 Okay, we're going to give a brief introduction into solutions and dilutions. We're going to talk about some definitions of some terms that you'll need to know when dealing with solutions and dilutions. And one of those terms is concentration. So concentration refers to the strength of a solution. And in general terms, you talk about this in your day-to-day life when you talk about something like, oh gosh, this coffee is really weak or this tea is too strong. That tells you how strong, how concentrated your coffee or tea are. We're going to talk about it in a little bit more scientific terms. We're going to call concentration the amount of solute dissolved in a given volume of solvent. And we'll talk in just a minute about the definitions of solvent and solute. But first I just want to talk about some measures of concentration. So capital M is the measure of concentration, and we've talked before about that being a measure of molarity. And molarity is moles of solute per liter of solvent. Another way that we might see concentration expressed is mass to volume. So for instance, if you have milligrams per milliliter concentration or grams per liter concentration, those are both mass to volume expressed concentrations. You might also see concentration expressed as a percent. It's a 40% ethylene glycol solution that gives you a concentration. One other way that we're going to see concentration expressed in this course and in the lab is by using x. So you might see something referred to as say a 50x solution. And this especially comes into play when we're talking about dilutions. When we're talking about dilutions, we're going to see a 50x solution, which means that that solution needs to be diluted 1 to 50 in order to get to a 1x solution. This is only useful if the 1x is related to something. So we have to know what the concentration is at 1x expressed in some other way, otherwise we don't know how strong to make a 50x solution in order to be diluted down to a 1x. So that's something that you'll have to pay attention to in the lab. You'll have to have some sort of procedure or recipe, if you will, to tell you how to make either a 50x solution or to tell you how to make the 1x that you then can translate into how to make the 50x. So you'll also need to know the definition of solution to work with solutions and dilutions. And this may look like a complicated definition when you first look at it, but we'll break it down a little bit. It's a homogenous mixture of two or more substances. So homogenous, if you look at the root homo, means the same, right? So a homogenous mixture is the same throughout. So if you take a sample from the middle of a homogenous mixture and a sample from the top of a homogenous mixture, those are going to be the same. Everything present in them will be the same concentration, the same proportions. So it's a mixture of two or more substances. Those two or more substances are the solute and the solvent. So if there's only one solute and one solvent, you only have two. If you have more than two substances in your solution, they're going to be more than one solute. You're always just going to have one solvent. It's also important to note that they are dissolved in a solution. So if you have a solute and it's not dissolving in the solvent, it's merely mixing with it. That's what we would consider a suspension. And those are some things we'll talk about later. So if we look at solutes dissolved in solvent, we're talking about a solution. And so the solute, black here, the solute or solutes are the substances being dissolved. And the solvent is the substance that solutes are dissolved in. So if you think about a salt water solution or a sugar water solution, the salt or sugar are the solutes and the water is the solvent. And so that brings us to the case where water is the solvent, those kinds of solutions are referred to as aqueous solutions. So an aqueous solution, if you see that word or you see anything referred to as an aqueous solution, that just means you're using water as your solvent. So there's one more term we have to talk about when we talk about solutions and dilutions. And that is dilution. So this is, again, going to seem like a kind of complicated definition, but we're going to talk about it in everyday terms so that you understand it. It's increasing the proportion of solvent to solute, thereby decreasing the concentration of solute per volume. So say you have a mug of coffee, and we're going to make this mug of coffee really strong. So that's really black coffee, it's really strong. So you want to dilute it. In order to dilute it, you're going to add some hot water. So you would be adding solvent, because hot water is what coffee is dissolved in. In order to make this coffee a little bit weaker, you're going to change the concentration. Now it's going to increase the total volume. So really if your strong coffee goes all the way up to the top of the mug, you obviously can't add hot water because it'll overflow the mug. If you add your hot water because the coffee hasn't made it all the way up to the top, then what you're going to get is coffee that's a little bit, there's a little bit more of it, but it's a little bit weaker. That's because the proportion of solvent to solute has increased. There's more solvent, but the same amount of solute. So the concentration of solute per volume, there's the same amount of solute, but there's more volume, has decreased. And so that's a dilution. And so you've diluted your coffee by adding more solvent, and then hopefully you can drink it.