Half-life and carbon dating

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Language: en

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SAL: In the last video we saw
all sorts of different types

00:00:02.960 --> 00:00:06.630
of isotopes of atoms
experiencing radioactive decay

00:00:06.630 --> 00:00:10.060
and turning into other atoms or
releasing different types

00:00:10.060 --> 00:00:10.630
of particles.

00:00:10.630 --> 00:00:14.530
But the question is, when
does an atom or

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nucleus decide to decay?

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Let's say I have a bunch of,
let's say these are all atoms.

00:00:20.820 --> 00:00:24.780
I have a bunch of atoms here.

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And let's say we're talking
about the type of decay where

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an atom turns into
another atom.

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So your proton number
is going to change.

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Your atomic number is
going to change.

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So it could either be beta
decay, which would release

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electrons from the neutrons and
turn them into protons.

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Or maybe positron emission
turning protons into neutrons.

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But that's not what's
relevant here.

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Let's say we have a collection
of atoms. And normally when we

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have any small amount of any
element, we really have huge

00:00:48.650 --> 00:00:50.690
amounts of atoms of
that element.

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And we've talked about moles
and, you know, one gram of

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carbon-12-- I'm sorry, 12
grams-- 12 grams of carbon-12

00:01:05.370 --> 00:01:07.870
has one mole of carbon-12
in it.

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One mole of carbon-12.

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And what is one mole
of carbon-12?

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That's 6.02 times 10 to the 23rd
carbon-12 atoms. This is

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a ginormous number.

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This is more than we can, than
my head can really grasp

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around how large of
a number this is.

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And this is only when we have
12 grams. 12 grams is not a

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large mass.

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For example, one kilogram
is about two pounds.

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So this is about, what?

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I want to say [? 1/50 ?]

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of a pound if I'm
doing [? it. ?]

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But this is not a lot
of mass right here.

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And pounds is obviously force.

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You get the idea.

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On Earth, well anywhere,
mass is invariant.

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This is not a tremendous
amount.

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So with that said, let's go back
to the question of how do

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we know if one of these
guys are going to

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decay in some way.

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And maybe not carbon-12, maybe
we're talking about carbon-14

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or something.

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How do we know that they're
going to decay?

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And the answer is, you don't.

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They all have some probability
of the decaying.

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At any given moment, for a
certain type of element or a

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certain type of isotope of
an element, there's some

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probability that one
of them will decay.

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That, you know, maybe this guy
will decay this second.

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And then nothing happens for a
long time, a long time, and

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all of a sudden two
more guys decay.

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And so, like everything in
chemistry, and a lot of what

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we're starting to deal with in
physics and quantum mechanics,

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everything is probabilistic.

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I mean, maybe if we really
got in detail on the

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configurations of the nucleus,
maybe we could get a little

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bit better in terms of our
probabilities, but we don't

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know what's going on inside of
the nucleus, so all we can do

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is ascribe some probabilities
to something reacting.

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Now you could say, OK, what's
the probability of any given

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molecule reacting
in one second?

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Or you could define
it that way.

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But we're used to dealing with
things on the macro level, on

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dealing with, you know, huge
amounts of atoms. So what we

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do is we come up with terms
that help us get our head

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around this.

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And one of those terms is
the term half-life.

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And let me erase this
stuff down here.

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So I have a description, and
we're going to hopefully get

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an intuition of what
half-life means.

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So I wrote a decay reaction
right here,

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where you have carbon-14.

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It decays into nitrogen-14.

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And we could just do a
little bit of review.

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You go from six protons
to seven protons.

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Your mass changes the same.

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So one of the neutrons must have
turned into a proton and

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that is what happened.

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And it does that by releasing
an electron, which is also

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call a beta particle.

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We could have written this
as minus 1 charge.

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Relatively zero mass.

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It does have some mass,
but they write zero.

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This is kind of notation.

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So this is beta decay.

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Beta decay, this is
just a review.

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But the way we think about
half-life is, people have

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studied carbon and they said,
look, if I start off with 10

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grams-- if I have just a block
of carbon that's 10 grams. If

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I wait carbon-14's half-life--
this is a

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specific isotope of carbon.

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Remember, isotopes, if there's
carbon, can come in 12, with

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an atomic mass number of 12, or
with 14, or I mean, there's

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different isotopes of
different elements.

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And the atomic number
defines the carbon,

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because it has six protons.

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Carbon-12 has six protons.

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Carbon-14 has six protons.

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But they have a different
number of neutrons.

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So when you have the same
element with varying number of

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neutrons, that's an isotope.

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So the carbon-14 version, or
this isotope of carbon, let's

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say we start with 10 grams. If
they say that it's half-life

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is 5,740 years, that means that
if on day one we start

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off with 10 grams of pure
carbon-14, after 5,740 years,

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half of this will
have turned into

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nitrogen-14, by beta decay.

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And you might say, oh OK, so
maybe-- let's see, let me make

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nitrogen magenta, right there--
so you might say, OK,

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maybe that half turns
into nitrogen.

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And I've actually seen this
drawn this way in some

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chemistry classes or physics
classes, and my immediate

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question is how does this
half know that it

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must turn into nitrogen?

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And how does this half know that
it must stay as carbon?

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And the answer is
they don't know.

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And it really shouldn't
be drawn this way.

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So let me redraw it.

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So this is our original block
of our carbon-14.

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What happens over that
5,740 years is that,

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probabilistically, some of these
guys just start turning

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into nitrogen randomly,
at random points.

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And over 5,740 years, you
determine that there's a 50%

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chance that any one of these
carbon atoms will turn into a

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nitrogen atom.

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So that after 5,740 years, the
half-life of carbon, a 50%

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chance that any of the
guys that are carbon

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will turn to nitrogen.

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So if you go back after a
half-life, half of the atoms

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will now be nitrogen.

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So now you have, after
one half-life-- So

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let's ignore this.

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So we started with this.

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All 10 grams were carbon.

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10 grams of c-14.

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This is after one half-life.

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And now we have five
grams of c-14.

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And we have five grams
of nitrogen-14.

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Fair enough.

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Let's think about what happens
after another half-life.

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Well we said that during a
half-life, 5,740 years in the

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case of carbon-14-- all
different elements have a

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different half-life, if they're
radioactive-- over

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5,740 years there's a 50%-- and
if I just look at any one

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atom-- there's a 50%
chance it'll decay.

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So if we go to another
half-life, if we go another

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half-life from there, I had
five grams of carbon-14.

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So let me actually copy
and paste this one.

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This is what I started with.

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Now after another half-life--
you can ignore all my little,

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actually let me erase some
of this up here.

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Let me clean it up
a little bit.

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After one one half-life,
what happens?

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Well I now am left with five
grams of carbon-14.

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Those five grams of carbon-14,
every one of those atoms still

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has, over the next-- whatever
that number was, 5,740 years--

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after 5,740 years,
all of those once

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again have a 50% chance.

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And by the law of large numbers,
half of them will

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have converted into
nitrogen-14.

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So we'll have even more
conversion into nitrogen-14.

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So now half of that five grams.
So now we're only left

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with 2.5 grams of c-14.

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And how much nitrogen-14?

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Well we have another two and
a half went to nitrogen.

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So now we have seven and a half
grams of nitrogen-14.

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And we could keep going further
into the future, and

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after every half-life, 5,740
years, we will have half of

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the carbon that we started.

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But we'll always have an

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infinitesimal amount of carbon.

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But let me ask you a question.

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Let's say I'm just staring
at one carbon atom.

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Let's say I just have this
one carbon atom.

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You know, I've got its nucleus,
with its c-14.

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So it's got its six protons.

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1, 2, 3, 4, 5, 6.

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It's got its eight neutrons.

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It's got its six electrons.

00:09:00.756 --> 00:09:04.870
1, 2, 3, 4, 5, 6, whatever.

00:09:04.870 --> 00:09:06.800
What's going to happen?

00:09:06.800 --> 00:09:13.130
What's going to happen
after one second?

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Well, I don't know.

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It'll probably still be carbon,
but there's some

00:09:18.320 --> 00:09:21.580
probability that after one
second it will have already

00:09:21.580 --> 00:09:24.000
turned into nitrogen-14.

00:09:24.000 --> 00:09:29.710
What's going to happen after
one billion years?

00:09:29.710 --> 00:09:31.960
Well, after one billion years
I'll say, well you know, it'll

00:09:31.960 --> 00:09:35.660
probably have turned into
nitrogen-14 at that point, but

00:09:35.660 --> 00:09:36.620
I'm not sure.

00:09:36.620 --> 00:09:39.690
This might be the one
ultra-stable nucleus that just

00:09:39.690 --> 00:09:41.740
happened to, kind of,
go against the

00:09:41.740 --> 00:09:43.960
odds and stay carbon-14.

00:09:43.960 --> 00:09:46.390
So after one half-life, if
you're just looking at one

00:09:46.390 --> 00:09:52.280
atom after 5,740 years, you
don't know whether this turned

00:09:52.280 --> 00:09:53.120
into a nitrogen or not.

00:09:53.120 --> 00:09:56.690
This exact atom, you just know
that it had a 50% chance of

00:09:56.690 --> 00:09:57.950
turning into a nitrogen.

00:09:57.950 --> 00:10:02.130
Now, if you look at it over a
huge number of atoms. I mean,

00:10:02.130 --> 00:10:04.340
if you start approaching, you
know, Avogadro's number or

00:10:04.340 --> 00:10:06.350
anything larger--
I erased that.

00:10:06.350 --> 00:10:08.460
Then all of a sudden you can use
the law of large numbers

00:10:08.460 --> 00:10:11.850
and say, OK, on average, if each
of those atoms must have

00:10:11.850 --> 00:10:16.220
had a 50% chance, and if I have
gazillions of them, half

00:10:16.220 --> 00:10:18.530
of them will have turned
into nitrogen.

00:10:18.530 --> 00:10:20.520
I don't know which half,
but half of them

00:10:20.520 --> 00:10:21.890
will turn into it.

00:10:21.890 --> 00:10:25.770
So you might get a question
like, I start with, oh I don't

00:10:25.770 --> 00:10:32.860
know, let's say I start with
80 grams of something with,

00:10:32.860 --> 00:10:36.580
let's just call it x, and it has
a half-life of two years.

00:10:36.580 --> 00:10:38.020
I'm just making up
this compound.

00:10:38.020 --> 00:10:39.720
A two-year half-life.

00:10:43.740 --> 00:10:46.200
And then let's say we go into
a time machine and we look

00:10:46.200 --> 00:10:50.670
back at our sample, and let's
say we only have 10 grams of

00:10:50.670 --> 00:10:51.760
our sample left.

00:10:51.760 --> 00:10:55.000
And we want to know how much
time has passed by.

00:10:55.000 --> 00:10:58.360
So 10 grams left of x.

00:10:58.360 --> 00:11:00.710
How much time, you know, x is
decaying the whole time, how

00:11:00.710 --> 00:11:02.540
much time has passed?

00:11:02.540 --> 00:11:04.380
Well let's think about it.

00:11:04.380 --> 00:11:12.300
We're starting at time, 0 with
80 grams. After two years, how

00:11:12.300 --> 00:11:13.400
much are we going
to have left?

00:11:13.400 --> 00:11:16.980
We're going to have 40
grams. So t equals 2.

00:11:16.980 --> 00:11:19.160
But after two more years, how
many are we going to have?

00:11:19.160 --> 00:11:22.540
We're going to have 20 grams.
So this is t equals 3 I'm

00:11:22.540 --> 00:11:24.650
sorry, this is t
equals 4 years.

00:11:24.650 --> 00:11:31.400
And then after two more years,
I'll only have half of that

00:11:31.400 --> 00:11:31.940
left again.

00:11:31.940 --> 00:11:34.620
So now I'm only going to
have 10 grams left.

00:11:34.620 --> 00:11:35.590
And that's where I am.

00:11:35.590 --> 00:11:37.390
And this is t equals 6.

00:11:37.390 --> 00:11:39.630
So if you know you have
some compound.

00:11:39.630 --> 00:11:42.210
You're starting off with 80
grams. You know it has a

00:11:42.210 --> 00:11:43.030
two-year half-life.

00:11:43.030 --> 00:11:44.340
You get in a time machine.

00:11:44.340 --> 00:11:47.130
And then you didn't build
your time machine well.

00:11:47.130 --> 00:11:49.080
You don't know how well it
calibrates against time.

00:11:49.080 --> 00:11:50.900
You just look at your sample.

00:11:50.900 --> 00:11:52.470
You say, oh, I only have
10 grams left.

00:11:52.470 --> 00:11:59.470
You know that 1, 2, 3 half-lives
have gone by.

00:11:59.470 --> 00:12:01.000
And you could also think
about it this way.

00:12:01.000 --> 00:12:04.760
1/2 to the 3rd power, because
every time you have 1/2 of the

00:12:04.760 --> 00:12:08.100
original sample-- that's the
number of half-lives-- after

00:12:08.100 --> 00:12:11.340
three half-lives you'll have 1/8
of your original sample.

00:12:11.340 --> 00:12:12.450
And that's what we have here.

00:12:12.450 --> 00:12:16.230
We have 1/8 of 80 grams. And
this is just when you're doing

00:12:16.230 --> 00:12:18.140
it with a discreet you know,
when you're right at the

00:12:18.140 --> 00:12:19.270
half-life point.

00:12:19.270 --> 00:12:21.200
In the next video we're going to
explore what if I asked you

00:12:21.200 --> 00:12:24.000
a question, how many of the
particles, or how many grams

00:12:24.000 --> 00:12:26.300
will you have in exactly
10 days?

00:12:26.300 --> 00:12:28.420
Or at two and a half years?

00:12:28.420 --> 00:12:30.820
And we'll do that in
the next video.


Types of decay

WEBVTT
Kind: captions
Language: en

00:00:00.690 --> 00:00:03.660
SAL: Everything we've been
dealing with so far in our

00:00:03.660 --> 00:00:06.410
journey through chemistry has
revolved around stability of

00:00:06.410 --> 00:00:08.420
electrons and where electrons
would rather

00:00:08.420 --> 00:00:10.340
be in stable shells.

00:00:10.340 --> 00:00:14.030
And like all things in life,
if you explore the atom a

00:00:14.030 --> 00:00:16.400
little further you'll realize
that electrons are not the

00:00:16.400 --> 00:00:19.250
only stuff that's going
on in an atom.

00:00:19.250 --> 00:00:24.250
That the nucleus itself has some
interactions, or has some

00:00:24.250 --> 00:00:27.140
instability, that needs to
be relieved in some way.

00:00:27.140 --> 00:00:28.740
That's what we'll talk
a little bit

00:00:28.740 --> 00:00:31.420
about in this video.

00:00:31.420 --> 00:00:35.110
And actually the mechanics of
it are well out of the scope

00:00:35.110 --> 00:00:37.450
of a first-year chemistry
course, but it's good to at

00:00:37.450 --> 00:00:39.570
least know that it occurs.

00:00:39.570 --> 00:00:43.110
And one day when we study the
strong nuclear force, and

00:00:43.110 --> 00:00:45.570
quantum physics, and all the
like, then we can start

00:00:45.570 --> 00:00:49.280
talking about exactly why these
protons and neutrons,

00:00:49.280 --> 00:00:52.810
and their constituent quarks
are interacting

00:00:52.810 --> 00:00:53.530
the way they do.

00:00:53.530 --> 00:00:55.500
But with that said, let's
at least think about the

00:00:55.500 --> 00:01:00.890
different types of ways that a
nucleus can essentially decay.

00:01:00.890 --> 00:01:03.880
So let's say I have a
bunch of protons.

00:01:03.880 --> 00:01:06.830
I'll just draw a couple here.

00:01:06.830 --> 00:01:09.590
Some protons there, and I'll
draw some neutrons.

00:01:09.590 --> 00:01:13.430
And I'll draw them in
a neutral-ish color.

00:01:13.430 --> 00:01:16.780
Maybe let me see, like a
grayish would be good.

00:01:16.780 --> 00:01:21.520
So let me just draw some
neutrons here.

00:01:21.520 --> 00:01:22.020
How many protons do I have?

00:01:22.020 --> 00:01:24.300
I have 1, 2, 3, 4, 5, 6, 7, 8.

00:01:24.300 --> 00:01:32.410
I'll do 1, 2, 3, 4, 5,
6, 7, 8, 9 neutrons.

00:01:32.410 --> 00:01:34.870
And so let's say this is the
nucleus of our atom.

00:01:34.870 --> 00:01:36.960
And remember-- and this is, you
know, in the very first

00:01:36.960 --> 00:01:39.860
video I made about the atom--
the nucleus, if you actually

00:01:39.860 --> 00:01:43.320
were to draw an actual atom--
and it's actually very hard to

00:01:43.320 --> 00:01:45.440
drawn an atom because it has
no well-defined boundaries.

00:01:45.440 --> 00:01:49.050
The electron really could be,
you know, at any given moment,

00:01:49.050 --> 00:01:49.980
it could be anywhere.

00:01:49.980 --> 00:01:52.740
But if you were to say, OK,
where is 90% of the time the

00:01:52.740 --> 00:01:53.700
electron is going to be in?

00:01:53.700 --> 00:01:55.680
You'd say, that's the radius,
or that's the

00:01:55.680 --> 00:01:57.750
diameter of our atom.

00:01:57.750 --> 00:02:00.530
We learned in that very first
video that the nucleus is

00:02:00.530 --> 00:02:05.450
almost an infinitesimal portion
of the volume of this

00:02:05.450 --> 00:02:08.340
sphere where the electron
will be 90% of the time.

00:02:08.340 --> 00:02:12.080
And the neat takeaway there
was that, well, most of

00:02:12.080 --> 00:02:15.280
whatever we look at in life
is just open free space.

00:02:15.280 --> 00:02:17.030
All of this is just
open space.

00:02:17.030 --> 00:02:19.400
But I just want to repeat
that because that little

00:02:19.400 --> 00:02:23.660
infinitesimal spot that we
talked about before, where

00:02:23.660 --> 00:02:26.320
even though it's a very small
part of the fraction of the

00:02:26.320 --> 00:02:29.030
volume of an atom-- it's
actually almost all of its

00:02:29.030 --> 00:02:31.890
mass-- that's what I'm zooming
out to this point here.

00:02:31.890 --> 00:02:34.240
These aren't atoms, these
aren't electrons.

00:02:34.240 --> 00:02:36.580
We're zoomed into the nucleus.

00:02:36.580 --> 00:02:40.040
And so it turns out that
sometimes the nucleus is a

00:02:40.040 --> 00:02:43.650
little bit unstable, and it
wants to get to a more stable

00:02:43.650 --> 00:02:44.400
configuration.

00:02:44.400 --> 00:02:46.600
We're not going to go into the
mechanics of exactly what

00:02:46.600 --> 00:02:48.700
defines an unstable nucleus
and all that.

00:02:48.700 --> 00:02:51.880
But in order to get into a
more unstable nucleus,

00:02:51.880 --> 00:02:55.820
sometimes it emits what's called
an alpha particle, or

00:02:55.820 --> 00:02:58.470
this is called alpha decay.

00:02:58.470 --> 00:03:04.440
Alpha decay.

00:03:04.440 --> 00:03:06.220
And it emits an alpha particle,

00:03:06.220 --> 00:03:09.160
which sounds very fancy.

00:03:09.160 --> 00:03:12.450
It's just a collection of
neutrons and protons.

00:03:12.450 --> 00:03:16.690
So an alpha particle is two
neutrons and two protons.

00:03:16.690 --> 00:03:20.850
So maybe these guys, they just
didn't feel like they'd fit in

00:03:20.850 --> 00:03:25.110
just right, so they're a
collection right here.

00:03:25.110 --> 00:03:27.740
And they get emitted.

00:03:27.740 --> 00:03:30.070
They leave the nucleus.

00:03:30.070 --> 00:03:33.870
So let's just think what
happens to an atom when

00:03:33.870 --> 00:03:36.050
something like that happens.

00:03:36.050 --> 00:03:38.500
So let's just say I have some
random element, I'll just call

00:03:38.500 --> 00:03:40.310
it element E.

00:03:40.310 --> 00:03:43.020
Let's say it has p, protons.

00:03:43.020 --> 00:03:45.660
Actually let me do it in the
color of my protons.

00:03:45.660 --> 00:03:47.800
It has p, protons.

00:03:47.800 --> 00:03:51.550
And then it has its atomic mass
number, is the number of

00:03:51.550 --> 00:03:55.510
protons plus the number
of neutrons.

00:03:55.510 --> 00:03:59.480
And do the neutrons
in gray, right?

00:03:59.480 --> 00:04:06.590
So when it experiences
alpha decay, what

00:04:06.590 --> 00:04:08.180
happens to the element?

00:04:08.180 --> 00:04:11.890
Well, its protons are going
to decrease by two.

00:04:11.890 --> 00:04:16.040
So its protons are going
to be p minus 2.

00:04:16.040 --> 00:04:19.450
And then its neutrons are also
going to decrease by two.

00:04:19.450 --> 00:04:21.320
So its mass number's going
to decrease by four.

00:04:21.320 --> 00:04:27.100
So up here you'll have p minus
2, plus our neutrons minus 2,

00:04:27.100 --> 00:04:28.940
so we're going to
have minus 4.

00:04:28.940 --> 00:04:31.080
So your mass is going to
decrease by four, and you're

00:04:31.080 --> 00:04:32.700
actually going to turn
to a new element.

00:04:32.700 --> 00:04:34.710
Remember, your elements
were defined by

00:04:34.710 --> 00:04:36.250
the number of protons.

00:04:36.250 --> 00:04:40.630
So in this alpha decay, when
you're losing two neutrons and

00:04:40.630 --> 00:04:43.300
two protons, but especially the
protons are going to make

00:04:43.300 --> 00:04:44.460
you into a different element.

00:04:44.460 --> 00:04:46.860
So if we call this element 1,
I'm just going to call it,

00:04:46.860 --> 00:04:50.590
we're going to be a different
element now, element 2.

00:04:50.590 --> 00:04:54.050
And if you think about what's
generated, we're emitting

00:04:54.050 --> 00:04:58.600
something that has two protons,

00:04:58.600 --> 00:05:00.340
and it has two neutrons.

00:05:00.340 --> 00:05:02.740
So that its mass is going to be
the mass of the two protons

00:05:02.740 --> 00:05:04.790
and two neutrons.

00:05:04.790 --> 00:05:05.830
So what are we emitting?

00:05:05.830 --> 00:05:09.810
We're emitting something that
has a mass of four.

00:05:09.810 --> 00:05:12.170
So if you look at, what is two
protons and two neutrons?

00:05:12.170 --> 00:05:14.740
I actually don't have the
periodic table on my

00:05:14.740 --> 00:05:14.880
[? head. ?]

00:05:14.880 --> 00:05:17.020
I forgot to cut and paste
it before this video.

00:05:17.020 --> 00:05:19.680
But it doesn't take you long on
the periodic table to find

00:05:19.680 --> 00:05:23.280
an element that has two protons,
and that's helium.

00:05:23.280 --> 00:05:25.590
It actually has an atomic
mass of four.

00:05:25.590 --> 00:05:29.390
So this is actually a helium
nucleus that gets emitted with

00:05:29.390 --> 00:05:30.080
alpha decay.

00:05:30.080 --> 00:05:31.875
This is actually a
helium nucleus.

00:05:35.010 --> 00:05:39.170
And because it's a helium
nucleus and it has no

00:05:39.170 --> 00:05:43.420
electrons to bounce off its two
protons, this would be a

00:05:43.420 --> 00:05:44.950
helium ion.

00:05:44.950 --> 00:05:48.490
So essentially it has
no electrons.

00:05:48.490 --> 00:05:50.830
It has two protons so it
has a plus 2 charge.

00:05:53.350 --> 00:05:59.110
So an alpha particle is really
just a helium ion, a plus 2

00:05:59.110 --> 00:06:01.960
charged helium ion that is
spontaneously emitted by a

00:06:01.960 --> 00:06:05.780
nucleus just to get to
a more stable state.

00:06:05.780 --> 00:06:07.670
Now that's one type of decay.

00:06:07.670 --> 00:06:08.850
Let's explore the other ones.

00:06:08.850 --> 00:06:14.050
So let me draw another
nucleus here.

00:06:14.050 --> 00:06:17.640
I'll draw some neutrons.

00:06:17.640 --> 00:06:19.310
I'll just draw some protons.

00:06:24.200 --> 00:06:27.920
So it turns out sometimes that
a neutron doesn't feel

00:06:27.920 --> 00:06:30.710
comfortable with itself.

00:06:30.710 --> 00:06:33.710
It looks at what the protons do
on a daily basis and says,

00:06:33.710 --> 00:06:34.560
you know what?

00:06:34.560 --> 00:06:37.780
For some reason when I look into
my heart, I feel like I

00:06:37.780 --> 00:06:39.220
really should be a proton.

00:06:39.220 --> 00:06:42.640
If I were a proton, the entire
nucleus would be a little bit

00:06:42.640 --> 00:06:43.870
more stable.

00:06:43.870 --> 00:06:46.860
And so what it does is, to
become a proton-- remember, a

00:06:46.860 --> 00:06:49.180
neutron has neutral charge.

00:06:49.180 --> 00:06:52.060
So what it does is, it
emits an electron.

00:06:52.060 --> 00:06:54.070
And I know you're saying, Sal,
you know, that's crazy, I

00:06:54.070 --> 00:06:55.760
didn't even know neutrons
had electrons in

00:06:55.760 --> 00:06:56.900
them, and all of that.

00:06:56.900 --> 00:06:58.050
And I agree with you.

00:06:58.050 --> 00:06:58.810
It is crazy.

00:06:58.810 --> 00:07:01.750
And one day we'll study
all of what exists

00:07:01.750 --> 00:07:03.540
inside of the nucleus.

00:07:03.540 --> 00:07:08.880
But let's just say that it
can emit an electron.

00:07:08.880 --> 00:07:10.206
So this emits an electron.

00:07:12.730 --> 00:07:15.460
And we signify that with its--
roughly its mass is zero.

00:07:15.460 --> 00:07:17.830
We know an electron really
doesn't have a zero mass, but

00:07:17.830 --> 00:07:19.970
we're talking about
atomic mass units.

00:07:19.970 --> 00:07:25.130
If the proton is one, an
electron is 1/1,836 of that.

00:07:25.130 --> 00:07:25.940
So we just round it.

00:07:25.940 --> 00:07:27.250
We say it has a mass of zero.

00:07:27.250 --> 00:07:29.380
Its mass really isn't zero.

00:07:29.380 --> 00:07:32.670
And its charge is minus 1.

00:07:32.670 --> 00:07:34.370
It's atomic, you can kind
of say its atomic

00:07:34.370 --> 00:07:35.200
number's minus 1.

00:07:35.200 --> 00:07:36.570
So it emits an electron.

00:07:36.570 --> 00:07:39.760
And by emitting an electron,
instead of being neutral, now

00:07:39.760 --> 00:07:41.020
it turns into a proton.

00:07:44.490 --> 00:07:47.090
And so this is called
beta decay.

00:07:52.500 --> 00:07:56.780
And a beta particle is really
just that emitted electron.

00:07:56.780 --> 00:08:00.480
So let's go back to our little
case of an element.

00:08:00.480 --> 00:08:03.940
It has some number of protons,
and then it has

00:08:03.940 --> 00:08:05.980
some number of neutrons.

00:08:05.980 --> 00:08:08.340
So you have the protons and
the neutrons, then you get

00:08:08.340 --> 00:08:09.660
your mass number.

00:08:09.660 --> 00:08:13.480
When it experiences beta
decay, what happens?

00:08:13.480 --> 00:08:15.490
Well, are the protons changed?

00:08:15.490 --> 00:08:18.890
Sure, we have one more proton
than we had before.

00:08:18.890 --> 00:08:20.500
Because our neutron
changed into one.

00:08:20.500 --> 00:08:23.410
So now our protons are plus 1.

00:08:23.410 --> 00:08:25.186
Has our mass number changed?

00:08:25.186 --> 00:08:26.720
Well let's see.

00:08:26.720 --> 00:08:28.750
The neutrons goes down
by one but your

00:08:28.750 --> 00:08:30.365
protons go up to by one.

00:08:30.365 --> 00:08:32.380
So your mass number
will not change.

00:08:32.380 --> 00:08:36.789
So it's still going
to be p plus N.

00:08:36.789 --> 00:08:39.909
so your mass stays the same,
unlike the situation with

00:08:39.909 --> 00:08:42.679
alpha decay, but your
element changes.

00:08:42.679 --> 00:08:44.039
Your number of protons
changes.

00:08:44.039 --> 00:08:47.975
So now, once again, you're
dealing with a new element in

00:08:47.975 --> 00:08:49.470
beta decay.

00:08:49.470 --> 00:08:52.530
Now, let's say we have
the other situation.

00:08:52.530 --> 00:08:57.360
Let's say we have a situation
where one of these protons

00:08:57.360 --> 00:09:00.750
looks at the neutrons and
says, you know what?

00:09:00.750 --> 00:09:02.240
I see how they live.

00:09:02.240 --> 00:09:04.170
It's very appealing to me.

00:09:04.170 --> 00:09:13.910
I think I would fit in better,
and our community of particles

00:09:13.910 --> 00:09:15.660
within the nucleus would
be happier if

00:09:15.660 --> 00:09:17.160
I too were a neutron.

00:09:17.160 --> 00:09:19.770
We'd all be in a more
stable condition.

00:09:19.770 --> 00:09:23.660
So what they do is, that little
uncomfortable proton

00:09:23.660 --> 00:09:27.340
has some probability of
emitting-- and now this is a

00:09:27.340 --> 00:09:31.020
new idea to you-- a positron,
not a proton.

00:09:31.020 --> 00:09:33.070
It emits a positron.

00:09:33.070 --> 00:09:34.670
And what's a positron?

00:09:34.670 --> 00:09:36.390
It's something that
has the exact

00:09:36.390 --> 00:09:38.610
same mass as an electron.

00:09:38.610 --> 00:09:42.890
So it's 1/1836 of the
mass of a proton.

00:09:42.890 --> 00:09:46.200
But we just write a zero there
because in atomic mass units

00:09:46.200 --> 00:09:47.830
it's pretty close to zero.

00:09:47.830 --> 00:09:50.006
But it has a positive charge.

00:09:50.006 --> 00:09:51.720
And it's a little confusing,
because they'll

00:09:51.720 --> 00:09:52.630
still write e there.

00:09:52.630 --> 00:09:54.440
Whenever I see an e, I
think an electron.

00:09:54.440 --> 00:09:56.720
But no, they say e because it's
kind of like the same

00:09:56.720 --> 00:09:59.500
type of particle, but instead
of having a negative charge,

00:09:59.500 --> 00:10:00.830
it has a positive charge.

00:10:00.830 --> 00:10:02.080
This is a positron.

00:10:04.980 --> 00:10:08.450
And now we're starting to get
kind of exotic with the types

00:10:08.450 --> 00:10:10.210
of particles and stuff
we're dealing with.

00:10:10.210 --> 00:10:11.730
But this does happen.

00:10:11.730 --> 00:10:15.920
And if you have a proton that
emits this particle, that

00:10:15.920 --> 00:10:19.370
pretty much had all of its
positive charge going with it,

00:10:19.370 --> 00:10:26.330
this proton turns
into a neutron.

00:10:26.330 --> 00:10:29.160
And that is called positron
emission.

00:10:29.160 --> 00:10:31.350
Positron emission is usually
pretty easy to figure out what

00:10:31.350 --> 00:10:33.510
it is, because they call
it positron emission.

00:10:33.510 --> 00:10:37.880
So if we start with the same E,
it has a certain number of

00:10:37.880 --> 00:10:41.500
protons, and a certain
number of neutrons.

00:10:41.500 --> 00:10:43.190
What's the new element
going to be?

00:10:43.190 --> 00:10:46.060
Well it's going to lose
a proton. p minus 1.

00:10:46.060 --> 00:10:47.770
And that's going to be turned
into a neutron.

00:10:47.770 --> 00:10:49.620
So p is going to
go down by one.

00:10:49.620 --> 00:10:51.030
N is going to go up by one.

00:10:51.030 --> 00:10:55.020
So that the mass of the whole
atom isn't going to change.

00:10:55.020 --> 00:10:57.550
So it's going to be p plus N.

00:10:57.550 --> 00:11:00.500
But we're still going to have
a different element, right?

00:11:00.500 --> 00:11:03.230
When we had beta decay,
we increased

00:11:03.230 --> 00:11:04.150
the number of protons.

00:11:04.150 --> 00:11:06.700
So we went, kind of, to the
right in the periodic table or

00:11:06.700 --> 00:11:09.070
we increased our, well,
you get the idea.

00:11:09.070 --> 00:11:12.440
When we do positron emission,
we decreased

00:11:12.440 --> 00:11:14.700
our number of protons.

00:11:14.700 --> 00:11:16.300
And actually I should
write that here in

00:11:16.300 --> 00:11:17.510
both of these reactions.

00:11:17.510 --> 00:11:20.460
So this is the positron
emission, and I'm left over

00:11:20.460 --> 00:11:22.060
with one positron.

00:11:22.060 --> 00:11:29.430
And in our beta decay, I'm left
over with one electron.

00:11:29.430 --> 00:11:30.670
They're written the
exact same way.

00:11:30.670 --> 00:11:32.660
You know this is an electron
because it's a minus 1 charge.

00:11:32.660 --> 00:11:33.890
You know this is a positron
because it

00:11:33.890 --> 00:11:35.810
has a plus 1 charge.

00:11:35.810 --> 00:11:38.170
Now there's one last
type of decay that

00:11:38.170 --> 00:11:39.140
you should know about.

00:11:39.140 --> 00:11:42.810
But it doesn't change the number
of protons or neutrons

00:11:42.810 --> 00:11:43.970
in a nucleus.

00:11:43.970 --> 00:11:46.940
But it just releases a ton of
energy, or sometimes, you

00:11:46.940 --> 00:11:48.350
know, a high-energy proton.

00:11:48.350 --> 00:11:50.160
And that's called gamma decay.

00:11:50.160 --> 00:11:52.510
And gamma decay means that these
guys just reconfigure

00:11:52.510 --> 00:11:52.795
themselves.

00:11:52.795 --> 00:11:54.460
Maybe they get a little
bit closer.

00:11:54.460 --> 00:11:57.990
And by doing that they release
energy in the form of a very

00:11:57.990 --> 00:12:03.180
high wavelength electromagnetic
wave. Which is

00:12:03.180 --> 00:12:05.820
essentially a gamma, you could
either call it a gamma

00:12:05.820 --> 00:12:08.230
particle or gamma ray.

00:12:08.230 --> 00:12:09.450
And it's very high energy.

00:12:09.450 --> 00:12:11.720
Gamma rays are something you
don't want to be around.

00:12:11.720 --> 00:12:15.460
They're very likely
to maybe kill you.

00:12:15.460 --> 00:12:17.130
Everything we did, I've said
is a little theoretical.

00:12:17.130 --> 00:12:20.000
Let's do some actual problems,
and figure out what type of

00:12:20.000 --> 00:12:21.750
decay we're dealing with.

00:12:21.750 --> 00:12:24.400
So here I have 7-beryllium
where seven

00:12:24.400 --> 00:12:26.900
is its atomic mass.

00:12:26.900 --> 00:12:30.520
And I have it being converted
to 7-lithium So

00:12:30.520 --> 00:12:31.440
what's going on here?

00:12:31.440 --> 00:12:36.000
My beryllium, my nuclear mass
is staying the same, but I'm

00:12:36.000 --> 00:12:42.240
going from four protons
to three protons.

00:12:42.240 --> 00:12:45.130
So I'm reducing my number
of protons.

00:12:45.130 --> 00:12:46.840
My overall mass hasn't
changed.

00:12:46.840 --> 00:12:49.100
So it's definitely
not alpha decay.

00:12:49.100 --> 00:12:50.960
Alpha decay was, you know,
you're releasing a whole

00:12:50.960 --> 00:12:52.770
helium from the nucleus.

00:12:52.770 --> 00:12:54.960
So what am I releasing?

00:12:54.960 --> 00:12:57.410
I'm kind of releasing one
positive charge, or I'm

00:12:57.410 --> 00:12:58.560
releasing a positron.

00:12:58.560 --> 00:13:00.940
And actually I have this
here in this equation.

00:13:00.940 --> 00:13:04.040
This is a positron.

00:13:04.040 --> 00:13:07.140
So this type of decay of
7-beryllium to 7-lithium is

00:13:07.140 --> 00:13:09.760
positron emission.

00:13:09.760 --> 00:13:10.830
Fair enough.

00:13:10.830 --> 00:13:12.400
Now let's look at
the next one.

00:13:12.400 --> 00:13:19.870
We have uranium-238 decaying
to thorium-234.

00:13:19.870 --> 00:13:25.140
And we see that the atomic mass
is decreasing by 4, minus

00:13:25.140 --> 00:13:28.910
4, and you see that your atomic
numbers decrease, or

00:13:28.910 --> 00:13:31.270
your protons are decreasing,
by 2.

00:13:31.270 --> 00:13:33.810
So you must be releasing,
essentially, something that

00:13:33.810 --> 00:13:37.390
has an atomic mass of four,
and a atomic number

00:13:37.390 --> 00:13:39.680
of two, or a helium.

00:13:39.680 --> 00:13:42.210
So this is alpha decay.

00:13:42.210 --> 00:13:46.100
So this right here is
an alpha particle.

00:13:46.100 --> 00:13:48.400
And this is an example
of alpha decay.

00:13:48.400 --> 00:13:51.110
Now you're probably saying, hey
Sal, wait, something weird

00:13:51.110 --> 00:13:51.850
is happening here.

00:13:51.850 --> 00:13:56.630
Because if I just go from 92
protons to 90 protons, I still

00:13:56.630 --> 00:13:59.430
have my 92 electrons out here.

00:13:59.430 --> 00:14:02.750
So wouldn't I now have
a minus 2 charge?

00:14:02.750 --> 00:14:08.270
And even better, this helium I'm
releasing, it doesn't have

00:14:08.270 --> 00:14:09.090
any electrons with it.

00:14:09.090 --> 00:14:10.390
It's just a helium nucleus.

00:14:10.390 --> 00:14:12.700
So doesn't that have
a plus 2 charge?

00:14:12.700 --> 00:14:15.180
And if you said that, you would
be absolutely correct.

00:14:15.180 --> 00:14:19.510
But the reality is that right
when this decay happens, this

00:14:19.510 --> 00:14:22.290
thorium, it has no reason
to hold on to those two

00:14:22.290 --> 00:14:25.050
electrons, so those two
electrons disappear and

00:14:25.050 --> 00:14:26.840
thorium becomes neutral again.

00:14:26.840 --> 00:14:30.480
And this helium, likewise,
it is very quick.

00:14:30.480 --> 00:14:33.040
It really wants two electrons
to get stable, so it's very

00:14:33.040 --> 00:14:36.880
quick to grab two electrons out
of wherever it's bumping

00:14:36.880 --> 00:14:38.460
into, and so that
becomes stable.

00:14:38.460 --> 00:14:40.305
So you could write
it either way.

00:14:40.305 --> 00:14:42.250
Now let's do another one.

00:14:42.250 --> 00:14:43.500
So here I have iodine.

00:14:45.820 --> 00:14:46.670
Let's see what's happening.

00:14:46.670 --> 00:14:51.020
My mass is not changing.

00:14:51.020 --> 00:14:53.790
So I must just have protons
turning into neutrons or

00:14:53.790 --> 00:14:55.560
neutrons turning into protons.

00:14:55.560 --> 00:14:58.810
And I see here that I
have 53 protons, and

00:14:58.810 --> 00:15:00.800
now I have 54 protons.

00:15:00.800 --> 00:15:04.060
So a neutron must have
turned into a proton.

00:15:04.060 --> 00:15:06.830
A neutron must have
gone to a proton.

00:15:06.830 --> 00:15:09.160
And the way that a neutron
goes to a proton is by

00:15:09.160 --> 00:15:11.620
releasing an electron.

00:15:11.620 --> 00:15:13.360
And we see that in this
reaction right here.

00:15:13.360 --> 00:15:16.880
An electron has been released.

00:15:16.880 --> 00:15:19.130
And so this is beta decay.

00:15:19.130 --> 00:15:20.380
This is a beta particle.

00:15:25.580 --> 00:15:26.750
And that same logic holds.

00:15:26.750 --> 00:15:32.780
You're like, hey wait, I just
went from 53 to 54 protons.

00:15:32.780 --> 00:15:34.440
Now that I have this extra
proton, won't I have a

00:15:34.440 --> 00:15:35.750
positive charge here?

00:15:35.750 --> 00:15:36.480
Well you would.

00:15:36.480 --> 00:15:40.810
But very quickly this might--
probably won't get these exact

00:15:40.810 --> 00:15:42.740
electrons, there's so many
electrons running around-- but

00:15:42.740 --> 00:15:45.950
it'll grab some electrons from
some place to get stable, and

00:15:45.950 --> 00:15:47.080
then it'll be stable again.

00:15:47.080 --> 00:15:48.890
But you're completely right in
thinking, hey, wouldn't it be

00:15:48.890 --> 00:15:51.690
an ion for some small
amount of time?

00:15:51.690 --> 00:15:52.900
Now let's do one more.

00:15:52.900 --> 00:15:57.210
So we have to 222-radon-- it
has atomic number of 86--

00:15:57.210 --> 00:16:01.720
going to 218-polonium, with
atomic number of 84.

00:16:01.720 --> 00:16:03.540
And this actually is an
interesting aside.

00:16:03.540 --> 00:16:08.380
Polonium is named after Poland,
because Marie Curie,

00:16:08.380 --> 00:16:11.220
she-- At the time Poland, this
was at the turn of the last

00:16:11.220 --> 00:16:15.120
century, around the end of the
1800's, Poland didn't exist as

00:16:15.120 --> 00:16:15.910
a separate country.

00:16:15.910 --> 00:16:19.540
It was split between Prussia,
Russia, and Austria.

00:16:19.540 --> 00:16:21.590
And they really wanted let
people know that, hey, you

00:16:21.590 --> 00:16:24.000
know, we think we're
one people.

00:16:24.000 --> 00:16:27.170
So they discovered that when,
you know, radon decayed it

00:16:27.170 --> 00:16:27.730
formed this element.

00:16:27.730 --> 00:16:31.430
And they named it after their
motherland, after Poland.

00:16:31.430 --> 00:16:33.880
It's the privileges of
discovering new elements.

00:16:33.880 --> 00:16:35.090
But anyway, back
to the problem.

00:16:35.090 --> 00:16:35.930
So what happened?

00:16:35.930 --> 00:16:39.210
Our atomic mass went
down by four.

00:16:39.210 --> 00:16:41.430
Our atomic number went
down by two.

00:16:41.430 --> 00:16:44.580
Once again, we must have
released a helium particle.

00:16:44.580 --> 00:16:47.070
A helium nucleus, something
that has an atomic mass of

00:16:47.070 --> 00:16:51.160
four, and an atomic
number of two.

00:16:51.160 --> 00:16:52.100
And so there we are.

00:16:52.100 --> 00:16:55.950
So this is alpha decay.

00:16:55.950 --> 00:16:57.810
We could write this as
a helium nucleus.

00:16:57.810 --> 00:16:59.145
So it has no electrons.

00:16:59.145 --> 00:17:00.820
We could even say immediately
that this would have a

00:17:00.820 --> 00:17:02.990
negative charge, but
then it loses


Hydrogen Peroxide Correction

WEBVTT
Kind: captions
Language: en

00:00:00.000 --> 00:00:04.470
Sal: I want to make a quick
correction to my second

00:00:04.470 --> 00:00:05.550
oxidation video.

00:00:05.550 --> 00:00:08.029
It was pointed out that I made
an error that you will

00:00:08.029 --> 00:00:09.980
probably find confusing.

00:00:09.980 --> 00:00:12.780
So I had written down
hydrogen peroxide.

00:00:12.780 --> 00:00:15.490
Because this was one of the
situations or the special

00:00:15.490 --> 00:00:19.680
cases where oxygen's oxidation
state isn't

00:00:19.680 --> 00:00:21.080
necessarily minus 2.

00:00:21.080 --> 00:00:25.580
So hydrogen peroxide is 2
hydrogens, 2 oxygens.

00:00:25.580 --> 00:00:27.780
And it's structure
looks like this.

00:00:27.780 --> 00:00:31.470
The oxygens are bonded to each
other, and they're each bonded

00:00:31.470 --> 00:00:33.740
to a hydrogen.

00:00:33.740 --> 00:00:36.350
And we know oxygen is really
electronegative.

00:00:36.350 --> 00:00:37.800
It likes to hog electrons.

00:00:37.800 --> 00:00:38.890
And I said that in that video.

00:00:38.890 --> 00:00:42.870
And because it hogs electrons,
the hydrogens lose their

00:00:42.870 --> 00:00:45.500
electron to oxygen, or at least
from the oxidation state

00:00:45.500 --> 00:00:46.570
point of view.

00:00:46.570 --> 00:00:50.910
So they each have a plus 1
oxidation state, which I did

00:00:50.910 --> 00:00:51.760
say in that video.

00:00:51.760 --> 00:00:55.240
And then I went on and my brain
was clearly-- and this

00:00:55.240 --> 00:00:57.850
is actually a good point for you
to realize how confusing

00:00:57.850 --> 00:00:59.150
this can sometimes
be if you're not

00:00:59.150 --> 00:01:00.920
careful with your work.

00:01:00.920 --> 00:01:02.620
I say in the last video,
and obviously

00:01:02.620 --> 00:01:04.970
oxygen gains an electron.

00:01:04.970 --> 00:01:08.530
And then I say and it's
oxidation state is plus 1.

00:01:08.530 --> 00:01:10.470
Which clearly makes no sense.

00:01:10.470 --> 00:01:13.440
If you gain an electron,
that will reduce

00:01:13.440 --> 00:01:14.250
your oxidation state.

00:01:14.250 --> 00:01:16.810
It will reduce that hypothetical
charge.

00:01:16.810 --> 00:01:20.470
And so your oxidation
state is minus 1 in

00:01:20.470 --> 00:01:22.230
each of these oxygens.

00:01:22.230 --> 00:01:24.250
And, of course, this is
a special case because

00:01:24.250 --> 00:01:27.240
traditionally, oxygen in
the case I always show

00:01:27.240 --> 00:01:30.030
it with, is in water.

00:01:30.030 --> 00:01:33.160
When it takes 2 electrons, 1
from this hydrogen and 1 from

00:01:33.160 --> 00:01:36.340
that hydrogen, it normally has
an oxidation state of minus 2

00:01:36.340 --> 00:01:38.760
and, of course, in this case,
it's plus 1 and plus 1 for the

00:01:38.760 --> 00:01:39.810
2 hydrogens.

00:01:39.810 --> 00:01:43.630
I think later, when I go back
to the molecular formula, I

00:01:43.630 --> 00:01:44.920
kind of corrected in my head.

00:01:44.920 --> 00:01:46.220
But I want to be very
clear to you.

00:01:46.220 --> 00:01:50.190
Oxygen does not have an
oxidation state of plus 1 in

00:01:50.190 --> 00:01:51.070
hydrogen peroxide.

00:01:51.070 --> 00:01:52.370
It is minus 1.

00:01:52.370 --> 00:01:54.950
I said it gained the electrons,
but then my brain

00:01:54.950 --> 00:01:57.370
obviously heard the word gaining
and wanted to put a

00:01:57.370 --> 00:01:58.230
plus sign there.

00:01:58.230 --> 00:01:58.820
No.

00:01:58.820 --> 00:02:02.080
it gained an electron that
reduces the oxygen.

00:02:02.080 --> 00:02:06.190
It makes its oxidation state
minus 1 for hydrogen peroxide.

00:02:06.190 --> 00:02:11.390
So hydrogen peroxide has 2
hydrogens with a plus 1

00:02:11.390 --> 00:02:12.590
oxidation state.

00:02:12.590 --> 00:02:16.210
And it has 2 oxygens with a
minus 1 oxidation state.

00:02:16.210 --> 00:02:21.910
One times 2 minus 1 times 2 is
equal to 0, so we're all cool.


Galvanic Cells

WEBVTT
Kind: captions
Language: en

00:00:00.770 --> 00:00:05.740
Let's say I had the reaction
where I had some copper ions.

00:00:05.740 --> 00:00:09.560
They have a positive
charge of 2.

00:00:09.560 --> 00:00:12.000
It's an aqueous solution.

00:00:12.000 --> 00:00:13.780
There could be some
other negative

00:00:13.780 --> 00:00:14.970
ions in that solution.

00:00:14.970 --> 00:00:16.600
Actually we could talk about
that in a little bit.

00:00:16.600 --> 00:00:19.820
But we know that when you have
these ions in solution, they

00:00:19.820 --> 00:00:20.890
all disassociate.

00:00:20.890 --> 00:00:22.910
So you just have to know you
have a bunch of ions just

00:00:22.910 --> 00:00:23.780
floating around in water.

00:00:23.780 --> 00:00:26.140
There could be some other
negative ones to neutralize

00:00:26.140 --> 00:00:28.580
the entire solution, but let's
just worry about the positive

00:00:28.580 --> 00:00:29.650
ones for now.

00:00:29.650 --> 00:00:37.940
And in that solution, I'm going
to put a bar of zinc.

00:00:37.940 --> 00:00:41.465
And what happens is that they
essentially switch places.

00:00:44.510 --> 00:00:48.260
The copper wants to jump out
of your aqueous solution.

00:00:48.260 --> 00:00:50.250
I should probably draw this.

00:00:50.250 --> 00:00:53.340
Let me draw it.

00:00:53.340 --> 00:00:56.500
This is my solution.

00:00:56.500 --> 00:01:02.460
And in my solution, we make it
blue, because it's aqueous, so

00:01:02.460 --> 00:01:04.010
most of it is water.

00:01:04.010 --> 00:01:08.275
I have some copper molecules
here in the solution.

00:01:08.275 --> 00:01:11.830
They're a plus-2 charge.

00:01:11.830 --> 00:01:15.490
I could have some other ions
that are negative, like some

00:01:15.490 --> 00:01:17.790
nitrate ions or whatever, but
they're all disassociated.

00:01:17.790 --> 00:01:20.490
They're all mixing around with
the water molecules that are

00:01:20.490 --> 00:01:23.940
polar, and that's why ions
disassociate, or salts in

00:01:23.940 --> 00:01:26.460
general, disassociate
well in water.

00:01:26.460 --> 00:01:28.360
And I stick a bar
of zinc in it.

00:01:28.360 --> 00:01:32.500
Solid zinc. So let me do that.

00:01:32.500 --> 00:01:35.640
So I stick of bar of
solid zinc into it.

00:01:35.640 --> 00:01:41.050
And so what this reaction says
is that these copper ions, if

00:01:41.050 --> 00:01:46.930
they can get a hold of some
electrons and essentially

00:01:46.930 --> 00:01:51.080
become neutral, they would
rather go back

00:01:51.080 --> 00:01:52.630
into the solid state.

00:01:52.630 --> 00:01:56.920
And the molecules of zinc out
here that are in the solid

00:01:56.920 --> 00:02:00.650
state, if they can lose some
electrons, they want to jump

00:02:00.650 --> 00:02:01.350
into the solution.

00:02:01.350 --> 00:02:03.210
So let me write down
the whole reaction.

00:02:03.210 --> 00:02:08.130
So if the copper can get some
electrons, they're going to go

00:02:08.130 --> 00:02:10.229
into the solid state.

00:02:10.229 --> 00:02:11.980
Copper will go into
the solid state.

00:02:11.980 --> 00:02:16.320
And if the zinc can lose some
electrons, they'll become

00:02:16.320 --> 00:02:18.740
positive ions or cations.

00:02:18.740 --> 00:02:23.630
And then they will go into the
solution, plus-- I'll do the

00:02:23.630 --> 00:02:30.550
same color-- zinc plus
2 plus aqueous.

00:02:30.550 --> 00:02:33.260
Actually just so, a little
side note here, these are

00:02:33.260 --> 00:02:34.170
actual ions.

00:02:34.170 --> 00:02:35.850
We've been dealing with
oxidation numbers.

00:02:35.850 --> 00:02:39.070
And when you want to know the
oxidation number of an ion,

00:02:39.070 --> 00:02:41.860
the oxidation number is the
same thing as its charge,

00:02:41.860 --> 00:02:43.780
because it's no longer
hypothetical.

00:02:43.780 --> 00:02:46.980
Remember oxidation numbers were
hypothetical charges if a

00:02:46.980 --> 00:02:47.910
bond were ionic.

00:02:47.910 --> 00:02:51.420
In this case they are ionic, so
the oxidation state, or the

00:02:51.420 --> 00:02:53.730
oxidation number is the
same as the charge.

00:02:53.730 --> 00:02:57.380
And just as a side note, the
convention, if it's written 2

00:02:57.380 --> 00:02:59.690
plus, this means that this
is a real charge.

00:02:59.690 --> 00:03:02.810
If it's written plus 2-- at
least this is the way I

00:03:02.810 --> 00:03:04.410
learned, and maybe there's
different conventions in

00:03:04.410 --> 00:03:06.980
different places-- then it would
be an oxidation state,

00:03:06.980 --> 00:03:09.300
which says, oh, it's not
necessarily an ion, but this

00:03:09.300 --> 00:03:11.380
is what it would be
if it was an ion.

00:03:11.380 --> 00:03:16.185
So if someone writes plus 2,
this is oxidation state.

00:03:16.185 --> 00:03:17.900
If they write 2 plus,
they say, hey

00:03:17.900 --> 00:03:19.400
this is a real charge.

00:03:19.400 --> 00:03:22.690
And likewise, if you just have
a regular ion that has, like,

00:03:22.690 --> 00:03:27.720
a charge of 1-- so let's say you
have Na plus-- this means

00:03:27.720 --> 00:03:28.830
that it's an actual charge.

00:03:28.830 --> 00:03:30.730
If you wanted to write its
oxidation state, you would

00:03:30.730 --> 00:03:32.270
write plus 1.

00:03:32.270 --> 00:03:34.870
Small little note, it doesn't
probably make a big difference

00:03:34.870 --> 00:03:36.560
in the whole scheme of things,
but sometimes it can get

00:03:36.560 --> 00:03:39.690
confusing whether something is
an oxidation state or an ion.

00:03:39.690 --> 00:03:42.820
But depending on where you're
going to school and what your

00:03:42.820 --> 00:03:45.090
teachers or conventions are, you
might want to clarify that

00:03:45.090 --> 00:03:47.425
and just make sure that they use
the same conventions that

00:03:47.425 --> 00:03:50.290
at least I remember when
I first learned it.

00:03:50.290 --> 00:03:52.390
So anyway, let's go back
to this reaction

00:03:52.390 --> 00:03:53.470
that's happening here.

00:03:53.470 --> 00:03:57.010
So let's do the half
reactions for this.

00:03:57.010 --> 00:03:59.230
So we start here, and actually
we can just look at the

00:03:59.230 --> 00:04:00.750
oxidation states
to begin with.

00:04:00.750 --> 00:04:01.720
This guy has an oxidation.

00:04:01.720 --> 00:04:05.890
He has a charge of 2, which is
also an oxidation number of 2.

00:04:05.890 --> 00:04:07.990
And he goes to a
neutral charge.

00:04:07.990 --> 00:04:12.760
So clearly, he gains two
electrons, which means that he

00:04:12.760 --> 00:04:13.830
was reduced.

00:04:13.830 --> 00:04:16.450
He went from a positive
charge to a zero

00:04:16.450 --> 00:04:18.170
oxidation state or charge.

00:04:18.170 --> 00:04:19.699
So his charge was reduced.

00:04:19.699 --> 00:04:21.760
Just let me write that.

00:04:21.760 --> 00:04:23.830
So this guy was reduced.

00:04:23.830 --> 00:04:27.220
And let me write his
half reaction.

00:04:27.220 --> 00:04:30.950
He essentially started off
with some copper in the

00:04:30.950 --> 00:04:36.370
aqueous state, and he
got two electrons.

00:04:36.370 --> 00:04:37.870
That's how you get reduced.

00:04:37.870 --> 00:04:40.440
So plus two electrons.

00:04:40.440 --> 00:04:45.035
And he ended up in the solid
state of copper.

00:04:45.035 --> 00:04:48.120
And his oxidation
number is now 0.

00:04:48.120 --> 00:04:52.930
Now let's see what happened to
the zinc. The zinc, it starts

00:04:52.930 --> 00:04:55.150
completely neutral in
the solid state.

00:04:55.150 --> 00:05:00.440
No extra electrons or deficiency
of electrons.

00:05:00.440 --> 00:05:05.100
But then once the zinc jumps
into the solution

00:05:05.100 --> 00:05:07.000
here, he has a charge.

00:05:07.000 --> 00:05:08.960
So he must have lost
electrons.

00:05:08.960 --> 00:05:13.060
So the half reaction for zinc--
in this situation you

00:05:13.060 --> 00:05:19.610
have zinc as a solid and he
reacts to produce two

00:05:19.610 --> 00:05:28.830
electrons and he's in the water
and he's now an ion.

00:05:28.830 --> 00:05:30.450
So let me put that there.

00:05:30.450 --> 00:05:32.120
An aqueous solution.

00:05:32.120 --> 00:05:36.140
So if we did this experiment
right here-- and I will tell

00:05:36.140 --> 00:05:38.160
you right now this reaction
moves forward.

00:05:38.160 --> 00:05:39.670
This is truly a reaction.

00:05:39.670 --> 00:05:42.560
We're going to talk about, in
a second, how badly do the

00:05:42.560 --> 00:05:46.240
electrons essentially want to
jump from-- where are they

00:05:46.240 --> 00:05:46.820
jumping from?

00:05:46.820 --> 00:05:51.860
They're jumping from the
zinc to the copper.

00:05:51.860 --> 00:05:54.240
So we're going to talk a little
bit about how strongly

00:05:54.240 --> 00:05:55.880
they want to jump
in the voltage.

00:05:55.880 --> 00:05:59.840
And voltage is really just how
badly does charge want to move

00:05:59.840 --> 00:06:03.020
or how much potential energy
does charge have. But this

00:06:03.020 --> 00:06:04.620
whole reaction, you just have
to think about what's

00:06:04.620 --> 00:06:07.820
happening, is that you have
charge moving from-- as the

00:06:07.820 --> 00:06:11.330
zinc jumps into the water, as
the zinc jumps into the

00:06:11.330 --> 00:06:15.070
aqueous solution, it's passing
on some charge to the copper

00:06:15.070 --> 00:06:17.330
that jumps into the
solid form.

00:06:17.330 --> 00:06:21.270
So electrons are moving here.

00:06:21.270 --> 00:06:23.770
And if somehow we could
harness these moving

00:06:23.770 --> 00:06:25.390
electrons, we could
create a current.

00:06:25.390 --> 00:06:26.920
In this situation, it's
all chemical.

00:06:26.920 --> 00:06:29.270
The electrons are moving around,
but they're not doing

00:06:29.270 --> 00:06:30.640
it in any organized way.

00:06:30.640 --> 00:06:32.270
Because the solution
is all mixed up.

00:06:32.270 --> 00:06:34.160
But this is an interesting
situation we're

00:06:34.160 --> 00:06:34.960
dealing with here.

00:06:34.960 --> 00:06:38.100
And we can even talk about how
badly the electrons want to

00:06:38.100 --> 00:06:40.080
move in these directions.

00:06:40.080 --> 00:06:41.470
You can look at these
half reactions.

00:06:41.470 --> 00:06:44.320
You can look it up in a table,
and you can get these energies

00:06:44.320 --> 00:06:46.740
or the voltage is for
these reactions.

00:06:46.740 --> 00:06:51.720
And this half reaction right
here has a voltage.

00:06:51.720 --> 00:06:52.970
So they'll sometimes right E.

00:06:52.970 --> 00:06:55.720
Sometimes it's an E not right
over there, but that's like

00:06:55.720 --> 00:06:57.800
kind of out of the scope
of at least a

00:06:57.800 --> 00:06:59.150
first-year chemistry course.

00:06:59.150 --> 00:07:02.760
But they'll say it's
0.34 volts.

00:07:02.760 --> 00:07:07.450
And then this reaction in this
direction has a potential

00:07:07.450 --> 00:07:08.770
difference.

00:07:08.770 --> 00:07:11.840
The energy is 0.76 volts.

00:07:11.840 --> 00:07:14.290
If I wrote this in the other
way, if I wrote this reaction

00:07:14.290 --> 00:07:19.090
of zinc plus 2 electrons going
to zinc solid, then you would

00:07:19.090 --> 00:07:20.480
just switch the sign.

00:07:20.480 --> 00:07:25.010
But what this says is that this
state, this state right

00:07:25.010 --> 00:07:28.020
here, is a higher energy
than that state.

00:07:28.020 --> 00:07:29.830
So it wants to go in
that direction.

00:07:29.830 --> 00:07:34.510
And it wants to do that with
an energy per coulomb.

00:07:34.510 --> 00:07:36.450
And you can watch the
physics playlist on

00:07:36.450 --> 00:07:38.160
more details of volts.

00:07:38.160 --> 00:07:40.720
But volt units are joules
per coulomb.

00:07:40.720 --> 00:07:43.710
This is how badly the electrons

00:07:43.710 --> 00:07:46.160
want to join the copper.

00:07:46.160 --> 00:07:47.520
That's the best way
of viewing it.

00:07:47.520 --> 00:07:51.090
And this is a measure of how
badly the electrons want to

00:07:51.090 --> 00:07:54.030
leave the zinc. So if you wanted
to talk about this

00:07:54.030 --> 00:07:58.370
whole reaction, so this whole
reaction that we have up here,

00:07:58.370 --> 00:08:02.510
we could say it's an energy, so
the energy of this entire

00:08:02.510 --> 00:08:04.510
reaction up here.

00:08:04.510 --> 00:08:08.530
We know that electrons really
want to join the copper with

00:08:08.530 --> 00:08:11.330
this energy, and they really
want to leave the zinc with

00:08:11.330 --> 00:08:12.250
this energy.

00:08:12.250 --> 00:08:15.600
So the energy of this entire
reaction, how badly do

00:08:15.600 --> 00:08:20.010
electrons want to move from zinc
to copper to form this

00:08:20.010 --> 00:08:22.340
over there, is just the
sum of the two.

00:08:22.340 --> 00:08:25.970
So you get what's 1.1 volts.

00:08:25.970 --> 00:08:28.530
You're probably saying, hey Sal,
all this talk of volts,

00:08:28.530 --> 00:08:30.190
this is interesting
and current.

00:08:30.190 --> 00:08:34.539
Is there some way that we could
construct a battery or a

00:08:34.539 --> 00:08:35.679
galvanic cell?

00:08:35.679 --> 00:08:38.179
If you don't know what a
galvanic cell is, it's what

00:08:38.179 --> 00:08:39.669
we're about to construct
right now.

00:08:39.669 --> 00:08:42.039
And the answer is obviously yes,
because that's the whole

00:08:42.039 --> 00:08:43.220
point of this video.

00:08:43.220 --> 00:08:46.080
So how can we somehow
harness that charge?

00:08:46.080 --> 00:08:50.370
So let's separate the
two reactions.

00:08:50.370 --> 00:08:52.830
Let's separate the two.

00:08:52.830 --> 00:09:01.310
So let me put my
zinc bar here.

00:09:01.310 --> 00:09:04.590
I'll try to stay true to the
colors that I used earlier.

00:09:04.590 --> 00:09:08.570
And let me put my copper
bar there.

00:09:08.570 --> 00:09:11.400
Actually maybe I should
copy and paste

00:09:11.400 --> 00:09:12.720
what I wrote up here.

00:09:12.720 --> 00:09:16.640
Just so we remember the
reaction itself.

00:09:16.640 --> 00:09:18.880
Actually, yeah let me do that.

00:09:18.880 --> 00:09:20.620
Never hurts.

00:09:20.620 --> 00:09:22.641
OK.

00:09:22.641 --> 00:09:24.760
I'll paste it down here.

00:09:24.760 --> 00:09:26.825
Ignore all the squiggly
lines around it.

00:09:26.825 --> 00:09:31.330
And let me put but both of my
bars in some aqueous solution.

00:09:31.330 --> 00:09:34.310
And there could be some other
dissolved ions in there to

00:09:34.310 --> 00:09:37.630
help neutralize the different--
so I put them both

00:09:37.630 --> 00:09:40.230
in an aqueous solution.

00:09:40.230 --> 00:09:41.480
But they're separate.

00:09:46.160 --> 00:09:49.060
And let me label them
appropriately.

00:09:49.060 --> 00:09:55.210
So this is my zinc. Zinc right
here, a bar of solid sync.

00:09:55.210 --> 00:09:57.490
And this is my bar
of solid copper.

00:09:57.490 --> 00:09:58.960
I should do that in
a different color.

00:09:58.960 --> 00:10:00.980
So this is copper right here.

00:10:00.980 --> 00:10:02.270
My bar of solid copper.

00:10:02.270 --> 00:10:04.470
And then I have an
aqueous solution.

00:10:04.470 --> 00:10:07.050
So what happens if we
were to connect

00:10:07.050 --> 00:10:08.640
these two metals, right?

00:10:08.640 --> 00:10:09.230
They're metals.

00:10:09.230 --> 00:10:10.480
If you look at the periodic
table they're

00:10:10.480 --> 00:10:13.660
both transition metals.

00:10:13.660 --> 00:10:15.570
They both have the
sea of electrons.

00:10:15.570 --> 00:10:17.350
So they both conduct
electricity well.

00:10:17.350 --> 00:10:21.880
What happens if you connect
these two with a wire?

00:10:21.880 --> 00:10:27.370
So if I connect them with a
wire right here like that.

00:10:27.370 --> 00:10:30.780
So we already know that the
zinc is just dying to jump

00:10:30.780 --> 00:10:33.880
into the water and lose
its electrons, right?

00:10:33.880 --> 00:10:36.670
So let's say that happens.

00:10:36.670 --> 00:10:40.430
So the zinc jumps into the
aqueous solution, and it turns

00:10:40.430 --> 00:10:44.720
into a positive ion of zinc.
And then its electrons are

00:10:44.720 --> 00:10:47.030
left behind, right?

00:10:47.030 --> 00:10:48.980
So it essentially has
two electrons.

00:10:48.980 --> 00:10:51.300
I did the half reaction
right here, right?

00:10:51.300 --> 00:10:54.410
The zinc jumps into the solution
and it leaves behind

00:10:54.410 --> 00:10:56.850
two electrons right here.

00:10:56.850 --> 00:10:59.810
Two electrons here, they really
want to jump off of the

00:10:59.810 --> 00:11:00.470
zinc.

00:11:00.470 --> 00:11:05.110
Now I have a lot of copper out
of here, out here in the

00:11:05.110 --> 00:11:09.850
solution, that really want to
jump on to this bar of copper.

00:11:09.850 --> 00:11:12.050
But right now they're
all ions.

00:11:12.050 --> 00:11:13.340
These are all plus 2 ions.

00:11:18.350 --> 00:11:20.970
And they really want to jump on
to the bar and join all of

00:11:20.970 --> 00:11:23.190
these other copper ions here.

00:11:23.190 --> 00:11:25.530
But in order to jump
on to that, they

00:11:25.530 --> 00:11:27.880
have to get some electrons.

00:11:27.880 --> 00:11:30.270
Each of these guys have
to grab two electrons.

00:11:30.270 --> 00:11:34.580
And we know that kind
of potential, or the

00:11:34.580 --> 00:11:37.170
electromotive force with which
they want to grab those

00:11:37.170 --> 00:11:41.830
electrons is 0.34 volts.

00:11:41.830 --> 00:11:45.940
These guys want to jump here
and grab electrons from

00:11:45.940 --> 00:11:49.260
someplace with plus
0.34 volts.

00:11:49.260 --> 00:11:52.350
These guys want to jump off
of the bar and leave their

00:11:52.350 --> 00:11:59.350
electrons behind with
0.76 volts.

00:11:59.350 --> 00:12:00.820
So what do you think's going
to happen if we have a

00:12:00.820 --> 00:12:02.500
conducting wire here?

00:12:02.500 --> 00:12:05.960
Well those electrons are, once
this zinc just jumps off,

00:12:05.960 --> 00:12:10.260
those electrons are going to
travel through the wire.

00:12:10.260 --> 00:12:13.050
And then they're going to be
available, because these are

00:12:13.050 --> 00:12:17.290
surplus electrons, to merge with
these copper ions that

00:12:17.290 --> 00:12:19.670
want to jump back
on to the bar.

00:12:19.670 --> 00:12:22.850
So these copper ions are going
to jump back on to the bar.

00:12:22.850 --> 00:12:24.780
But from this reaction
what's happening?

00:12:24.780 --> 00:12:27.380
You're having a current flow.

00:12:27.380 --> 00:12:28.750
Current is actually flowing.

00:12:28.750 --> 00:12:30.610
And what is the voltage
across this?

00:12:30.610 --> 00:12:34.450
How badly does an electron want
to go from the zinc on

00:12:34.450 --> 00:12:37.420
this bar to over here, join
with some copper in the

00:12:37.420 --> 00:12:40.400
solution and let that copper
join on to that bar?

00:12:40.400 --> 00:12:44.960
It wants to do it with
plus 1.1 volts.

00:12:44.960 --> 00:12:47.520
Now the question is the
electrons are flowing in that

00:12:47.520 --> 00:12:51.480
way, what is the cathode
and what is the anode?

00:12:51.480 --> 00:12:59.660
So the cathode is the positive
terminal of, well, you can

00:12:59.660 --> 00:13:02.430
already imagine, this is a
battery of sorts, right?

00:13:02.430 --> 00:13:05.270
Because we are able to generate
a current by having a

00:13:05.270 --> 00:13:07.430
voltage difference across
two terminals.

00:13:07.430 --> 00:13:11.550
The cathode is the positive
terminal.

00:13:11.550 --> 00:13:14.460
That's where the electrons
want to go to.

00:13:14.460 --> 00:13:19.450
And then the anode-- and you can
familiarize yourself with,

00:13:19.450 --> 00:13:24.570
you know, just a cation is a
positive ion and anion is a

00:13:24.570 --> 00:13:26.010
negative ion.

00:13:26.010 --> 00:13:29.430
So the anode is a negative
terminal.

00:13:29.430 --> 00:13:30.890
So what's the negative
terminal here?

00:13:30.890 --> 00:13:33.800
The negative terminal is where
the electrons come from.

00:13:33.800 --> 00:13:36.560
See, electrons are coming from
the zinc jumping off.

00:13:36.560 --> 00:13:38.980
So is your negative terminal.

00:13:38.980 --> 00:13:40.140
And what's the positive
terminal?

00:13:40.140 --> 00:13:41.790
That's where the electrons
want to go to.

00:13:41.790 --> 00:13:46.200
They want to go down here and be
available for these coppers

00:13:46.200 --> 00:13:47.700
that want to jump out
of the solution.

00:13:47.700 --> 00:13:53.200
So this is our positive
terminal, or our cathode.

00:13:53.200 --> 00:13:54.510
This is the cathode.

00:13:54.510 --> 00:13:56.650
This is the anode.

00:13:56.650 --> 00:13:59.460
And if someone says, hey, does
oxidation or reduction occur

00:13:59.460 --> 00:14:00.690
at the cathode or the anode?

00:14:00.690 --> 00:14:02.220
Well what's occurring
right here?

00:14:02.220 --> 00:14:07.620
We have zinc in its solid
state right here.

00:14:07.620 --> 00:14:11.170
We have solid zinc jumping in--
and it's neutral-- and it

00:14:11.170 --> 00:14:14.180
jumps into the solution and it
leaves two electrons behind.

00:14:14.180 --> 00:14:16.100
So it's losing electrons.

00:14:16.100 --> 00:14:19.750
When you lose electrons
you're being oxidized.

00:14:19.750 --> 00:14:23.140
So this is where the oxidation
is occurring.

00:14:23.140 --> 00:14:26.090
Likewise, on this side you
have copper ions that are

00:14:26.090 --> 00:14:30.090
already in the solution, and
they're gaining electrons.

00:14:30.090 --> 00:14:32.250
So their charge is
being reduced.

00:14:32.250 --> 00:14:36.280
So the cathode is where
reduction is taking place.

00:14:36.280 --> 00:14:38.690
Reduction.

00:14:38.690 --> 00:14:40.860
Now you're probably saying, oh
Sal, this is a nice cute

00:14:40.860 --> 00:14:45.190
little, you know, battery-- or
this is called a galvanic

00:14:45.190 --> 00:14:47.630
cell-- that, you know, you've
created this current.

00:14:47.630 --> 00:14:48.860
But I see a problem here.

00:14:48.860 --> 00:14:51.780
Because as this happens, you're
going to have more and

00:14:51.780 --> 00:14:56.670
more positive zinc ions jump
into the solution here.

00:14:56.670 --> 00:14:59.960
You have more and more positive
zinc ions in here as

00:14:59.960 --> 00:15:02.270
this progresses.

00:15:02.270 --> 00:15:07.940
And you're going to have fewer
and fewer copper ions in here.

00:15:07.940 --> 00:15:10.720
So if you assume that there
were some other, let's say

00:15:10.720 --> 00:15:17.560
there was, I mean, maybe to keep
the solution neutral--

00:15:17.560 --> 00:15:20.460
the copper is positive-- maybe
you had some chloride in

00:15:20.460 --> 00:15:28.190
there, chloride anions
that were keeping

00:15:28.190 --> 00:15:29.250
this solution neutral.

00:15:29.250 --> 00:15:31.450
And maybe you had some chlorine
anions here that were

00:15:31.450 --> 00:15:34.910
keeping, well, it started
negative but then it maybe

00:15:34.910 --> 00:15:37.150
gets a little bit more neutral
as the zinc jumps in.

00:15:37.150 --> 00:15:39.060
But once this happens a
lot then it becomes

00:15:39.060 --> 00:15:40.160
very positive, right?

00:15:40.160 --> 00:15:41.960
This is becoming more and more
positive as more and

00:15:41.960 --> 00:15:43.170
more zinc jumps in.

00:15:43.170 --> 00:15:45.780
And this is becoming more and
more negative as more copper

00:15:45.780 --> 00:15:47.020
jumps on to this bar.

00:15:47.020 --> 00:15:50.340
So what can we do to
solve that problem?

00:15:50.340 --> 00:15:52.710
What they do is-- and this is
just one way to solve the

00:15:52.710 --> 00:15:54.770
problem, there's actually many
but this probably what you

00:15:54.770 --> 00:15:57.020
might encounter in your
first-year chemistry class--

00:15:57.020 --> 00:16:01.185
is they create something
called a salt bridge.

00:16:01.185 --> 00:16:03.620
And what they do is they create
a, I guess we could

00:16:03.620 --> 00:16:07.280
call it a pseudo-aqueous
solution of salt.

00:16:07.280 --> 00:16:11.980
Maybe it's potassium chloride.

00:16:11.980 --> 00:16:15.320
So in here we have potassium.

00:16:15.320 --> 00:16:17.370
Potassium has a plus charge.

00:16:17.370 --> 00:16:20.600
It's aqueous, plus
chlorine with a

00:16:20.600 --> 00:16:22.300
negative charge aqueous.

00:16:22.300 --> 00:16:25.330
And I say pseudo-aqueous
because it's not really

00:16:25.330 --> 00:16:26.490
super-liquid water.

00:16:26.490 --> 00:16:28.280
What they do is they try to
make it more viscous so it

00:16:28.280 --> 00:16:29.580
just doesn't mix completely.

00:16:29.580 --> 00:16:32.190
If this was pure water, then all
of it would just fall into

00:16:32.190 --> 00:16:34.800
the solution, and you would
really have nothing up here.

00:16:34.800 --> 00:16:37.150
It would be a useless device.

00:16:37.150 --> 00:16:40.460
But what they do is they create
a gel that's still

00:16:40.460 --> 00:16:43.210
aqueous enough that the
ions can move around.

00:16:43.210 --> 00:16:46.780
The sodium and chloride
ions can move around.

00:16:46.780 --> 00:16:50.520
So let's say that those are
the-- sorry, not the sodium,

00:16:50.520 --> 00:16:52.565
the potassium-- let's say
that's the potassium.

00:16:52.565 --> 00:16:56.195
And let's say the chlorine ions
are-- I already did it in

00:16:56.195 --> 00:16:58.870
that blue-- so chlorine
are the minus.

00:16:58.870 --> 00:17:02.910
And what happens is as we have
this oxidation reduction

00:17:02.910 --> 00:17:06.160
reaction that's causing these
electrons to travel from the

00:17:06.160 --> 00:17:08.880
anode to the cathode, this
becomes positives, this

00:17:08.880 --> 00:17:10.089
becomes negative.

00:17:10.089 --> 00:17:13.740
The salt bridge allows the
negative components of the

00:17:13.740 --> 00:17:17.240
ionized salt and just waste the
chlorine to go into the

00:17:17.240 --> 00:17:18.589
solution to neutralize it.

00:17:18.589 --> 00:17:21.220
So they'll end up having more
and more chlorine as

00:17:21.220 --> 00:17:24.130
the zinc pops off.

00:17:24.130 --> 00:17:26.020
If you were to evaporate the
solution you'd end up with a

00:17:26.020 --> 00:17:27.500
bunch of zinc chloride.

00:17:27.500 --> 00:17:32.040
And on this side, to keep the
balance here, you'll have a

00:17:32.040 --> 00:17:36.610
lot of the positive parts,
components, of the salt.

00:17:36.610 --> 00:17:40.450
So the sodium would jump in to
replace the copper that's

00:17:40.450 --> 00:17:41.610
jumping out.

00:17:41.610 --> 00:17:43.810
So when you have this whole
thing it enables the current

00:17:43.810 --> 00:17:47.150
to keep flowing without having
a bad effect on the charge.

00:17:47.150 --> 00:17:48.490
Because, you know, what
happens if this

00:17:48.490 --> 00:17:50.140
becomes really positive?

00:17:50.140 --> 00:17:52.350
If this becomes really
positive-- I'll do it in

00:17:52.350 --> 00:17:56.310
vibrant color because there's no
salt bridge-- at some point

00:17:56.310 --> 00:17:58.650
the electrons are going to say,
hey, I can either go over

00:17:58.650 --> 00:18:01.120
here and drive this reaction
or, hey, I got a lot of

00:18:01.120 --> 00:18:02.860
positive stuff hanging
out here.

00:18:02.860 --> 00:18:04.430
Maybe I don't want
to leave it all.

00:18:04.430 --> 00:18:07.290
So you have to do something to
neutralize the charge here.

00:18:07.290 --> 00:18:10.310
Likewise, if this becomes really
negative from all the

00:18:10.310 --> 00:18:13.780
chlorine atoms jumping out,
electrons aren't going to want

00:18:13.780 --> 00:18:14.390
to go here.

00:18:14.390 --> 00:18:16.940
Because like charges
repel each other.

00:18:16.940 --> 00:18:19.670
So that's what having the salt
bridge neutralizing the

00:18:19.670 --> 00:18:20.650
solution does for you.

00:18:20.650 --> 00:18:22.600
It keeps it from getting
negative, and then our

00:18:22.600 --> 00:18:25.500
galvanic cell can
keep operating.


Redox Reactions

WEBVTT
Kind: captions
Language: en

00:00:00.550 --> 00:00:04.640
We now know what an oxidation
state or an oxidation number

00:00:04.640 --> 00:00:06.350
is and what it means
when things

00:00:06.350 --> 00:00:07.610
are oxidized or reduced.

00:00:07.610 --> 00:00:10.510
So let's see how that actually
happens in reactions.

00:00:10.510 --> 00:00:16.050
So what we're going to study
in this video is oxidation

00:00:16.050 --> 00:00:19.060
slash reduction reactions.

00:00:19.060 --> 00:00:21.270
All that is is a reaction
where somebody's being

00:00:21.270 --> 00:00:24.640
oxidized, which means that
electrons are being taken away

00:00:24.640 --> 00:00:27.700
from them, and someone's being
reduced, which means that

00:00:27.700 --> 00:00:29.860
they're being handed electrons,
or they're taking

00:00:29.860 --> 00:00:32.110
electrons away from
someone else.

00:00:32.110 --> 00:00:35.260
Sometimes this has been termed--
because you have the

00:00:35.260 --> 00:00:39.630
R-E-D in reduction and you have
the ox in oxidation, and

00:00:39.630 --> 00:00:42.130
they switch them around and
they call this a redox

00:00:42.130 --> 00:00:45.440
reaction, which sounds like a
very fancy chemistry term, but

00:00:45.440 --> 00:00:48.880
it just means a reaction where
something is getting oxidized.

00:00:48.880 --> 00:00:50.820
And if something is getting
oxidized, something else is

00:00:50.820 --> 00:00:52.090
getting reduced.

00:00:52.090 --> 00:00:53.920
So let's study a
couple of them.

00:00:53.920 --> 00:00:55.770
So right here, I actually
have combustion.

00:00:55.770 --> 00:00:57.510
This is actually methane.

00:00:57.510 --> 00:01:01.220
So methane is a fuel.

00:01:01.220 --> 00:01:04.120
You can make a motor powered
on methane right there.

00:01:04.120 --> 00:01:05.050
It's a hydrocarbon.

00:01:05.050 --> 00:01:08.200
Most fuels that we use are
hydrocarbons, which just mean

00:01:08.200 --> 00:01:11.020
carbons bonded in a bunch of
different ways to a bunch of

00:01:11.020 --> 00:01:12.080
different hydrogens.

00:01:12.080 --> 00:01:15.980
If you add enough heat for the
reaction to happen-- so its

00:01:15.980 --> 00:01:18.660
activation energy you have to
put it in there with some

00:01:18.660 --> 00:01:21.510
oxygen around-- it's going to
combust and it's going to

00:01:21.510 --> 00:01:24.570
produce carbon dioxide and
water-- and I didn't put it

00:01:24.570 --> 00:01:26.810
here-- and even more heat
than you put into it.

00:01:26.810 --> 00:01:28.560
So it's actually an exothermic
reaction.

00:01:28.560 --> 00:01:30.980
It produces more heat than
you put into it.

00:01:30.980 --> 00:01:33.650
I'll do a lot more of that in
future videos on endothermic

00:01:33.650 --> 00:01:35.230
and exothermic reactions.

00:01:35.230 --> 00:01:37.790
But anyway, we care about the
oxidation and the reduction.

00:01:37.790 --> 00:01:40.340
So let's see if anyone's getting
oxidized, or anyone is

00:01:40.340 --> 00:01:42.270
getting reduced here.

00:01:42.270 --> 00:01:45.110
So let's look at
their oxidation

00:01:45.110 --> 00:01:47.100
numbers, or their states.

00:01:47.100 --> 00:01:50.470
Here, carbon is bonded
to 4 hydrogens.

00:01:50.470 --> 00:01:52.810
Who's giving, who's taking?

00:01:52.810 --> 00:01:55.120
So let's go to our
Periodic Table.

00:01:55.120 --> 00:01:56.660
Carbon is here.

00:01:56.660 --> 00:01:58.400
Hydrogen is here.

00:01:58.400 --> 00:02:00.520
Carbon is more electronegative.

00:02:00.520 --> 00:02:04.840
It's adjacent to the
Three Musketeers of

00:02:04.840 --> 00:02:05.840
electronegativity.

00:02:05.840 --> 00:02:07.970
These guys are the most
electronegative.

00:02:07.970 --> 00:02:13.730
We always ignore the noble gases
because they pretty much

00:02:13.730 --> 00:02:14.990
don't react at all.

00:02:14.990 --> 00:02:17.310
They're always happy with their
8 valence electrons.

00:02:17.310 --> 00:02:19.100
These guys love to
get electrons.

00:02:19.100 --> 00:02:20.970
They're small molecules.

00:02:20.970 --> 00:02:24.620
Their outermost shell is
close to the nucleus.

00:02:24.620 --> 00:02:28.580
They're so close to becoming
noble that they just love

00:02:28.580 --> 00:02:29.900
hogging electrons.

00:02:29.900 --> 00:02:30.980
Carbon's almost there.

00:02:30.980 --> 00:02:33.200
Carbon's much further to the
right on the periodic table

00:02:33.200 --> 00:02:34.220
than the hydrogen.

00:02:34.220 --> 00:02:38.580
So if you have carbon bonding
with hydrogen, carbon is going

00:02:38.580 --> 00:02:41.280
to be the electron hog.

00:02:41.280 --> 00:02:45.610
So in the situation,
let's go down here.

00:02:45.610 --> 00:02:48.450
So if carbon's the electron hog
and hydrogen is having its

00:02:48.450 --> 00:02:52.170
electrons taken away from it--
remember, this is all kind of

00:02:52.170 --> 00:02:52.950
hypothetical.

00:02:52.950 --> 00:02:54.540
It's more partial,
is the reality.

00:02:54.540 --> 00:02:57.480
But if you had to pick or
choose, hydrogen's going to

00:02:57.480 --> 00:03:00.280
lose an electron each.

00:03:00.280 --> 00:03:02.610
So it's going to have an
oxidation state of plus 1 for

00:03:02.610 --> 00:03:03.830
each hydrogen.

00:03:03.830 --> 00:03:07.040
You have 4 hydrogens each
giving up an electron.

00:03:07.040 --> 00:03:13.010
So the carbon must be
taking 4 electrons.

00:03:13.010 --> 00:03:15.710
So its oxidation number
is minus 4.

00:03:15.710 --> 00:03:19.320
It's taken 4 electrons so its
charge will go down by 4.

00:03:19.320 --> 00:03:20.790
So that's why it's negative.

00:03:20.790 --> 00:03:21.670
Fair enough.

00:03:21.670 --> 00:03:25.170
What's the oxidation state of
this oxygen right there?

00:03:25.170 --> 00:03:26.700
Well, it's just bonded
to itself.

00:03:26.700 --> 00:03:29.530
There's no reason to believe
that 1 oxygen should be able

00:03:29.530 --> 00:03:32.400
to take any electrons
from another oxygen.

00:03:32.400 --> 00:03:36.860
So it has a 0 oxidation state.

00:03:36.860 --> 00:03:40.140
It's not hogging more than its
fair share of electrons that

00:03:40.140 --> 00:03:42.380
it was essentially born with.

00:03:42.380 --> 00:03:42.760
Now.

00:03:42.760 --> 00:03:45.040
After the combustion
occurs, what are

00:03:45.040 --> 00:03:47.660
the oxidation numbers?

00:03:47.660 --> 00:03:52.920
Well, I have 2 oxygens
bonded with carbon.

00:03:52.920 --> 00:03:56.470
Now we know oxidation
was, to some

00:03:56.470 --> 00:03:57.930
degree, named after oxygen.

00:03:57.930 --> 00:04:00.210
It is one of the most
electronegative.

00:04:00.210 --> 00:04:03.010
Almost anything bonded with
oxygen is going to be giving

00:04:03.010 --> 00:04:04.310
up its electrons.

00:04:04.310 --> 00:04:06.480
We also know that oxygen likes
to take 2 electrons.

00:04:10.780 --> 00:04:11.780
If it takes 1, it gets here.

00:04:11.780 --> 00:04:12.530
If 2, it gets here.

00:04:12.530 --> 00:04:16.070
It has a configuration like it
has 8 valence electrons.

00:04:16.070 --> 00:04:20.440
So its typical oxidation
number is minus 2.

00:04:20.440 --> 00:04:24.350
So carbon, in this in the
situation, each oxygen is

00:04:24.350 --> 00:04:28.180
going to have a minus
2 oxidation number.

00:04:28.180 --> 00:04:31.930
The carbon dioxide molecule
is neutral.

00:04:31.930 --> 00:04:34.080
So everything has
to add up to 0.

00:04:34.080 --> 00:04:36.340
The oxygens, you have 2 of
them, each of them with a

00:04:36.340 --> 00:04:37.880
minus 2 oxidation number.

00:04:37.880 --> 00:04:39.390
So that's minus 4.

00:04:39.390 --> 00:04:46.860
So carbon must be plus 4, which
means that it has given

00:04:46.860 --> 00:04:50.140
up 4 electrons, right?

00:04:50.140 --> 00:04:52.650
Really it only has 4 electrons
to give up.

00:04:52.650 --> 00:04:58.480
It has 1, 2, 3, 4 valence
electrons in its second shell,

00:04:58.480 --> 00:05:00.100
which is its reactive shell.

00:05:00.100 --> 00:05:01.600
So its oxidation number
is plus 4.

00:05:01.600 --> 00:05:03.200
Now let's look at the water.

00:05:03.200 --> 00:05:04.480
We've done about a bunch.

00:05:04.480 --> 00:05:09.410
When the hydrogens each give up
an electron, they have an

00:05:09.410 --> 00:05:10.770
oxidation number of 1.

00:05:10.770 --> 00:05:13.310
Each oxygen takes 2 electrons.

00:05:13.310 --> 00:05:14.110
There's only 1 of them.

00:05:14.110 --> 00:05:16.170
So it's minus 2.

00:05:16.170 --> 00:05:18.200
So what's going on here?

00:05:18.200 --> 00:05:20.070
What's getting oxidized,
what's getting reduced?

00:05:20.070 --> 00:05:21.250
You have the carbon.

00:05:21.250 --> 00:05:24.320
It went from an oxidation number
of minus 4 an oxidation

00:05:24.320 --> 00:05:26.970
number of plus 4.

00:05:26.970 --> 00:05:30.250
So let me just draw what's
happening to the carbon.

00:05:30.250 --> 00:05:33.070
Carbon goes from minus 4, which
means it's hogging 4

00:05:33.070 --> 00:05:41.700
electrons, to a situation where
it's having 4 electrons

00:05:41.700 --> 00:05:43.020
being hogged from it.

00:05:43.020 --> 00:05:45.260
It's kind of giving
away 4 electrons.

00:05:45.260 --> 00:05:49.450
So someplace in this process,
this guy must have given away

00:05:49.450 --> 00:05:50.300
8 electrons.

00:05:50.300 --> 00:05:51.930
This is a difference
of 8 electrons.

00:05:51.930 --> 00:05:56.480
So plus 8 electrons.

00:05:56.480 --> 00:05:58.500
So what's happened to carbon?

00:05:58.500 --> 00:06:02.970
Carbon, has it been oxidized
or reduced?

00:06:02.970 --> 00:06:04.540
Its charge has gone up.

00:06:04.540 --> 00:06:05.690
So it hasn't been reduced.

00:06:05.690 --> 00:06:08.550
Or the other way is that you
can say electrons have been

00:06:08.550 --> 00:06:09.680
taken away from it.

00:06:09.680 --> 00:06:10.930
So it has been oxidized.

00:06:16.960 --> 00:06:21.590
Now, let's look at the
oxygen itself.

00:06:21.590 --> 00:06:26.090
Oxygen, over here you have
4 oxygen molecules.

00:06:26.090 --> 00:06:28.830
So I'll just write 4 oxygen
molecules here.

00:06:28.830 --> 00:06:33.750
And they all have an oxidation
state of 0.

00:06:33.750 --> 00:06:37.130
From an oxidation-number point
of view, they're neutral.

00:06:37.130 --> 00:06:39.750
On the side, we have
2, and then we

00:06:39.750 --> 00:06:42.910
have 4 oxygen molecules.

00:06:42.910 --> 00:06:44.880
What's their oxidation state?

00:06:44.880 --> 00:06:46.130
They're all minus 2.

00:06:48.800 --> 00:06:53.200
So each of these oxygens must
have gained an electron.

00:06:53.200 --> 00:06:57.550
So actually, let me let me
re-write this reaction.

00:06:57.550 --> 00:06:58.940
Let me erase a little
bit of it.

00:07:01.780 --> 00:07:03.640
Even better, let me just
move this over.

00:07:11.720 --> 00:07:12.290
There you go.

00:07:12.290 --> 00:07:15.570
Let me fill in that, so
aesthetically it's pleasing.

00:07:15.570 --> 00:07:16.720
There you go.

00:07:16.720 --> 00:07:18.190
All right.

00:07:18.190 --> 00:07:21.560
So we have 4 oxygens with a 0
oxidation state turning into 4

00:07:21.560 --> 00:07:24.110
oxygens with a minus
2 oxidation state.

00:07:24.110 --> 00:07:28.650
So each of these 4 oxygens
took 2 electrons.

00:07:28.650 --> 00:07:35.110
There's 4 of them, so we must
have gained 8 electrons.

00:07:35.110 --> 00:07:36.640
So what happened to oxygen?

00:07:36.640 --> 00:07:40.000
It's oxidation state went down,
or its hypothetical

00:07:40.000 --> 00:07:44.300
charge went down, or its
charge was reduced.

00:07:44.300 --> 00:07:47.255
So this is reduced oxygen.

00:07:50.870 --> 00:07:52.820
What was it reduced by?

00:07:52.820 --> 00:07:57.820
It was reduced by the carbon.

00:07:57.820 --> 00:08:00.100
What was the carbon
oxidized by?

00:08:00.100 --> 00:08:05.570
It was oxidized by the oxygen,
which oxygen tends to do.

00:08:05.570 --> 00:08:06.970
It tends to oxidize things.

00:08:06.970 --> 00:08:10.340
What is the oxidizing agent?

00:08:10.340 --> 00:08:12.410
Well it's the thing that
did the oxidizing.

00:08:12.410 --> 00:08:19.150
So the oxygen is the
oxidizing agent.

00:08:19.150 --> 00:08:21.150
What is the reducing agent?

00:08:21.150 --> 00:08:22.790
Well it's the thing that
did the reducing?

00:08:22.790 --> 00:08:26.950
It's the reducing agent,
is the carbon.

00:08:26.950 --> 00:08:30.320
So you see in this redox
reaction, carbon was oxidized.

00:08:30.320 --> 00:08:33.559
It gave away 8 electrons from
this state to that state,

00:08:33.559 --> 00:08:36.350
hypothetically, and oxygen
was reduced.

00:08:36.350 --> 00:08:40.900
Its charge was reduced by a
total of 8 electrons, 2 for

00:08:40.900 --> 00:08:42.280
each oxygen.

00:08:42.280 --> 00:08:44.380
So its oxidation number
went down.

00:08:44.380 --> 00:08:45.910
Let's do a couple more.

00:08:45.910 --> 00:08:47.940
Each of the things that I
wrote-- just to kind of do a

00:08:47.940 --> 00:08:50.790
side-note-- this is called a
half reaction, because I'm

00:08:50.790 --> 00:08:53.090
writing just what happened
to the carbon.

00:08:53.090 --> 00:08:56.260
Here I'm writing just what
happened to the oxygen.

00:08:56.260 --> 00:08:57.440
I did ignore something.

00:08:57.440 --> 00:08:58.880
I did ignore the hydrogen.

00:08:58.880 --> 00:09:00.150
I encourage you to
do something like

00:09:00.150 --> 00:09:00.830
this with the hydrogen.

00:09:00.830 --> 00:09:02.590
But you'll see that
hydrogen was

00:09:02.590 --> 00:09:04.250
neither oxidized or reduced.

00:09:04.250 --> 00:09:08.220
On both sides of the equation,
all the hydrogens had a plus 1

00:09:08.220 --> 00:09:10.050
oxidation state.

00:09:10.050 --> 00:09:11.980
Let's do another one.

00:09:11.980 --> 00:09:14.440
Here I have another combustion
situation.

00:09:14.440 --> 00:09:16.280
This is what happened
to the Hindenburg.

00:09:16.280 --> 00:09:18.600
They filled a balloon full of
hydrogen because they wanted

00:09:18.600 --> 00:09:22.650
it to float, because hydrogen
is a very light gas.

00:09:22.650 --> 00:09:26.220
Unfortunately, there must have
been a spark in the presence

00:09:26.220 --> 00:09:28.600
of oxygen, and it combusted.

00:09:28.600 --> 00:09:30.490
And actually, this is
what is used for a

00:09:30.490 --> 00:09:31.800
rocket fuel as well.

00:09:31.800 --> 00:09:34.350
If you have liquid hydrogen--
actually, I don't think they

00:09:34.350 --> 00:09:34.680
have liquid hydrogen.

00:09:34.680 --> 00:09:36.330
Well, I don't know enough
about rocket science.

00:09:36.330 --> 00:09:38.130
I'll have to do another video
that in the future.

00:09:38.130 --> 00:09:39.770
But let's look at the
oxidation states.

00:09:39.770 --> 00:09:41.750
What's the oxidation state
of hydrogen here, in its

00:09:41.750 --> 00:09:43.050
elemental form?

00:09:43.050 --> 00:09:43.750
It's 0.

00:09:43.750 --> 00:09:45.840
2 hydrogens bonded to each
other, no reason why they

00:09:45.840 --> 00:09:50.340
should hog or be hogged
by another hydrogen.

00:09:50.340 --> 00:09:53.210
2 oxygen molecules or atoms
bonded to each other?

00:09:53.210 --> 00:09:55.620
Once again, 0 oxidation state.

00:09:55.620 --> 00:09:58.270
Once they combust and
form water, what's

00:09:58.270 --> 00:09:59.200
their oxidation states?

00:09:59.200 --> 00:10:00.800
We've done this multiple
times.

00:10:00.800 --> 00:10:03.370
The oxygen has a minus
2 oxidation state.

00:10:03.370 --> 00:10:06.490
Each hydrogen has a plus 1.

00:10:06.490 --> 00:10:08.420
So let's write the
half reactions.

00:10:08.420 --> 00:10:13.670
We have 2 hydrogens that are
just happy as they are in

00:10:13.670 --> 00:10:14.950
neutral state.

00:10:14.950 --> 00:10:20.900
They end up being 2 H2's, or
we could have written 4

00:10:20.900 --> 00:10:22.390
hydrogens, either way.

00:10:22.390 --> 00:10:25.890
They turn into 2 hydrogen
molecules, because there's

00:10:25.890 --> 00:10:30.150
actually 4 hydrogen atoms, with
a plus 1 oxidation state.

00:10:30.150 --> 00:10:34.110
So they must have each given
away 1 electron.

00:10:34.110 --> 00:10:36.080
Now, how many total hydrogens
are there?

00:10:36.080 --> 00:10:37.070
There are 4.

00:10:37.070 --> 00:10:41.890
So we must have given
away 4 electrons.

00:10:41.890 --> 00:10:44.410
So this is a half reaction
for hydrogen.

00:10:44.410 --> 00:10:45.140
Now.

00:10:45.140 --> 00:10:48.720
Let's do the same thing
for our oxygen.

00:10:48.720 --> 00:10:51.450
We have some oxygen here.

00:10:51.450 --> 00:10:56.060
On the left-hand side, it has
a neutral oxidation state.

00:10:56.060 --> 00:11:02.580
Then we end up with 2 oxygens
on the right-hand side.

00:11:02.580 --> 00:11:06.570
I'll write it like this, 2O,
each with the minus 2

00:11:06.570 --> 00:11:07.290
oxidation states.

00:11:07.290 --> 00:11:11.500
So each of these oxygens must
have gotten 2 electrons.

00:11:11.500 --> 00:11:16.890
So it got 2 electrons each,
or it gained 4 electrons.

00:11:16.890 --> 00:11:18.900
So what was oxidized?

00:11:18.900 --> 00:11:23.600
Oxidized means that electrons
were taken away from you.

00:11:23.600 --> 00:11:30.700
The hydrogen was oxidized,
oxidized by oxygen.

00:11:30.700 --> 00:11:33.010
What was reduced?

00:11:33.010 --> 00:11:40.820
The oxygen was reduced
by the hydrogen.

00:11:40.820 --> 00:11:43.540
If you actually add these two
reactions up, if you make this

00:11:43.540 --> 00:11:46.450
the left-hand side of your
equation and you make this the

00:11:46.450 --> 00:11:50.080
right-hand side of your
equation, you can say, OK,

00:11:50.080 --> 00:11:51.960
let's remove the electrons
from both sides.

00:11:51.960 --> 00:11:54.950
Then you'll end up with your
original reaction.

00:11:54.950 --> 00:11:56.650
Just to make sure our
terminology is right, what's

00:11:56.650 --> 00:11:57.740
our oxidizing agent?

00:11:57.740 --> 00:11:58.960
It's the thing doing
the oxidizing.

00:11:58.960 --> 00:11:59.980
It's the oxygen.

00:11:59.980 --> 00:12:01.270
What's our reducing agent?

00:12:01.270 --> 00:12:02.860
It's the hydrogen.

00:12:02.860 --> 00:12:04.990
Let's do one more.

00:12:04.990 --> 00:12:09.530
So here I have iron plus
some hydrochloric acid.

00:12:09.530 --> 00:12:11.660
Let's say this is in an
aqueous solution.

00:12:11.660 --> 00:12:14.510
You end up with iron (II)
chloride plus some hydrogen.

00:12:14.510 --> 00:12:16.070
So let's do some oxidation
numbers.

00:12:16.070 --> 00:12:17.870
I'll do it fast this time.

00:12:17.870 --> 00:12:19.250
Iron is just by itself.

00:12:19.250 --> 00:12:21.370
It's got a 0 oxidation state.

00:12:21.370 --> 00:12:24.860
Hydrogen with chloride,
chloride's a halogen.

00:12:24.860 --> 00:12:27.130
These guys love to
take electrons.

00:12:27.130 --> 00:12:28.590
They love to take 1 electron.

00:12:28.590 --> 00:12:32.020
They typically have a minus
1 oxidation state.

00:12:32.020 --> 00:12:35.400
So the chlorine is going
to have minus 1.

00:12:35.400 --> 00:12:38.890
The hydrogen is going
to be plus 1.

00:12:38.890 --> 00:12:40.720
You add them together, you get
to a neutral compound.

00:12:40.720 --> 00:12:41.890
Fair enough.

00:12:41.890 --> 00:12:43.890
Now you go on this side.

00:12:43.890 --> 00:12:46.480
What is chlorine's
oxidation state?

00:12:46.480 --> 00:12:48.780
Well, once again, it always
likes to take 1 electron.

00:12:48.780 --> 00:12:50.520
So this is minus 1.

00:12:50.520 --> 00:12:52.480
But I have 2 chlorines here.

00:12:52.480 --> 00:12:54.990
This is a neutral compound.

00:12:54.990 --> 00:12:57.720
So the iron oxidation state
must be plus 2.

00:13:00.570 --> 00:13:01.520
What about the hydrogen?

00:13:01.520 --> 00:13:03.790
Now it's just in its
elemental form so

00:13:03.790 --> 00:13:04.860
it's going to be neutral.

00:13:04.860 --> 00:13:07.480
So it has a 0 oxidation state.

00:13:07.480 --> 00:13:09.580
So what was oxidized?

00:13:09.580 --> 00:13:16.450
Our iron went from neutral to
having 2 electrons taken away

00:13:16.450 --> 00:13:18.960
from it, which may give
it a positive charge.

00:13:18.960 --> 00:13:22.360
So plus 2 electrons
got taken away.

00:13:22.360 --> 00:13:23.610
So this was oxidized.

00:13:29.660 --> 00:13:31.890
What about the hydrogen?

00:13:31.890 --> 00:13:38.410
The hydrogen went from 2
hydrogens with a plus 1 state,

00:13:38.410 --> 00:13:41.770
and essentially, they
went to 2 hydrogen

00:13:41.770 --> 00:13:42.720
with a neutral state.

00:13:42.720 --> 00:13:45.700
So 2 electrons must have been
added to the hydrogens.

00:13:48.220 --> 00:13:50.200
Their charge was reduced.

00:13:50.200 --> 00:13:52.790
So they were reduced.

00:13:52.790 --> 00:13:53.780
What were they reduced by?

00:13:53.780 --> 00:13:55.580
They were reduced by the iron.

00:13:55.580 --> 00:13:57.890
What was the iron oxidized by?

00:13:57.890 --> 00:14:00.690
It was oxidized by
the hydrogen.

00:14:00.690 --> 00:14:02.190
What about the chlorine?

00:14:02.190 --> 00:14:05.300
The chlorine has a minus 1
oxidation number here.

00:14:05.300 --> 00:14:08.130
It has a minus 1 oxidation
number here.

00:14:08.130 --> 00:14:11.230
It was a neutral relative
to the redox reaction.

00:14:11.230 --> 00:14:12.860
Anyway, I think you
get the point now.

00:14:12.860 --> 00:14:14.290
You can do this with a
bunch of reactions.

00:14:14.290 --> 00:14:16.100
But this will give you a little
bit more insight of

00:14:16.100 --> 00:14:17.640
actually what's going
on, and who's

00:14:17.640 --> 00:14:19.120
gaining or losing electrons.

00:14:19.120 --> 00:14:21.500
In the future, it will also help
us think about a lot of

00:14:21.500 --> 00:14:23.220
the structures of molecules.

00:14:23.220 --> 00:14:25.310
Anyway, see you in
the next video.