1 00:00:00,000 --> 00:00:00,690 2 00:00:00,690 --> 00:00:03,680 Let's figure out the oxidation states for some more 3 00:00:03,680 --> 00:00:05,710 constituent atoms and molecules. 4 00:00:05,710 --> 00:00:13,129 So let's say I had magnesium oxide. 5 00:00:13,130 --> 00:00:14,560 MgO. 6 00:00:14,560 --> 00:00:17,060 I'll do oxygen in a different color. 7 00:00:17,059 --> 00:00:18,890 So what are going to be their oxidation states? 8 00:00:18,890 --> 00:00:20,550 And you might know this already, but let's look at the 9 00:00:20,550 --> 00:00:22,789 periodic table, because it never hurts to get 10 00:00:22,789 --> 00:00:23,480 familiar with it. 11 00:00:23,480 --> 00:00:25,550 So we have magnesium. 12 00:00:25,550 --> 00:00:27,719 Magnesium has two valance electrons. 13 00:00:27,719 --> 00:00:29,239 It's a Group 2 element. 14 00:00:29,239 --> 00:00:32,559 It would love to lose those two electrons. 15 00:00:32,560 --> 00:00:34,620 Oxygen, we already know, is one of the most 16 00:00:34,619 --> 00:00:38,989 electronegative atoms. It's so electronegative that oxidized 17 00:00:38,990 --> 00:00:42,510 has essentially been named after them. 18 00:00:42,509 --> 00:00:45,629 And we know that oxygen loves to gain two electrons. 19 00:00:45,630 --> 00:00:47,490 So this is kind of a marriage made in heaven. 20 00:00:47,490 --> 00:00:50,760 This guy wants to lose two electrons and this guy wants 21 00:00:50,759 --> 00:00:52,799 to gain two electrons. 22 00:00:52,799 --> 00:00:54,349 So what's going to happen? 23 00:00:54,350 --> 00:00:57,630 The magnesium is going to lose two electrons. 24 00:00:57,630 --> 00:00:58,789 It was neutral. 25 00:00:58,789 --> 00:01:03,509 So it's going to have a plus 2 charge, hypothetically. 26 00:01:03,509 --> 00:01:06,870 And then, the oxygen is going to have a minus 2 charge, 27 00:01:06,870 --> 00:01:10,490 because it gained the two electrons. 28 00:01:10,489 --> 00:01:14,709 So in this molecule of magnesium oxide, the oxidation 29 00:01:14,709 --> 00:01:17,689 state of magnesium is plus 2. 30 00:01:17,689 --> 00:01:22,409 And the oxidation state of the oxygen is minus 2. 31 00:01:22,409 --> 00:01:26,090 Now let's do a slightly harder one. 32 00:01:26,090 --> 00:01:35,990 Let's say we had magnesium hydroxide. 33 00:01:35,989 --> 00:01:38,789 So hydroxide is OH2. 34 00:01:38,790 --> 00:01:41,400 35 00:01:41,400 --> 00:01:47,080 OH2 right there, where there's two hydroxide groups in this. 36 00:01:47,079 --> 00:01:48,829 So, my temptation would still be, look. 37 00:01:48,829 --> 00:01:52,840 Magnesium likes to lose its electrons, its two electrons, 38 00:01:52,840 --> 00:01:55,420 which would make it's charge positive-- it's hypothetical 39 00:01:55,420 --> 00:01:57,500 oxidation state positive. 40 00:01:57,500 --> 00:01:59,980 So my temptation is to say, hey, magnesium here 41 00:01:59,980 --> 00:02:00,500 would be plus 2. 42 00:02:00,500 --> 00:02:03,329 So let me write that there. 43 00:02:03,329 --> 00:02:06,829 And remember, in order for everything to work out, if 44 00:02:06,829 --> 00:02:10,840 it's a neutral compound, all of the oxidation states in it 45 00:02:10,840 --> 00:02:11,939 have to add up to 1. 46 00:02:11,939 --> 00:02:13,699 So let's see if that's going to work out. 47 00:02:13,699 --> 00:02:15,129 Now, oxygen. 48 00:02:15,129 --> 00:02:17,740 My impulse is that its oxidation state 49 00:02:17,740 --> 00:02:19,909 tends to be minus 2. 50 00:02:19,909 --> 00:02:21,159 So let me write that down. 51 00:02:21,159 --> 00:02:24,419 52 00:02:24,419 --> 00:02:27,239 And hydrogen, when it's bonded with an oxygen-- remember. 53 00:02:27,240 --> 00:02:30,050 In this case, the hydrogen is bonded with the oxygen first. 54 00:02:30,050 --> 00:02:33,490 And then that's bonded to the magnesium. 55 00:02:33,490 --> 00:02:36,010 So the hydrogen is bonded to an oxygen. 56 00:02:36,009 --> 00:02:38,789 Hydrogen, if it was bonded to a magnesium, you might want to 57 00:02:38,789 --> 00:02:41,810 say, hey, maybe it'll take the electrons and it'll have a 58 00:02:41,810 --> 00:02:43,180 negative oxidation state. 59 00:02:43,180 --> 00:02:46,290 But when hydrogen is bonded with oxygen, it 60 00:02:46,289 --> 00:02:49,590 gives up the electrons. 61 00:02:49,590 --> 00:02:51,700 It only has one electron to give up. 62 00:02:51,699 --> 00:02:54,542 So it has a plus 1 oxidation state. 63 00:02:54,542 --> 00:02:55,159 So let's see. 64 00:02:55,159 --> 00:02:57,120 At first, you might say, hey, I'm adding up 65 00:02:57,120 --> 00:02:58,099 the oxidation states. 66 00:02:58,099 --> 00:03:00,840 Plus 2 minus 2 is 0 plus 1. 67 00:03:00,840 --> 00:03:03,840 I get a plus 1 oxidation state here. 68 00:03:03,840 --> 00:03:04,879 That doesn't make sense, Sal. 69 00:03:04,879 --> 00:03:06,349 This is a neutral compound. 70 00:03:06,349 --> 00:03:08,699 And what you to remember is oh, no, but you have two of 71 00:03:08,699 --> 00:03:10,959 these hydroxides right here. 72 00:03:10,960 --> 00:03:15,570 So what you do is you figure out the sum of the oxidation 73 00:03:15,569 --> 00:03:17,389 states of the hydroxide. 74 00:03:17,389 --> 00:03:20,500 So that's minus 2 plus 1. 75 00:03:20,500 --> 00:03:23,150 So for the entire hydroxide molecule, you 76 00:03:23,150 --> 00:03:25,819 have a minus 1 sum. 77 00:03:25,819 --> 00:03:27,459 And then you have two of them. 78 00:03:27,460 --> 00:03:27,750 Right? 79 00:03:27,750 --> 00:03:30,900 You have two hydroxide molecules here. 80 00:03:30,900 --> 00:03:35,250 So the contribution to the entire compound's oxidation 81 00:03:35,250 --> 00:03:37,569 state will be minus 1 for each hydroxide. 82 00:03:37,569 --> 00:03:39,500 But then you have two of them. 83 00:03:39,500 --> 00:03:42,960 So it's minus 2 and then plus 2 from the magnesium. 84 00:03:42,960 --> 00:03:45,599 And it all adds up to 0. 85 00:03:45,599 --> 00:03:47,439 So that worked out. 86 00:03:47,439 --> 00:03:49,349 Now, I want to do a little bit of an aside. 87 00:03:49,349 --> 00:03:51,829 I want to go back to doing some problems again. 88 00:03:51,830 --> 00:03:53,580 But I want to do a little bit of an aside on some of my 89 00:03:53,580 --> 00:03:54,310 terminology. 90 00:03:54,310 --> 00:03:56,629 Because I've kind of used oxidation state, and oxidized, 91 00:03:56,629 --> 00:04:00,359 and reduced interchangeably, to a certain degree. 92 00:04:00,360 --> 00:04:05,030 But, we've done so many problems with water 93 00:04:05,030 --> 00:04:10,560 autoionizing into-- actually, let me do 2 moles of water. 94 00:04:10,560 --> 00:04:19,838 And it's in equilibrium with 1 mole of H30 plus OH minus. 95 00:04:19,838 --> 00:04:22,649 And obviously, everything is in an aqueous solution. 96 00:04:22,649 --> 00:04:23,839 Now, let's look at the water. 97 00:04:23,839 --> 00:04:26,619 What are the oxidation states in this water right here? 98 00:04:26,620 --> 00:04:28,620 Well, we've done this already in the previous video. 99 00:04:28,620 --> 00:04:32,340 Oxidation state of oxygen is minus 2, because it's hogging 100 00:04:32,339 --> 00:04:34,399 the two electrons from the two hydrogens. 101 00:04:34,399 --> 00:04:36,704 Each hydrogen is giving up an electron. 102 00:04:36,704 --> 00:04:39,209 So it has an oxidation state of plus 1. 103 00:04:39,209 --> 00:04:40,399 And we see this molecule. 104 00:04:40,399 --> 00:04:41,620 Everything adds up. 105 00:04:41,620 --> 00:04:43,699 Because you have two hydrogens with a plus 1. 106 00:04:43,699 --> 00:04:45,349 So that's plus 2. 107 00:04:45,350 --> 00:04:48,180 Plus 2 minus 2 for that one oxygen, and you get to 0. 108 00:04:48,180 --> 00:04:49,990 And it's a neutral compound. 109 00:04:49,990 --> 00:04:52,650 Now here, what are the oxidation states? 110 00:04:52,649 --> 00:04:58,659 So one of these hydrogens left one of these water molecules 111 00:04:58,660 --> 00:05:01,220 and joined the other of the water molecules without taking 112 00:05:01,220 --> 00:05:02,420 its electron with it. 113 00:05:02,420 --> 00:05:04,560 So it left the electron over here. 114 00:05:04,560 --> 00:05:09,930 So that oxygen still has a minus 2 oxidation state. 115 00:05:09,930 --> 00:05:13,290 And this hydrogen still has a plus 1. 116 00:05:13,290 --> 00:05:15,189 And that's why you do minus 2 plus 1. 117 00:05:15,189 --> 00:05:16,300 You get minus 1. 118 00:05:16,300 --> 00:05:18,660 And this time, it works out, because that's the actual 119 00:05:18,660 --> 00:05:20,910 charge on this hydroxide ion. 120 00:05:20,910 --> 00:05:22,939 Now, here, what are the oxidation states? 121 00:05:22,939 --> 00:05:28,230 Each of the hydrogens have a plus 1 oxidation state. 122 00:05:28,230 --> 00:05:32,069 And then this oxygen has a minus 2. 123 00:05:32,069 --> 00:05:33,860 And so if you look at the charge for the entire 124 00:05:33,860 --> 00:05:38,730 molecule, plus 1 on three hydrogens, so that's plus 3. 125 00:05:38,730 --> 00:05:39,610 I just added them up. 126 00:05:39,610 --> 00:05:41,480 Minus 2. 127 00:05:41,480 --> 00:05:45,080 So plus 3 minus 2, I should have a plus 1 charge on this 128 00:05:45,079 --> 00:05:47,370 entire molecule, which is the case. 129 00:05:47,370 --> 00:05:51,259 Now, my question to you is has any of the oxidation states 130 00:05:51,259 --> 00:05:52,930 changed for any of the atoms? 131 00:05:52,930 --> 00:05:55,850 All of the hydrogens here-- and we could call 132 00:05:55,850 --> 00:05:58,120 this 2 moles of water. 133 00:05:58,120 --> 00:06:00,569 Or maybe I just have two molecules of water. 134 00:06:00,569 --> 00:06:02,279 But I have four hydrogens here. 135 00:06:02,279 --> 00:06:02,599 Right? 136 00:06:02,600 --> 00:06:04,890 And all of them had an oxidation state of 1. 137 00:06:04,889 --> 00:06:07,050 On the right-hand side, I have four hydrogens. 138 00:06:07,050 --> 00:06:10,050 All of them have an oxidation state of 1. 139 00:06:10,050 --> 00:06:14,370 So although their oxidation state is 1, in this reaction-- 140 00:06:14,370 --> 00:06:16,860 and you can pick either direction of the reaction-- 141 00:06:16,860 --> 00:06:19,720 hydrogen has not been oxidized. 142 00:06:19,720 --> 00:06:21,715 Its oxidation state did not change. 143 00:06:21,714 --> 00:06:24,269 144 00:06:24,269 --> 00:06:26,569 Maybe it was oxidized in a previous reaction where the 145 00:06:26,569 --> 00:06:30,310 water was formed, but in this reaction, it was not oxidized. 146 00:06:30,310 --> 00:06:34,160 Likewise, the oxygens-- we have two oxygen molecules, or 147 00:06:34,160 --> 00:06:35,040 atoms, here. 148 00:06:35,040 --> 00:06:37,650 Each have a minus 2 oxidation state. 149 00:06:37,649 --> 00:06:39,379 Here, we have two oxygen molecules. 150 00:06:39,379 --> 00:06:41,629 Each have a minus 2 oxidation state. 151 00:06:41,629 --> 00:06:46,000 Due to this reaction, at least, no electrons changed 152 00:06:46,000 --> 00:06:48,139 hands in our oxidation state world. 153 00:06:48,139 --> 00:06:52,250 So this is not an oxidation or a reduction reaction. 154 00:06:52,250 --> 00:06:54,250 And I'm going to cover that in detail in the next video. 155 00:06:54,250 --> 00:06:57,079 And I just want to be clear that nothing here was oxidized 156 00:06:57,079 --> 00:07:01,159 or reduced, because their oxidation 157 00:07:01,160 --> 00:07:03,180 states stayed the same. 158 00:07:03,180 --> 00:07:07,870 Because sometimes I'll say, hey, look. 159 00:07:07,870 --> 00:07:10,579 Magnesium has an oxidation state of plus 2. 160 00:07:10,579 --> 00:07:13,649 And oxygen has an oxidation state of minus 2. 161 00:07:13,649 --> 00:07:15,310 Magnesium was oxidized. 162 00:07:15,310 --> 00:07:17,220 Two electrons were taken away from it. 163 00:07:17,220 --> 00:07:18,670 And oxygen was reduced. 164 00:07:18,670 --> 00:07:20,180 Two electrons were given to it. 165 00:07:20,180 --> 00:07:22,620 And I'll say that implying some reaction that produced 166 00:07:22,620 --> 00:07:24,680 it, but that's not always the case. 167 00:07:24,680 --> 00:07:26,120 You could have a reaction where that 168 00:07:26,120 --> 00:07:27,120 necessarily didn't happen. 169 00:07:27,120 --> 00:07:29,759 But the oxidation state for magnesium is 170 00:07:29,759 --> 00:07:31,050 definitely plus 2. 171 00:07:31,050 --> 00:07:35,520 And the oxidation state for the oxygen, or the oxidation 172 00:07:35,519 --> 00:07:37,379 number, is minus 2. 173 00:07:37,379 --> 00:07:38,959 But I think you know what I'm talking about when I say it 174 00:07:38,959 --> 00:07:40,329 was oxidized. 175 00:07:40,329 --> 00:07:44,129 At some point, it went from a neutral magnesium to a 176 00:07:44,129 --> 00:07:47,310 positively charged magnesium by losing two electrons. 177 00:07:47,310 --> 00:07:49,509 So it got oxidized. 178 00:07:49,509 --> 00:07:53,279 Now, let's do some harder problems. So hydrogen 179 00:07:53,279 --> 00:07:57,259 peroxide-- I've said multiple times already that oxygen 180 00:07:57,259 --> 00:08:01,599 tends to have a minus 2 oxidation state. 181 00:08:01,600 --> 00:08:02,450 This is minus 1. 182 00:08:02,449 --> 00:08:04,909 I think you see the pattern. 183 00:08:04,910 --> 00:08:06,900 These guys are plus 1. 184 00:08:06,899 --> 00:08:09,099 Hydrogen is plus or minus 1. 185 00:08:09,100 --> 00:08:10,450 These guys are plus 2. 186 00:08:10,449 --> 00:08:11,519 I think you see the pattern. 187 00:08:11,519 --> 00:08:15,069 It's whether you want to lose or gain electrons. 188 00:08:15,069 --> 00:08:17,449 You might say, well see, water normally 189 00:08:17,449 --> 00:08:19,589 has a minus 2 oxidation. 190 00:08:19,589 --> 00:08:22,469 So you might be tempted to do-- OK. 191 00:08:22,470 --> 00:08:25,470 Hydrogen has plus 1, because it's bonding with water. 192 00:08:25,470 --> 00:08:28,690 And oxygen has a minus 2. 193 00:08:28,689 --> 00:08:31,439 But when you do that, you immediately have a conundrum. 194 00:08:31,439 --> 00:08:34,240 This is a neutral molecule-- let's see. 195 00:08:34,240 --> 00:08:35,480 Two hydrogens plus 2. 196 00:08:35,480 --> 00:08:36,610 Two oxygens at minus 2. 197 00:08:36,610 --> 00:08:37,289 Minus 4. 198 00:08:37,289 --> 00:08:40,129 So this would end up with a minus 4 total 199 00:08:40,129 --> 00:08:41,720 net oxidation state. 200 00:08:41,720 --> 00:08:42,779 And that's not the case because this 201 00:08:42,779 --> 00:08:44,299 doesn't have any charge. 202 00:08:44,299 --> 00:08:45,979 So there's a conundrum here. 203 00:08:45,980 --> 00:08:48,389 And the conundrum is because, if you actually look at the 204 00:08:48,389 --> 00:08:52,139 structure of hydrogen peroxide, the oxygens are 205 00:08:52,139 --> 00:08:53,830 actually bonded to each other. 206 00:08:53,830 --> 00:08:56,120 That's where the peroxide comes from. 207 00:08:56,120 --> 00:09:00,590 And then each of those are bonded to a hydrogen. 208 00:09:00,590 --> 00:09:04,670 So in this case, especially in a first-year chemistry course, 209 00:09:04,669 --> 00:09:07,189 the peroxide molecules, especially hydrogen peroxide, 210 00:09:07,190 --> 00:09:09,110 tends to be that one special case. 211 00:09:09,110 --> 00:09:11,659 There are others, but this is the one special case where 212 00:09:11,659 --> 00:09:15,539 oxygen does not have a minus 2 oxidation state. 213 00:09:15,539 --> 00:09:17,549 Let's look at this and try to figure out what oxygen's 214 00:09:17,549 --> 00:09:20,750 oxidation state would be in hydrogen peroxide. 215 00:09:20,750 --> 00:09:23,735 So in this case, the hydrogen-oxygen bond, oxygen 216 00:09:23,735 --> 00:09:26,460 is going to hog the electron and hydrogen is 217 00:09:26,460 --> 00:09:27,320 going to lose it. 218 00:09:27,320 --> 00:09:28,780 So it's going to have a plus 1 there. 219 00:09:28,779 --> 00:09:30,429 Same thing on the side. 220 00:09:30,429 --> 00:09:33,059 Oxygen, at least on this bond, is going to have a plus 1. 221 00:09:33,059 --> 00:09:34,789 It's going to gain an electron. 222 00:09:34,789 --> 00:09:37,379 What about from this other bond with the other oxygen? 223 00:09:37,379 --> 00:09:39,759 Well, there's no reason why one oxygen should hog the 224 00:09:39,759 --> 00:09:41,169 electron from the other oxygen. 225 00:09:41,169 --> 00:09:43,559 So it's not going to have any net impact on 226 00:09:43,559 --> 00:09:45,000 its oxidation state. 227 00:09:45,000 --> 00:09:49,470 So in this case, this oxygen's oxidation state is plus 1. 228 00:09:49,470 --> 00:09:53,580 This oxygen's oxidation state is also plus 1. 229 00:09:53,580 --> 00:09:59,620 So each of the hydrogens have an oxidation number of plus 1. 230 00:09:59,620 --> 00:10:03,080 You said the oxygens have an oxidation number of minus 1. 231 00:10:03,080 --> 00:10:05,930 And so you have a net of 0. 232 00:10:05,929 --> 00:10:09,259 2 times plus 1, plus 2 times minus 1, is 0. 233 00:10:09,259 --> 00:10:11,080 So that's just a special case. 234 00:10:11,080 --> 00:10:13,290 That's a good one to be familiar with. 235 00:10:13,289 --> 00:10:14,169 Let's do another one. 236 00:10:14,169 --> 00:10:15,969 Iron 3 carbonate. 237 00:10:15,970 --> 00:10:18,410 And now, for the first time-- I remember when we first 238 00:10:18,409 --> 00:10:19,919 encountered iron 3 carbonate. 239 00:10:19,919 --> 00:10:22,990 You probably thought, hey, why is it called iron 3 carbonate 240 00:10:22,990 --> 00:10:25,269 when there are only two iron molecules, or 241 00:10:25,269 --> 00:10:26,350 two iron atoms, here? 242 00:10:26,350 --> 00:10:27,840 And you're about to learn why. 243 00:10:27,840 --> 00:10:30,310 Let's look at the oxidation numbers. 244 00:10:30,309 --> 00:10:31,849 So oxygen. 245 00:10:31,850 --> 00:10:35,610 Oxygen's oxidation number tends to be minus 2. 246 00:10:35,610 --> 00:10:38,529 247 00:10:38,529 --> 00:10:41,759 Now, if carbon is bonding with oxygen-- let's look at the 248 00:10:41,759 --> 00:10:43,330 periodic table. 249 00:10:43,330 --> 00:10:46,910 We have carbon bonding with oxygen. 250 00:10:46,909 --> 00:10:48,719 Carbon can go either way. 251 00:10:48,720 --> 00:10:51,120 Carbon, sometimes it likes to give away electrons. 252 00:10:51,120 --> 00:10:53,039 Sometimes it likes to gain electrons. 253 00:10:53,039 --> 00:10:57,269 When carbon is bonding with oxygen, this right here is the 254 00:10:57,269 --> 00:10:58,809 electron hog. 255 00:10:58,809 --> 00:11:01,159 If we had to say who's taking the electrons, 256 00:11:01,159 --> 00:11:03,009 it's going to be oxygen. 257 00:11:03,009 --> 00:11:03,539 Right? 258 00:11:03,539 --> 00:11:07,039 So carbon is going to be giving away its electrons. 259 00:11:07,039 --> 00:11:10,199 But how many electrons can carbon give away? 260 00:11:10,200 --> 00:11:10,936 Well, let's see. 261 00:11:10,936 --> 00:11:14,720 It has 1, 2, 3, 4 valence electrons. 262 00:11:14,720 --> 00:11:16,240 So the most it can really do is give away 263 00:11:16,240 --> 00:11:19,389 four valence electrons. 264 00:11:19,389 --> 00:11:21,669 So let's go back to the carbonate. 265 00:11:21,669 --> 00:11:27,039 So the carbon could at most give away its 266 00:11:27,039 --> 00:11:29,929 four valence electrons. 267 00:11:29,929 --> 00:11:32,399 So what will be the net oxidation number for the 268 00:11:32,399 --> 00:11:33,769 carbonate molecule? 269 00:11:33,769 --> 00:11:36,809 For the CO3? 270 00:11:36,809 --> 00:11:39,429 So this is a plus 4 oxidation, because it only has 271 00:11:39,429 --> 00:11:40,269 four to give away. 272 00:11:40,269 --> 00:11:42,259 If it's bonding with oxygen, it's going to give them away. 273 00:11:42,259 --> 00:11:44,629 Oxygen is more of a hog. 274 00:11:44,629 --> 00:11:47,639 Each oxygen has a minus 2. 275 00:11:47,639 --> 00:11:48,590 So let's think about it. 276 00:11:48,590 --> 00:11:54,210 I have plus 4 minus, 3 times minus 2. 277 00:11:54,210 --> 00:11:54,700 Right? 278 00:11:54,700 --> 00:11:56,870 I have 3 oxygen molecules. 279 00:11:56,870 --> 00:12:00,289 So I have 4 minus 6 is equal to minus 2. 280 00:12:00,289 --> 00:12:02,730 So we can kind of view it as the oxidation number for the 281 00:12:02,730 --> 00:12:06,990 entire carbonate molecule is minus 2. 282 00:12:06,990 --> 00:12:11,210 Now, if this entire carbonate molecule is minus 2, its 283 00:12:11,210 --> 00:12:16,920 contribution to the oxidation state for this whole kind of-- 284 00:12:16,919 --> 00:12:18,620 the carbonate part of the molecule. 285 00:12:18,620 --> 00:12:20,980 We have 3 carbonate molecules. 286 00:12:20,980 --> 00:12:22,710 Each of them is contributing minus 2. 287 00:12:22,710 --> 00:12:25,740 So I have a minus 6 contribution. 288 00:12:25,740 --> 00:12:29,379 If this is minus 6 and this is a neutral molecule, then our 2 289 00:12:29,379 --> 00:12:32,879 irons are also going to have to have a 290 00:12:32,879 --> 00:12:35,289 plus 6 oxidation state. 291 00:12:35,289 --> 00:12:38,029 Because it all has to add up to 0. 292 00:12:38,029 --> 00:12:42,399 If both irons combined have a plus 6 contribution to 293 00:12:42,399 --> 00:12:44,379 oxidation state, then each of the irons must 294 00:12:44,379 --> 00:12:46,460 have a plus 3 oxidation. 295 00:12:46,460 --> 00:12:50,930 Or that, in our hypothetical world, if this happens, at 296 00:12:50,929 --> 00:12:53,509 least three electrons are going to favor the carbonate 297 00:12:53,509 --> 00:12:55,240 from each of the irons. 298 00:12:55,240 --> 00:12:57,980 So why is it called iron 3 carbonate? 299 00:12:57,980 --> 00:13:01,340 I think you may have figured this out by now. 300 00:13:01,340 --> 00:13:04,600 Because this is iron in its third oxidation state. 301 00:13:04,600 --> 00:13:06,519 Iron-- a lot of the metals, especially a lot of the 302 00:13:06,519 --> 00:13:09,789 transition metals-- can have multiple oxidation states. 303 00:13:09,789 --> 00:13:11,969 When you have iron 3 carbonate, you're literally 304 00:13:11,970 --> 00:13:14,129 saying, this is the third oxidation state. 305 00:13:14,129 --> 00:13:18,120 Or iron's oxidation number in this molecule 306 00:13:18,120 --> 00:13:20,779 will be positive 3. 307 00:13:20,779 --> 00:13:21,899 Now, let's do another one. 308 00:13:21,899 --> 00:13:23,000 This is interesting. 309 00:13:23,000 --> 00:13:24,009 Acetic acid. 310 00:13:24,009 --> 00:13:25,559 And I think is the first time that I've actually shown you 311 00:13:25,559 --> 00:13:30,739 the formula for acetic acid. 312 00:13:30,740 --> 00:13:33,409 I won't go into the whole organic chemistry of it. 313 00:13:33,409 --> 00:13:37,289 But let's try to figure out what the different charges 314 00:13:37,289 --> 00:13:38,834 are, or the different oxidation states. 315 00:13:38,835 --> 00:13:41,509 316 00:13:41,509 --> 00:13:43,610 Sometimes you'll just see it written like this. 317 00:13:43,610 --> 00:13:45,430 You'd say, OK. 318 00:13:45,429 --> 00:13:47,529 Oxygens, each of those are going to have minus 2. 319 00:13:47,529 --> 00:13:51,129 320 00:13:51,129 --> 00:13:52,570 Hydrogens are each going to have plus 1. 321 00:13:52,570 --> 00:13:56,270 322 00:13:56,269 --> 00:13:58,519 So how are we doing so far? 323 00:13:58,519 --> 00:14:02,100 So these oxygens are going to contribute minus 4. 324 00:14:02,100 --> 00:14:06,200 And then the hydrogens-- here you have plus 3. 325 00:14:06,200 --> 00:14:09,259 And then here you have plus 1. 326 00:14:09,259 --> 00:14:10,924 You add these up and you get to 0. 327 00:14:10,924 --> 00:14:11,740 And you're like, oh. 328 00:14:11,740 --> 00:14:14,430 So the carbons must have no oxidation state. 329 00:14:14,429 --> 00:14:17,279 They must have an oxidation number of 0. 330 00:14:17,279 --> 00:14:22,179 Because we're already at 0, if we just consider the hydrogens 331 00:14:22,179 --> 00:14:23,370 and the oxygens. 332 00:14:23,370 --> 00:14:26,230 So let's look at that and see if that's actually the case. 333 00:14:26,230 --> 00:14:29,360 So when carbon is bonding with hydrogen, who's going to hog 334 00:14:29,360 --> 00:14:32,100 the electrons? 335 00:14:32,100 --> 00:14:35,330 When carbon is bonding with hydrogen. 336 00:14:35,330 --> 00:14:37,320 Electronegativity-- as you go to the right. 337 00:14:37,320 --> 00:14:39,330 Carbon is more electronegative. 338 00:14:39,330 --> 00:14:42,590 It likes to keep the electrons, or hog them, more 339 00:14:42,590 --> 00:14:43,310 than hydrogen. 340 00:14:43,309 --> 00:14:46,079 So hydrogen is going to lose the electrons in our oxidation 341 00:14:46,080 --> 00:14:46,860 state world. 342 00:14:46,860 --> 00:14:50,375 It's actually a covalent bond, but of course, we know that 343 00:14:50,375 --> 00:14:52,429 when we're dealing with oxidation states, we pretend 344 00:14:52,429 --> 00:14:53,629 that it's ionic. 345 00:14:53,629 --> 00:14:56,029 So in this case, your hydrogens are 346 00:14:56,029 --> 00:14:58,100 going to lose electrons. 347 00:14:58,100 --> 00:15:00,920 So they're each going to have an oxidation state of plus 1. 348 00:15:00,919 --> 00:15:03,399 That's consistent with what we know so far. 349 00:15:03,399 --> 00:15:04,730 And actually, that's another thing. 350 00:15:04,730 --> 00:15:06,769 When I did this exercise, right here, I immediately 351 00:15:06,769 --> 00:15:10,419 assumed hydrogen has an oxidation state of plus 1. 352 00:15:10,419 --> 00:15:12,189 I did that because, oh, everything else in the 353 00:15:12,190 --> 00:15:15,000 molecule is carbon and oxygen, which are more electronegative 354 00:15:15,000 --> 00:15:15,700 than the hydrogen. 355 00:15:15,700 --> 00:15:18,190 So the hydrogen is going to go into its plus 1 state. 356 00:15:18,190 --> 00:15:20,960 If, over here, I had a bunch of alkali and alkaline earth 357 00:15:20,960 --> 00:15:22,740 metals, I wouldn't be so sure. 358 00:15:22,740 --> 00:15:24,090 I'd say, oh, maybe hydrogen would take 359 00:15:24,090 --> 00:15:25,910 electrons from them. 360 00:15:25,909 --> 00:15:27,279 But anyway. 361 00:15:27,279 --> 00:15:30,679 So these all gave an electron to this carbon. 362 00:15:30,679 --> 00:15:36,784 So just from these hydrogens, that carbon would have a minus 363 00:15:36,784 --> 00:15:39,740 3 oxidation state, right? 364 00:15:39,740 --> 00:15:41,259 These lost electrons. 365 00:15:41,259 --> 00:15:43,559 This guy gained three electrons, so his charge 366 00:15:43,559 --> 00:15:45,429 goes down by 3. 367 00:15:45,429 --> 00:15:46,679 The carbon-carbon bond. 368 00:15:46,679 --> 00:15:48,719 Well, there's no reason one carbon should take electrons 369 00:15:48,720 --> 00:15:49,570 from another carbon. 370 00:15:49,570 --> 00:15:51,620 All carbons are created equal. 371 00:15:51,620 --> 00:15:53,919 So there should be no transfer here. 372 00:15:53,919 --> 00:15:56,159 So this carbon's oxidation status is 3. 373 00:15:56,159 --> 00:15:57,230 Now what about on this side? 374 00:15:57,230 --> 00:16:01,560 So we know that this hydrogen is going to have a plus 1 375 00:16:01,559 --> 00:16:02,919 oxidation state. 376 00:16:02,919 --> 00:16:05,469 It's going to give its electron to this oxygen. 377 00:16:05,470 --> 00:16:08,870 This oxygen, like most oxygens, are going to take up 378 00:16:08,870 --> 00:16:09,639 two electrons. 379 00:16:09,639 --> 00:16:12,980 One from this carbon, and one from this hydrogen. 380 00:16:12,980 --> 00:16:16,460 So it's going to have a minus 2 oxidation state. 381 00:16:16,460 --> 00:16:19,139 This oxygen is also going to take two electrons. 382 00:16:19,139 --> 00:16:20,600 In this case, both of them are going to be 383 00:16:20,600 --> 00:16:22,370 from this orange carbon. 384 00:16:22,370 --> 00:16:24,870 So it's going to have a minus 2 oxidation state. 385 00:16:24,870 --> 00:16:26,840 So what's the oxidation state of this carbon? 386 00:16:26,840 --> 00:16:33,190 It lost two electrons to this guy up here, and it lost one 387 00:16:33,190 --> 00:16:35,450 electron to this oxygen down here. 388 00:16:35,450 --> 00:16:37,640 Remember, this guy got one electron from the carbon and 389 00:16:37,639 --> 00:16:39,049 one from the hydrogen. 390 00:16:39,049 --> 00:16:41,990 So it lost one electron here, two there. 391 00:16:41,990 --> 00:16:43,769 It lost three electrons. 392 00:16:43,769 --> 00:16:49,049 So in that reality, it would have a plus 3 charge. 393 00:16:49,049 --> 00:16:53,079 So it turns out that the average oxidation state for 394 00:16:53,080 --> 00:16:54,930 the carbon in acetic acid is 0. 395 00:16:54,929 --> 00:16:58,149 Because if you average minus 3 and plus 3, you get to 0. 396 00:16:58,149 --> 00:17:00,269 And that's why I said, oh, maybe these are a 0. 397 00:17:00,269 --> 00:17:03,730 But if you actually write out their oxidation numbers, this 398 00:17:03,730 --> 00:17:07,410 green C has a minus 3 oxidation state. 399 00:17:07,410 --> 00:17:10,660 And this orange C, this orange carbon, has a 400 00:17:10,660 --> 00:17:12,880 plus 3 oxidation state. 401 00:17:12,880 --> 00:17:15,500 If you got this one, and I don't think it's overly 402 00:17:15,500 --> 00:17:22,130 complex, you will be an oxidation state jock. 403 00:17:22,130 --> 00:17:23,720 So I think you're all set now. 404 00:17:23,720 --> 00:17:26,515 In the next video, we're going to start exploring oxidation 405 00:17:26,515 --> 00:17:28,150 reduction reactions. 406 00:17:28,150 --> 00:17:28,267