WEBVTT 00:00:00.000 --> 00:00:02.580 Let's figure out the oxidation states 00:00:02.640 --> 00:00:05.440 for some more constituent atoms and molecules. 00:00:05.490 --> 00:00:11.830 So let's say I had magnesium oxide. 00:00:11.840 --> 00:00:14.490 MgO. 00:00:14.570 --> 00:00:16.570 I'll do oxygen in a different color. 00:00:16.580 --> 00:00:18.970 So what are going to be their oxidation states? 00:00:18.980 --> 00:00:20.190 And you might know this already, 00:00:20.200 --> 00:00:21.570 but let's look at the periodic table, 00:00:21.580 --> 00:00:23.700 because it never hurts to get familiar with it. 00:00:23.720 --> 00:00:24.730 So we have magnesium. 00:00:24.740 --> 00:00:27.840 Magnesium has two valance electrons. 00:00:27.940 --> 00:00:29.240 It's a Group 2 element. 00:00:29.260 --> 00:00:32.270 It would love to lose those two electrons. 00:00:32.290 --> 00:00:34.120 Oxygen, we already know, 00:00:34.130 --> 00:00:36.960 is one of the most electronegative atoms. 00:00:36.980 --> 00:00:38.480 It's so electronegative that 00:00:38.490 --> 00:00:42.080 oxidized has essentially been named after them. 00:00:42.130 --> 00:00:45.620 And we know that oxygen loves to gain two electrons. 00:00:45.640 --> 00:00:47.700 So this is kind of a marriage made in heaven. 00:00:47.740 --> 00:00:49.340 This guy wants to lose two electrons 00:00:49.350 --> 00:00:51.980 and this guy wants to gain two electrons. 00:00:52.010 --> 00:00:53.970 So what's going to happen? 00:00:53.980 --> 00:00:57.340 The magnesium is going to lose two electrons. 00:00:57.350 --> 00:00:58.920 It was neutral. 00:00:58.930 --> 00:01:03.100 So it's going to have a plus 2 charge, hypothetically. 00:01:03.120 --> 00:01:06.800 And then, the oxygen is going to have a minus 2 charge, 00:01:06.810 --> 00:01:08.990 because it gained the two electrons. 00:01:09.000 --> 00:01:13.410 So in this molecule of magnesium oxide, 00:01:13.430 --> 00:01:17.620 the oxidation state of magnesium is plus 2. 00:01:17.630 --> 00:01:22.560 And the oxidation state of the oxygen is minus 2. 00:01:22.570 --> 00:01:25.780 Now let's do a slightly harder one. 00:01:25.800 --> 00:01:34.590 Let's say we had magnesium hydroxide. 00:01:34.610 --> 00:01:40.790 So hydroxide is OH2. 00:01:40.810 --> 00:01:45.050 OH2 right there, where there's two hydroxide groups in this. 00:01:45.070 --> 00:01:49.190 So, my temptation would still be, look. 00:01:49.200 --> 00:01:52.620 Magnesium likes to lose its electrons, its two electrons, 00:01:52.640 --> 00:01:54.810 which would make it's charge positive 00:01:54.820 --> 00:01:57.120 -- it's hypothetical oxidation state positive. 00:01:57.130 --> 00:01:59.300 So my temptation is to say, 00:01:59.320 --> 00:02:01.090 hey, magnesium here would be plus 2. 00:02:01.100 --> 00:02:02.190 So let me write that there. 00:02:02.210 --> 00:02:06.070 And remember, in order for everything to work out, 00:02:06.090 --> 00:02:08.220 if it's a neutral compound, 00:02:08.230 --> 00:02:11.970 all of the oxidation states in it have to add up to 1. 00:02:11.990 --> 00:02:13.470 So let's see if that's going to work out. 00:02:13.490 --> 00:02:14.920 Now, oxygen. 00:02:14.930 --> 00:02:17.740 My impulse is that its oxidation state 00:02:17.750 --> 00:02:19.910 tends to be minus 2. 00:02:19.930 --> 00:02:21.260 So let me write that down. 00:02:21.270 --> 00:02:23.190 Minus 2. 00:02:23.200 --> 00:02:27.240 And hydrogen, when it's bonded with an oxygen 00:02:27.250 --> 00:02:28.480 -- remember. In this case, the hydrogen is bonded 00:02:28.490 --> 00:02:29.940 with the oxygen first. 00:02:29.960 --> 00:02:32.350 And then that's bonded to the magnesium. 00:02:32.360 --> 00:02:35.370 So the hydrogen is bonded to an oxygen. 00:02:35.390 --> 00:02:38.360 Hydrogen, if it was bonded to a magnesium, 00:02:38.370 --> 00:02:39.530 you might want to say, hey, 00:02:39.550 --> 00:02:40.630 maybe it'll take the electrons 00:02:40.640 --> 00:02:43.170 and it'll have a negative oxidation state. 00:02:43.180 --> 00:02:45.940 But when hydrogen is bonded with oxygen, 00:02:45.990 --> 00:02:47.530 it gives up the electrons. 00:02:47.550 --> 00:02:51.340 It only has one electron to give up. 00:02:51.350 --> 00:02:53.920 So it has a plus 1 oxidation state. 00:02:53.930 --> 00:02:56.340 So let's see. At first, you might say, hey, 00:02:56.350 --> 00:02:58.090 I'm adding up the oxidation states. 00:02:58.120 --> 00:03:00.790 Plus 2 minus 2 is 0 plus 1. 00:03:00.810 --> 00:03:03.650 I get a plus 1 oxidation state here. 00:03:03.670 --> 00:03:05.160 That doesn't make sense, Sal. 00:03:05.180 --> 00:03:06.340 This is a neutral compound. 00:03:06.350 --> 00:03:08.080 And what you to remember is oh, no, 00:03:08.090 --> 00:03:10.260 but you have two of these hydroxides right here. 00:03:10.270 --> 00:03:12.150 So what you do is you figure out 00:03:12.160 --> 00:03:16.710 the sum of the oxidation states of the hydroxide. 00:03:17.390 --> 00:03:20.500 So that's minus 2 plus 1. 00:03:20.260 --> 00:03:23.030 So for the entire hydroxide molecule, 00:03:23.040 --> 00:03:25.550 you have a minus 1 sum. 00:03:25.560 --> 00:03:27.810 And then you have two of them. Right? 00:03:27.830 --> 00:03:30.070 You have two hydroxide molecules here. 00:03:30.080 --> 00:03:34.690 So the contribution to the entire compound's 00:03:34.710 --> 00:03:37.380 oxidation state will be minus 1 for each hydroxide. 00:03:37.390 --> 00:03:39.460 But then you have two of them. 00:03:39.470 --> 00:03:43.300 So it's minus 2 and then plus 2 from the magnesium. 00:03:43.310 --> 00:03:45.260 And it all adds up to 0. 00:03:45.280 --> 00:03:47.060 So that worked out. 00:03:47.080 --> 00:03:49.470 Now, I want to do a little bit of an aside. 00:03:49.480 --> 00:03:51.400 I want to go back to doing some problems again. 00:03:51.420 --> 00:03:52.930 But I want to do a little bit of an aside 00:03:52.940 --> 00:03:54.480 on some of my terminology. 00:03:54.530 --> 00:03:57.060 Because I've kind of used oxidation state, and oxidized, 00:03:57.080 --> 00:04:00.890 and reduced interchangeably, to a certain degree. 00:04:00.910 --> 00:04:04.270 But, we've done so many problems with water 00:04:04.280 --> 00:04:07.200 with water autoionizing into 00:04:07.220 --> 00:04:10.040 -- actually, let me do 2 moles of water. 00:04:10.050 --> 00:04:12.020 And it's in equilibrium 00:04:12.030 --> 00:04:20.090 with 1 mole of H30 plus OH minus. 00:04:20.110 --> 00:04:22.280 And obviously, everything is in an aqueous solution. 00:04:22.290 --> 00:04:24.350 Now, let's look at the water. 00:04:24.360 --> 00:04:25.970 What are the oxidation states in this water right here? 00:04:25.990 --> 00:04:28.780 Well, we've done this already in the previous video. 00:04:28.790 --> 00:04:31.040 Oxidation state of oxygen is minus 2, 00:04:31.050 --> 00:04:34.110 because it's hogging the two electrons from the two hydrogens. 00:04:34.140 --> 00:04:36.940 Each hydrogen is giving up an electron. 00:04:36.950 --> 00:04:38.890 So it has an oxidation state of plus 1. 00:04:38.900 --> 00:04:40.570 And we see this molecule. 00:04:40.590 --> 00:04:41.600 Everything adds up. 00:04:41.610 --> 00:04:43.730 Because you have two hydrogens with a plus 1. 00:04:43.740 --> 00:04:44.830 So that's plus 2. 00:04:44.840 --> 00:04:48.380 Plus 2 minus 2 for that one oxygen, and you get to 0. 00:04:48.400 --> 00:04:49.630 And it's a neutral compound. 00:04:49.640 --> 00:04:51.950 Now here, what are the oxidation states? 00:04:51.960 --> 00:04:56.420 So one of these hydrogens left one of these water molecules 00:04:56.430 --> 00:05:00.610 and joined the other of the water molecules 00:05:00.630 --> 00:05:02.130 without taking its electron with it. 00:05:02.140 --> 00:05:04.210 So it left the electron over here. 00:05:04.220 --> 00:05:08.940 So that oxygen still has a minus 2 oxidation state. 00:05:08.960 --> 00:05:12.010 And this hydrogen still has a plus 1. 00:05:12.020 --> 00:05:15.230 And that's why you do minus 2 plus 1. 00:05:15.240 --> 00:05:16.370 You get minus 1. 00:05:16.380 --> 00:05:17.910 And this time, it works out, 00:05:17.930 --> 00:05:20.010 because that's the actual charge on this hydroxide ion. 00:05:20.020 --> 00:05:22.680 Now, here, what are the oxidation states? 00:05:22.690 --> 00:05:28.170 Each of the hydrogens have a plus 1 oxidation state. 00:05:28.190 --> 00:05:30.800 And then this oxygen has a minus 2. 00:05:30.810 --> 00:05:34.440 And so if you look at the charge for the entire molecule, 00:05:34.450 --> 00:05:37.410 plus 1 on three hydrogens, so that's plus 3. 00:05:37.420 --> 00:05:39.780 I just added them up. 00:05:39.800 --> 00:05:40.810 Minus 2. 00:05:40.830 --> 00:05:44.890 So plus 3 minus 2, I should have a plus 1 charge 00:05:44.900 --> 00:05:47.050 on this entire molecule, which is the case. 00:05:47.070 --> 00:05:48.900 Now, my question to you is 00:05:48.920 --> 00:05:52.860 has any of the oxidation states changed for any of the atoms? 00:05:52.880 --> 00:05:54.450 All of the hydrogens here 00:05:54.460 --> 00:05:58.130 -- and we could call this 2 moles of water. 00:05:58.140 --> 00:06:00.450 Or maybe I just have two molecules of water. 00:06:00.460 --> 00:06:02.120 But I have four hydrogens here. 00:06:02.140 --> 00:06:04.680 Right? And all of them had an oxidation state of 1. 00:06:04.690 --> 00:06:07.040 On the right-hand side, I have four hydrogens. 00:06:07.050 --> 00:06:09.460 All of them have an oxidation state of 1. 00:06:09.470 --> 00:06:13.580 So although their oxidation state is 1, in this reaction 00:06:13.600 --> 00:06:16.490 -- and you can pick either direction of the reaction-- 00:06:16.500 --> 00:06:19.250 hydrogen has not been oxidized. 00:06:19.290 --> 00:06:21.980 Its oxidation state did not change. 00:06:22.000 --> 00:06:26.410 Maybe it was oxidized in a previous reaction 00:06:26.420 --> 00:06:27.840 where the water was formed, 00:06:27.850 --> 00:06:29.910 but in this reaction, it was not oxidized. 00:06:29.930 --> 00:06:31.870 Likewise, the oxygens 00:06:31.880 --> 00:06:35.080 -- we have two oxygen molecules, or atoms, here. 00:06:35.090 --> 00:06:37.610 Each have a minus 2 oxidation state. 00:06:37.620 --> 00:06:39.520 Here, we have two oxygen molecules. 00:06:39.530 --> 00:06:41.390 Each have a minus 2 oxidation state. 00:06:41.400 --> 00:06:43.650 Due to this reaction, at least, 00:06:43.660 --> 00:06:48.210 no electrons changed hands in our oxidation state world. 00:06:48.230 --> 00:06:52.310 So this is not an oxidation or a reduction reaction. 00:06:52.330 --> 00:06:54.410 And I'm going to cover that in detail in the next video. 00:06:54.420 --> 00:06:55.530 And I just want to be clear that 00:06:55.550 --> 00:06:58.000 nothing here was oxidized or reduced, 00:06:58.020 --> 00:07:02.570 because their oxidation states stayed the same. 00:07:02.600 --> 00:07:08.170 Because sometimes I'll say, hey, look. 00:07:08.190 --> 00:07:10.230 Magnesium has an oxidation state of plus 2. 00:07:10.250 --> 00:07:13.370 And oxygen has an oxidation state of minus 2. 00:07:13.390 --> 00:07:15.400 Magnesium was oxidized. 00:07:15.420 --> 00:07:16.960 Two electrons were taken away from it. 00:07:16.980 --> 00:07:18.740 And oxygen was reduced. 00:07:18.750 --> 00:07:20.240 Two electrons were given to it. 00:07:20.260 --> 00:07:22.920 And I'll say that implying some reaction that produced it, 00:07:22.930 --> 00:07:24.610 but that's not always the case. 00:07:24.620 --> 00:07:25.820 You could have a reaction 00:07:25.830 --> 00:07:27.540 where that necessarily didn't happen. 00:07:27.570 --> 00:07:29.550 But the oxidation state for magnesium 00:07:29.560 --> 00:07:30.930 is definitely plus 2. 00:07:30.940 --> 00:07:34.210 And the oxidation state for the oxygen, 00:07:34.230 --> 00:07:36.890 or the oxidation number, is minus 2. 00:07:36.900 --> 00:07:38.860 But I think you know what I'm talking about 00:07:38.870 --> 00:07:40.300 when I say it was oxidized. 00:07:40.310 --> 00:07:43.080 At some point, it went from a neutral magnesium 00:07:43.100 --> 00:07:45.770 to a positively charged magnesium 00:07:45.790 --> 00:07:47.140 by losing two electrons. 00:07:47.160 --> 00:07:48.550 So it got oxidized. 00:07:48.570 --> 00:07:52.150 Now, let's do some harder problems. 00:07:52.160 --> 00:07:53.980 So hydrogen peroxide 00:07:53.990 --> 00:07:56.290 -- I've said multiple times already that 00:07:56.300 --> 00:08:01.440 oxygen tends to have a minus 2 oxidation state. 00:08:01.450 --> 00:08:02.670 This is minus 1. 00:08:02.680 --> 00:08:06.340 I think you see the pattern. These guys are plus 1. 00:08:06.350 --> 00:08:08.590 Hydrogen is plus or minus 1. 00:08:08.600 --> 00:08:10.560 These guys are plus 2. 00:08:10.570 --> 00:08:11.840 I think you see the pattern. 00:08:11.850 --> 00:08:14.160 It's whether you want to lose or gain electrons. 00:08:14.170 --> 00:08:16.050 You might say, well see, 00:08:16.060 --> 00:08:19.690 water normally has a minus 2 oxidation. 00:08:19.700 --> 00:08:21.120 So you might be tempted to do 00:08:21.140 --> 00:08:22.250 -- OK. 00:08:22.260 --> 00:08:25.190 Hydrogen has plus 1, because it's bonding with water. 00:08:25.200 --> 00:08:28.480 And oxygen has a minus 2. 00:08:28.490 --> 00:08:31.290 But when you do that, you immediately have a conundrum. 00:08:31.310 --> 00:08:32.750 This is a neutral molecule 00:08:32.770 --> 00:08:35.410 -- let's see. Two hydrogens plus 2. 00:08:35.430 --> 00:08:36.880 Two oxygens at minus 2. 00:08:36.890 --> 00:08:37.920 Minus 4. 00:08:37.940 --> 00:08:39.470 So this would end up with a minus 4 00:08:39.480 --> 00:08:41.510 total net oxidation state. 00:08:41.530 --> 00:08:42.860 And that's not the case 00:08:42.870 --> 00:08:44.120 because this doesn't have any charge. 00:08:44.140 --> 00:08:45.790 So there's a conundrum here. 00:08:45.800 --> 00:08:47.480 And the conundrum is because, 00:08:47.490 --> 00:08:50.410 if you actually look at the structure of hydrogen peroxide, 00:08:50.440 --> 00:08:53.550 the oxygens are actually bonded to each other. 00:08:53.570 --> 00:08:55.170 That's where the peroxide comes from. 00:08:55.180 --> 00:08:59.630 And then each of those are bonded to a hydrogen. 00:08:59.650 --> 00:09:01.720 So in this case, 00:09:01.730 --> 00:09:03.960 especially in a first-year chemistry course, 00:09:03.970 --> 00:09:07.370 the peroxide molecules, especially hydrogen peroxide, 00:09:07.390 --> 00:09:08.840 tends to be that one special case. 00:09:08.860 --> 00:09:11.390 There are others, but this is the one special case 00:09:11.410 --> 00:09:15.350 where oxygen does not have a minus 2 oxidation state. 00:09:15.370 --> 00:09:17.090 Let's look at this and try to figure out 00:09:17.100 --> 00:09:18.600 what oxygen's oxidation state would be 00:09:18.610 --> 00:09:20.080 in hydrogen peroxide. 00:09:20.090 --> 00:09:23.030 So in this case, the hydrogen-oxygen bond, 00:09:23.040 --> 00:09:25.270 oxygen is going to hog the electron 00:09:25.280 --> 00:09:27.510 and hydrogen is going to lose it. 00:09:27.520 --> 00:09:29.000 So it's going to have a plus 1 there. 00:09:29.020 --> 00:09:30.040 Same thing on the side. 00:09:30.060 --> 00:09:33.160 Oxygen, at least on this bond, is going to have a plus 1. 00:09:33.180 --> 00:09:34.410 It's going to gain an electron. 00:09:34.420 --> 00:09:36.710 What about from this other bond with the other oxygen? 00:09:36.720 --> 00:09:39.660 Well, there's no reason why one oxygen should 00:09:39.670 --> 00:09:41.230 hog the electron from the other oxygen. 00:09:41.250 --> 00:09:43.850 So it's not going to have any net impact 00:09:43.870 --> 00:09:45.000 on its oxidation state. 00:09:45.010 --> 00:09:48.000 So in this case, this oxygen's oxidation state is plus 1. 00:09:48.010 --> 00:09:52.770 This oxygen's oxidation state is also plus 1. 00:09:52.780 --> 00:09:59.400 So each of the hydrogens have an oxidation number of plus 1. 00:09:59.420 --> 00:10:03.070 You said the oxygens have an oxidation number of minus 1. 00:10:03.090 --> 00:10:05.740 And so you have a net of 0. 00:10:05.750 --> 00:10:08.790 2 times plus 1, plus 2 times minus 1, is 0. 00:10:08.810 --> 00:10:10.680 So that's just a special case. 00:10:10.690 --> 00:10:12.970 That's a good one to be familiar with. 00:10:12.980 --> 00:10:14.330 Let's do another one. 00:10:14.340 --> 00:10:15.840 Iron 3 carbonate. 00:10:15.850 --> 00:10:17.690 And now, for the first time 00:10:17.700 --> 00:10:19.970 -- I remember when we first encountered iron 3 carbonate. 00:10:19.980 --> 00:10:21.220 You probably thought, hey, 00:10:21.230 --> 00:10:22.960 why is it called iron 3 carbonate 00:10:22.970 --> 00:10:25.250 when there are only two iron molecules, 00:10:25.260 --> 00:10:26.430 or two iron atoms, here? 00:10:26.440 --> 00:10:27.820 And you're about to learn why. 00:10:27.830 --> 00:10:29.410 Let's look at the oxidation numbers. 00:10:29.430 --> 00:10:31.410 So oxygen. 00:10:31.420 --> 00:10:35.870 Oxygen's oxidation number tends to be minus 2. 00:10:35.890 --> 00:10:38.210 Minus 2. 00:10:38.220 --> 00:10:40.650 Now, if carbon is bonding with oxygen 00:10:40.670 --> 00:10:42.540 -- let's look at the periodic table. 00:10:42.550 --> 00:10:45.680 We have carbon bonding with oxygen. 00:10:45.700 --> 00:10:48.510 Carbon can go either way. 00:10:48.520 --> 00:10:51.270 Carbon, sometimes it likes to give away electrons. 00:10:51.300 --> 00:10:52.870 Sometimes it likes to gain electrons. 00:10:52.890 --> 00:10:55.100 When carbon is bonding with oxygen, 00:10:55.110 --> 00:10:58.110 this right here is the electron hog. 00:10:58.130 --> 00:11:01.140 If we had to say who's taking the electrons, 00:11:01.150 --> 00:11:02.670 it's going to be oxygen. 00:11:02.680 --> 00:11:03.890 Right? 00:11:03.900 --> 00:11:06.860 So carbon is going to be giving away its electrons. 00:11:06.870 --> 00:11:09.760 But how many electrons can carbon give away? 00:11:09.780 --> 00:11:11.470 Well, let's see. 00:11:11.480 --> 00:11:14.990 It has 1, 2, 3, 4 valence electrons. 00:11:15.010 --> 00:11:16.070 So the most it can really do is 00:11:16.080 --> 00:11:18.560 give away four valence electrons. 00:11:18.570 --> 00:11:21.450 So let's go back to the carbonate. 00:11:21.460 --> 00:11:26.110 So the carbon could at most 00:11:26.120 --> 00:11:29.370 give away its four valence electrons. 00:11:29.390 --> 00:11:32.400 So what will be the net oxidation number 00:11:32.420 --> 00:11:33.870 for the carbonate molecule? 00:11:33.880 --> 00:11:36.390 For the CO3? 00:11:36.400 --> 00:11:38.770 So this is a plus 4 oxidation, 00:11:38.790 --> 00:11:40.290 because it only has four to give away. 00:11:40.300 --> 00:11:42.680 If it's bonding with oxygen, it's going to give them away. 00:11:42.690 --> 00:11:43.880 Oxygen is more of a hog. 00:11:43.890 --> 00:11:46.270 Each oxygen has a minus 2. 00:11:46.280 --> 00:11:48.790 So let's think about it. 00:11:48.800 --> 00:11:54.130 I have plus 4 minus, 3 times minus 2. 00:11:54.150 --> 00:11:55.210 Right? 00:11:55.260 --> 00:11:57.220 I have 3 oxygen molecules. 00:11:57.240 --> 00:12:00.350 So I have 4 minus 6 is equal to minus 2. 00:12:00.370 --> 00:12:02.850 So we can kind of view it as the oxidation number 00:12:02.860 --> 00:12:05.790 for the entire carbonate molecule is minus 2. 00:12:05.810 --> 00:12:10.640 Now, if this entire carbonate molecule is minus 2, 00:12:10.660 --> 00:12:14.370 its contribution to the oxidation state 00:12:14.390 --> 00:12:16.940 for this whole kind of 00:12:16.950 --> 00:12:18.730 -- the carbonate part of the molecule. 00:12:18.740 --> 00:12:20.630 We have 3 carbonate molecules. 00:12:20.640 --> 00:12:22.630 Each of them is contributing minus 2. 00:12:22.640 --> 00:12:24.680 So I have a minus 6 contribution. 00:12:24.700 --> 00:12:28.360 If this is minus 6 and this is a neutral molecule, 00:12:28.380 --> 00:12:32.210 then our 2 irons are also going 00:12:32.220 --> 00:12:35.370 to have to have a plus 6 oxidation state. 00:12:35.380 --> 00:12:36.820 Because it all has to add up to 0. 00:12:36.830 --> 00:12:40.160 If both irons combined 00:12:40.180 --> 00:12:43.380 have a plus 6 contribution to oxidation state, 00:12:43.400 --> 00:12:46.410 then each of the irons must have a plus 3 oxidation. 00:12:46.420 --> 00:12:49.600 Or that, in our hypothetical world, if this happens, 00:12:49.620 --> 00:12:52.650 at least three electrons are going to 00:12:52.670 --> 00:12:54.800 favor the carbonate from each of the irons. 00:12:54.840 --> 00:12:58.120 So why is it called iron 3 carbonate? 00:12:58.120 --> 00:13:00.400 I think you may have figured this out by now. 00:13:00.420 --> 00:13:04.870 Because this is iron in its third oxidation state. 00:13:04.880 --> 00:13:06.070 Iron-- a lot of the metals, 00:13:06.090 --> 00:13:07.550 especially a lot of the transition metals-- 00:13:07.560 --> 00:13:09.560 can have multiple oxidation states. 00:13:09.570 --> 00:13:11.290 When you have iron 3 carbonate, 00:13:11.300 --> 00:13:12.680 you're literally saying, 00:13:12.690 --> 00:13:14.330 this is the third oxidation state. 00:13:14.340 --> 00:13:17.810 Or iron's oxidation number in this molecule 00:13:17.820 --> 00:13:19.600 will be positive 3. 00:13:19.610 --> 00:13:21.940 Now, let's do another one. 00:13:21.960 --> 00:13:23.030 This is interesting. 00:13:23.050 --> 00:13:24.200 Acetic acid. 00:13:24.210 --> 00:13:25.560 And I think is the first time that 00:13:25.570 --> 00:13:29.990 I've actually shown you the formula for acetic acid. 00:13:30.010 --> 00:13:33.160 I won't go into the whole organic chemistry of it. 00:13:33.170 --> 00:13:37.620 But let's try to figure out what the different charges are, 00:13:37.640 --> 00:13:39.200 or the different oxidation states. 00:13:41.570 --> 00:13:43.280 Sometimes you'll just see it written like this. 00:13:43.290 --> 00:13:44.600 You'd say, OK. 00:13:44.610 --> 00:13:48.050 Oxygens, each of those are going to have minus 2. 00:13:50.920 --> 00:13:53.270 Hydrogens are each going to have plus 1. 00:13:56.570 --> 00:13:57.600 So how are we doing so far? 00:13:57.630 --> 00:14:01.520 So these oxygens are going to contribute minus 4. 00:14:01.540 --> 00:14:03.290 And then the hydrogens 00:14:03.300 --> 00:14:08.930 -- here you have plus 3. And then here you have plus 1. 00:14:08.950 --> 00:14:12.070 You add these up and you get to 0. And you're like, oh. 00:14:12.090 --> 00:14:14.890 So the carbons must have no oxidation state. 00:14:14.900 --> 00:14:16.780 They must have an oxidation number of 0. 00:14:16.790 --> 00:14:20.480 Because we're already at 0, 00:14:20.490 --> 00:14:23.040 if we just consider the hydrogens and the oxygens. 00:14:23.050 --> 00:14:25.670 So let's look at that and see if that's actually the case. 00:14:25.680 --> 00:14:28.770 So when carbon is bonding with hydrogen, 00:14:28.780 --> 00:14:30.230 who's going to hog the electrons? 00:14:30.240 --> 00:14:34.670 When carbon is bonding with hydrogen. 00:14:34.680 --> 00:14:37.160 Electronegativity-- as you go to the right. 00:14:37.170 --> 00:14:39.330 Carbon is more electronegative. 00:14:39.350 --> 00:14:42.690 It likes to keep the electrons, or hog them, 00:14:42.700 --> 00:14:43.800 more than hydrogen. 00:14:43.810 --> 00:14:45.470 So hydrogen is going to lose the electrons 00:14:45.480 --> 00:14:46.980 in our oxidation state world. 00:14:46.990 --> 00:14:50.600 It's actually a covalent bond, but of course, 00:14:50.620 --> 00:14:51.870 we know that when we're dealing with oxidation states, 00:14:51.880 --> 00:14:53.260 we pretend that it's ionic. 00:14:53.280 --> 00:14:56.620 So in this case, your hydrogens are going 00:14:56.630 --> 00:14:58.140 to lose electrons. 00:14:58.160 --> 00:15:00.170 So they're each going to have an oxidation state of plus 1. 00:15:00.190 --> 00:15:02.940 That's consistent with what we know so far. 00:15:02.950 --> 00:15:04.740 And actually, that's another thing. 00:15:04.760 --> 00:15:06.680 When I did this exercise, right here, 00:15:06.710 --> 00:15:07.750 I immediately assumed hydrogen has 00:15:07.760 --> 00:15:10.810 an oxidation state of plus 1. 00:15:10.820 --> 00:15:11.850 I did that because, oh, 00:15:11.860 --> 00:15:13.620 everything else in the molecule is carbon and oxygen, 00:15:13.630 --> 00:15:15.800 which are more electronegative than the hydrogen. 00:15:15.810 --> 00:15:17.950 So the hydrogen is going to go into its plus 1 state. 00:15:17.960 --> 00:15:19.670 If, over here, I had a bunch of 00:15:19.680 --> 00:15:21.500 alkali and alkaline earth metals, 00:15:21.520 --> 00:15:22.910 I wouldn't be so sure. 00:15:22.930 --> 00:15:24.540 I'd say, oh, maybe hydrogen would take electrons from them. 00:15:24.550 --> 00:15:26.470 But anyway. 00:15:26.490 --> 00:15:30.270 So these all gave an electron to this carbon. 00:15:30.290 --> 00:15:32.270 So just from these hydrogens, 00:15:32.290 --> 00:15:39.200 that carbon would have a minus 3 oxidation state, right? 00:15:39.220 --> 00:15:41.450 These lost electrons. 00:15:41.460 --> 00:15:43.170 This guy gained three electrons, 00:15:43.190 --> 00:15:44.620 so his charge goes down by 3. 00:15:44.630 --> 00:15:47.450 The carbon-carbon bond. Well, there's no reason 00:15:47.470 --> 00:15:49.620 one carbon should take electrons from another carbon. 00:15:49.630 --> 00:15:51.400 All carbons are created equal. 00:15:51.410 --> 00:15:53.770 So there should be no transfer here. 00:15:53.800 --> 00:15:56.120 So this carbon's oxidation status is 3. 00:15:56.140 --> 00:15:57.490 Now what about on this side? 00:15:57.500 --> 00:16:00.130 So we know that this hydrogen is going 00:16:00.140 --> 00:16:02.750 to have a plus 1 oxidation state. 00:16:02.770 --> 00:16:04.830 It's going to give its electron to this oxygen. 00:16:04.850 --> 00:16:07.880 This oxygen, like most oxygens, 00:16:07.890 --> 00:16:09.680 are going to take up two electrons. 00:16:09.690 --> 00:16:12.960 One from this carbon, and one from this hydrogen. 00:16:12.970 --> 00:16:15.800 So it's going to have a minus 2 oxidation state. 00:16:15.810 --> 00:16:19.100 This oxygen is also going to take two electrons. 00:16:19.110 --> 00:16:20.700 In this case, both of them are going 00:16:20.720 --> 00:16:22.100 to be from this orange carbon. 00:16:22.120 --> 00:16:24.490 So it's going to have a minus 2 oxidation state. 00:16:24.510 --> 00:16:26.720 So what's the oxidation state of this carbon? 00:16:26.730 --> 00:16:30.190 It lost two electrons to this guy up here, 00:16:30.200 --> 00:16:35.350 and it lost one electron to this oxygen down here. 00:16:35.360 --> 00:16:37.700 Remember, this guy got one electron from the carbon 00:16:37.710 --> 00:16:38.830 and one from the hydrogen. 00:16:38.840 --> 00:16:41.600 So it lost one electron here, two there. 00:16:41.610 --> 00:16:43.390 It lost three electrons. 00:16:43.410 --> 00:16:47.570 So in that reality, it would have a plus 3 charge. 00:16:47.590 --> 00:16:52.010 So it turns out that the average oxidation state 00:16:52.020 --> 00:16:54.990 for the carbon in acetic acid is 0. 00:16:55.010 --> 00:16:56.990 Because if you average minus 3 and plus 3, 00:16:57.000 --> 00:16:58.300 you get to 0. 00:16:58.320 --> 00:17:00.520 And that's why I said, oh, maybe these are a 0. 00:17:00.530 --> 00:17:03.180 But if you actually write out their oxidation numbers, 00:17:03.200 --> 00:17:07.300 this green C has a minus 3 oxidation state. 00:17:07.310 --> 00:17:10.020 And this orange C, this orange carbon, 00:17:10.030 --> 00:17:12.640 has a plus 3 oxidation state. 00:17:12.660 --> 00:17:14.050 If you got this one, 00:17:14.070 --> 00:17:16.060 and I don't think it's overly complex, 00:17:16.080 --> 00:17:21.880 you will be an oxidation state jock. 00:17:21.890 --> 00:17:23.750 So I think you're all set now. 00:17:23.760 --> 00:17:25.150 In the next video, we're going to start exploring 00:17:25.160 --> 00:17:28.150 oxidation reduction reactions.