In this video, we’re gonna take a look at solutions, which are a type of mixture used
a lot in chemistry. We’ll look at some different kinds of solutions, we’ll see how they’re made,
and we’ll look at the general characteristics that all solutions have. So to start off with,
what’s a solution? Well, a solution is a homogeneous mixture of two or more substances.
Homogeneous is an important word here: And it means that the parts are evenly distributed,
there is a uniform, even distribution throughout. Let’s take a look at this.
If we dissolve a little drink mix in water and stir it around, the parts mix together evenly,
and we get a homogeneous mixture or a solution. Take a look at this uniform, even distribution.
You can look at it here or here or here and all areas are the same as anywhere else in the
solution: everything is evenly distributed. The parts mix evenly. OK? Now to better understand
this, let’s do a comparison with something that isn’t a solution. So we’ve got our solution or
our homogeneous mixture right here, the parts mix evenly, it’s uniform. Over here we have a
heterogeneous mixture, where the parts do not mix evenly. We have oil here and water here:
you can see the different parts distinctly. This is not uniform and even. This is not a solution.
Now, if you had a heterogeneous mixture like this, you can stir it up or shake it up.
And temporarily form a suspension, which looks like this, where everything is kind of all mixed
up in there, but everything will eventually settle and separate out and end up like this again. The
parts eventually separate out when you have a heterogeneous mixture. But on the other hand,
the parts of a solution never separate out. They’re just gonna stay mixed basically forever.
So that’s solutions versus not solutions. Now let’s start getting into the details of solutions.
First off, the parts. Every solution has two parts. Let’s say we’re dissolving sugar
in water. The substance we’re dissolving, we call that the solute (here that’s the sugar). And the
substance the solute is dissolving in, we call that the solvent (that would be the water here).
So in other words, the solute dissolves in the solvent. You can see that here. Now, a solution
can have more than one solute, but it can have only one solvent. For instance, we could also
dissolve some salt into this solution. So salt would also be a solute, along with sugar, and we’d
have two solutes, but the solvent is still just water. So solutes dissolve in solvent.
Now to add a little bit more, the solvent is usually the substance that's present
in the greatest amount. And the solutes are what we have less of. But there are exceptions.
Anyway, let's talk a little bit more about solutes.
So, here we have
have the solutes that we’ve talked about so far: drink mix, salt, and sugar, and we saw those
dissolved in liquid (water) to make a solution. They’re all solids. But solutes don’t have to be
solids. We can also make a solution by dissolving a liquid into another liquid. And we can also make
solutions by dissolving gas into liquid. So now let’s look at examples of some of these
other solutions. Here’s an example where we make a solution by mixing two liquids.
The “rubbing alcohol” in your medicine cabinet is a solution of isopropyl alcohol mixed with water.
Those are two different liquids: you can stir them together, and they spread out through each other.
Dissolving evenly, in uniform. And these liquids don’t separate out over time. So this rubbing
alcohol that we end up, this is a solution. Now, if you were looking at the labels here,
you might wonder why we said that water is the solvent and alcohol is the solute, becuase it
looks like we kinda have the same amount of both. Well, just so you know, we sometimes
say that water is the solvent, even when we don't have more of it. Even when it's not present in a
greater amount. You don't have to worry about this too much, just keep an eye out for it. Anyway,
here’s another good example of a solution made by mixing liquids. This is antifreeze, which is used
in cars to cool the engine. Antifreeze is made by taking propylene glycol, which is a thick,
viscous clear liquid, and mixing it with water. Sometimes, there's a little fluorescent dye
in there as well. That’s another solute. But as you’d expect, the liquid solution is homogeneous:
it looks uniform in composition. And it doesn’t separate or settle out over time. Now you can
also make a solution by dissolving a gas into a liquid. If you dissolve carbon dioxide gas
in water, you make seltzer. Here, the gas is the solute and the liquid is the solvent.
And if you add some flavoring and sugar (those are also solutes, but they’re not gases), you have
soda or pop. In these bottles, as you can see, the mixture is nice and uniform. Another example
of a gas dissolved in liquid is ammonia cleaning solution. This is a solution of ammonia gas solute
that’s dissolved in water. Now if you think about all the solutions that we’ve looked at so far,
you might notice that they’re all in the liquid state. They’re all liquids. We call these “liquid
solutions.” If your solvent is a liquid, your final solution will also be in the liquid state,
no matter what the solute is. So the solute can be solid, gas, liquid, if the solvent is liquid
the final solution will be liquid. And going a step further here, we saw that
all of our solutions had water as the solvent. And that’s not really unusual,
because water is the most common solvent in chemistry. Yeah, sometimes you’ll see others,
but water is the most common. We have a special name for these solutions: aqueous solutions
are solutions where water is the solvent. You might know that “aqua” means water: that’s where
aqueous comes from. Aqueous solutions are super common. They’re all over your house,
most beverages are aqueous solutions, and most of the solutions that we use in the chemistry lab
are aqueous solutions as well. They’re really everywhere.
So just to review here, we’ve talked about liquid solutions, and aqueous solutions have been the
star. But not all solutions are in the liquid state. There are also non-liquid solutions.
These aren’t usually what we think of when thinking of “solutions” or dissolving,
but they’re also important. So to finish up this video, we’ll talk about solutions of gases,
and solutions of solids, which are often metals.So we’ll start with some solutions of gases.
Whenever we mix together gases, they usually blend together evenly. So we usually form a
solution or homogeneous mixture. The most common solution of gases is the one you’re breathing
right now. Air is a solution or homogeneous mixture. It's a mixture of nitrogen, oxygen,
and a bunch of other gasses. Now, how can we tell that air is a solution? If you took a sample
of the air at one place (that’s right here), then compared it with a sample taken close by
(over here), your two samples would have a uniform composition. They’d contain the same proportions
of gases, evenly distributed throughout each other. And also, the gases in air don’t
separate out over time. So, we need oxygen to breathe, but you don’t ever have to worry that
all the oxygen one day is gonna separate out and float up into the sky. So for air,
the composition is even and the gases don’t separate out over time: air is a solution.
And now finally, there are also solutions that are made from mixing solids together. An alloy is a
homogeneous mixture, or a solution of metals. Now how would you dissolve and mix solids together?
It’s actually pretty cool. You make an alloy by taking two different metals (or sometimes more),
and then melting them and mixing them together while they’re still molten.
After they cool and solidify, the two metals are evenly spread throughout each other.
But, to your naked eye, it looks like one single metal, nice and uniform: the hallmark
of a solution. People make alloys because they have better properties than individual metals
alone. One of the first alloys people learned to make was bronze, a mixture of copper and tin.
Steel is an alloy of a metal and a nonmetal: iron and carbon. And most steel also contains
other metals besides iron. The important thing to remember here is these alloys are solutions
or homogeneous mixtures: the parts are evenly distributed, and the alloys look uniform to
the naked eye. So…let’s review what we’ve talked about here. A solution is a homogeneous mixture
made by dissolving a solute into a solvent. Because a solution is a homogeneous mixture,
these substances are evenly distributed, and the solutions have a uniform appearance. A
liquid solution is in the liquid form, and is made by dissolving a solid, a gas, or a liquid
into a liquid solvent. Most liquid solutions that we talk about in chemistry are aqueous solutions,
which means water is the solvent. But…keep in mind that solutions can also be mixtures of gases,
or they can be mixtures of solids, like metal alloys. So that, is an introduction to solutions.