In this video, I want to
cover several topics
that are all related.
And on some level, they're
really simple, but on a whole
other level, they tend to
confuse people a lot.
So hopefully we can
make some headway.
So a good place to start-- let's
just imagine that I have
some type of container here.
Let's say that's my container
and inside of that container,
I have a bunch of
water molecules.
It's just got a bunch
of water molecules.
They're all rubbing against
each other.
It's in its liquid form,
this is liquid water.
and inside of the water
molecules, I
have some sugar molecules.
Maybe I'll do sugar in
this pink color.
So I have a bunch of sugar
molecules right here.
I have many, many more water
molecules though.
I want to make that clear.
I have many, many more water molecules in this container that we are dealing with.
Now in this type of situation,
we call, we call the thing that there's
more of, the solvent.
So in this case, there's more
water molecules and you can
literally just view more as
the number of molecules.
I'm not going to go into a whole
discussion of moles and
all of that because you may or
may not have been exposed to
that yet, but just imagine
whatever there's more of,
that's what we're going
to call the solvent.
So in this case, water
is the solvent.
And whatever there is less of, so the more water is the solvent and in that case, that is the
in this case, that is the
sugar-- that is considered
the solute.
this is the solute, so the sugar.
It doesn't have to be sugar.
It could be any molecule that
there's less of, in the water,
in this case,sugar.
is the solute
And we say that the sugar has
been dissolved into the water.
sugar,has been dissolved, dissolved into, into the water
And this whole thing right here,
the combination of the
water and the sugar molecules,
we call a solution.
We call this whole
thing a solution.
And a solution has a solvent
and the solute.
The solvent is water.
That's the thing doing the
dissolving and the thing that
is dissolved is the sugar.
That's the solute.
Now all of this may or may not
be review for you, but I'm
doing it for a reason-- because
I want to talk about, I want to talk about
the idea of diffusion, diffusion
And the,the idea is actually
pretty straightforward.
If I have, let's say,let's same
the same container.
Let me do it in a slightly
different container here, just
to talk about diffusion.
We'll go back to water
and sugar--
especially back to water.
Let's say we have a container
here and let's say it just has
a bunch of-- let's say it just
has some air particles in it.
It could be anything-- oxygen
or carbon dioxide.
So let me just draw a couple
of air molecules here.
So let's say that that is a
gaseous-- just for the sake of
argument-- gaseous oxygen.
So each of this is an O2--
each of those, right?
And let's say that this is the
current configuration, that
all of this is a vacuum here
and that there's some
temperatures.
So these water molecules,
they have some
type, some type of kinetic energy.
They're moving in some type of
random directions right there.
So my question is, what is going
to happen, what is goign to happen in this type
of container?
Well, any of these guys are
going to be randomly bumping
into each other.
They're more likely to bump into
things in this down-left
direction than they are in
the up-right direction.
So if this guy was happening
to go in this down-left
direction, he's going to bump
into something and then
ricochet into the up-right
direction.
But in the up-right
direction, there's
nothing to bounce into.
So in general, everything is
moving in random directions,
but you're more likely
to be able to move in
the rightward direction.
When you go to the left, you're
more likely to bump
into each other, into something.
So it's almost common sense.
Over time, if you just let this
system come to some type
of equilibrium-- I'm not
going to go into detail
on what that means.
You can watch the thermodynamics
videos if you'd
like to see that.
You'll eventually see the
container will look
something like this.
I can't guarantee it.
There's some probability it
would actually stay like this,
but very likely that those five
particles are going to
get relatively spread out.
This is diffusion and so it's
really just the spreading of
particles or molecules from
high concentration to low
concentration areas, right?
In this case, the molecules are
going to spread in that
direction from a high
concentration to a low
concentration area.
Now you're saying, Sal,
what is concentration?
And there's many ways to measure
concentration and you
can go into molarity and
molality and all of that.
But the very simple idea is, how
much of that particle do
you have per unit space?
So here, you have a lot of those
particles per unit space
and here you have very
few of those
particles per unit space.
So this is a high concentration
and that's a low
concentration.
So you could imagine other
experiments like this.
You could imagine a solution
like-- let's do
something like this.
let me make
Let's say I have
two containers.
let's see two container.
Let's go back to the
solution situation.
This was a gas, but I started
off with that example so let's
stay with that example.
So let's say that I have a door
right there that's larger
than either the water or
the sugar molecules.
On either side, I have a bunch
of water molecules.
I have a bunch of water molecules on either side, just like that on either side
So I have a lot of
water molecules.
So if I just had water molecules
here-- they're all
bouncing around in random
directions-- and so the odds
of a water molecule going this
way, equivalent to what odds of a
water molecule going that way,
assuming that both sides have
the same level of water
molecule, otherwise the
pressures would be different.
But let's say, you know that the top
of this is the same
as the top of this.
So there's no more pressure
going in one
direction or another.
So you know if,it for whatever reason, a
bunch of more water molecules
were going in the rightward
direction, then all of a
sudden this would fill up with
more water and we know that
that isn't likely to occur.
So this is,you know, this is just a solution, with or , this is just two containers of waters
of water.
Now let's put some
solute in it.
Let's dissolve some solute in it
and let's say we do all the
dissolving on the
left-hand side.
So we put some sugar molecules
on the left-hand side.
And these are small enough to
fit through this little pipe.
right, that's just one assumption
that I'm making.
So what's going to happen?
All of these things have some
type of kinetic energy.
They're all bouncing , they're all bouncing around.
Well, over time,you know, the water's
going back and forth.
This water molecule
might go that way.
That water molecule might go
that way, but they net out each
other out, but over time one of
these big sugar molecules
will be going in just the
right direction to go
through--maybe you know maybe this guy's,
instead of going that
direction, he starts off going
in that direction.
He goes just through this,throught this,uhm throught this tunnel
connecting this two
containers and he'll end
up there, right?
And this guy will still
be bouncing around.
There's some probability he goes
back, but there's still
more particles,more sugar particles
here than there.
So there's still more
probability that one of, so these
guys will go to that side
than one of these guys
will go to that side, that one of these guys will go to that side,
So you can imagine if you're
doing this with gazillions of
particles-- I'm only doing it
with four-- over time, the
particles will have spread out
so that their concentrations
are roughly equal.
So that maybe you'll have
two here over time.
But if, but when you're only dealing
with three or four or five
particles, there's some
probability it doesn't happen,
but when you're doing it with a
gazillion and they're super
small, it's a very, very,
very high likelihood.
But anyway, this whole process--
we went from a
container of high concentration
to a container
of low concentration and the
particles would have spread
from the low concentration
container to the high
concentration container.
So they diffused.
This is diffusion.
This is diffusion
And just so that we learn some
other words that tend to be
used with the idea of
diffusion-- when we started
off, this had a higher
concentration.
The left-hand side container
had higher concentration.
Higher concentration, higher concentration
It's all relative, right?
It's higher than this guy,higher concentration
And this right here had
a lower concentration.
Lower concentrarion
And there are words
for these things.
This solution with a high
concentration is called a
hypertonic solution.
Let me write that in yellow.
Hyoer, Hypertonic solution
Hyper, in general, meaning
having a lot of something,
having too much of something.
And this lower concentration
is hypo, hypotonic
Hypotonic solution,lower concentration
You might have heard maybe one
of your relatives, if they
haven't had a meal in awhile
say, I'm hypoglycemic.
That means that they have
not-- they're feeling
lightheaded.
There's not enough sugar in
their bloodstream and they
want to pass out so
they want a meal.
If you just had a candy bar,
maybe you're hyperglycemic--
or maybe you're just
hyper in general.
But, so, you know, so these are just good
prefixes to know, but
hypertonic-- you have
a lot of the solute.
You have a high concentration.
And then in hypotonic, not too
much of the solute so you have
a low concentration.
These are good words to know.
So in general, diffusion-- if
there's no barriers to the
diffusion like we had here, you
will have the solute go
from a high concentration or
hypertonic solution if they
can travel to a hypotonic
solution, to a hypo, where the
concentration is lower.
Now let's do an interesting
experiment here.
We've talked about diffusion and
so far we've been talking
about the diffusion of
the solute, right?
And in general-- and this is not
always the case-- if you
want to be as general as
possible, the solute is
whatever you have less of,
the solvent is whatever
you have more of.
And the most common solvent
tends to be water, but it
doesn't have to be water.
It could be some type
of alcohol.
It could be a...you, know it could be mercury.
It could be a whole set of
molecules, but water in most
biological or chemical systems
tends to be the
most typical solvent.
It's what other things
are dissolved into.
But what happens if we have a
tunnel where the solute is too
big to travel, but water is
small enough to travel?
Let's think about
that situation, let's think about the situation
In order to think about it,
I'm going to do something
interesting.
Let's say we have a
container here,let's say
Actually, I won't even
draw a container.
Let's just say we have an
outside environment that has a
bunch of water.
This is the outside environment
and then you have
some type of membrane.
you have some type of membrane here, that's a membrane
Water can go in and out
of this membrane.
So it's semi-permeable.
Well, it's permeable to water,
but the solute cannot go
through the membrane.
So let's say that the
solute is sugar.
So we have water on
the outside and
also inside the membrane.
So these are little small
water molecules.
This is a membrane right here.
And let's say that we have some
sugar molecules again--
I'm just picking on sugar.
It could have been anything.
So we have some sugar molecules
here that are just a
little bit bigger-- or they
could be a lot bigger.
Actually, they're a lot bigger
than water molecules.
You have a bunch of-- and I only
draw four, but you have a
gazillion of them, right?
You have that much more
water molecules.
I'm just trying to show you have
more water molecules than
sugar molecules.
And this membrane is
semi-permeable.
Permeable means it allows
things to pass.
Semi-permeables means it's
not completely permeable.
So semi-permeable-- in this
context, I'm saying I allow
water to pass through
the membrane.
So water can pass,
but sugar cannot.
Sugar is too large.
So if we were to zoom in on the
actual membrane itself--
maybe the membrane
looks like this.
I'm going to zoom in
on this membrane.
So it has little holes in the
membrane, just like that.
And maybe the water molecules
are about that size.
So they can go through
those holes.
So the water molecules can go
back and forth through the
holes, but the sugar molecules
are about that big.
So they cannot go through
that hole.
They're too big for this opening
right here to go back
and forth between them.
Now what do you think is going
to happen in this situation?
So first of all, let's
use our terminology.
Remember, sugar is our solute.
Water is our solvent.
Semi-permeable membrane.
Which side of the membrane
has a higher or lower
concentration of solute?
Well, the inside does.
The inside is hypertonic.
The outside has a lower
concentration so it's hypotonic.
Now, if these openings were big
enough, based on what we
just talked about-- these guys
are bouncing around, water is
travelling in either direction,
and equal
probability or-- actually
I'm going to talk
about that in a second.
If everything was wide open, it
would be equal probability,
but if it was wide open, these
guys eventually would bounce
their ways over to this side and
you'd probably end up with
equal concentrations
eventually.
And so you would have your
traditional diffusion, where
high concentration
of solute to low
concentrations of solute.
But in this case, these
guys-- they can't
fit through the hole.
Only water can go
back and forth.
If these guys were not here,
water would have an equal
likelihood of going in this
direction as they would be
going in that direction, a
completely equal likelihood.
But because these guys are on
the right-hand side of-- or in
this case, on the inside
of our membrane.
This is our inside of our
membrane zoomed up-- it's less
likely because these guys
might be in the approach
position of the holes-- that's
slightly less likely for water
to be in the approach position
for the holes so it's actually
more probable that water could
enter than water exit.
And I want to make
that very clear.
If these sugar molecules were
not here, obviously it's
equally likely for water to
go in either direction.
Now that these sugar molecules
are there, these sugar
molecules might be on
the right-hand side.
They might be blocking-- I guess
the best way to think
about it is blocking the
approach to the hole.
They'll never be able to go
through the hole themselves
and might not even be blocking
the hole, but they're going in
some random direction.
So if a water molecule was
approaching-- it's all
probabilistic and we're dealing
with gazillions of
molecules-- it's that much more
likely to be blocked to
get outside.
But the water molecules from the
outside-- there's nothing
blocking them to get in so
you're going to have a flow of
water inside.
So in this situation, with a
semi-permeable membrane,
you're going to have water.
You're going to have a net
inward flow of water.
And so this is kind
of interesting.
We have the solvent flowing from
a hypotonic situation to
a hypertonic solution,
but it's only
hypotonic in the solute.
But water-- if you flip it the
other way-- if you've used
sugar as the solvent, then you
could say, we're going from a
high concentration of water to
a low concentration of water.
I don't want to confuse
you too much.
This is what tends to confuse
people, but just think about
what's going to happen.
No matter in what situation,
the solution is going to do
what it can to try to
equilibriate the
concentration.
To make the concentrations
on both
sides as close as possible.
And it's not just some magic.
It's not like the
solution knows.
It's all based on probabilities
and these things
bumping around, but in this
situation, water is more
likely to flow into
the container.
So it's actually going to go
from the hypotonic side when
we talk about low concentration
of solute to the
side that has high
concentrations of solute, of
sugar-- and actually, if this
thing is stretchable, more
water will keep flowing
in and this membrane
will stretch out.
I won't go to too much detail
here, but this idea of water--
of the solvent-- if in this
case, water is the solvent--
of water as a solvent
diffusing through a
semi-permeable membrane,
this is called osmosis.
You've probably heard learning
by osmosis-- if you put a book
against your head, maybe it'll
just seep into your brain.
Same idea.
That's where the word
comes from.
This idea of water seeping
through membranes to try to
make concentrations
more equal.
So if you say, well, I have high
concentration here, low
concentration here.
If there was no membrane here,
these big molecules would
exit, but because there's this
semi-permeable membrane here,
they can't.
So the system just
probabilistically-- no magic
here-- more water will enter
to try to equilibriate
concentration.
Eventually-- if maybe there's a
few molecules out here-- not
as high concentration here--
eventually if everything was
allowed to happen fully, you'll
get to the point where
you have just as many--
you have just as high
concentration on this side as
you have on the right-hand
side because this right-hand
side is going to fill with
water and also probably become
a larger volume.
And then, once again, the
probabilities of a water
molecule going to the right and
to the left will be the
same and you'll get to some
type of equilibrium.
But I want to make it very
clear-- diffusion is the idea
of any particle going from
higher concentration and
spreading into a region that has
a lower concentration and
just spreading out.
Osmosis is the diffusion
of water.
And usually you're talking about
the diffusion of water
as a solvent and usually it's
in the context of a
semi-permeable membrane, where
the actual solute cannot
travel through the membrane.
Anyway, hopefully you've
found that useful and
not completely confusing.