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PROFESSOR: So, you have now
10 seconds, go ahead and

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click in your answer.
 

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OK.
 

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We have a little bit of
a mixed response here.

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So for those of you coming in
late, I'm going to give you a

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second chance, and we say now
what if the p k a was 4.

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Everything else is the same,
but the p k a is now 4 --

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what would the answer be?
 

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OK, go ahead and click in your
response for a p k a of 4,

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everything else being the same.
 

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OK, let's do 10 seconds.
 

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Interesting.
 

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More people got that right.
 

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So it's the same answer for a p
k a of 3 as a p k a of 4, but

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it gave people the opportunity
to think about that a little

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more and see what their
neighbors had voted and make a

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decision based on that.
 

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And so more people came up
with the right answer.

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So let's consider now for a
minute why this is true.

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So if you can switch to my
lecture notes, I have a couple

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of slides on this that are not
in your handout but that

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are related to things
we've talked about.

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So just a brief sort of
reminder of where we were

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with acid based titrations.
 

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So, we last time talked about
what's happening at different

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points of the p h curve, and
introduced this concept of 1/2

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equivalence point where the p h
equals the p k a, where you

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have equal number of moles
of molecules that are

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pronated as depronated.
 

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And another way to sort of
think about this whole thing is

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that in the beginning at p h's
that are lower than the

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p k a, you have more
pronated molecules.

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And if p h is much above
the p k a, you have more

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depronated molecules.
 

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So, we can think about
things that way.

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So let's think about the last
question that I asked where

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are have a p k a of 4.
 

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So, if you gave someone a
sample of molecules where the p

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h was equal to the p k a of the
molecule, you'd be giving them

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a sample where there would be
equal amounts of pronated

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and depronated.
 

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But instead, if you gave a
sample where the p h is much

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above the p k a, then you're
going to be giving

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them a sample that's
mostly depronated.

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And I emphasize about using, in
terms of titrations, using

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Henderson Hasselbalch for
buffer, but it also can be

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applied to thinking about
this type of problem.

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And so you can be thinking
about what sort of ratio are

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you going to get of your
pronated to depronated when

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you have given a particular
p k a and a particular p h.

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And so, if the p h is really
very far above the p k a, then

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you're going to be largely
depronated, and here's the

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math for these two numbers.
 

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If you're at a p h that's
really below the p k a,

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then your molecules are
going to be pronated.

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And so, you're going to be
thinking about this kind of

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thing when you get to
organic chemistry, and

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also biochemistry.
 

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Biochemists spend a lot of time
thinking about the p k a's of

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amino acid side chains, and
there are often mechanisms that

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people propose of how an enzyme
works, and they're proposing

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that some residue is going to
play a role as a catalytic

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acid or a base in an
enzyme mechanism.

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And often people are proposing
things that really just don't

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make much sense in terms of the
p k a of that molecule, that

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they're proposing, that it's
going to be giving off a

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proton, but given the p h of
the enzyme in the body

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and given the p k a, it
wouldn't be pronated.

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So how is it going to
give off something it's

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not going to have.
 

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So these are the kinds of
questions people talk about in

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biochemistry, and if you're in
a biochemistry seminar and

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someone's talking about
something like this, there will

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probably be a hand go up in the
audience and say "What do you

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think the p k a is of that
amino acid that you're

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proposing that role in this
enzyme mechanism?" And there

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have been people who are pretty
high profile who've gotten

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themselves in trouble
over p k a issues.

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So now, you should all be ready
to raise your hand in those

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seminars and say "What do you
think the p k a is of that

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residue?" So, you'll be hearing
about p k a's later, and the

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thing that makes me very
excited is that some other

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people who are taking chemistry
here, may not be as aware of

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the sort of biological
role of p k a's.

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Now you know something, you've
had some of these in your

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problem-sets, and so when you
go into those advanced classes

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and there's a discussion of p k
a, you'll raise your hand and

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impress my colleagues with your
tremendous knowledge

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of p k a's.
 

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So I'm very excited about that.
 

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And please send me an email
when you get extra points

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because of knowledge
of p k a's.

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I want to collect that
information and use it

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for evil purposes.
 

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No.
 

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But anyway, you can think about
p k a's of molecules now, which

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will be very handy
to you later on.

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So it's not just -- some people
tell me, if I promise never to

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titrate a weak acid with a
strong base, do I have to

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take that part of the test?
 

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Well, you know it's not just
about acid based titrations.

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Some of the things you learn in
that are actually relevant to

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other things that most of you
will see later in your career.

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All right.
 

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So, I love enzymes, enzymes
are great, I'm a biochemist.

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Acid base is very important
in biochemistry.

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And the other thing that is
very important in biochemistry

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is oxidation reduction.
 

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So, in these two units that
we're doing now that'll be on

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the third exam, you're learning
a lot of the basic principles

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that apply to how enzymes work.
 

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And so we started last time
talking about some rules.

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Rules of assigning
oxidation number.

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So this is sort of the very
basic knowledge that you need

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to know to go on and do
oxidation reduction problems.

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And here are those rules, and
now let's see look at some

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examples of how we're going
to apply these rules.

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So, first let's look at a
compound that has lithium

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and oxygen in it.
 

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All right.
 

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What do I know about
lithium's oxidation number?

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What's it going to be?
 

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Plus 1.
 

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So, things in group 1
are going to be plus 1,

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and I have 2 of them.
 

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So we're going to be using
one of those rules up

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there to assign it.
 

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What about oxygen?
 

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What's oxygen going to
be in this molecule?

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Minus 2.
 

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So it's not in a peroxide
here, so it'll be minus 2.

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And then we have plus 2 minus 2
is equal to 0, and that's good,

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because there's no charge on
this particular molecule, so

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all of the oxidation numbers
should add up to 0.

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That's also one of our rules.
 

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All right, so let's
look at p c l 5.

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So, what we know about
oxidation number of chloride?

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What are you guessing?
 

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Minus 1.
 

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What's the exception to that?
 

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When it's with what?
 

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When it's with oxygen
it can be different.

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All right, so
there's 5 of those.

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I haven't told you anything
about phosphorous, but what can

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you guess it's going to be?
 

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STUDENT: 5.
 

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PROFESSOR: I love that
enthusiasm, good.

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So, it will be 5, and so
overall, we're going

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to add up to 0.
 

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So you won't always have a rule
about everything in your

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molecule, but you'll be given
something that you can get a

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handle on and then predict what
the other thing is going to be.

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So let's do a couple more.
 

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So, what about h n o 3?
 

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So let's start with oxygen --
you told me about oxygen,

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what's oxygen going to be here?
 

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STUDENT: Negative 2.
 

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PROFESSOR: Negative 2
and there's 3 of those.

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And we need to have this
all add up to 0 again.

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So, what about hydrogen?
 

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STUDENT: Plus 1.
 

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PROFESSOR: Plus 1.
 

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What's the exception
to that rule?

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When its with a metal.
 

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So what does that
leave for nitrogen?

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Plus 5.
 

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And that will all add up.
 

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All right, so you're very good
at this, so let's bring in that

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clicker competition, and you
can tell me about

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this molecule.
 

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All right, 10 seconds.
 

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Excellent -- not necessarily
for the competition since most

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people got it right, but I love
seeing people get it right.

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So, 2 times plus 1 minus 2 is
0, so we know our states here.

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And I'll just tell you another
thing you can do in doing these

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problems, if you recognize that
something is often seen has a

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unit here, you can also think
about this as h plus and n o 3

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minus, and you would get the
same answers to the problem.

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So, if it's a little
complicated and you want to

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break it apart, you can do
that too, you'll get

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the same answers there.
 

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All right, so as I said, in
this unit it's a lot of adding

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and subtracting, so this part
is not too complicated, but you

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just have to be paying
attention and doing your math,

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simple math, correctly.
 

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All right, so we looked
at some examples.

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So now we're going to
give some definitions.

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What is oxidation?
 

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What happens when
something is oxidized?

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Yup.
 

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So, when you oxidize something,
electrons are lost.

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What happens when you
reduce something?

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STUDENT: Gain electrons.
 

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PROFESSOR: You gain electrons.
 

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Most people are good
with those definitions.

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Here are some that give people
a little bit more trouble.

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Oxidizing agent.
 

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So it is an agent of oxidation,
so it accepts -- an oxidation

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agent is something that wants
to oxidize something else,

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so it gets reduced itself.
 

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So it's an agent of oxidation.
 

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It runs around trying to
oxidize other things, but it

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itself is going to get reduced,
and then you can probably

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figure out what a reducing
agent is, it's an

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agent of reduction.
 

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And so it itself
will be oxidized.

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It'll try to reduce
something else.

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It'll run around trying to
reduce something, trying to

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give off its electrons,
donate its electrons so

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that it can be oxidized.
 

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So, keep these definitions in
mind, because you're going

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to be using them a
lot in this unit.

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So now we're going to use them,
we're going to look at a

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reaction, and we're going to
think about what's being

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oxidized and what
is being reduced.

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And this particular type of
reaction, a disproportionation

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00:14:01 --> 00:14:10
reaction, the same element can
be both oxidized and reduced.

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So let's break this down
into two equations.

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In every reaction there's going
to be an oxidation and a

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reduction, and so you can
write those separately.

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And poor sodium, sodium is
getting kind of a jip.

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A lot in these last few units
in acid base, and here again,

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it's a spectator ion here,
so it doesn't even make

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it into the equation.
 

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And it was ineffective as
a conjugate acid, it

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hasn't really been doing
very much recently.

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But that's OK.
 

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All right, so let's look at
what's going on here and try to

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figure out what's happening in
terms of what's being reduced

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and what's being oxidized.
 

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So let's start over here,
let's think about what the

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oxidation numbers are in
this particular molecule.

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So what would be true about
oxygen here and chloride.

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What do we know about this
combination of things in

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00:15:08 --> 00:15:14
terms of oxidation numbers?
 

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So let's start with chloride,
what's that going to be here?

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00:15:25 --> 00:15:28
So, we have a minus 2 here.
 

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And the whole thing is going
to be minus 1, and so what

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is that about chloride?
 

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Plus 1, right.
 

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So this is one of
the exceptions.

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Chloride is usually minus 1,
except when it's with oxygen,

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and here we have an overall
charge of the molecule of minus

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1, so it all has to add up
to minus 1 and it does.

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00:15:47 --> 00:15:51
All right, so now
let's do that side.

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00:15:51 --> 00:15:54
So what's going on here?
 

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Are they going to be
similar or different?

256
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Let's start with the oxygen,
what's that going to be?

257
00:16:01 --> 00:16:04
So we have three negative 2's.
 

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It's not a peroxide, so it's
negative 2 for oxygen.

259
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The overall has to be
equal to minus 1, so

260
00:16:11 --> 00:16:12
what is chloride here?
 

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Plus 5, right.
 

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So that's unusual, but
that's what it is.

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00:16:17 --> 00:16:19
So we use our rules.
 

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Chloride is usually minus
1, except when it's with

265
00:16:22 --> 00:16:24
oxygen, and then it can
be something different.

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So, here chloride's going
from plus 1 to plus 5, so

267
00:16:28 --> 00:16:29
what's happening to it?
 

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Is it being oxidized
or reduced?

269
00:16:37 --> 00:16:38
Yup.
 

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So it's going from plus
1 to plus 5, so we have

271
00:16:41 --> 00:16:43
an oxidation going on.
 

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00:16:43 --> 00:16:46
So to tell whether something is
an oxidation or not, you need

273
00:16:46 --> 00:16:49
to figure out what the
oxidation numbers are and then

274
00:16:49 --> 00:16:52
see what's changing in the
course of that reaction.

275
00:16:52 --> 00:16:57
All right, so down here, we've
already done this one, so

276
00:16:57 --> 00:16:59
we can put that down here.
 

277
00:16:59 --> 00:17:03
So we have minus 2 for oxygen,
overall minus 1, and so

278
00:17:03 --> 00:17:05
chloride is plus 1 again.
 

279
00:17:05 --> 00:17:11
And what's the oxidation number
on the other side for chlorine?

280
00:17:11 --> 00:17:12
Minus 1.
 

281
00:17:12 --> 00:17:15
I just have to look,
and so that's minus 1.

282
00:17:15 --> 00:17:20
So here we're going from plus 1
to minus 1, so what is that?

283
00:17:20 --> 00:17:22
That's a reduction.
 

284
00:17:22 --> 00:17:25
And if we had figured out that
they're both oxidations and

285
00:17:25 --> 00:17:28
something we would have done
incorrectly, because in these

286
00:17:28 --> 00:17:31
reactions you're going to have
oxidations and reductions.

287
00:17:31 --> 00:17:35
So, here, and this is
disproportionation.

288
00:17:35 --> 00:17:37
So, you have chloride in one
state, and in another, it's

289
00:17:37 --> 00:17:43
undergoing a reduction.
 

290
00:17:43 --> 00:17:46
OK, so that's how you sort of
think about what's happening

291
00:17:46 --> 00:17:48
in these types of reactions.
 

292
00:17:48 --> 00:17:51
So now we need to
balance reactions.

293
00:17:51 --> 00:17:54
And this is very important in
getting the correct answer to

294
00:17:54 --> 00:17:58
the later problems, and so
we'll go through an example of

295
00:17:58 --> 00:17:59
how you're going to balance.
 

296
00:17:59 --> 00:18:02
You need to think about whether
it's an acidic solution or

297
00:18:02 --> 00:18:07
basic solution, and we'll
talk about that at the end.

298
00:18:07 --> 00:18:12
So, first here, we can look at
the two 1/2 reactions going on,

299
00:18:12 --> 00:18:14
we have iron, we have chromium,
and so we're going to look

300
00:18:14 --> 00:18:17
at those separately.
 

301
00:18:17 --> 00:18:22
So here is the first one, and
let's think about what's

302
00:18:22 --> 00:18:23
happening over here.
 

303
00:18:23 --> 00:18:38
So, what would our oxidation
number of the oxygen be here?

304
00:18:38 --> 00:18:39
What is happening to it?
 

305
00:18:39 --> 00:18:42
So, figure out what the
oxidation numbers are of the

306
00:18:42 --> 00:18:45
chromium on one side, you know
what it is on the other side,

307
00:18:45 --> 00:19:06
and then tell me what's
happening to it.

308
00:19:06 --> 00:19:07
I hear some murmuring.
 

309
00:19:07 --> 00:19:10
People in one recitation aren't
helping out people in the

310
00:19:10 --> 00:19:16
other recitation, are they?
 

311
00:19:16 --> 00:19:19
All right.
 

312
00:19:19 --> 00:19:21
Do you need more times?
 

313
00:19:21 --> 00:19:22
You good?
 

314
00:19:22 --> 00:19:22
You clicked in?
 

315
00:19:22 --> 00:19:39
Let's do 10 seconds.
 

316
00:19:39 --> 00:19:40
OK.
 

317
00:19:40 --> 00:19:42
People did pretty
well on that one.

318
00:19:42 --> 00:19:44
Let's look at the
answer to that.

319
00:19:44 --> 00:19:50
So, let's go back
to my Powerpoint.

320
00:19:50 --> 00:19:56
And so, oxidation number
for oxygen here, minus 2.

321
00:19:56 --> 00:20:00
The overall charge
on that is minus 2.

322
00:20:00 --> 00:20:04
So you have to figure out
what the math equals there.

323
00:20:04 --> 00:20:08
And so, if you run through the
math, then you see that you're

324
00:20:08 --> 00:20:17
going from a plus 6 to a plus 3
state, so we have a reduction.

325
00:20:17 --> 00:20:21
OK, 75% did that,
got that, good.

326
00:20:21 --> 00:20:25
So, most of you should be able
to get this one now, iron

327
00:20:25 --> 00:20:26
plus 2 to iron plus 3.
 

328
00:20:26 --> 00:20:29
Just yell it out, what is that?
 

329
00:20:29 --> 00:20:30
Yeah.
 

330
00:20:30 --> 00:20:33
So here we have our oxidation.
 

331
00:20:33 --> 00:20:35
Now let's balance this.
 

332
00:20:35 --> 00:20:39
And I left some nice blanks in
your notes, but not so many

333
00:20:39 --> 00:20:42
that you won't be able to keep
up and you should feel free to

334
00:20:42 --> 00:20:46
yell out the answers and we'll
go through balancing

335
00:20:46 --> 00:20:49
this pretty quickly.
 

336
00:20:49 --> 00:20:51
So there's a couple
of different rules.

337
00:20:51 --> 00:20:53
I'll just say some books
have things differently.

338
00:20:53 --> 00:20:56
If you can get the right
answer, you can use whatever

339
00:20:56 --> 00:20:58
procedure you want.
 

340
00:20:58 --> 00:21:01
I have found in the past that
this particular procedure a

341
00:21:01 --> 00:21:04
lot of people find
to be the easiest.

342
00:21:04 --> 00:21:08
So I'll teach you this one, but
you're free to use whichever

343
00:21:08 --> 00:21:09
ones work well for you.
 

344
00:21:09 --> 00:21:13
All right, so the first thing
we want to do is balance all

345
00:21:13 --> 00:21:17
elements that are not
oxygen or hydrogen.

346
00:21:17 --> 00:21:19
To make it equal on both sides,
we're going to do oxygen

347
00:21:19 --> 00:21:21
and hydrogen later.
 

348
00:21:21 --> 00:21:25
But what do we need to
do up here to balance

349
00:21:25 --> 00:21:29
our non-oxygens?
 

350
00:21:29 --> 00:21:31
We need to add a what?
 

351
00:21:31 --> 00:21:35
A 2.
 

352
00:21:35 --> 00:21:37
So we need to add a 2 over
here, two chromiums here,

353
00:21:37 --> 00:21:39
two on the other side.
 

354
00:21:39 --> 00:21:40
What about for iron?
 

355
00:21:40 --> 00:21:43
Nothing.
 

356
00:21:43 --> 00:21:46
All right, so that
was pretty simple.

357
00:21:46 --> 00:21:52
Now, in this procedure you add
water to balance the oxygens.

358
00:21:52 --> 00:21:56
So, what are we going
to do up here.

359
00:21:56 --> 00:22:01
How many waters do
we need to add?

360
00:22:01 --> 00:22:05
So we need to add 7 waters.
 

361
00:22:05 --> 00:22:08
And the bottom one, bottom
one's pretty easy so far, we

362
00:22:08 --> 00:22:11
don't have to do anything.
 

363
00:22:11 --> 00:22:15
So, go ahead and write
in your 7 waters.

364
00:22:15 --> 00:22:18
Next step is we're going to
balance the hydrogens that we

365
00:22:18 --> 00:22:24
just added, and we can balance
here with h plus, and I say

366
00:22:24 --> 00:22:26
here's one place that
books are different.

367
00:22:26 --> 00:22:29
Some of them balance in the
more sort of technically

368
00:22:29 --> 00:22:32
correct way with hydroium ions,
but then your oxygens get

369
00:22:32 --> 00:22:37
unbalanced again, so it's OK to
use the simpler approach, and

370
00:22:37 --> 00:22:39
just balance with h plus.
 

371
00:22:39 --> 00:22:42
So how many h plusses
do we need to add to

372
00:22:42 --> 00:22:46
balance the top part?
 

373
00:22:46 --> 00:22:49
Yup, so we need to
add 14 over here.

374
00:22:49 --> 00:22:53
Again, the bottom
one, nothing to do.

375
00:22:53 --> 00:22:56
Pretty simple.
 

376
00:22:56 --> 00:23:00
Now we need to balance the
charge, so we just added h

377
00:23:00 --> 00:23:04
plusses, so we just added some
charge to this, and now we have

378
00:23:04 --> 00:23:08
to balance the overall charge,
so you want the charge on one

379
00:23:08 --> 00:23:11
side of the equation to be
equal to the charge on the

380
00:23:11 --> 00:23:13
other side of the equation.
 

381
00:23:13 --> 00:23:16
So how many electrons are
we going to have to add

382
00:23:16 --> 00:23:30
to this top equation
to balance the charge?

383
00:23:30 --> 00:23:31
I heard the answer.
 

384
00:23:31 --> 00:23:34
6.
 

385
00:23:34 --> 00:23:36
So we have to add 6.
 

386
00:23:36 --> 00:23:41
I told you, this unit involves
adding and subtracting in your

387
00:23:41 --> 00:23:45
head, and you always want to
check your work when you're

388
00:23:45 --> 00:23:49
doing this on an exam, because
it's really sad when you lose

389
00:23:49 --> 00:23:52
points for something that
is adding and subtracting.

390
00:23:52 --> 00:23:54
So you want to make sure
that you don't lose points

391
00:23:54 --> 00:23:57
on these on an exam.
 

392
00:23:57 --> 00:23:59
So what about the bottom
-- finally we get to do

393
00:23:59 --> 00:24:03
something with the bottom
one, what do we do?

394
00:24:03 --> 00:24:07
So, we add how many electrons?
 

395
00:24:07 --> 00:24:08
1, right.
 

396
00:24:08 --> 00:24:12
OK, so now our
charge is balanced.

397
00:24:12 --> 00:24:18
So now, we want to multiply up
one of the 1/2 reactions so

398
00:24:18 --> 00:24:23
that the electrons are going to
cancel, and so what do we have

399
00:24:23 --> 00:24:27
to multiply by the bottom
equation so that the electrons

400
00:24:27 --> 00:24:30
cancel with the first?
 

401
00:24:30 --> 00:24:32
6.
 

402
00:24:32 --> 00:24:40
So we have 6, 6, and 6.
 

403
00:24:40 --> 00:24:43
And now, we're going to add
those together and make the

404
00:24:43 --> 00:24:48
appropriate cancellations.
 

405
00:24:48 --> 00:24:53
So here is our overall equation
-- we have the 6 electrons, the

406
00:24:53 --> 00:24:57
14 protons, we have our
chromium oxide compound, we

407
00:24:57 --> 00:25:01
have the 6 iron 2 plusses, on
the other side, the 2 chromium

408
00:25:01 --> 00:25:05
3 plusses, the 7 waters, the 6
iron 3 plusses, and

409
00:25:05 --> 00:25:07
the 6 electrons.
 

410
00:25:07 --> 00:25:10
So, we should be able to
cancel the electrons,

411
00:25:10 --> 00:25:15
so we cancel those out.
 

412
00:25:15 --> 00:25:18
And now we want to double check
that, in fact, it's balanced.

413
00:25:18 --> 00:25:21
Again, this is very important
to do on the test, it's really

414
00:25:21 --> 00:25:24
easy to make some kind of math
mistake, but you should be able

415
00:25:24 --> 00:25:26
to figure it out at this point.
 

416
00:25:26 --> 00:25:29
It won't be balanced if
you've made a math mistake.

417
00:25:29 --> 00:25:33
So there should be 14 hydrogens
over here, 14 over there, 2

418
00:25:33 --> 00:25:37
chromiums, 2 chromiums, you
have 7 oxygens here, 7 oxygens

419
00:25:37 --> 00:25:40
there, 6 irons, 6 irons.
 

420
00:25:40 --> 00:25:44
And the charge also should
be balanced on both sides.

421
00:25:44 --> 00:25:47
So you can double check
that and if it's good,

422
00:25:47 --> 00:25:48
then you're done.
 

423
00:25:48 --> 00:25:52
And this was in acidic
solution, so we should have

424
00:25:52 --> 00:25:57
again this number and a charge
of plus 24 on each side, double

425
00:25:57 --> 00:26:01
check, make sure it's correct.
 

426
00:26:01 --> 00:26:05
So, that was acidic solution
and we ended up with an

427
00:26:05 --> 00:26:07
equation that had
h plusses in it.

428
00:26:07 --> 00:26:11
You can also be asked to do it
in basic solution, and again,

429
00:26:11 --> 00:26:14
books have different
approaches here.

430
00:26:14 --> 00:26:19
What I like to do is the
simplest thing, which is to use

431
00:26:19 --> 00:26:24
the same steps all the way up
to here to get your same answer

432
00:26:24 --> 00:26:28
that you had for the acidic
solution, and then neutralize

433
00:26:28 --> 00:26:29
it at this point.
 

434
00:26:29 --> 00:26:34
So, adjust the p h in quotes by
adding hydroxide ions to both

435
00:26:34 --> 00:26:40
sides, and so, if we have 14 h
plusses here, we can add 14 o

436
00:26:40 --> 00:26:45
h's on one side, and 14 o h
minus on the other side.

437
00:26:45 --> 00:26:49
And then we can add
those guys together.

438
00:26:49 --> 00:26:52
So we have now 14
waters over here.

439
00:26:52 --> 00:26:55
And we have still our 7 waters
on this side, and then the

440
00:26:55 --> 00:26:58
14 hydroxides on this side.
 

441
00:26:58 --> 00:27:00
And now, we should be
able to cancel out

442
00:27:00 --> 00:27:03
some of those waters.
 

443
00:27:03 --> 00:27:07
So, we had 14 over here, 7
over here, so we can just

444
00:27:07 --> 00:27:09
have 7 on this side.
 

445
00:27:09 --> 00:27:11
And now we have an equation
that looks like it's

446
00:27:11 --> 00:27:13
in basic solution.
 

447
00:27:13 --> 00:27:15
So instead of having h plus,
which you would have in

448
00:27:15 --> 00:27:18
acid, you have hydroxide
for basic solution.

449
00:27:18 --> 00:27:20
So you can follow
the same rules.

450
00:27:20 --> 00:27:21
Again, some books
do it differently.

451
00:27:21 --> 00:27:25
I think this is the simplest
way to do it, the least likely

452
00:27:25 --> 00:27:29
to make those kind of adding
and subtracting errors.

453
00:27:29 --> 00:27:31
So those are sort of
the fundamentals you

454
00:27:31 --> 00:27:32
need for this unit.
 

455
00:27:32 --> 00:27:36
You need to figure out
oxidation numbers, looking at

456
00:27:36 --> 00:27:40
the composition of a molecule,
and you need to be able

457
00:27:40 --> 00:27:41
to balance equations.
 

458
00:27:41 --> 00:27:44
When you can do that, you can
go on to do other things.

459
00:27:44 --> 00:27:49
So, at this point -- oh, let me
just say, those are the two

460
00:27:49 --> 00:27:53
answers there, so you can
see acid and then in base.

461
00:27:53 --> 00:27:58
So, at this point then, I want
to try to do a little demo to

462
00:27:58 --> 00:28:04
show you that when you do do
oxidation reduction reactions,

463
00:28:04 --> 00:28:08
cool things can happen.
 

464
00:28:08 --> 00:28:12
So, it's more exciting,
perhaps, in real life

465
00:28:12 --> 00:28:15
when oxidation happens
than on paper.

466
00:28:15 --> 00:28:20
So I'm going to turn it over
now to Dr. Taylor and Dr.

467
00:28:20 --> 00:28:24
Patti Christie who's here
to help us with this demo.

468
00:28:24 --> 00:28:26
And they will -- go for it.
 

469
00:28:26 --> 00:28:28
PROFESSOR: OK, so this is
mostly visual, there's not

470
00:28:28 --> 00:28:29
too much we'll need to say.
 

471
00:28:29 --> 00:28:31
Basically what we're
going to do for you

472
00:28:31 --> 00:28:33
is oxidize magnesium.
 

473
00:28:33 --> 00:28:39
So we have a source of
oxidation, which is going to be

474
00:28:39 --> 00:28:43
carbon dioxide, which is dry
ice, and what we put inside the

475
00:28:43 --> 00:28:45
dry ice is solid magnesium.
 

476
00:28:45 --> 00:28:49
So we're going to set the
magnesium on fire, and then put

477
00:28:49 --> 00:28:53
the oxidating agent on top of
it, and you can see the rest of

478
00:28:53 --> 00:28:55
what's going to happen there.
 

479
00:28:55 --> 00:28:57
And you can actually also
determine if this is an

480
00:28:57 --> 00:29:34
exothermic or an endothermic
reaction while you're at it.

481
00:29:34 --> 00:29:35
[EXPERIMENTING]
 

482
00:29:35 --> 00:29:36
[APPLAUSE]
 

483
00:29:36 --> 00:30:36
PROFESSOR: Thanks
to my helpers.

484
00:30:36 --> 00:30:46
All right.
 

485
00:30:46 --> 00:30:50
So oxidation reduction
reactions can be quite

486
00:30:50 --> 00:30:56
interesting, and don't
try that at home.

487
00:30:56 --> 00:31:00
So, we're going to continue on
now, you know the basics and

488
00:31:00 --> 00:31:03
we're going to talk about
electric chemical cells.

489
00:31:03 --> 00:31:06
We're going to introduce
Faraday's law, and a thing I

490
00:31:06 --> 00:31:11
love to do, is come back to my
friend Gibb's free energy.

491
00:31:11 --> 00:31:16
So, thermodynamics is all over
the place in chemistry and you

492
00:31:16 --> 00:31:18
can't get very far
away from it.

493
00:31:18 --> 00:31:20
So hopefully, by the end
of the class today, we'll

494
00:31:20 --> 00:31:23
come back to free energy.
 

495
00:31:23 --> 00:31:25
All right, so what is an
electric chemical cell.

496
00:31:25 --> 00:31:30
It's any device in which
electric current, which is a

497
00:31:30 --> 00:31:35
flow of electrons through a
circuit, is either produced

498
00:31:35 --> 00:31:39
by a spontaneous reaction,
or used to bring about a

499
00:31:39 --> 00:31:41
non-spontaneous reaction.
 

500
00:31:41 --> 00:31:45
And so a battery is technically
a collection of cells in a

501
00:31:45 --> 00:31:50
series, so that the voltage
that each cell produces is the

502
00:31:50 --> 00:31:55
sum, the battery has the sum
of the voltages of each cell.

503
00:31:55 --> 00:31:59
So, let's take a look at what
some of these might look like.

504
00:31:59 --> 00:32:02
Here's a little cartoon
of a simple version.

505
00:32:02 --> 00:32:06
We have a beaker -- 2 beakers
with different solutions in

506
00:32:06 --> 00:32:11
them, 2 electrodes, a salt
bridge across, and as electrons

507
00:32:11 --> 00:32:18
transfer through this, you can
read a current on an amp meter

508
00:32:18 --> 00:32:21
here, you can read some kind
of voltage coming off.

509
00:32:21 --> 00:32:26
And so, I like to talk about
how good you guys have it at

510
00:32:26 --> 00:32:31
MIT with the Web and handouts
and everything and how students

511
00:32:31 --> 00:32:33
in the old days at MIT, if
they're going to do their

512
00:32:33 --> 00:32:36
problem-sets at night, first
they had to build a battery to

513
00:32:36 --> 00:32:39
get electricity to
be able to see.

514
00:32:39 --> 00:32:42
So you guys have it easy, you
have these electric lights and

515
00:32:42 --> 00:32:47
all this fancy stuff now here.
 

516
00:32:47 --> 00:32:49
So, let's sort of break
apart sort of a components.

517
00:32:49 --> 00:32:55
Here is my beautiful picture
that I drew of this system,

518
00:32:55 --> 00:32:57
that's why I show you a
better cartoon first.

519
00:32:57 --> 00:33:00
So this is a beaker that you
-- here's one beaker with

520
00:33:00 --> 00:33:04
one solution on this side,
here is the other beaker.

521
00:33:04 --> 00:33:09
So we have two electrodes put
in, we have a salt bridge, and

522
00:33:09 --> 00:33:13
then we have a wire across
where we can measure voltage.

523
00:33:13 --> 00:33:17
So, let's think about what
is happening on each side.

524
00:33:17 --> 00:33:23
So in one beaker you're going
to have an oxidation reduction,

525
00:33:23 --> 00:33:26
and in the other beaker you're
going to have a reduction.

526
00:33:26 --> 00:33:30
So if we think about what's
happening over here, you could

527
00:33:30 --> 00:33:36
have a zinc system, is oxidized
from zinc 0 to zinc plus 2.

528
00:33:36 --> 00:33:39
And so, this is sort of a view
of what would be happening at

529
00:33:39 --> 00:33:42
the electrode, you have zinc
solid or zinc 0, and you've

530
00:33:42 --> 00:33:45
also have zinc plus
2 in solution.

531
00:33:45 --> 00:33:50
And so, as you take a zinc
solid atom, going into

532
00:33:50 --> 00:33:53
zinc plus 2, you can have
an oxidation reaction.

533
00:33:53 --> 00:33:56
And here would be the
equation going down.

534
00:33:56 --> 00:33:59
So zinc solid to zinc plus
2 with two electrons.

535
00:33:59 --> 00:34:03
Those electrons can go through
to our other beaker on this

536
00:34:03 --> 00:34:10
other side, and so here we have
a copper solid electrode or a

537
00:34:10 --> 00:34:15
cathode in this case, and we
have copper plus 2 in solution,

538
00:34:15 --> 00:34:19
which is being reduced
to copper solid, and so

539
00:34:19 --> 00:34:22
we're plating on to our
electrode on this side.

540
00:34:22 --> 00:34:24
And so, here we have the
reduction reaction, copper

541
00:34:24 --> 00:34:27
2 with two electrons
going to copper solid.

542
00:34:27 --> 00:34:30
So our oxidation is
happening at an electrode

543
00:34:30 --> 00:34:31
called the anode.
 

544
00:34:31 --> 00:34:33
The reduction is happening
in an electrode

545
00:34:33 --> 00:34:34
called the cathode.
 

546
00:34:34 --> 00:34:37
And as these reactions
occur, you're changing the

547
00:34:37 --> 00:34:39
charge on either side.
 

548
00:34:39 --> 00:34:43
So, you have this salt bridge,
and so to neutralize the change

549
00:34:43 --> 00:34:47
in charge, you would have
negative ions come down here,

550
00:34:47 --> 00:34:49
because we're producing
more plus 2.

551
00:34:49 --> 00:34:53
And on the other side potassium
is going in as we're going from

552
00:34:53 --> 00:34:57
copper plus 2 to copper solid,
again, to balance this change

553
00:34:57 --> 00:34:59
in charge that's occurring.
 

554
00:34:59 --> 00:35:03
So those are the basic
components of a simple

555
00:35:03 --> 00:35:06
electrochemical cell.
 

556
00:35:06 --> 00:35:09
So, we could talk about
the cell -- here's

557
00:35:09 --> 00:35:12
some nomenclature that
represents the cell.

558
00:35:12 --> 00:35:18
So, the one that I just showed
you, you have one electrode, a

559
00:35:18 --> 00:35:23
zinc solid, and we also have
zinc plus 2 in solution.

560
00:35:23 --> 00:35:27
You have a single line between
the solid and the zinc plus

561
00:35:27 --> 00:35:30
2 ions in solution, that
indicates there's a phase

562
00:35:30 --> 00:35:34
boundary, so you're changing
phase from solid to aqueous.

563
00:35:34 --> 00:35:38
Then if you see two little
lines that tells you, okay, one

564
00:35:38 --> 00:35:41
part of the reaction's in one
beaker, the other part is in

565
00:35:41 --> 00:35:44
the other beaker, that
represents the salt bridge

566
00:35:44 --> 00:35:47
which separates out the
two 1/2 reactions.

567
00:35:47 --> 00:35:50
And then on this side, we're
going from copper 2 in

568
00:35:50 --> 00:35:54
solution, single line which
indicates the phase boundary,

569
00:35:54 --> 00:35:59
to a copper solid over here.
 

570
00:35:59 --> 00:36:08
So the amount of charge that
goes through the system, it

571
00:36:08 --> 00:36:12
depends -- and how much of the
zinc that is consumed or the

572
00:36:12 --> 00:36:15
copper that is deposited, is
proportional to that charge,

573
00:36:15 --> 00:36:18
the number of electrons that go
through the system, and this

574
00:36:18 --> 00:36:23
is called Faraday's law.
 

575
00:36:23 --> 00:36:26
So let's look at what is
happening a little bit here, so

576
00:36:26 --> 00:36:30
we have a little movie that
shows the oxidation reaction.

577
00:36:30 --> 00:36:35
So in green is the electrode,
and then here are the water

578
00:36:35 --> 00:36:38
molecules, and let's look
at what happens when

579
00:36:38 --> 00:36:40
there's this oxidation.
 

580
00:36:40 --> 00:36:42
So here things are floating
around, and there

581
00:36:42 --> 00:36:43
go the electrons.
 

582
00:36:43 --> 00:36:47
And this pops off into
solutions, so if this is zinc,

583
00:36:47 --> 00:36:50
so then as this is happening,
we have a zinc plus 2

584
00:36:50 --> 00:36:51
now, it's aqueous.
 

585
00:36:51 --> 00:36:54
There go electrons, we
have our oxidation.

586
00:36:54 --> 00:36:57
Here comes off zinc plus 2
floating around, there's

587
00:36:57 --> 00:37:00
another zinc plus 2
that just came off.

588
00:37:00 --> 00:37:04
And so our electrode here
is being consumed as

589
00:37:04 --> 00:37:06
this oxidation occurs.
 

590
00:37:06 --> 00:37:08
I think it's really cool,
the electrons, you can see

591
00:37:08 --> 00:37:13
them as this green going
along in this movie.

592
00:37:13 --> 00:37:18
So, this is a little thing to
think about what's happening.

593
00:37:18 --> 00:37:21
So what's happening at the
cathode, we have a reduction.

594
00:37:21 --> 00:37:24
So if we have our copper
ions are going to plate

595
00:37:24 --> 00:37:25
onto our electrode.
 

596
00:37:25 --> 00:37:28
So here in blue is the
electrode, and again the water

597
00:37:28 --> 00:37:32
molecules, here's a little
copper 2 in solution.

598
00:37:32 --> 00:37:37
And when it gets electrons and
gets reduced, it's going to

599
00:37:37 --> 00:37:40
start plating, so let's
take a look at that.

600
00:37:40 --> 00:37:42
So, here's -- oh, there
comes the electrons.

601
00:37:42 --> 00:37:45
And so now it becomes part of
the electrode there, the

602
00:37:45 --> 00:37:49
electrons come in, and so
you're building up, you're

603
00:37:49 --> 00:37:51
adding, your plating
on to your electrode.

604
00:37:51 --> 00:37:55
Now it got its electrons, it
got reduced, got reduced again,

605
00:37:55 --> 00:38:05
and it becomes solid, and
plates onto the electrode.

606
00:38:05 --> 00:38:08
And we see the
electrons coming in.

607
00:38:08 --> 00:38:11
So again, the amount of current
that flows, the number of

608
00:38:11 --> 00:38:15
electrons that flow are going
to be proportional to the

609
00:38:15 --> 00:38:18
chemistry that's happening
at the two electrodes.

610
00:38:18 --> 00:38:22
So you can figure out how much
zinc would be consumed, how

611
00:38:22 --> 00:38:25
much of the zinc solid
electrode could be consumed,

612
00:38:25 --> 00:38:28
and how much copper would be
deposited on the copper

613
00:38:28 --> 00:38:32
electrode for a particular
amount of current.

614
00:38:32 --> 00:38:37
So say we have 1 amp of current
for 1 hour, what are we

615
00:38:37 --> 00:38:39
going to do to our system?
 

616
00:38:39 --> 00:38:44
So we can calculate this out,
so we use this equation to find

617
00:38:44 --> 00:38:47
out how much charge is going to
pass through the system, we

618
00:38:47 --> 00:38:51
have this term q, the magnitude
of charge and it's in Coulombs,

619
00:38:51 --> 00:38:56
those are our units, and that's
equal to the current in amps,

620
00:38:56 --> 00:39:01
and just for unit conversion,
amps are Coulombs per second,

621
00:39:01 --> 00:39:04
so that's very convenient
because we're going to take

622
00:39:04 --> 00:39:07
the current and times
second, so times time.

623
00:39:07 --> 00:39:12
And so if we work that out, we
had 1 amp and we had 1 hour, so

624
00:39:12 --> 00:39:18
we're going to have 3
Coulombs that are our

625
00:39:18 --> 00:39:21
magnitude of our charge.
 

626
00:39:21 --> 00:39:25
So once we know that, we can
convert, using Faraday's

627
00:39:25 --> 00:39:30
constant from charge into moles
of electrons that had to pass

628
00:39:30 --> 00:39:33
through the system to generate
that kind of current.

629
00:39:33 --> 00:39:37
And here is our friend
Faraday's constant, and so

630
00:39:37 --> 00:39:39
that's in Coulombs per mole.
 

631
00:39:39 --> 00:39:43
And so, we can we can convert
the number of Coulombs into the

632
00:39:43 --> 00:39:47
number of moles of electrons
that were passed through the

633
00:39:47 --> 00:39:51
system with that amount of
current, 1 amp for 1 hour.

634
00:39:51 --> 00:39:55
Now, how is this going to
relate to the zinc consumed

635
00:39:55 --> 00:39:57
or the copper deposited?
 

636
00:39:57 --> 00:40:00
So we know the total number
of moles that passed

637
00:40:00 --> 00:40:02
through the system.
 

638
00:40:02 --> 00:40:06
And so, then we have to think
about for every 1 mole of zinc

639
00:40:06 --> 00:40:12
that was consumed, how many
moles of electrons went

640
00:40:12 --> 00:40:13
through the system?
 

641
00:40:13 --> 00:40:18
So why don't you yell out and
tell me what you think that is.

642
00:40:18 --> 00:40:20
What do you think?
 

643
00:40:20 --> 00:40:26
2, right.
 

644
00:40:26 --> 00:40:30
So we are going from zinc
solid to zinc plus 2.

645
00:40:30 --> 00:40:35
So, we need to do -- to consume
one, we need two electrons.

646
00:40:35 --> 00:40:42
So then we can look up the
atomic weight of zinc and

647
00:40:42 --> 00:40:45
calculate the number of grams.
 

648
00:40:45 --> 00:40:49
We can do the same with copper.
 

649
00:40:49 --> 00:40:52
So for one mole of copper
deposited, how many moles of

650
00:40:52 --> 00:41:02
electrons needed to pass
through the system? two, right.

651
00:41:02 --> 00:41:06
And then we look up the atomic
weight, which is very similar,

652
00:41:06 --> 00:41:09
and actually with significant
figures, it's the same amount,

653
00:41:09 --> 00:41:13
which won't be true
for most things.

654
00:41:13 --> 00:41:19
All right, so these problems
are not too complicated.

655
00:41:19 --> 00:41:21
So let me just tell you a
little bit more about types of

656
00:41:21 --> 00:41:24
electrodes that can be used.
 

657
00:41:24 --> 00:41:28
It's not always true that you
have to use electrodes that are

658
00:41:28 --> 00:41:32
going to be consumed or have
species deposited on them.

659
00:41:32 --> 00:41:37
You can use an inert electrode,
such as a platinum electorate,

660
00:41:37 --> 00:41:39
and here is an example of that.
 

661
00:41:39 --> 00:41:44
So here, this cell has a
platinum electrode, and the

662
00:41:44 --> 00:41:47
reaction that's happening, you
have actually two things in

663
00:41:47 --> 00:41:50
solution instead of going
from a solid to a solution.

664
00:41:50 --> 00:41:54
So this is just another
example of a type of cell.

665
00:41:54 --> 00:41:57
So let's think about, then,
what equations we would

666
00:41:57 --> 00:42:00
write for this chemistry
and what's going on.

667
00:42:00 --> 00:42:03
So over here at the cathode,
what happens at a cathode,

668
00:42:03 --> 00:42:11
oxidation or reduction?
 

669
00:42:11 --> 00:42:13
I'm hearing somewhat
of a consensus.

670
00:42:13 --> 00:42:13
That's correct.
 

671
00:42:13 --> 00:42:14
Reduction.
 

672
00:42:14 --> 00:42:17
That's the thing you're going
to need to memorize, it'll be

673
00:42:17 --> 00:42:20
important in doing
problems later on.

674
00:42:20 --> 00:42:23
So, what is the reduction
reaction that you imagine would

675
00:42:23 --> 00:42:31
be happening if you have copper
plus 2 and copper solid?

676
00:42:31 --> 00:42:34
So, if you're reducing it,
you're going to be reducing

677
00:42:34 --> 00:42:38
copper plus 2 with two
electrons to copper solid.

678
00:42:38 --> 00:42:41
So, same reaction
we saw before.

679
00:42:41 --> 00:42:42
So what about over here.
 

680
00:42:42 --> 00:42:46
This is the anode, which has
the oxidation reaction going

681
00:42:46 --> 00:42:50
on, and what oxidation reaction
can you imagine happening with

682
00:42:50 --> 00:42:53
chromium plus 3 and
chromium plus 2.

683
00:42:53 --> 00:43:03
What's going to what?
 

684
00:43:03 --> 00:43:08
So, you're going from plus 2 to
plus 3 with one electron here.

685
00:43:08 --> 00:43:11
So that would be the
oxidation reaction.

686
00:43:11 --> 00:43:13
So let's think about
how we would actually

687
00:43:13 --> 00:43:15
write this down then.
 

688
00:43:15 --> 00:43:18
So the notation for this type
of cell, we're going to have a

689
00:43:18 --> 00:43:22
platinum that indicates the
electrode, a single line that

690
00:43:22 --> 00:43:23
indicates a phase boundary.
 

691
00:43:23 --> 00:43:27
And in solution, you have the
chromium plus 2, chromium plus

692
00:43:27 --> 00:43:30
3, those are both aqueous, so
they have a comma between them.

693
00:43:30 --> 00:43:34
So this is on one side in one
of the beakers, so that's

694
00:43:34 --> 00:43:37
the reaction at the anode.
 

695
00:43:37 --> 00:43:40
And then we have a bar here
that indicates a salt bridge.

696
00:43:40 --> 00:43:44
And then in the other beaker,
we would have the copper plus 2

697
00:43:44 --> 00:43:47
and the copper solid, separated
by a single line, because

698
00:43:47 --> 00:43:49
there's a phase boundary
between the aqueous

699
00:43:49 --> 00:43:50
and the solid.
 

700
00:43:50 --> 00:43:54
And then here are
our two equations.

701
00:43:54 --> 00:43:57
At the anode, we
have copper plus 2.

702
00:43:57 --> 00:44:01
Aqueous going to copper plus
3 aqueous in an electron

703
00:44:01 --> 00:44:02
at the cathode.
 

704
00:44:02 --> 00:44:04
We have copper plus 2
aqueous and two electrons

705
00:44:04 --> 00:44:06
going to copper solid.
 

706
00:44:06 --> 00:44:08
So those are our two
equations and how we

707
00:44:08 --> 00:44:12
would write that down.
 

708
00:44:12 --> 00:44:16
Another example of an electrode
is a hydrogen electrode.

709
00:44:16 --> 00:44:18
And this is very common.
 

710
00:44:18 --> 00:44:21
In fact, most potential
standard reduction potentials,

711
00:44:21 --> 00:44:25
or as they're also known,
oxidation reduction potentials

712
00:44:25 --> 00:44:29
are measured against a standard
hydrogen electrode, and

713
00:44:29 --> 00:44:31
it'll be abbreviated s h e.
 

714
00:44:31 --> 00:44:34
And so, if you see it was
measured against s h e, you

715
00:44:34 --> 00:44:36
will now know what that means.
 

716
00:44:36 --> 00:44:39
So that's a standard
hydrogen electrode.

717
00:44:39 --> 00:44:41
So there's a couple of
different variations.

718
00:44:41 --> 00:44:45
It can be used at the
cathode or at the anode.

719
00:44:45 --> 00:44:49
And so, if you're using it
at the cathode, h plus

720
00:44:49 --> 00:44:54
is reduced, and at the
anode, h 2 is oxidized.

721
00:44:54 --> 00:44:58
And often you have a platinum
system there as well, for the

722
00:44:58 --> 00:45:01
standard hydrogen, so platinum
is commonly used in a

723
00:45:01 --> 00:45:04
standard hydrogen electrode.
 

724
00:45:04 --> 00:45:08
So, let's just sort of look
at a little picture of this.

725
00:45:08 --> 00:45:11
So here, we may have like
a glass cylinder here,

726
00:45:11 --> 00:45:13
we're pumping in h 2 gas.
 

727
00:45:13 --> 00:45:16
And here you can see it
sort of bubbling down.

728
00:45:16 --> 00:45:20
We may have a solution of
hydrochloric acid, which would

729
00:45:20 --> 00:45:23
have a lot of h plus in it, and
so this would be a hydrogen

730
00:45:23 --> 00:45:27
electrode on one side, the
other side may have something

731
00:45:27 --> 00:45:30
more common or something that
we saw before with the zinc

732
00:45:30 --> 00:45:33
solid and the zinc in solution.
 

733
00:45:33 --> 00:45:37
So since on this side we have
the cathode, of we can write

734
00:45:37 --> 00:45:44
about the h plus aqueous, a bar
for the phase transition to h 2

735
00:45:44 --> 00:45:47
gas, and then we indicate that
there's also a platinum

736
00:45:47 --> 00:45:49
electrode going on here.
 

737
00:45:49 --> 00:45:53
And the other side is what we
saw before, the zinc solid

738
00:45:53 --> 00:45:54
and the zinc plus 2.
 

739
00:45:54 --> 00:45:56
So you're just introducing
different types of electrodes

740
00:45:56 --> 00:46:00
that you may be seeing
in this particular unit.

741
00:46:00 --> 00:46:02
And again, you want to remember
what reaction's going on at the

742
00:46:02 --> 00:46:04
cathode, and at the anode.
 

743
00:46:04 --> 00:46:14
All right, so just very
briefly, I will mention cell

744
00:46:14 --> 00:46:16
potential, which has many
different names -- cell

745
00:46:16 --> 00:46:19
voltage, EMF it's often called.
 

746
00:46:19 --> 00:46:23
And so the flow of electrons
generates a potential

747
00:46:23 --> 00:46:26
difference between the
electrodes in the current.

748
00:46:26 --> 00:46:34
And this can be related back
to our friend, delta g.

749
00:46:34 --> 00:46:39
So in this equation you have
this potential difference

750
00:46:39 --> 00:46:45
that's generated by the flow of
the electrons, and that times

751
00:46:45 --> 00:46:50
Faraday's constant times the
number moles of electrons, and

752
00:46:50 --> 00:46:52
if you have a negative sign
here, that's equal to the

753
00:46:52 --> 00:46:56
free energy of the cell.
 

754
00:46:56 --> 00:47:00
So we can relate that back.
 

755
00:47:00 --> 00:47:03
And a little bit
of information.

756
00:47:03 --> 00:47:05
We have the standard
terms as well.

757
00:47:05 --> 00:47:09
We can have the delta e nought,
the cell potential, cell

758
00:47:09 --> 00:47:11
voltage, you'll see
many names for this.

759
00:47:11 --> 00:47:14
And that's when the products
and reactants are in

760
00:47:14 --> 00:47:15
their standard states.
 

761
00:47:15 --> 00:47:18
The units we're talking about
here are in volts, sometimes

762
00:47:18 --> 00:47:22
you'll see things reported
in millivolts as well.

763
00:47:22 --> 00:47:27
And let's end with one final
clicker question, and then we

764
00:47:27 --> 00:48:11
can announce our clicker
winner for today.

765
00:48:11 --> 00:48:18
OK, 10 seconds.
 

766
00:48:18 --> 00:48:21
Most people should
get this right.

767
00:48:21 --> 00:48:27