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 --> 00:00:13,130
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
00:00:17,060 --> 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 --> 00:00:22,790
periodic table, because
it never hurts to get

10
00:00:22,790 --> 00:00:23,480
familiar with it.

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00:00:23,480 --> 00:00:25,550
So we have magnesium.

12
00:00:25,550 --> 00:00:27,720
Magnesium has two valance
electrons.

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00:00:27,720 --> 00:00:29,240
It's a Group 2 element.

14
00:00:29,240 --> 00:00:32,560
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
00:00:34,620 --> 00:00:38,990
electronegative atoms. It's so
electronegative that oxidized

17
00:00:38,990 --> 00:00:42,510
has essentially been
named after them.

18
00:00:42,510 --> 00:00:45,630
And we know that oxygen loves
to gain two electrons.

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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
00:00:50,760 --> 00:00:52,800
to gain two electrons.

22
00:00:52,800 --> 00:00:54,350
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 --> 00:00:58,790
It was neutral.

25
00:00:58,790 --> 00:01:03,510
So it's going to have a plus
2 charge, hypothetically.

26
00:01:03,510 --> 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.

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00:01:10,490 --> 00:01:14,710
So in this molecule of magnesium
oxide, the oxidation

29
00:01:14,710 --> 00:01:17,690
state of magnesium is plus 2.

30
00:01:17,690 --> 00:01:22,410
And the oxidation state of
the oxygen is minus 2.

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00:01:22,410 --> 00:01:26,090
Now let's do a slightly
harder one.

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00:01:26,090 --> 00:01:35,990
Let's say we had magnesium
hydroxide.

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00:01:35,990 --> 00:01:38,790
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.

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00:01:47,080 --> 00:01:48,830
So, my temptation would
still be, look.

37
00:01:48,830 --> 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.

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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 --> 00:02:03,330
So let me write that there.

43
00:02:03,330 --> 00:02:06,830
And remember, in order for
everything to work out, if

44
00:02:06,830 --> 00:02:10,840
it's a neutral compound, all of
the oxidation states in it

45
00:02:10,840 --> 00:02:11,940
have to add up to 1.

46
00:02:11,940 --> 00:02:13,700
So let's see if that's
going to work out.

47
00:02:13,700 --> 00:02:15,130
Now, oxygen.

48
00:02:15,130 --> 00:02:17,740
My impulse is that its
oxidation state

49
00:02:17,740 --> 00:02:19,910
tends to be minus 2.

50
00:02:19,910 --> 00:02:21,160
So let me write that down.

51
00:02:21,160 --> 00:02:24,420


52
00:02:24,420 --> 00:02:27,240
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.

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00:02:36,010 --> 00:02:38,790
Hydrogen, if it was bonded to a
magnesium, you might want to

57
00:02:38,790 --> 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
00:02:46,290 --> 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
00:02:51,700 --> 00:02:54,542
So it has a plus 1
oxidation state.

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00:02:54,542 --> 00:02:55,160
So let's see.

64
00:02:55,160 --> 00:02:57,120
At first, you might say,
hey, I'm adding up

65
00:02:57,120 --> 00:02:58,100
the oxidation states.

66
00:02:58,100 --> 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 --> 00:03:04,880
That doesn't make sense, Sal.

69
00:03:04,880 --> 00:03:06,350
This is a neutral compound.

70
00:03:06,350 --> 00:03:08,700
And what you to remember is oh,
no, but you have two of

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00:03:08,700 --> 00:03:10,960
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

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00:03:15,570 --> 00:03:17,390
states of the hydroxide.

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00:03:17,390 --> 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

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00:03:23,150 --> 00:03:25,820
have a minus 1 sum.

77
00:03:25,820 --> 00:03:27,460
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 --> 00:03:37,570
state will be minus 1
for each hydroxide.

82
00:03:37,570 --> 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 --> 00:03:45,600
And it all adds up to 0.

85
00:03:45,600 --> 00:03:47,440
So that worked out.

86
00:03:47,440 --> 00:03:49,350
Now, I want to do a little
bit of an aside.

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00:03:49,350 --> 00:03:51,830
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 --> 00:03:56,630
Because I've kind of used
oxidation state, and oxidized,

91
00:03:56,630 --> 00:04:00,360
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 --> 00:04:19,839
And it's in equilibrium with 1
mole of H30 plus OH minus.

95
00:04:19,839 --> 00:04:22,650
And obviously, everything is
in an aqueous solution.

96
00:04:22,650 --> 00:04:23,840
Now, let's look at the water.

97
00:04:23,840 --> 00:04:26,620
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
00:04:32,340 --> 00:04:34,400
the two electrons from
the two hydrogens.

101
00:04:34,400 --> 00:04:36,705
Each hydrogen is giving
up an electron.

102
00:04:36,705 --> 00:04:39,210
So it has an oxidation
state of plus 1.

103
00:04:39,210 --> 00:04:40,400
And we see this molecule.

104
00:04:40,400 --> 00:04:41,620
Everything adds up.

105
00:04:41,620 --> 00:04:43,700
Because you have two hydrogens
with a plus 1.

106
00:04:43,700 --> 00:04:45,350
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?

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00:04:52,650 --> 00:04:58,660
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 --> 00:05:15,190
And that's why you do
minus 2 plus 1.

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00:05:15,190 --> 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 --> 00:05:22,940
Now, here, what are the
oxidation states?

121
00:05:22,940 --> 00:05:28,230
Each of the hydrogens have
a plus 1 oxidation state.

122
00:05:28,230 --> 00:05:32,070
And then this oxygen
has a minus 2.

123
00:05:32,070 --> 00:05:33,860
And so if you look at the
charge for the entire

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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
00:05:45,080 --> 00:05:47,370
entire molecule, which
is the case.

129
00:05:47,370 --> 00:05:51,260
Now, my question to you is has
any of the oxidation states

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00:05:51,260 --> 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

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00:05:55,850 --> 00:05:58,120
this 2 moles of water.

133
00:05:58,120 --> 00:06:00,570
Or maybe I just have two
molecules of water.

134
00:06:00,570 --> 00:06:02,280
But I have four hydrogens
here.

135
00:06:02,280 --> 00:06:02,600
Right?

136
00:06:02,600 --> 00:06:04,890
And all of them had an
oxidation state of 1.

137
00:06:04,890 --> 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
00:06:21,715 --> 00:06:24,270


144
00:06:24,270 --> 00:06:26,570
Maybe it was oxidized in a
previous reaction where the

145
00:06:26,570 --> 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
00:06:37,650 --> 00:06:39,380
Here, we have two oxygen
molecules.

150
00:06:39,380 --> 00:06:41,630
Each have a minus 2
oxidation state.

151
00:06:41,630 --> 00:06:46,000
Due to this reaction, at least,
no electrons changed

152
00:06:46,000 --> 00:06:48,140
hands in our oxidation
state world.

153
00:06:48,140 --> 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 --> 00:06:57,080
And I just want to be clear that
nothing here was oxidized

156
00:06:57,080 --> 00:07:01,160
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 --> 00:07:10,580
Magnesium has an oxidation
state of plus 2.

160
00:07:10,580 --> 00:07:13,650
And oxygen has an oxidation
state of minus 2.

161
00:07:13,650 --> 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 --> 00:07:29,760
But the oxidation state
for magnesium is

170
00:07:29,760 --> 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
00:07:35,520 --> 00:07:37,380
number, is minus 2.

173
00:07:37,380 --> 00:07:38,960
But I think you know what I'm
talking about when I say it

174
00:07:38,960 --> 00:07:40,330
was oxidized.

175
00:07:40,330 --> 00:07:44,130
At some point, it went from
a neutral magnesium to a

176
00:07:44,130 --> 00:07:47,310
positively charged magnesium
by losing two electrons.

177
00:07:47,310 --> 00:07:49,510
So it got oxidized.

178
00:07:49,510 --> 00:07:53,280
Now, let's do some harder
problems. So hydrogen

179
00:07:53,280 --> 00:07:57,260
peroxide-- I've said multiple
times already that oxygen

180
00:07:57,260 --> 00:08:01,600
tends to have a minus
2 oxidation state.

181
00:08:01,600 --> 00:08:02,450
This is minus 1.

182
00:08:02,450 --> 00:08:04,910
I think you see the pattern.

183
00:08:04,910 --> 00:08:06,900
These guys are plus 1.

184
00:08:06,900 --> 00:08:09,100
Hydrogen is plus or minus 1.

185
00:08:09,100 --> 00:08:10,450
These guys are plus 2.

186
00:08:10,450 --> 00:08:11,520
I think you see the pattern.

187
00:08:11,520 --> 00:08:15,070
It's whether you want to
lose or gain electrons.

188
00:08:15,070 --> 00:08:17,450
You might say, well see,
water normally

189
00:08:17,450 --> 00:08:19,590
has a minus 2 oxidation.

190
00:08:19,590 --> 00:08:22,470
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
00:08:28,690 --> 00:08:31,440
But when you do that, you
immediately have a conundrum.

194
00:08:31,440 --> 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 --> 00:08:37,290
Minus 4.

198
00:08:37,290 --> 00:08:40,130
So this would end up with
a minus 4 total

199
00:08:40,130 --> 00:08:41,720
net oxidation state.

200
00:08:41,720 --> 00:08:42,780
And that's not the
case because this

201
00:08:42,780 --> 00:08:44,300
doesn't have any charge.

202
00:08:44,300 --> 00:08:45,980
So there's a conundrum here.

203
00:08:45,980 --> 00:08:48,390
And the conundrum is because,
if you actually look at the

204
00:08:48,390 --> 00:08:52,140
structure of hydrogen peroxide,
the oxygens are

205
00:08:52,140 --> 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
00:09:04,670 --> 00:09:07,190
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 --> 00:09:11,660
There are others, but this is
the one special case where

212
00:09:11,660 --> 00:09:15,540
oxygen does not have a minus
2 oxidation state.

213
00:09:15,540 --> 00:09:17,550
Let's look at this and try to
figure out what oxygen's

214
00:09:17,550 --> 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
00:09:28,780 --> 00:09:30,430
Same thing on the side.

220
00:09:30,430 --> 00:09:33,060
Oxygen, at least on this bond,
is going to have a plus 1.

221
00:09:33,060 --> 00:09:34,790
It's going to gain
an electron.

222
00:09:34,790 --> 00:09:37,380
What about from this other bond
with the other oxygen?

223
00:09:37,380 --> 00:09:39,760
Well, there's no reason why
one oxygen should hog the

224
00:09:39,760 --> 00:09:41,170
electron from the
other oxygen.

225
00:09:41,170 --> 00:09:43,560
So it's not going to have
any net impact on

226
00:09:43,560 --> 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
00:10:05,930 --> 00:10:09,260
2 times plus 1, plus 2
times minus 1, is 0.

233
00:10:09,260 --> 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
00:10:13,290 --> 00:10:14,170
Let's do another one.

236
00:10:14,170 --> 00:10:15,970
Iron 3 carbonate.

237
00:10:15,970 --> 00:10:18,410
And now, for the first time--
I remember when we first

238
00:10:18,410 --> 00:10:19,920
encountered iron 3 carbonate.

239
00:10:19,920 --> 00:10:22,990
You probably thought, hey, why
is it called iron 3 carbonate

240
00:10:22,990 --> 00:10:25,270
when there are only two
iron molecules, or

241
00:10:25,270 --> 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
00:10:30,310 --> 00:10:31,850
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 --> 00:10:38,530


247
00:10:38,530 --> 00:10:41,760
Now, if carbon is bonding with
oxygen-- let's look at the

248
00:10:41,760 --> 00:10:43,330
periodic table.

249
00:10:43,330 --> 00:10:46,910
We have carbon bonding
with oxygen.

250
00:10:46,910 --> 00:10:48,720
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 --> 00:10:53,040
Sometimes it likes to
gain electrons.

253
00:10:53,040 --> 00:10:57,270
When carbon is bonding with
oxygen, this right here is the

254
00:10:57,270 --> 00:10:58,810
electron hog.

255
00:10:58,810 --> 00:11:01,160
If we had to say who's
taking the electrons,

256
00:11:01,160 --> 00:11:03,010
it's going to be oxygen.

257
00:11:03,010 --> 00:11:03,540
Right?

258
00:11:03,540 --> 00:11:07,040
So carbon is going to be giving
away its electrons.

259
00:11:07,040 --> 00:11:10,200
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 --> 00:11:19,390
four valence electrons.

264
00:11:19,390 --> 00:11:21,670
So let's go back to
the carbonate.

265
00:11:21,670 --> 00:11:27,040
So the carbon could at
most give away its

266
00:11:27,040 --> 00:11:29,930
four valence electrons.

267
00:11:29,930 --> 00:11:32,400
So what will be the net
oxidation number for the

268
00:11:32,400 --> 00:11:33,770
carbonate molecule?

269
00:11:33,770 --> 00:11:36,810
For the CO3?

270
00:11:36,810 --> 00:11:39,430
So this is a plus 4 oxidation,
because it only has

271
00:11:39,430 --> 00:11:40,270
four to give away.

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00:11:40,270 --> 00:11:42,260
If it's bonding with oxygen,
it's going to give them away.

273
00:11:42,260 --> 00:11:44,630
Oxygen is more of a hog.

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00:11:44,630 --> 00:11:47,640
Each oxygen has a minus 2.

275
00:11:47,640 --> 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 --> 00:12:00,290
So I have 4 minus 6 is
equal to minus 2.

280
00:12:00,290 --> 00:12:02,730
So we can kind of view it as the
oxidation number for the

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00:12:02,730 --> 00:12:06,990
entire carbonate molecule
is minus 2.

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00:12:06,990 --> 00:12:11,210
Now, if this entire carbonate
molecule is minus 2, its

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00:12:11,210 --> 00:12:16,920
contribution to the oxidation
state for this whole kind of--

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00:12:16,920 --> 00:12:18,620
the carbonate part
of the molecule.

285
00:12:18,620 --> 00:12:20,980
We have 3 carbonate molecules.

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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 --> 00:12:29,380
If this is minus 6 and this is a
neutral molecule, then our 2

289
00:12:29,380 --> 00:12:32,880
irons are also going
to have to have a

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00:12:32,880 --> 00:12:35,290
plus 6 oxidation state.

291
00:12:35,290 --> 00:12:38,030
Because it all has
to add up to 0.

292
00:12:38,030 --> 00:12:42,400
If both irons combined have
a plus 6 contribution to

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00:12:42,400 --> 00:12:44,380
oxidation state, then each
of the irons must

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00:12:44,380 --> 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

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00:12:50,930 --> 00:12:53,510
least three electrons are going
to favor the carbonate

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00:12:53,510 --> 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?

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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 --> 00:13:06,520
Iron-- a lot of the metals,
especially a lot of the

302
00:13:06,520 --> 00:13:09,790
transition metals-- can have
multiple oxidation states.

303
00:13:09,790 --> 00:13:11,970
When you have iron 3 carbonate,
you're literally

304
00:13:11,970 --> 00:13:14,130
saying, this is the third
oxidation state.

305
00:13:14,130 --> 00:13:18,120
Or iron's oxidation number
in this molecule

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00:13:18,120 --> 00:13:20,780
will be positive 3.

307
00:13:20,780 --> 00:13:21,900
Now, let's do another one.

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00:13:21,900 --> 00:13:23,000
This is interesting.

309
00:13:23,000 --> 00:13:24,010
Acetic acid.

310
00:13:24,010 --> 00:13:25,560
And I think is the first time
that I've actually shown you

311
00:13:25,560 --> 00:13:30,740
the formula for acetic acid.

312
00:13:30,740 --> 00:13:33,410
I won't go into the whole
organic chemistry of it.

313
00:13:33,410 --> 00:13:37,290
But let's try to figure out
what the different charges

314
00:13:37,290 --> 00:13:38,835
are, or the different
oxidation states.

315
00:13:38,835 --> 00:13:41,510


316
00:13:41,510 --> 00:13:43,610
Sometimes you'll just see
it written like this.

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00:13:43,610 --> 00:13:45,430
You'd say, OK.

318
00:13:45,430 --> 00:13:47,530
Oxygens, each of those are
going to have minus 2.

319
00:13:47,530 --> 00:13:51,130


320
00:13:51,130 --> 00:13:52,570
Hydrogens are each going
to have plus 1.

321
00:13:52,570 --> 00:13:56,270


322
00:13:56,270 --> 00:13:58,520
So how are we doing so far?

323
00:13:58,520 --> 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 --> 00:14:09,260
And then here you have plus 1.

326
00:14:09,260 --> 00:14:10,925
You add these up and
you get to 0.

327
00:14:10,925 --> 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
00:14:14,430 --> 00:14:17,280
They must have an oxidation
number of 0.

330
00:14:17,280 --> 00:14:22,180
Because we're already at 0, if
we just consider the hydrogens

331
00:14:22,180 --> 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
00:14:43,310 --> 00:14:46,080
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 --> 00:14:52,430
when we're dealing with
oxidation states, we pretend

344
00:14:52,430 --> 00:14:53,630
that it's ionic.

345
00:14:53,630 --> 00:14:56,030
So in this case, your
hydrogens are

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00:14:56,030 --> 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
00:15:00,920 --> 00:15:03,400
That's consistent with
what we know so far.

349
00:15:03,400 --> 00:15:04,730
And actually, that's
another thing.

350
00:15:04,730 --> 00:15:06,770
When I did this exercise, right
here, I immediately

351
00:15:06,770 --> 00:15:10,420
assumed hydrogen has an
oxidation state of plus 1.

352
00:15:10,420 --> 00:15:12,190
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
00:15:25,910 --> 00:15:27,280
But anyway.

361
00:15:27,280 --> 00:15:30,680
So these all gave an electron
to this carbon.

362
00:15:30,680 --> 00:15:36,785
So just from these hydrogens,
that carbon would have a minus

363
00:15:36,785 --> 00:15:39,740
3 oxidation state, right?

364
00:15:39,740 --> 00:15:41,260
These lost electrons.

365
00:15:41,260 --> 00:15:43,560
This guy gained three electrons,
so his charge

366
00:15:43,560 --> 00:15:45,430
goes down by 3.

367
00:15:45,430 --> 00:15:46,680
The carbon-carbon bond.

368
00:15:46,680 --> 00:15:48,720
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 --> 00:15:53,920
So there should be
no transfer here.

372
00:15:53,920 --> 00:15:56,160
So this carbon's oxidation
status is 3.

373
00:15:56,160 --> 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
00:16:01,560 --> 00:16:02,920
oxidation state.

376
00:16:02,920 --> 00:16:05,470
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 --> 00:16:09,640
two electrons.

379
00:16:09,640 --> 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 --> 00:16:19,140
This oxygen is also going
to take two electrons.

382
00:16:19,140 --> 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
00:16:37,640 --> 00:16:39,050
one from the hydrogen.

390
00:16:39,050 --> 00:16:41,990
So it lost one electron
here, two there.

391
00:16:41,990 --> 00:16:43,770
It lost three electrons.

392
00:16:43,770 --> 00:16:49,050
So in that reality, it would
have a plus 3 charge.

393
00:16:49,050 --> 00:16:53,080
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
00:16:54,930 --> 00:16:58,150
Because if you average minus
3 and plus 3, you get to 0.

396
00:16:58,150 --> 00:17:00,270
And that's why I said, oh,
maybe these are a 0.

397
00:17:00,270 --> 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