WEBVTT

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Let's think a little bit
about some of the

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properties of alcohol.

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So the general formula for an
alcohol we saw is some type of

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group or chain of carbons bonded
to an oxygen, bonded to

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a hydrogen.

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And of course, the oxygen
will have two lone

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pairs just like that.

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Let's compare this to water.

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So water just looks like this.

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You have a hydrogen bonded to
an oxygen, bonded to another

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hydrogen with two lone pairs.

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Now in the case of water,
the oxygen is much more

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electronegative than the
hydrogen, so it hogs the

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electrons towards it.

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So you have a partial negative
charge at the oxygen end.

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Then you have partial positive
charges at the hydrogen ends.

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That's what allows oxygen to
kind of-- or sorry-- that's

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what allows water to bond to
itself or to have not a

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ridiculously low
boiling point.

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So let me show this.

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Let me copy and paste this.

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We've seen all this before
in regular chemistry.

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So copy and paste.

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So let me draw some more
water molecules here.

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Let me draw another water
molecule here.

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So you see water because the
oxygen end has a partial

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negative charge and the hydrogen
ends have partial

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positive charges, the oxygen of
one water molecule will be

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attracted to the hydrogen of
another water molecule.

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And we've seen this before.

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This we call hydrogen bonding.

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So that right there is
hydrogen bonding.

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The exact same thing can happen
with alcohols, although

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alcohols really only have
the partial positive

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charge on the hydrogen.

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We don't know exactly what's
going on here.

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We probably have carbons
bonded to the oxygen.

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And with the carbons, they're
reasonably electronegative.

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They're not going to have their
electrons hogged as much

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as a hydrogen would.

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So in the case of an alcohol--
let me draw.

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Instead of having this R for
radical there, let me make it

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a little bit more concrete.

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Let me draw an actual alcohol.

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So an actual alcohol.

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Maybe we have methanol.

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Maybe we have methanol that
would look like that.

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It has a hydrogen
right over here.

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Oxygen is much more
electronegative than the

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hydrogen, so you have a partial
negative charge there.

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And then you have a partial
positive charge there.

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So it too, because of these
hydrogen bonds, it will have a

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reasonable boiling point.

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It won't just turn immediately
into the gaseous state.

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It would actually try to
bond to each other.

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Let me copy and paste that.

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So it can also form the
hydrogen bonds.

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Although they won't to be quite
as strong as what you

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see in water.

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And that's why something like
methanol actually has a lower

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boiling point than water.

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It's easy to make it boil.

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It's easier to make these bonds
break apart because you

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don't have as much of the
hydrogen bonding.

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So this is an example
of hydrogen

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bonding with methanol.

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Now because methanol can have
hydrogen bonding and it has

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this slight polarity to it and
water obviously has hydrogen

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bonding, methanol is actually
miscible in water.

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And all that means is that it's
soluble in water in any

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proportion.

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No matter how much methanol
or how much water

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you have, it is soluble.

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So if I were to draw some
methanol molecules-- actually,

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maybe this is the water
right here.

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So if you draw a methanol
molecule right there, that

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would have a hydrogen bond
right over there.

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If I were to draw another
methanol molecule maybe right

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over here, you would have
another hydrogen bond right

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over there.

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And that's what allows
methanol to

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be soluble in water.

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Now, as this chain grows, or
if you have alcohols with

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longer radical chains, then
they become less and less

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soluble in water.

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But their boiling points
actually do go up.

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And let's think about
why that is.

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So if I have something like--
let me do butanol.

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So butanol's going to
have 4 carbons.

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So it's going to be H3C, H3--
let me just draw it like H3C,

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CH2, Ch2, CH-- let me
do it like this.

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H2C.

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Then that carbon, that last
carbon right there is going to

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be bonded to the oxygen.

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It's going to be bonded
to an oxygen, which

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is bonded to a hydrogen.

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Now, when you have a situation
like this, the oxygen will

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have a partial negative
charge.

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The hydrogen will still have
a partial positive charge.

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Just like we saw up
here with both the

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water and the methanol.

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But now you have this big thing

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here that has no polarity.

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So this part of the alcohol is
not going to be soluble in

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water, and it's going to make it
harder for this part to be

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soluble over here.

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So this right here
is less soluble.

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This is less soluble.

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It'd still be a little
bit soluble.

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So if you have some oxygen here,
you will still have a

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little bit of the hydrogen
bonding.

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You still will have a little
bit of the hydrogen

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bonding going on.

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But this part is kind of-- you
can imagine it's almost-- it

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doesn't want to dissolve
with the water.

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It is non-polar.

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You could actually, for
example, butanol in

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particular, it actually
is soluble in water.

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But not in any proportion.

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So methanol is miscible.

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Let me write this.

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This is a new word.

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I don't think I've ever used
it before in the context of

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the organic chemistry videos.

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So methanol is-- let me write
that in a brighter color since

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it's a new word.

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Methanol is miscible, which
just means soluble in any

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proportion.

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So I don't care what percent
is methanol,

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what percent is water.

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The methanol will dissolve
into the water in any

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proportion.

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If you look at butanol, it
is soluble but not in any

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proportion.

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If you had a ton of butanol,
some of it would not dissolve

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in the water.

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So this is soluble.

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So the butanol right here
is soluble, but

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not miscible in water.

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If you have too much of the
butanol, all of a sudden, some

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of it will not actually be
able to be dissolved.

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If this was a decanol or
something with a really long

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carbon chain, then of
course, it's going

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to be very non soluble.

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You might be able to get a
couple of molecules in the

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water, but most of them
will not dissolve.

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Now the other reason-- I
hinted-- look, you know the

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reason why the alcohols have a
reasonable-- not too low of a

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boiling point is that
they're able to do

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this hydrogen bonding.

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But you would say well, look.

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You know, these longer carbon
chains, these are going to

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have less of the hydrogen
bonding going on.

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Maybe these would have
lower boiling points.

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But actually, the longer the
chain gets, these actually

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have higher boiling points.

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And that's because
these chains can

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interact with each other.

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So the longer the chain, so
longer R or the longer R

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chain, I guess, I could say,
we could say the higher the

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boiling point in an alcohol.

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Higher boiling point.

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It's harder.

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You have to put more heat into
the system or the temperature

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has to be higher for the
things to break apart.

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And that's because this is one
decanol molecule here, another

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decanol molecule might
look like this.

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Maybe it might look like this.

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You have an oxygen and a
hydrogen and then you have

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your carbons.

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So you have your CH,
your CH2, CH2, H3C.

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So you have this other
butanol here.

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And what the interaction between
these two chains are--

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these are the van
der Waal forces.

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So even though they have
no [INAUDIBLE],

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so these guys are going to have
some polar interactions.

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They're going to have the
hydrogen bonding.

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We've seen that multiple
times already.

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But these long chains, they're
going to have the London

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dispersion forces, which are a
subset of van der Waal forces.

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Where even though they're
neutral, every now and then,

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one of these might become
slightly negative on one side.

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So you might have
a very temporary

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partial negative charge.

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And that's just because
of the randomness of

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how electrons move.

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On this side of the molecule,
all of a sudden, you might

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have more electrons
over there.

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So you have a partial
negative charge.

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And because of that, you're
going to have-- the electrons

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over here, they're not going
to want to be there.

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So you're going to want to have
a partial positive charge

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there and you're going to have
a very temporary interaction.

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That's a very weak force.

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Much weaker than
hydrogen bonds.

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But as these chains get longer
and longer, as they possibly

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even get intertwined with each
other and get close to each

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other, these London dispersion
forces or van der Waal forces

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are going to keep propagating.

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So all of a sudden, maybe these
guys are going to be

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attracted to each other and
that's going to disappear.

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Than these guys are going be
attracted to each other and

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then that's going
to disappear.

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And then these are going to be
attracted to each other and

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then that's going
to disappear.

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And so you can imagine, the
longer the chain, the more of

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these type of interactions
you're going to have. The more

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attracted they're going
to be to each other.

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And it's going to be harder to
break them apart, higher

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boiling point.

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So those are just kind of the
two big takeaways on the

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properties of alcohols.

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Especially smaller chained
alcohols are soluble in water.

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The very small ones are
completely miscible.

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And the longer the chain you
have, the harder it is to

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dissolve in water.

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But also, the higher
the boiling point.

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The harder it is to break them
apart because you have these

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London dispersion forces.

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