2 00:00:09,653 --> 00:00:14,077 When CO2 disolves in sea water it does some interesting chemistry, 3 00:00:14,077 --> 00:00:18,659 the same chemistry that goes on in our cell plasma, 4 00:00:18,659 --> 00:00:22,980 and in our blood. 5 00:00:22,980 --> 00:00:27,970 The CO2 reacts with water, which is what it did for photosynthesis, 6 00:00:27,970 --> 00:00:34,930 but that was a totally different reaction. This is just a an a-biological chemical 7 00:00:34,930 --> 00:00:37,260 reaction, where you join those two 8 00:00:37,260 --> 00:00:43,440 molecules together and make a carbonic acid, H2CO3. 10 00:00:43,440 --> 00:00:46,930 If you figure out the oxidation state of the 11 00:00:46,930 --> 00:00:51,638 carbon here, it's the same as the oxidation state was here. 12 00:00:51,638 --> 00:00:56,110 Because adding an H20, you know you get plus, you're minus two 13 00:00:56,110 --> 00:00:59,440 for this and plus two for that, and so it balances, 14 00:00:59,440 --> 00:01:00,480 It's the same, 15 00:01:00,480 --> 00:01:02,310 we're not changing the oxidation state. 16 00:01:02,310 --> 00:01:07,720 It doesn't take energy to do this reaction, it just happens all by itself. 17 00:01:09,030 --> 00:01:13,690 Carbonic acid is called an acid, a chemical is 18 00:01:13,690 --> 00:01:18,490 called an acid, if it can release H+ to the water. 19 00:01:18,490 --> 00:01:21,790 A water solution that has 20 00:01:21,790 --> 00:01:25,590 a high concentration of H+, of protons, 21 00:01:25,590 --> 00:01:28,700 is what they call an acidic solution. 22 00:01:28,700 --> 00:01:31,850 The reason why we mention it 23 00:01:31,850 --> 00:01:35,660 at all is because H+ is a very aggressive chemical. 24 00:01:35,660 --> 00:01:38,690 if you spill acid on your skin you'll burn yourself, because the 25 00:01:38,690 --> 00:01:43,460 H+ can react with the the molecules in your skin. 26 00:01:43,460 --> 00:01:46,770 It can dissolve the threads in your pants. 27 00:01:47,990 --> 00:01:50,800 Carbonic acid 28 00:01:50,800 --> 00:01:54,230 is what they call a diprotic acid, 29 00:01:54,230 --> 00:01:58,990 because it can release first one and then a second H+. 30 00:01:58,990 --> 00:02:04,710 This is bicarbonate, like baking soda is sodium bicarbonate. 31 00:02:04,710 --> 00:02:09,080 And this is carbonate ion. Has a charge of minus two. 32 00:02:10,540 --> 00:02:16,660 How this chemistry works is kind of complicated and it can be best understood 33 00:02:16,660 --> 00:02:21,460 by writing the chemical reactions in a way that don't just vaguely 34 00:02:21,460 --> 00:02:26,160 sluff off these H+'s, because there aren't that many H+'s in solution. 35 00:02:26,160 --> 00:02:28,340 It's not like some infinite slush fund that you can 36 00:02:28,340 --> 00:02:31,580 just throw stuff into as much as you want to. 37 00:02:31,580 --> 00:02:34,100 Actually the best approximation is to write 38 00:02:34,100 --> 00:02:36,030 these reactions where it's not changing the 39 00:02:36,030 --> 00:02:39,722 H+ at all, because there's so much more carbon than there is H+. 40 00:02:39,722 --> 00:02:41,680 Writing the reaction in that way, 41 00:02:41,680 --> 00:02:47,410 we have CO2 plus this carbonate ion ( CO3(2-) ) and 42 00:02:47,410 --> 00:02:53,610 a water on one side and on the other side, we have two of these bicarbonates ( HCO3(-) ). 43 00:02:54,920 --> 00:02:58,920 This is an equilibrium chemical reaction, to which we can 44 00:02:58,920 --> 00:03:02,796 apply an idea known as the Le Chatelier's principle. 45 00:03:02,796 --> 00:03:06,740 Le Chatelier's principle says that if a system 46 00:03:06,740 --> 00:03:11,420 is in equilibrium, and then you perturb it by adding some chemical... 47 00:03:11,420 --> 00:03:16,170 on one side of the reaction, it will push the reaction in 48 00:03:16,170 --> 00:03:21,110 the other direction to try to minimize the imbalance that you've created. 49 00:03:21,110 --> 00:03:28,540 If you add CO2 to this, what happens is it consumes this carbonate ion, 50 00:03:28,540 --> 00:03:31,790 and shifts more toward the bicarbonate. 51 00:03:31,790 --> 00:03:37,340 It's as though the carbonate ion here is sharing one of its two minus charges 52 00:03:37,340 --> 00:03:42,840 with the CO2. The importance of that is that these 53 00:03:42,840 --> 00:03:48,310 guys that have electrical charges, They're called ions. 54 00:03:48,310 --> 00:03:53,540 An ion can't evaporate into the air, there are no ions in the air. 55 00:03:54,960 --> 00:03:57,680 because they're just not stable. 57 00:03:57,680 --> 00:03:59,690 You can find them in water because the water 58 00:03:59,690 --> 00:04:01,920 allows it to form, but not in the air. 59 00:04:01,920 --> 00:04:07,410 By lending one of its negative charges to the CO2 to make a bicarbonate 60 00:04:07,410 --> 00:04:13,140 out of it, the carbonate is essentially hiding that CO2 from the atmosphere. 61 00:04:13,140 --> 00:04:18,770 The existence of this chemical reaction allows 62 00:04:18,770 --> 00:04:21,960 the water to take up more CO2 than it would if 63 00:04:21,960 --> 00:04:23,590 there were no such chemistry. 64 00:04:24,700 --> 00:04:29,000 It turns out there's ten times more of this carbonate ion 65 00:04:29,000 --> 00:04:32,090 than there is dissolved CO2 in water. 66 00:04:32,090 --> 00:04:36,950 That means that the buffer strength, the ability of the water to take 67 00:04:36,950 --> 00:04:42,840 up CO2, is ten times stronger than it would be if this chemistry didn't exist. 68 00:04:42,840 --> 00:04:47,150 Oxygen, for example, or nitrogen are gases that can dissolve in water. 70 00:04:47,150 --> 00:04:50,040 But they don't do any of this wondrous pH chemistry. 71 00:04:50,040 --> 00:04:53,930 And so they don't have this buffer. 72 00:04:53,930 --> 00:04:59,920 They don't have much ability to take up those gases as CO2. 73 00:05:01,450 --> 00:05:06,670 The depletion of the carbonate ion by this 74 00:05:06,670 --> 00:05:12,500 buffer chemistry is what's known as ocean acidification. 75 00:05:12,500 --> 00:05:14,900 When you acidify the water you have 76 00:05:14,900 --> 00:05:18,470 less of this carbonate ion, and this is 77 00:05:18,470 --> 00:05:21,070 the part of the acidification that has the strongest impact 78 00:05:21,070 --> 00:05:25,230 on the biota of the ocean, 79 00:05:25,230 --> 00:05:30,630 especially life forms that make calcium carbonate shells like corals, 80 00:05:30,630 --> 00:05:34,780 or there are little plankton that have shells of calcium carbonate. 81 00:05:34,780 --> 00:05:38,420 Looking at this chemical reaction as an equilibrium again 82 00:05:40,730 --> 00:05:45,340 you could imagine that if some process takes out carbonate ion, 83 00:05:45,340 --> 00:05:50,230 this calcium carbonate is going to dissolve, to replenish that carbonate ion. 84 00:05:50,230 --> 00:05:52,540 It's paradoxical. 85 00:05:52,540 --> 00:05:57,145 You look a coral reef, and it's a big chunk of stuff made out of carbon, 86 00:05:57,145 --> 00:05:59,846 And you would think that putting more carbon 87 00:05:59,846 --> 00:06:03,054 into the system would make that chunk grow bigger. 88 00:06:03,054 --> 00:06:06,051 But actually because of this PH chemistry, 89 00:06:06,051 --> 00:06:09,266 it makes the makes corals dissolve.