Hi. It's Mr. Andersen and this is chemistry essentials video 15, which is
on solutions. We generally think of solutions as being liquids, like this beverage right
here. But remember solutions could also be made of gases, like air. And then we could
also have solids that are solutions. So steel is an example of that. We have carbon atoms
inside these iron atoms. And so a solution remember is going to be made of two things.
Solvent and solute. Solutes are going to be dissolved within the solvent. And generally
we're going to have more of the solvent then the solute. They should be homogenous in nature.
That means they're going to be smooth throughout the whole. We can't see different parts or
different concentrations in various areas. This is based on scale. Obviously if we look
at the molecular level, nothing is going to be smooth. And so what we usually use is the
human eye. If it looks homogenous to the human eye we're going to call it a solution. That's
one of the indicators. It could be made of liquids, solids and gases. And if we have
a liquid solution we could have solids and gases dissolved within it. And so generally
we're talking about liquids when we're talking about solutions. So what are some properties?
Does it scatter light? We'd have to put a big no there. If it scatters light it's not
going to be a solution. How do we separate the solute? How do we get it out of this solution?
Could we run it through a filter? No. We can't filter it. It's going to run right through
a filter. And so we have to have another way to get those solutes out. One way would be
through a process called chromatography. And what we're looking at is the different intermolecular
forces between the solutes. And we're using that to separate them. And then we could also
use distillation. That also is looking at intermolecular forces. But we're looking at
differences in vapor pressure to separate them. And so those are two ways that we can
separate the solutes from the solvent. When they form, that formation of a solution could
either be exothermic, so it's releasing heat. Or endothermic, where it's consuming heat.
And that's all based on intermolecular forces as well. And then finally the composition
of a solution. We're going to measure that in molarity, which is going to be the moles
of the solute in the liters of the solution. And in chemistry you should be able to prepare
a basic molar solution. And so remember solutions could be solids, liquids, gases. It has to
hit these three things. It has to be homogenous to the naked eye. It can't scatter light.
And then finally it can not be filtered. And if it hits all of those, it's probably going
to be a solution. We can't filter it remember so how are we going to separate the different
parts of it? Well one of these two processes. Either chromatography or distillation. Both
of them use intermolecular forces. So the forces between the solutes and the forces
between the solute and the solvent itself. So basic chromatography is just using these
interactions. But if we were to heat them up, eventually some of them are going to move
from a liquid into a gas phase. And so that's going to increase the vapor pressure. And
so distillation is going to use differences in this vapor pressure to separate. So for
example this might be alcohol. It has a high vapor pressure. That means it easily is going
to evaporate so we can use that to separate it. So chromatography comes in two different
types. We could either have paper chromatography or column chromatography. In paper chromatography,
what we do is we take our solution. And so a great example we use in biology class is
we'll mash up leaves. We filter the material inside the leaf and then we want to separate
it into the different pigments that are found within the leaf. And so what we'll do is put
that in some kind of a solution. We'll generally dissolve it in some kind of an alcohol. And
then we just have paper. And we'll put the paper inside that solution. And what happens
over time is it's going to migrate up. We're going to have a front that migrates up. And
eventually what we can do is separate that all into its different solutes. Some of these
would be like chlorophyll. And so how does that work? Well, it's based on intermolecular
connections. And so it's based on how well these solutes adhere to the solvent that they're
dissolved in. Because if they really love the solvent they're going to be pulled all
the way to the top. And also how much did they adhere to the paper. And so it's the
sum of all of these connections that allow us to separate them apart. Column chromatography
is going to work in a little bit different way. What we'll use is a big column. So it's
going to be a big glass column. And it's going to have an exit point at the bottom. We're
going to put some absorbent inside there. Usually that's going to be like a silica gel.
And then we'll put some aluminum oxide inside it. So we have the absorbent in there. And
then we're simply going to dump our solution up at the top. And timing is important when
we're doing column chromatography. What's going to happen in here is that we have two
different solutes dissolved in that one solution. So as we let it run, they're going to move
down the column at different rates. Why is that? Well let's say A is not adhering to
the absorbent as much as the red is. The blue is not going to adhere to the absorbent as
much as the red is. And so it's quickly going to move through there. And so what we can
do is we can collect that first solute. And then we can move it over and we can collect
the second solute. We're still looking at these intermolecular forces. We're just doing
it in a slightly different way. Distillation works in a different way. Distillation, what
we're looking at is differences in vapor pressure. And we've been distilling for a long time.
Humans have. So an example, we could take wine and we could put wine in here. And what's
going to happen is the alcohol is going to evaporate. So it's going to evaporate, turn
into a gas phase. We have condensers up here. And then it's going to turn it into a liquid
phase over here. And so since they're, excuse me, since they're going to have different
vapor pressures, ones that are more volatile, ones that have a higher vapor pressure that
are going to evaporate more quickly, are going to separate off. Where do we use this distillation
process, aside from making brandy out of wine? We'd use it in oil refining for example, to
get the different parts out of crude oil. Ionic compounds are important in solutions
as well. And so in this simulation what I'm going to do is I'm going to take some salt
and add it to water. And so as we add salt to water, first of all water by itself doesn't
conduct electricity. And so what we'll do is shake a little bit of salt in there. And
then we could use a conductivity measure to figure out, okay, now we're transmitting a
little bit of energy. Let's say we add a little bit of salt to it. What's going to happen
to the conductivity? It's going to increase. You can also see in the upper right that we're
increasing the concentration of that salt. But now let's evaporate some of that water.
So as the water evaporates, look at the concentration. It's increasing. And then right at the end
we just have a layer of salt at the bottom. Let's look at the microscopic levels. So sodium
chloride remember is an ionic compound. And so as we add that to water it's going to separate
into both sodium and chloride ions. And so they're each going to dissolve in the water.
As we remove the water again, what happens? The concentration increases. And then bang
we're back to this ionic compound again. What's going on at the molecular level, we'll let's
watch. If we add the sodium chloride to the water, it's going to break apart into its
ions. The sodium which are positive are going to be attracted to the negative ends of the
water. You could say the negative ends of the water are going to be adjacent to the
sodium. And then the positive parts of the water are going to be adjacent to the chloride
ions. And so it's really easy to take something like water, which is a clear dipole, and we
could absorb ions with it. Formation of those solids is going to either take in energy or
release energy. And so what we can look at is the formation of a solid. These are going
to be the enthalpies of that solution. Some are positive. Some are negative. And so if
we were to look at these ones, ammonium nitrate, if we were to add that one to water, it's
going to be an endothermic process. That means it's going to take in energy. And so we could
use that, ammonium nitrate and water to make these instant cold packs. What we're doing
is just combining them together. It's taking in heat from the surroundings and it feels
really, really cold. A lot of these are going to be exothermic. So when we mix them with
water it's going to release energy. And all of this has to do with intermolecular forces.
An example of this could be hydrochloric acid. Hydrochloric acid, when you mix it with water
is going to create a huge amount of heat. If you were to have a huge amount of hydrochloric
acid and just dump a little water in there, you'd have this massive reaction. Huge amount
of heat. And that's why in the chemistry lab we always add acid, small amounts of acid
to the water. Because it's going to generate heat and that water is able to mediate some
of that change. Remember we measure the concentration of a solution using molarity, which is going
to be the moles of solute in liters of total solution. And let's say you're doing a lab
and they say prepare a 0.5 molar sodium chloride solution or salt solution. How would you do
that? Well they're already telling you how many moles you're going to put into the solution.
They're saying 0.5 moles of sodium chloride. So we have to convert that to a mass, something
that we can actually deal with. So we're going to use this conversion to convert that to
grams. Where are we getting this 58.44? We're using the atomic weight of both sodium and
chlorine. We're then going to make that conversion. And that's going to be 29.22 grams. So what
would we do in an Erlenmeyer flask, we could add a certain amount of water. Then we're
going to add our salt to it. We're going to make sure it dissolves. And then we're going
to bring that volume up to 1 liter to make that 0.5 molar sodium chloride solution. So
did you learn the following? To separate solutes we could use chromatography, both paper and
column. And that's going to be based on intermolecular forces. Did you figure out how to use representations
to show the interactions between them? Remember if we look at that molecular level, we were able
to show how water is able to dissolve these ions. We're we able to use representations
to link molarity to particle view? And so we were able to do that and also kind of calculate
a certain molar solution. And then finally, could we design something like a distillation
process where we could separate solutes? Yeah. We just have to look at their different vapor
pressures to pull them apart. Those are solutions and I hope that was helpful.