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PROFESSOR: All right, so we're
going to try to finish up

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oxidation reduction today.
 

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The next unit we're heading
into is transition metals.

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So, in the last class we were
talking about delta e knots of

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cells, so the standard
potential of a particular

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electric chemical cell.
 

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And as we ended class last
time, you had a clicker

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question, which you told me
what the reaction was at the

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anode and the reaction at the
cathode for this particular

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electric chemical cell.
 

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So, now we're going to
consider, we're going to

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calculate what this delta e
nought is for this cell.

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00:01:05 --> 00:01:09
So we have an equation that we
can use to calculate delta e

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nought of a cell, and that is
that the delta e or the

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potential of the cell, is equal
to the standard reduction

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potential for the reaction
that's occurring at the

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cathode, minus the standard
reduction potential for

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the reaction that's
occurring at the anode.

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So you told me which reaction
was occurring at the anode and

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which at the cathode last time.
 

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So we can just go ahead and
use that information in here.

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So the reaction that's
occurring at the cathode is the

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copper reaction, and the
reaction and the anode is the

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zinc reaction, and note here, I
have these written as reduction

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potentials, because we're going
to be plugging in the standard

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reduction potential
into this equation.

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So, where do we get our
standard reduction potentials?

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00:02:00 --> 00:02:04
Well, your textbook has
tables of many standard

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reduction potentials.
 

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And, of course, on an
exam you would be given

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that information.
 

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And the standard reduction
potentials were measured

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against the standard
hydrogen electrode.

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So, now we talked last time
about what some of these

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abbreviations mean.
 

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So we can look up the values
and they're all going to be

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listed as reduction reactions,
because they are standard

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reduction potentials.
 

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So all the reactions, if you're
looking for ones written as

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oxidation, you'll be out
of luck, they'll all be

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written as reductions.
 

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So here, written as a
reduction, zinc plus 2, two

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electrons to zinc solid, copper
plus 2 plus two electrons to

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copper solid, and you can
look up those standard

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reduction potentials.
 

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And then you can plug them
in to your equation.

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Again, the equation is the
standard reduction potential

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for the couple at the
cathode minus the standard

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reduction potential for the
reaction at the anode.

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So the reaction at the cathode
is the copper reaction, and so

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we have -- we put in here 0 .
 

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3 4 0 2, and then minus, and
the zinc reduction potential's

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negative, so it's
minus a minus 0 .

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7 6 2 8, and then if we add
that together we get a

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positive value of 1 .
 

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1 0 3.
 

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And so in doing these, this is
a pretty easy thing to do, but

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I'm sort of emphasizing it
because a lot of people

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out-clever themselves
in doing this.

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They say, well, one thing's
being oxidized in this

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reaction, one thing's being
reduced, so I'm looking up a

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standard reduction potential,
I'm going to change the sign,

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and then plug it in and
change the sign again.

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And so they change the sign
so many times and they come

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up with the wrong answer.
 

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So just a hint in doing these
problems, if you always think

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that the equation is asking you
for the standard reduction

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potential, look that
value up and put it in.

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Don't do anything fancy with
signs, just use this equation

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as written, plugging in the
standard reduction potentials,

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and you'll be all set and you
won't have any problems

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00:04:10 --> 00:04:11
getting it wrong.
 

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So try not to out-clever
yourself and flip signs

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around many times in
doing these problems.

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All right, so we have a value,
a positive value then for

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our potential for the cell.
 

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So we can ask the question, in
this type of cell, would the

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flow of electrons
be spontaneous?

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What tells us if something
is spontaneous?

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Delta g tells us if something
is going to be spontaneous.

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And we mentioned last time
a connection between

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delta g and delta e.
 

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So, delta g tells us if
something will be spontaneous,

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00:04:50 --> 00:04:55
and we talked last time of this
equation that delta g nought

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for the cell is equal to minus
n, n here being moles of

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00:04:59 --> 00:05:03
electrons times Faraday's
constant, times the delta

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e nought for the cell.
 

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00:05:05 --> 00:05:09
So here again, we're relating
back to thermodynamics, back to

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00:05:09 --> 00:05:12
delta g, and we're thinking
about whether things are going

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00:05:12 --> 00:05:14
to be spontaneous or not.
 

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So, if we have a positive value
for delta e nought of the cell,

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00:05:19 --> 00:05:23
what's going to be true
then for delta g?

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It'll be negative, and so
will it be spontaneous?

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Yes.
 

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So, if delta e nought is
positive, delta g will be

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negative, and if delta g is
negative, the reaction will,

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00:05:38 --> 00:05:41
in fact, be spontaneous.
 

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So the answer, then, is yes.
 

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So now let me introduce
some more terms to you.

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Galvanic cell is an electric
chemical cell in which a

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00:05:55 --> 00:06:00
spontaneous chemical reaction
is used to generate

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00:06:00 --> 00:06:02
an electric current.
 

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So on a problem, which you may
have on your problem-set and

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00:06:04 --> 00:06:07
have already looked at this,
it'll say something about

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00:06:07 --> 00:06:09
for a galvanic cell.
 

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00:06:09 --> 00:06:12
Well, that wasn't just kind of
random information they're

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00:06:12 --> 00:06:14
throwing out, they're telling
you that the reaction's going

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00:06:14 --> 00:06:16
to be spontaneous in that cell.
 

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00:06:16 --> 00:06:20
So that will often tell you
what reaction had to be

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happening at the anode, and
what reaction had to be

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happening at the cathode.
 

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Because you need to have it be
spontaneous, you need a value

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for delta e nought,
then it's positive.

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00:06:30 --> 00:06:33
So, the information that it's
a galvanic cell tells you

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00:06:33 --> 00:06:36
a lot about the problem.
 

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In contrast, we have
electrolitic cell, and in this

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case, we can put in energy to
provide, to be able to drive a

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00:06:46 --> 00:06:48
non-spontaneous reaction.
 

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00:06:48 --> 00:06:52
So you can generate a
current to then force and

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non-spontaneous reaction to go.
 

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So these are 2 different
kinds of cells.

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00:07:02 --> 00:07:05
So again, whether something's
spontaneous or not comes

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back to our friend delta g.
 

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00:07:08 --> 00:07:12
So if a cell is operating
spontaneously, that means

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00:07:12 --> 00:07:14
you're going to have a delta e
nought of the cell that's

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00:07:14 --> 00:07:17
positive, which means that the
delta g of the cell

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00:07:17 --> 00:07:18
will be negative.
 

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00:07:18 --> 00:07:21
And we can calculate these
delta e noughts of the cell

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00:07:21 --> 00:07:24
from the standard reduction
potentials, which some nice

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00:07:24 --> 00:07:26
person measured for us
against the standard

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00:07:26 --> 00:07:27
hydrogen electrode.
 

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And so we can look up those
values and then we can

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00:07:31 --> 00:07:36
calculate delta e nought of a
cell, we'll know something

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00:07:36 --> 00:07:39
about whether it will be a
spontaneous reaction or not.

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00:07:39 --> 00:07:48
So now let's think about the
size and the sign of standard

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00:07:48 --> 00:07:52
reduction potentials and what
they tell us about a

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00:07:52 --> 00:07:54
particular reaction.
 

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00:07:54 --> 00:07:57
So the meaning of the standard
reduction potential that you

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00:07:57 --> 00:07:59
can look up in your book.
 

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00:07:59 --> 00:08:01
So first let's think about
what happens or what would

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00:08:01 --> 00:08:05
be true if we had a large
positive delta e nought.

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00:08:05 --> 00:08:10
And that's going to mean that
the element is easy to reduce.

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00:08:10 --> 00:08:12
So let's look at an example.
 

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00:08:12 --> 00:08:15
At the top of your table,
you're going to see this

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00:08:15 --> 00:08:20
particular reduction with this
particular reduction potential.

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00:08:20 --> 00:08:24
So we have f two gas plus 2
electrons going to 2 f minus.

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00:08:24 --> 00:08:27
And the standard reduction
potential for this is

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00:08:27 --> 00:08:29
measured at plus 2 .
 

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00:08:29 --> 00:08:32
8 7 volts.
 

158
00:08:32 --> 00:08:35
So, as written, that's the
value of the standard

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00:08:35 --> 00:08:37
reduction potential.
 

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00:08:37 --> 00:08:41
That's a large positive number,
so that's going to mean

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00:08:41 --> 00:08:45
that it's easy to add
electrons to f 2.

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00:08:45 --> 00:08:49
The delta g nought would
be favorable for that.

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00:08:49 --> 00:08:57
So then, you can tell me, does
that make f 2 a good oxidizing

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00:08:57 --> 00:09:26
agent or not and why?
 

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00:09:26 --> 00:09:42
OK, let's do 10 seconds.
 

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00:09:42 --> 00:09:44
Good.
 

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00:09:44 --> 00:09:46
Yes, it is easy to reduce.
 

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00:09:46 --> 00:09:49
So it's easy to add electrons,
which makes it a good

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00:09:49 --> 00:09:50
oxidizing agent.
 

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00:09:50 --> 00:09:54
So let's go back to the slides.
 

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00:09:54 --> 00:10:00
So, a good oxidizing agent is
something that oxidizes other

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00:10:00 --> 00:10:01
elements and gets
reduced itself.

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00:10:01 --> 00:10:04
So it goes around
oxidizing things, it's

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00:10:04 --> 00:10:06
an agent of oxidation.
 

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00:10:06 --> 00:10:09
So something that easy to
reduce is going to be a

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00:10:09 --> 00:10:12
good oxidizing agent.
 

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00:10:12 --> 00:10:15
And something that's easy to
reduce is going to have a

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00:10:15 --> 00:10:20
large positive standard
reduction potential.

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00:10:20 --> 00:10:24
So, one way to sort of
remember this is for

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00:10:24 --> 00:10:26
a particular couple.
 

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00:10:26 --> 00:10:30
If something has a large
positive delta e nought, the

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00:10:30 --> 00:10:35
oxidized species, the oxidized
species here is the f 2, it's,

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00:10:35 --> 00:10:38
of these two things, it's
the one that's oxidized.

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00:10:38 --> 00:10:41
So the oxidized species
is very oxidizing.

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00:10:41 --> 00:10:45
So that's one way
to remember it.

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00:10:45 --> 00:10:48
Large positive delta e
nought, oxidized species

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00:10:48 --> 00:10:52
is very oxidizing.
 

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00:10:52 --> 00:10:57
So, here is a list that is
similar to what you would see

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00:10:57 --> 00:11:00
in the back of your book, and
we just talked about this

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00:11:00 --> 00:11:05
couple between fluoride gas and
a fluoride minus up here with

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00:11:05 --> 00:11:09
this large positive standard
reduction potential, and as it

192
00:11:09 --> 00:11:13
says up here, oxidized form
is strongly oxidizing.

193
00:11:13 --> 00:11:16
Now, here we have positive
numbers, and now we start to go

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00:11:16 --> 00:11:19
to small negative numbers, and
by the time we get down here,

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00:11:19 --> 00:11:23
we have a large negative number
for the standard reduction

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00:11:23 --> 00:11:27
potential, and this is between
lithium plus and lithium solid.

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00:11:27 --> 00:11:30
So, let's consider what
would be true down on the

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00:11:30 --> 00:11:33
other end of the table.
 

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00:11:33 --> 00:11:37
So a large negative delta
e nought means that the

200
00:11:37 --> 00:11:40
element is hard to reduce.
 

201
00:11:40 --> 00:11:43
So let's look at this
reaction with lithium.

202
00:11:43 --> 00:11:47
So we have lithium plus
with lithium plus 1.

203
00:11:47 --> 00:11:50
When you add one electron to
it, you get lithium solid.

204
00:11:50 --> 00:11:53
And the standard reduction
potential for doing that

205
00:11:53 --> 00:11:55
reaction is minus 3 .
 

206
00:11:55 --> 00:11:59
0 4 5 volts.
 

207
00:11:59 --> 00:12:03
So, that's hard to add
electrons to lithium plus 1 --

208
00:12:03 --> 00:12:08
lithium plus 1 is very happy
being lithium plus 1, it

209
00:12:08 --> 00:12:12
doesn't want that electron
back, and so that would

210
00:12:12 --> 00:12:17
be a non-spontaneous,
unfavorable reaction.

211
00:12:17 --> 00:12:25
So, is lithium plus 1 a
good oxidizing agent?

212
00:12:25 --> 00:12:29
No, it's not a good oxidizing
agent, but something around

213
00:12:29 --> 00:12:32
here is going to
be a good agent.

214
00:12:32 --> 00:12:36
Lithium solid is a
good reducing agent.

215
00:12:36 --> 00:12:42
So, lithium solid likes to
reduce other things, lithium

216
00:12:42 --> 00:12:45
solid likes to be oxidized,
lithium prefers to

217
00:12:45 --> 00:12:47
be lithium plus 1.
 

218
00:12:47 --> 00:12:52
So it's very happy to be
lithium plus 1, so the solid

219
00:12:52 --> 00:12:57
form is a good reducing agent.
 

220
00:12:57 --> 00:13:00
So, if we think about what's
true at the bottom of the

221
00:13:00 --> 00:13:06
table, then if we have a couple
of plus 1 to the solid, then if

222
00:13:06 --> 00:13:09
you have a large negative
standard reduction potential,

223
00:13:09 --> 00:13:12
the reduced species
is very reducing.

224
00:13:12 --> 00:13:16
So the reduced species here
is the lithium solid, it

225
00:13:16 --> 00:13:18
is a good reducing agent.
 

226
00:13:18 --> 00:13:26
So, large negative reduced
species is reducing.

227
00:13:26 --> 00:13:29
And if we go back to work table
then, up here we have the

228
00:13:29 --> 00:13:31
big positive numbers.
 

229
00:13:31 --> 00:13:36
The oxidized form of this first
couple is very oxidizing, at

230
00:13:36 --> 00:13:39
the bottom you have the large
negative numbers, and the

231
00:13:39 --> 00:13:43
reduced form of that
couple is very reducing.

232
00:13:43 --> 00:13:46
And you're going to be asked
questions, given different

233
00:13:46 --> 00:13:50
elements in problem-sets or on
exams and saying which of these

234
00:13:50 --> 00:13:53
is the better oxidizing agent,
which of these is the better

235
00:13:53 --> 00:13:57
reducing agent, and be able to
compare, and you need to think

236
00:13:57 --> 00:14:01
about where it is, which are
the bigger positive numbers,

237
00:14:01 --> 00:14:05
bigger negative numbers, and
you can make those comparisons,

238
00:14:05 --> 00:14:09
and if you remember on the top,
big positive, oxidized form

239
00:14:09 --> 00:14:12
very oxidizing, big negative,
reduced form very reducing,

240
00:14:12 --> 00:14:17
you'll be all set to
answer those questions.

241
00:14:17 --> 00:14:21
And some of this should be sort
of intuitive of the things

242
00:14:21 --> 00:14:23
that we've talked about
already in this course.

243
00:14:23 --> 00:14:27
So we think about the periodic
table for a minute, and here

244
00:14:27 --> 00:14:31
are some of the potentials,
lithium is easy to oxidize,

245
00:14:31 --> 00:14:33
it's a good reducing agent.
 

246
00:14:33 --> 00:14:37
If it's lithium plus 1, then it
has a noble gas configuration,

247
00:14:37 --> 00:14:39
it's very happy there.
 

248
00:14:39 --> 00:14:42
Whereas fluoride can get its
noble gas configuration if

249
00:14:42 --> 00:14:46
it's f minus, so it's easy
to reduce and that makes

250
00:14:46 --> 00:14:48
it a good oxidizing agent.
 

251
00:14:48 --> 00:14:51
So you can think about this in
terms of it's sort of intuitive

252
00:14:51 --> 00:14:54
if you think about what you
know about those elements

253
00:14:54 --> 00:14:59
going into this unit.
 

254
00:14:59 --> 00:15:04
So now, let's think about
calculating a standard

255
00:15:04 --> 00:15:06
reduction potential
for this particular

256
00:15:06 --> 00:15:07
electric chemical cell.
 

257
00:15:07 --> 00:15:13
So we're given equations and we
want to calculate a standard

258
00:15:13 --> 00:15:16
potential for this.
 

259
00:15:16 --> 00:15:21
So, in doing this then, we're
going to use our standard

260
00:15:21 --> 00:15:24
reduction potentials on this
table, it's a little hard

261
00:15:24 --> 00:15:26
to see, so I'll go
back over there.

262
00:15:26 --> 00:15:30
So now we have to figure out if
we see this equation, what's

263
00:15:30 --> 00:15:35
the reaction that's going
on at the cathode?

264
00:15:35 --> 00:15:38
First tell me what's happening
at the cathode -- is it an

265
00:15:38 --> 00:15:41
oxidation or reduction
happening at the cathode?

266
00:15:41 --> 00:15:46
The reduction is happening
at the cathode.

267
00:15:46 --> 00:15:53
Now look at that equation up
there and tell me what is being

268
00:15:53 --> 00:15:59
reduced -- which element is
being reduced in that equation?

269
00:15:59 --> 00:16:01
The iron is being reduced.
 

270
00:16:01 --> 00:16:05
So we're going to write the
1/2 reaction, that's balance,

271
00:16:05 --> 00:16:09
so there were two iron 3's.
 

272
00:16:09 --> 00:16:16
And on the other side there's
two iron plus 2's, and how

273
00:16:16 --> 00:16:22
many electrons am I talking
about here? two electrons.

274
00:16:22 --> 00:16:25
So we have the
reduction reaction.

275
00:16:25 --> 00:16:32
Then at the anode, the anode
has an oxidation going on, and

276
00:16:32 --> 00:16:36
we only have one choice left
of what's being oxidized.

277
00:16:36 --> 00:16:41
So, we have -- and
again balanced.

278
00:16:41 --> 00:16:47
We have 2 i minus, and this is
an aqueous solution going to i

279
00:16:47 --> 00:16:54
2 solid plus two electrons.
 

280
00:16:54 --> 00:17:00
So we have now our two 1/2
reactions written out, and we

281
00:17:00 --> 00:17:04
can look at the potentials
for the standard reduction

282
00:17:04 --> 00:17:13
potentials, which we'll need to
calculate the e for the cell.

283
00:17:13 --> 00:17:17
So now we want to calculate e
nought for the cell, and that's

284
00:17:17 --> 00:17:25
going to be equal to the e
for the cathode reaction.

285
00:17:25 --> 00:17:30
And that particular couple at
the cathode, we're looking then

286
00:17:30 --> 00:17:38
at iron 3 plus going to iron 2
plus -- that's the reduction

287
00:17:38 --> 00:17:40
potential that we're
going to be looking up.

288
00:17:40 --> 00:17:46
And then we also need another
standard reduction potential,

289
00:17:46 --> 00:17:50
the one for the couple at the
anode, and the couple at the

290
00:17:50 --> 00:17:55
anode that we're looking
up is i 2 to i minus.

291
00:17:55 --> 00:18:00
So, if you can see that up
there, it's also in your

292
00:18:00 --> 00:18:05
handout, then we can
plug in those values.

293
00:18:05 --> 00:18:10
So, for iron, we have plus 0 .
 

294
00:18:10 --> 00:18:19
7 7 0 volts minus plus 0 .
 

295
00:18:19 --> 00:18:24
5 3 5 volts.
 

296
00:18:24 --> 00:18:28
And that's going to equal 0 .
 

297
00:18:28 --> 00:18:34
2 3 5 volts, which is
a positive number.

298
00:18:34 --> 00:18:37
So what would be true about
this reaction in terms of

299
00:18:37 --> 00:18:42
it being spontaneous
or non-spontaneous?

300
00:18:42 --> 00:18:44
Right, so it would be
spontaneous, because you have a

301
00:18:44 --> 00:18:47
positive value for delta e, so
we'd have a negative

302
00:18:47 --> 00:18:49
value for delta g.
 

303
00:18:49 --> 00:18:55
All right, so now, let's think
about what the good oxidizing

304
00:18:55 --> 00:19:00
and reducing agents are here,
and let's have a clicker

305
00:19:00 --> 00:19:06
question for that.
 

306
00:19:06 --> 00:19:11
So, which is the better
oxidizing agent, iron plus

307
00:19:11 --> 00:19:16
3 or i 2, and which is the
better reducing agent,

308
00:19:16 --> 00:19:19
i minus or iron plus 2?
 

309
00:19:19 --> 00:20:01
So think about that one.
 

310
00:20:01 --> 00:20:18
All right, let's
take 10 seconds.

311
00:20:18 --> 00:20:21
Very good.
 

312
00:20:21 --> 00:20:24
So the trick here is to,
again, think about these

313
00:20:24 --> 00:20:26
two different potentials.
 

314
00:20:26 --> 00:20:30
Now, unlike the example we had
before, we had a big positive

315
00:20:30 --> 00:20:34
and a big negative value, these
are both positive values.

316
00:20:34 --> 00:20:40
But one of them is bigger than
the other, and so the better

317
00:20:40 --> 00:20:47
oxidizing one is going to be
the one of these two, these

318
00:20:47 --> 00:20:49
are both the oxidized form.
 

319
00:20:49 --> 00:20:52
So the one with the bigger
positive number, the oxidized

320
00:20:52 --> 00:20:56
species will be better at
oxidizing, and so that would be

321
00:20:56 --> 00:21:01
the iron plus 3, that's the
bigger positive number.

322
00:21:01 --> 00:21:04
Whereas here, when we're
considering which is the better

323
00:21:04 --> 00:21:07
reducing agent, we're looking
at the two reduced species

324
00:21:07 --> 00:21:11
here, and here the thing with
the smaller a positive number,

325
00:21:11 --> 00:21:14
the reduced form will be a
better reducing agent,

326
00:21:14 --> 00:21:16
more reducing.
 

327
00:21:16 --> 00:21:20
So again, you can look at where
those are in the table and the

328
00:21:20 --> 00:21:24
size difference between them
to get the right answer.

329
00:21:24 --> 00:21:27
So, very good.
 

330
00:21:27 --> 00:21:35
OK, so now, I want to consider
a biological example for a

331
00:21:35 --> 00:21:38
minute, and I'm going to ask a
question that we we'll then

332
00:21:38 --> 00:21:41
answer at the end of class.
 

333
00:21:41 --> 00:21:45
So in cells, things have
reduction potentials.

334
00:21:45 --> 00:21:48
Vitamin B12 has a
reduction potential.

335
00:21:48 --> 00:21:52
In fact, it has one of the
largest negative reduction

336
00:21:52 --> 00:21:56
potentials of any biologically
occurring molecule.

337
00:21:56 --> 00:22:00
And so it has to be reduced
to be active in the body.

338
00:22:00 --> 00:22:04
So how can something with a
very large negative reduction

339
00:22:04 --> 00:22:08
potential be reduced?
 

340
00:22:08 --> 00:22:10
That's the question.
 

341
00:22:10 --> 00:22:11
Why should you care?
 

342
00:22:11 --> 00:22:16
Well, because vitamin B12 needs
to be reduced to be active.

343
00:22:16 --> 00:22:20
And the proper functioning of
enzymes, there's only actually

344
00:22:20 --> 00:22:24
two that you have in humans
that require B12 -- one that

345
00:22:24 --> 00:22:28
requires B12 and folic acid is
thought to be important in

346
00:22:28 --> 00:22:33
preventing heart disease, birth
defects, and B12 hs recently

347
00:22:33 --> 00:22:36
been linked to mental health.
 

348
00:22:36 --> 00:22:40
In particular, a lack of B12
has been linked to dementia.

349
00:22:40 --> 00:22:44
So, these are all pretty
significant things.

350
00:22:44 --> 00:22:49
So, one thing that I think is
kind of interesting here when

351
00:22:49 --> 00:22:54
they talk about heart disease,
how many people have

352
00:22:54 --> 00:22:57
heard of cholesterol?
 

353
00:22:57 --> 00:23:02
How many people have
heard of homocysteine?

354
00:23:02 --> 00:23:05
Would you be surprised to know
that homocysteine is a better

355
00:23:05 --> 00:23:08
indicator of whether you'll
have heart trouble

356
00:23:08 --> 00:23:10
than cholesterol?
 

357
00:23:10 --> 00:23:11
Yes.
 

358
00:23:11 --> 00:23:12
You would think that you
would have heard of the one

359
00:23:12 --> 00:23:14
that was a better link.
 

360
00:23:14 --> 00:23:17
Well, homocysteine is actually
a better link to indicate

361
00:23:17 --> 00:23:21
whether you might have heart
problems, but the thing is that

362
00:23:21 --> 00:23:24
there's not a whole lot of
money to be made there, whereas

363
00:23:24 --> 00:23:26
there's a lot of money to be
made in drugs that

364
00:23:26 --> 00:23:27
lower cholesterol.
 

365
00:23:27 --> 00:23:30
So you may realize, if you
think about where you get your

366
00:23:30 --> 00:23:33
medical information, it's often
from commercials where

367
00:23:33 --> 00:23:34
someone's trying to
sell you something.

368
00:23:34 --> 00:23:38
And so if there isn't much
money to be made, say, the

369
00:23:38 --> 00:23:41
treatment for a condition might
be taking vitamins, which

370
00:23:41 --> 00:23:43
there's not a whole lot of
money to be made there, you

371
00:23:43 --> 00:23:45
don't hear as much about it.
 

372
00:23:45 --> 00:23:48
So, it's important to consider
the source of information about

373
00:23:48 --> 00:23:52
your health, and as scientists,
you can all evaluate

374
00:23:52 --> 00:23:54
information about
your health now.

375
00:23:54 --> 00:23:57
All right, so vitamin B12 is
very important, you really

376
00:23:57 --> 00:24:00
need vitamin B12 to
be a healthy person.

377
00:24:00 --> 00:24:04
And most people at MIT are
maybe at this stage are not

378
00:24:04 --> 00:24:08
that worried of heart disease.
 

379
00:24:08 --> 00:24:10
Many of you are probably not
worried yet about having

380
00:24:10 --> 00:24:13
children with birth defects,
but maybe some of you are

381
00:24:13 --> 00:24:19
worried about mental
recognition of particular facts

382
00:24:19 --> 00:24:23
for exams coming up, and so you
may be concerned about B12 to

383
00:24:23 --> 00:24:25
keep sharp mentally.
 

384
00:24:25 --> 00:24:29
So, where do you get vitamin
B12 and folic acid in your

385
00:24:29 --> 00:24:32
diet and how is it reduced?
 

386
00:24:32 --> 00:24:36
So let's first consider where
you get it in your diet.

387
00:24:36 --> 00:24:42
So, does anyone know where you
get vitamin B12 in your diet?

388
00:24:42 --> 00:24:47
I heard vegetables.
 

389
00:24:47 --> 00:24:52
Anyone agree with vegetables?
 

390
00:24:52 --> 00:24:55
I didn't say if anyone liked
vegetables, does anyone agree

391
00:24:55 --> 00:24:58
that vitamin B12 come
from vegetables.

392
00:24:58 --> 00:25:00
It doesn't.
 

393
00:25:00 --> 00:25:14
Where does vitamin
B12 come from?

394
00:25:14 --> 00:25:19
So, red meat is a good source
of vitamin B12, all meat is a

395
00:25:19 --> 00:25:21
good source the vitamin B12.
 

396
00:25:21 --> 00:25:25
Plants do not use
vitamin B12 at all.

397
00:25:25 --> 00:25:31
So, people who are vegan are in
trouble in terms of how much

398
00:25:31 --> 00:25:34
vitamin B12 they get, but
luckily there are vitamin

399
00:25:34 --> 00:25:36
tablets that can help
take care of this.

400
00:25:36 --> 00:25:41
So meat is really the best
source of vitamin B12.

401
00:25:41 --> 00:25:47
So, I'm always looking for good
references to vitamin B12,

402
00:25:47 --> 00:25:49
and I saw one recently.
 

403
00:25:49 --> 00:25:54
Has anyone seen the HBO
series, True Blood.

404
00:25:54 --> 00:25:55
One person.
 

405
00:25:55 --> 00:25:58
OK, if you watch that, you will
notice that if you date a

406
00:25:58 --> 00:26:02
vampire, you have to make sure
you get extra vitamin B12, and

407
00:26:02 --> 00:26:07
that Sookie, of True Blood is
taking vitamin B12 tablets

408
00:26:07 --> 00:26:09
just to be on the safe side.
 

409
00:26:09 --> 00:26:13
So, vitamin B12.
 

410
00:26:13 --> 00:26:17
What about folic acid?
 

411
00:26:17 --> 00:26:24
Anyone know where
you get folic acid?

412
00:26:24 --> 00:26:27
In the fall, what happens,
people say let's go outside

413
00:26:27 --> 00:26:32
and look at the trees or
look at the pretty foliage.

414
00:26:32 --> 00:26:38
Any suggestion of where
folic acid comes from?

415
00:26:38 --> 00:26:43
Oh, wait a minute.
 

416
00:26:43 --> 00:26:46
I was at a meeting once where
there was a whole lecture about

417
00:26:46 --> 00:26:50
how Norwegian beer was the best
source of folic acid, and

418
00:26:50 --> 00:26:53
it was, perhaps, not
coincidentally reported by

419
00:26:53 --> 00:26:56
Norwegian scientists.
 

420
00:26:56 --> 00:26:59
They would not vouch for any
other kinds, but some -- but

421
00:26:59 --> 00:27:03
it does come from barleys,
vegetables, this kind of thing.

422
00:27:03 --> 00:27:08
So, here is a secret
for healthy diet.

423
00:27:08 --> 00:27:11
Have some of you seen the
orange juice commercial that

424
00:27:11 --> 00:27:16
says "Drink orange juice, it's
good for your heart." That's

425
00:27:16 --> 00:27:20
because of this, so that
actually is potentially true.

426
00:27:20 --> 00:27:24
So you get a lot of folic acid
in orange juice, and folic acid

427
00:27:24 --> 00:27:27
is, in fact, good
for your heart.

428
00:27:27 --> 00:27:31
So, who would have guessed,
some of the claims

429
00:27:31 --> 00:27:33
are actually true.
 

430
00:27:33 --> 00:27:36
All right, but we still have a
problem, we still need to know

431
00:27:36 --> 00:27:38
how its reduced in the body.
 

432
00:27:38 --> 00:27:40
And so we're going to come back
to that at the end of the

433
00:27:40 --> 00:27:46
lecture and answer that
if we get that far.

434
00:27:46 --> 00:27:48
All right, so we need to do a
couple more things first so

435
00:27:48 --> 00:27:52
everyone can finish their
problem-sets, and the things

436
00:27:52 --> 00:27:54
we're going to do is we're
going to look adding and

437
00:27:54 --> 00:27:57
subtracting 1/2 cell reactions,
and then get to one of my

438
00:27:57 --> 00:28:02
favorite things, which
is the Nernst equation.

439
00:28:02 --> 00:28:03
All right.
 

440
00:28:03 --> 00:28:05
So, some of you may have
encountered this problem on

441
00:28:05 --> 00:28:07
the problem-set already.
 

442
00:28:07 --> 00:28:10
Suppose you need you know a
standard reduction potential

443
00:28:10 --> 00:28:14
and it's not given to you in
the back of the book, but

444
00:28:14 --> 00:28:17
other things are given to
you in the back of the book.

445
00:28:17 --> 00:28:21
Can you calculate the thing you
need from related equations?

446
00:28:21 --> 00:28:26
So suppose you really want to
know the reduction couple for

447
00:28:26 --> 00:28:28
copper 2 going to copper 1.
 

448
00:28:28 --> 00:28:29
But that's not given.
 

449
00:28:29 --> 00:28:34
You find copper 2 with two
electrons going to copper 0,

450
00:28:34 --> 00:28:37
and you find copper 0 going
to copper plus 1 with one

451
00:28:37 --> 00:28:42
electron, and you'll realize
that if you combine these

452
00:28:42 --> 00:28:44
equations, you'll get
the desired one.

453
00:28:44 --> 00:28:48
So if you add these together,
you have copper 2 with one

454
00:28:48 --> 00:28:51
electron, one electron
cancels out here.

455
00:28:51 --> 00:28:54
The copper solids cancel
out and you're left

456
00:28:54 --> 00:28:56
with copper plus 1.
 

457
00:28:56 --> 00:28:59
So you add these together,
and you know the

458
00:28:59 --> 00:29:00
potentials for these.
 

459
00:29:00 --> 00:29:02
How do you get the standard
potential for the thing

460
00:29:02 --> 00:29:06
that you've come up with,
for the sum of those?

461
00:29:06 --> 00:29:10
So, as someone actually asked
me before class, you have to go

462
00:29:10 --> 00:29:15
back to free energy, and you
do, but I'm going to drive an

463
00:29:15 --> 00:29:18
equation so that you don't have
to go all the way back, but

464
00:29:18 --> 00:29:20
this is, in fact, how you do
the problem, you think about

465
00:29:20 --> 00:29:24
the different free energies.
 

466
00:29:24 --> 00:29:29
So, the new reaction, the new
delta g for that new reaction

467
00:29:29 --> 00:29:32
will be equal to the delta g
knot for the reduction minus

468
00:29:32 --> 00:29:34
the oxidation reaction here.
 

469
00:29:34 --> 00:29:39
But we can substitute for delta
g this minus n, Faraday's

470
00:29:39 --> 00:29:42
constant times our reduction
potential, and put it in

471
00:29:42 --> 00:29:44
to this equation here.
 

472
00:29:44 --> 00:29:47
And so we have it for the new
reaction, and then the 2

473
00:29:47 --> 00:29:51
reactions that we're
adding together.

474
00:29:51 --> 00:29:55
So we have Faraday's constant
in common, so that's

475
00:29:55 --> 00:29:56
going to cancel out.
 

476
00:29:56 --> 00:30:00
And we can also move n 3 to the
other side, because we want to

477
00:30:00 --> 00:30:04
solve for this new e
value, this new standard

478
00:30:04 --> 00:30:05
reduction potential.
 

479
00:30:05 --> 00:30:09
And so that's going to be equal
to the number of moles that are

480
00:30:09 --> 00:30:13
involved in the reaction that's
the reduction times its

481
00:30:13 --> 00:30:16
reduction potential minus the
number of moles involved in the

482
00:30:16 --> 00:30:20
oxidation reaction with its
reduction potential, and then

483
00:30:20 --> 00:30:23
the number of moles for the
reaction that -- this new

484
00:30:23 --> 00:30:25
reaction in question.
 

485
00:30:25 --> 00:30:29
So we can use, then, this
equation to look for a 1/2

486
00:30:29 --> 00:30:35
cell reaction that is the
sum of two other reactions.

487
00:30:35 --> 00:30:37
So let's go and use
that equation, then.

488
00:30:37 --> 00:30:41
So here we have the known
values -- we know the couple

489
00:30:41 --> 00:30:45
for copper 2 to copper 0, we
know the couple for copper 1

490
00:30:45 --> 00:30:53
to copper solid, and this
is what we want to know.

491
00:30:53 --> 00:30:56
So we can use this equation.
 

492
00:30:56 --> 00:30:59
Which of these reactions is
the reduction, what value

493
00:30:59 --> 00:31:06
am I going to put in here?
 

494
00:31:06 --> 00:31:17
Which of these goes
into the reduction?

495
00:31:17 --> 00:31:23
Which of these is a
reduction reaction?

496
00:31:23 --> 00:31:24
Yeah.
 

497
00:31:24 --> 00:31:29
And how many moles of
electrons are involved?

498
00:31:29 --> 00:31:31
So, we put in 2 times 0 .
 

499
00:31:31 --> 00:31:39
3 4 0 volts, and then over here
in the oxidation, there's one

500
00:31:39 --> 00:31:42
electron involved, and we
put in our other potential.

501
00:31:42 --> 00:31:44
So 1 times 0 .
 

502
00:31:44 --> 00:31:46
5 2 2.
 

503
00:31:46 --> 00:31:49
And what are the number of
moles of electrons for our

504
00:31:49 --> 00:31:52
desired, final reaction?
 

505
00:31:52 --> 00:31:54
1.
 

506
00:31:54 --> 00:31:56
And so, then we can do the
math and come up with

507
00:31:56 --> 00:31:58
an answer of 0 .
 

508
00:31:58 --> 00:32:00
1 5 8 volts.
 

509
00:32:00 --> 00:32:04
And so now we've just come up
with a new reduction potential,

510
00:32:04 --> 00:32:07
we've calculated a new
reduction potential for this

511
00:32:07 --> 00:32:11
1/2 cell reaction right here.
 

512
00:32:11 --> 00:32:14
So, this equation will be given
to you on an exam and all you

513
00:32:14 --> 00:32:19
need to do is know
how to use it.

514
00:32:19 --> 00:32:23
So we've calculated now the
standard reduction potential

515
00:32:23 --> 00:32:27
for copper 2 to copper plus 1.
 

516
00:32:27 --> 00:32:31
So, just a little note about
when you're going to use this

517
00:32:31 --> 00:32:33
and when you're going to use
the other equation

518
00:32:33 --> 00:32:35
that I showed you.
 

519
00:32:35 --> 00:32:39
So, if we're talking about a
whole electric chemical cell,

520
00:32:39 --> 00:32:42
the number of moles that are
released at the anode are going

521
00:32:42 --> 00:32:46
to equal the number of moles
taken up at the cathode and be

522
00:32:46 --> 00:32:49
the number of moles involved
in the overall equation.

523
00:32:49 --> 00:32:54
So this equation is not
necessary, and for a full

524
00:32:54 --> 00:32:56
electric chemical cell, we're
going to use the equation that

525
00:32:56 --> 00:32:59
I gave you before for this
delta e nought for the

526
00:32:59 --> 00:33:01
cell, so we just use this.
 

527
00:33:01 --> 00:33:04
But if it's not a whole
electric chemical cell you're

528
00:33:04 --> 00:33:06
talking about, if you're
talking about calculating a

529
00:33:06 --> 00:33:09
1/2 cell potential, then you
need to use this equation.

530
00:33:09 --> 00:33:13
Both of these equations
will be given to you on

531
00:33:13 --> 00:33:14
sheets for the exam.
 

532
00:33:14 --> 00:33:16
This one's for an electric
chemical cell, this

533
00:33:16 --> 00:33:20
one's for calculating a
1/2 cell potential.

534
00:33:20 --> 00:33:23
So again, if it's 1/2
cell potential, you want

535
00:33:23 --> 00:33:27
to use this equation.
 

536
00:33:27 --> 00:33:31
OK, so now the Nernst equation.
 

537
00:33:31 --> 00:33:36
So, some of you may have
encountered in your life where

538
00:33:36 --> 00:33:41
you go to turn something on
and you discover that

539
00:33:41 --> 00:33:44
the battery is dead.
 

540
00:33:44 --> 00:33:49
So, an exhausted battery is
a sign that your chemical

541
00:33:49 --> 00:33:58
reaction has reached
equilibrium.

542
00:33:58 --> 00:33:59
At equilibrium, you're going
to have a zero difference

543
00:33:59 --> 00:34:00
potential across your
electrodes, and the battery

544
00:34:00 --> 00:34:03
will be not useful to
you at that point.

545
00:34:03 --> 00:34:07
So, if you -- instead of
getting annoyed next time you

546
00:34:07 --> 00:34:09
have a dead battery, you can
think about all, ah, it's

547
00:34:09 --> 00:34:14
finally reached equilibrium.
 

548
00:34:14 --> 00:34:18
So, we need to think about,
then, to think about how these

549
00:34:18 --> 00:34:22
cell reactions are happening,
how the potential is going to

550
00:34:22 --> 00:34:26
change with the composition of
the ingredients in those

551
00:34:26 --> 00:34:29
electrochemical cells.
 

552
00:34:29 --> 00:34:33
So, we know something about
equilibrium and components

553
00:34:33 --> 00:34:36
of reactions again.
 

554
00:34:36 --> 00:34:38
So this is a nice lecture to
give coming up with a week

555
00:34:38 --> 00:34:41
before the exam, because now
we're going back and reviewing

556
00:34:41 --> 00:34:46
the first material on the exam
from chemical equilibrium.

557
00:34:46 --> 00:34:50
So, we know that delta g is
going to change as the

558
00:34:50 --> 00:34:54
components change until
equilibrium is reached.

559
00:34:54 --> 00:34:57
And when equilibrium is
reached our delta g is

560
00:34:57 --> 00:35:00
going to be equal to zero.
 

561
00:35:00 --> 00:35:06
Before equilibrium is reached,
delta g will depend on the

562
00:35:06 --> 00:35:10
delta g nought for the
equation, r t and the natural

563
00:35:10 --> 00:35:14
log of q, where q is what?
 

564
00:35:14 --> 00:35:17
What's q?
 

565
00:35:17 --> 00:35:19
The reaction quotient.
 

566
00:35:19 --> 00:35:24
So we saw this before and
we're back to using it again.

567
00:35:24 --> 00:35:27
So what do we know about the
relationship between delta

568
00:35:27 --> 00:35:30
g nought and delta e?
 

569
00:35:30 --> 00:35:34
We know that delta g nought is
equal to minus n, moles of

570
00:35:34 --> 00:35:39
electrons times Faraday's
constant times delta e nought.

571
00:35:39 --> 00:35:44
So, we can combine
some things around.

572
00:35:44 --> 00:35:47
So we can take our equation
that we saw in chemical

573
00:35:47 --> 00:35:51
equilibrium and substitute in
values that are related to

574
00:35:51 --> 00:35:53
standard reduction potentials.
 

575
00:35:53 --> 00:35:57
So we can put in, for this
delta g, minus n Faraday's

576
00:35:57 --> 00:36:00
constant times the delta e.
 

577
00:36:00 --> 00:36:03
And for delta g nought, we put
in the same thing but now

578
00:36:03 --> 00:36:05
we have delta e nought.
 

579
00:36:05 --> 00:36:08
And we have r t, gas constant
times temperature times the

580
00:36:08 --> 00:36:12
natural log of q, our
reaction quotient.

581
00:36:12 --> 00:36:17
Now we can divide both sides by
n and Faraday's constant and we

582
00:36:17 --> 00:36:19
come up with the
Nernst equation.

583
00:36:19 --> 00:36:24
So the Nernst equation tells us
the potential for a cell at any

584
00:36:24 --> 00:36:28
given time, at any given
component of ingredients in the

585
00:36:28 --> 00:36:34
cell, any amounts of, say, your
zinc plus 2, compared to the

586
00:36:34 --> 00:36:37
standard potential for that
cell, which you're going to

587
00:36:37 --> 00:36:40
calculate from your standard
reduction potentials in the

588
00:36:40 --> 00:36:44
table, and then you have this
term, gas constant times

589
00:36:44 --> 00:36:47
temperature, number of moles of
electrons involved, Faraday's

590
00:36:47 --> 00:36:51
constant, and you need to know
q, the particular composition

591
00:36:51 --> 00:36:56
of the cell at that given time.
 

592
00:36:56 --> 00:36:59
So, just a hint in doing Nernst
equation problems, if you're

593
00:36:59 --> 00:37:03
given a problem and it's giving
you concentrations of things at

594
00:37:03 --> 00:37:07
a particular time, that should
be a clue that the Nernst

595
00:37:07 --> 00:37:10
equation is going to be
what you're going to

596
00:37:10 --> 00:37:13
want to use here.
 

597
00:37:13 --> 00:37:15
So, let let's look
at an example.

598
00:37:15 --> 00:37:19
Say we have a -- we want to
calculate the cell potential at

599
00:37:19 --> 00:37:22
a given time at 25 degrees,
and we know our zinc

600
00:37:22 --> 00:37:24
plus 2 ions or 0 .
 

601
00:37:24 --> 00:37:28
1 0 molar and copper
2 ions are 0 .

602
00:37:28 --> 00:37:34
0 0 1 0 molar, and this is
the equation for that cell.

603
00:37:34 --> 00:37:44
So we can look up, again, our
values in the table, and the

604
00:37:44 --> 00:37:47
first thing we're going to do,
if we're going to use to Nernst

605
00:37:47 --> 00:37:52
equation, is to calculate the
standard potential for that

606
00:37:52 --> 00:37:58
particular cell, and here are
the values from the table, and

607
00:37:58 --> 00:38:48
why don't you go ahead and
calculate that for me.

608
00:38:48 --> 00:39:11
All right, so let's just take
10 more seconds on that.

609
00:39:11 --> 00:39:16
OK, so let's see if we can get
into the 90's pretty soon,

610
00:39:16 --> 00:39:20
because we should be able to do
that for this particular one.

611
00:39:20 --> 00:39:25
All right, let's go back
to the presentation here.

612
00:39:25 --> 00:39:29
So it was actually,
this was pretty easy.

613
00:39:29 --> 00:39:33
I didn't actually mean for
these two things to show up, to

614
00:39:33 --> 00:39:35
help you out of what the
reaction at the cathode and the

615
00:39:35 --> 00:39:38
anode was, so that was an
easier question than

616
00:39:38 --> 00:39:39
I had intended.
 

617
00:39:39 --> 00:39:41
So, first you need to think
about if you're given an

618
00:39:41 --> 00:39:44
equation here, what's happening
at the cathode, what's

619
00:39:44 --> 00:39:46
happening at the anode.
 

620
00:39:46 --> 00:39:49
As it's written, you can look
and see so copper plus 2 is

621
00:39:49 --> 00:39:54
going to copper solid, zinc
solid's going to zinc plus 2,

622
00:39:54 --> 00:39:58
so you can think about which is
the cathode reaction, which is

623
00:39:58 --> 00:40:01
the anode, which has a
reduction, which has an

624
00:40:01 --> 00:40:05
oxidation going on, and then
once you know which couples

625
00:40:05 --> 00:40:09
you're talking about, then you
can plug in your values.

626
00:40:09 --> 00:40:13
So, at the cathode, we're
going from copper plus

627
00:40:13 --> 00:40:15
2 to copper solid.
 

628
00:40:15 --> 00:40:18
We put in our standard
reduction potential, using the

629
00:40:18 --> 00:40:21
equation we have a minus, and
then the standard reduction

630
00:40:21 --> 00:40:25
potential at the anode, so we
have the oxidation from zinc

631
00:40:25 --> 00:40:29
solid to zinc plus 2, and we
put in this value and we

632
00:40:29 --> 00:40:33
calculate the number here.
 

633
00:40:33 --> 00:40:39
So then, we have that,
we also need to know q.

634
00:40:39 --> 00:41:10
So why don't you tell
me what q is now?

635
00:41:10 --> 00:41:27
OK, let's just do 10
more seconds on this.

636
00:41:27 --> 00:41:32
OK.
 

637
00:41:32 --> 00:41:38
So here, if we go back, q is
going to be equal to products

638
00:41:38 --> 00:41:43
over reactants, except things
that are solids are not are not

639
00:41:43 --> 00:41:46
changing during the equilibrium
so we leave those out.

640
00:41:46 --> 00:41:49
So it's going to be
concentration of zinc plus 2

641
00:41:49 --> 00:41:52
over the concentration of
copper, which gives

642
00:41:52 --> 00:41:53
you a value of 1 .
 

643
00:41:53 --> 00:41:56
0 times 10 to the 2.
 

644
00:41:56 --> 00:42:01
So, just a review of q, if you
need help calculating q's,

645
00:42:01 --> 00:42:04
we're going to have to extra
problems for the exam coming

646
00:42:04 --> 00:42:06
up to be posted on Friday.
 

647
00:42:06 --> 00:42:12
So, this'll be used
in several units.

648
00:42:12 --> 00:42:14
So then you need to know n, and
then we have everything to go

649
00:42:14 --> 00:42:16
back to the Nernst equation.
 

650
00:42:16 --> 00:42:23
So how many moles of electrons
are involved in this?

651
00:42:23 --> 00:42:26
2.
 

652
00:42:26 --> 00:42:29
Sometimes it's not so obvious,
so this can trick people, so

653
00:42:29 --> 00:42:31
make sure that you pay
attention to this.

654
00:42:31 --> 00:42:33
This one is a pretty
obvious one.

655
00:42:33 --> 00:42:36
All right, now we have
everything that we can put in.

656
00:42:36 --> 00:42:41
You calculated the standard
potential for the cell, you

657
00:42:41 --> 00:42:44
calculated q, and you told
me how many moles of

658
00:42:44 --> 00:42:45
electrons there are.
 

659
00:42:45 --> 00:42:46
So we can go and put this in.
 

660
00:42:46 --> 00:42:49
So we calculated positive 1 .
 

661
00:42:49 --> 00:42:53
0 3 volts minus the gas
constant times the temperature,

662
00:42:53 --> 00:42:57
it was at room temperature,
natural log of q.

663
00:42:57 --> 00:43:02
We had two moles of electrons
and Faraday's constant here.

664
00:43:02 --> 00:43:08
And now if we do the math, this
whole term comes out to 0 .

665
00:43:08 --> 00:43:13
0 5 9 2 volts, and we get
our answer, which is a

666
00:43:13 --> 00:43:15
positive number there.
 

667
00:43:15 --> 00:43:18
So, just a note about
units and constants.

668
00:43:18 --> 00:43:20
Where did volts come from here?
 

669
00:43:20 --> 00:43:24
Well, the moles canceled out,
and the kelvin canceled out,

670
00:43:24 --> 00:43:28
and we are left with joules
per Coulomb, and conveniently

671
00:43:28 --> 00:43:31
for us, joules per
Coulomb is a volt.

672
00:43:31 --> 00:43:34
So, all our units add up here.
 

673
00:43:34 --> 00:43:38
And just a note about a
significant figures in

674
00:43:38 --> 00:43:42
doing these problems, the
Nernst equation, boy,

675
00:43:42 --> 00:43:44
significant figure fun.
 

676
00:43:44 --> 00:43:46
If you want to make sure
you know significant

677
00:43:46 --> 00:43:47
figures, here you go.
 

678
00:43:47 --> 00:43:51
Significant figure rules for
logs, we have significant

679
00:43:51 --> 00:43:55
figure rules for multiplication
and division, and then

680
00:43:55 --> 00:43:58
significant figure
rules for subtraction.

681
00:43:58 --> 00:44:03
So, one equation gives
you every type of

682
00:44:03 --> 00:44:04
significant figure rule.
 

683
00:44:04 --> 00:44:10
So, that can be a
lot of fun as well.

684
00:44:10 --> 00:44:13
All right, but I'm going to try
to make it easier for you on an

685
00:44:13 --> 00:44:17
exam and avoid some
math mistakes.

686
00:44:17 --> 00:44:18
All the problems I'm
going to give you are

687
00:44:18 --> 00:44:20
at room temperature.
 

688
00:44:20 --> 00:44:24
And so, the gas constant is a
constant, temperature for these

689
00:44:24 --> 00:44:26
problems is going to be a
constant, always room

690
00:44:26 --> 00:44:29
temperature, Faraday's
constant is a constant.

691
00:44:29 --> 00:44:34
So, all of these, I'm going to
give you the value that they

692
00:44:34 --> 00:44:40
all add up to, and if you use
log instead of natural log,

693
00:44:40 --> 00:44:41
there's this value as well.
 

694
00:44:41 --> 00:44:46
So, these will be given to you
on an exam, so you'll see these

695
00:44:46 --> 00:44:51
equations on the exam as
well and you can use them.

696
00:44:51 --> 00:44:55
So, this is for natural log,
this is for log, so we are not

697
00:44:55 --> 00:44:58
going to test your ability to
multiply room temperature times

698
00:44:58 --> 00:45:01
the gas constant divided
by Faraday's constant.

699
00:45:01 --> 00:45:03
So that's going to make
it a little easier in

700
00:45:03 --> 00:45:07
doing these problems.
 

701
00:45:07 --> 00:45:11
All right, so what
about at equilibrium.

702
00:45:11 --> 00:45:15
What does q equal
at equilibrium?

703
00:45:15 --> 00:45:18
So, q equals k at equilibrium.
 

704
00:45:18 --> 00:45:22
What does delta g
equal at equilibrium?

705
00:45:22 --> 00:45:23
Zero.
 

706
00:45:23 --> 00:45:28
And so that means that we knew
before, from this equation,

707
00:45:28 --> 00:45:33
when this is equal to zero,
then delta g knot equals minus

708
00:45:33 --> 00:45:38
r t, natural log of k, so q
equals k at equilibrium.

709
00:45:38 --> 00:45:41
And so we had this equation
that we used before.

710
00:45:41 --> 00:45:46
We now have this equation, so
here it related delta g knot to

711
00:45:46 --> 00:45:50
the equilibrium constant, here
we relate delta g nought to

712
00:45:50 --> 00:45:54
delta e nought And so, I think
you can see what's coming.

713
00:45:54 --> 00:46:00
We are going to relate these
two together and come up with

714
00:46:00 --> 00:46:04
an expression where are you
can calculate equilibrium

715
00:46:04 --> 00:46:08
constants from standard
reduction potentials.

716
00:46:08 --> 00:46:12
So, you may be asked
to do this as well.

717
00:46:12 --> 00:46:15
So everything in these units
are, in fact, related

718
00:46:15 --> 00:46:16
to each other.
 

719
00:46:16 --> 00:46:20
And the only thing we have left
today, the answer to this

720
00:46:20 --> 00:46:23
question about how B12
is reduced in the body.

721
00:46:23 --> 00:46:26
So, you're just going to have
to wait to find out, don't

722
00:46:26 --> 00:46:29
worry you won't get heart
disease between now and Friday,

723
00:46:29 --> 00:46:33
and I'll let you know how
it all works out on Friday.

724
00:46:33 --> 00:46:34