50:28,560 --> 00:50:31,410 So we'll see you Thursday for the last lecture 849 00:50:31,410 --> 00:50:33,260 in this series.