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.
Now in this type of situation, 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-- in this case, that is the
sugar-- that is considered the solute.
It doesn't have to be sugar.
It can be any molecule that there's less of, in the water,
in this case.
And we say that the sugar has been dissolved 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 the 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
the idea of a diffusion.
And the idea is actually pretty straightforward.
If I have, let's say, 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 of kinetic energy.
They're moving in some type of random directions right there.
So my question is, what is going 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 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's say I have two containers.
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.
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 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 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 if for whatever reason, a bunch 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 just two containers 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.
That's 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 around.
Well, over time, the water's going back and forth.
This water molecule might go that way.
That water molecule might go that way, but they net each
other out, but over time one of these big sugar molecules
will be going in just the right direction to go
through-- maybe this guy's, instead of going that
direction, he starts off going in that direction.
He goes just through this tunnel connecting the 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 sugar particles here than there.
So there's still more probability that one of these
guys will go to that side than 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 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.
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.
It's all relative, right?
It's higher than this guy.
And this right here had a lower concentration.
And there are words for these things.
This solution with a high concentration is called a
hypertonic solution.
Let me write that in yellow.
Hyper, in general, meaning having a lot of something,
having too much of something.
And this lower concentration is hypotonic.
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.
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 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.
In order to think about it, I'm going to do something
interesting.
Let's say we have a container here.
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.
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.