Aqueous solutions | Solutions, acids, and bases | High school chemistry | Khan Academy

What we have here are drawings of five different glass beakers, each holding different liquids or combinations of liquids and other things.

Now, the first one here, I would just call that liquid water. That's in this beaker. We're going to assume everything here is a liquid.

Now the next one gets a little bit interesting. I have water, but inside of that water, I have stirred in some sand. So we would definitely call this over here a mixture. We have mixed that water, that sand into that water.

Now, you'll sometimes hear the terms homogeneous and nonhomogeneous. Homogeneous really means that the concentration of whatever is mixed in is the same throughout. So maybe if that sand is mixed in really well and the concentration is uniform throughout, someone might call that a homogeneous mixture.

But more likely, that sand is going to settle at the bottom of the container if it's the sand that I'm familiar with, and then the concentration is clearly not the same throughout the water or throughout the volume of this mixture, and then it would be a nonhomogeneous mixture.

Now in this next beaker, I'm not dealing with water anymore, but I'm still dealing with liquids. These are two different types of alcohols. We have mostly ethanol here, and then we have a little bit of propanol. You don't have to know the difference between ethanol and propanol for this video, but you just need to know that those are two different types of alcohols, and they've been mixed together really, really, really well.

So in this one, the concentrations of the two are going to be not the same to each other, but the percent, if you took any amount of this mixture right over here, we're going to find that it's 5% propanol and 95% ethanol. So it's uniform relative concentrations throughout.

So this one I definitely would call a homogeneous mixture. When we're talking about a homogeneous mixture where you can't filter out, say, the propanol here, we would call this a solution.

When you're dealing with a solution, generally speaking, you have the thing that you have a smaller amount of being dissolved in the thing that you have a larger amount of. The thing that we are dissolving, that we have a generally speaking smaller amount of, is called the solute, and the thing that we have the larger amount of, in this case the ethanol, we would call that the solvent.

The solute is dissolved inside of that solvent. So this right over here is a solution.

Now next over here, we're back to having water, and now inside that water, we have dissolved sodium chloride, which is table salt. Sodium chloride, when you dissolve it—let me show the sodium—it dissolves into sodium positive ions and chloride negative ions.

Do it in a different color, chloride negative ions. Obviously, they're nowhere near this big, and we're talking about a much larger number than I'm showing right over here. So this is also a solution.

You're going to have the same concentration of the sodiums and the chlorides throughout, assuming that it is mixed in well. So this once again is a solution.

Pause this video. What is the solute here, and what is the solvent? Well, the solvent is what we have more of. So this is a solution where the solvent—I know these arrows are getting a little complicated—the solvent is water, and the solute over here is the sodium chloride or we could think of it as the sodium positive ions and then the chloride negative ions right over there.

This solution in particular, which is salt water, what's interesting about it is it's dissolved what's known as an electrolyte, sodium chloride. This is an electrolyte, and when it's dissolved, then you have these positive ions here which can move around. So this is actually really good at conducting electricity.

Now there's also another word when we talk about a solution where water is the solvent. We call this an aqueous solution. Let me just write that in blue because that feels appropriate: aqueous. Aqueous solution. Sometimes you'll see that abbreviated as AQ, which is going on right over here.

Now last but not least, I have glucose mixed in with water. Now this again is going to be a solution and not just any solution, it is an aqueous solution because the solvent is water.

Now the solute in this case right over here, glucose—it's a molecule that won't disassociate into negative and positive ions—but it does have parts of the molecule that are polar, and that's what makes it good for dissolving in water.

So it will dissolve well in water, but this one is nowhere near as good at the salt water at conducting electricity, but it is an aqueous solution.

Now the last set of words I'll tell you because we might as well while we're talking about this, and there's no hard cut off here. But if I have a lot of solute here, we tend to say that it is concentrated, and if we have very little solute here, we tend to say that it is dilute.

So I will leave you there. I've just thrown a lot of terminology at you, but hopefully this helps you understand some of these terms like solutions, homogeneous mixtures, and aqueous solutions a little bit better.