 Okay, so when we're working with solutions, we have lots of different ways that concentrations are expressed. So we just wanted to talk quickly about the different concentration expressions for solutions. One of these is percent solutions. So percent solutions, as all with all percents, are per 100. If you're given a volume-to-volume concentration, so sometimes that's expressed with a V over a V in parentheses after, that's telling you that it's a liquid being added to a liquid. And so say we're given that we want a 5% volume-to-volume solution. We know that 5mLs out of 100mLs is our 5%. And so we'll add 5mLs and bring to volume of 100mLs to get a 5% volume-to-volume. Weight-to-volume is very similar. It's expressed with W over V. So if you're given that you need a 7% weight-to-volume you know that you need 7 grams out of 100 grams. But if you're doing an aqueous solution, a water solution, water is 100 grams in 100 mLs because it's 1 gram per mL. And so you can just say that this is 7 grams in 100 mLs if you're dissolving in water. And again, you bring to a final volume of 100 mLs to get a 7% weight-to-volume solution. Parts is another way that concentration is expressed with solutions. It's expressed less often this way in the lab, but we just want to be familiar with it so we understand. We might see 3 to 2 to 1 ethylene to chloroform isoamyl alcohol. And that tells us that we want 3 parts ethylene plus 2 parts chloroform and 1 part isoamyl alcohol. And so you're going to have 6 parts total. And so sometimes they tell you what the final volume needs to be, but sometimes you just get that you need parts 3 to 2 to 1. And so you could add 30 mLs of ethylene, 20 mLs of chloroform, excuse me, and 10 mLs of isoamyl alcohol for a final volume of 60 mLs. And that would give you 3 to 2 to 1. Molarity we've talked a lot about, but this is just a quick refresher. It's moles per liter, so if you're given a solution concentration of 3 molar, it's 3 moles in 1 liter. This is a kind of different notation we sometimes call this direct notation. And it's where you're just given an amount and a volume. So if we want to have a concentration of 20 mG per mL, that's an amount, 20 mG in a volume, 1 mL. If you only want 1 mL of the solution, you would just add 20 mG and bring to a final volume of 1 mL. But if you want 100 mLs, you're going to multiply the concentration by the final volume, and then you'll know how much to add. So it's 2,000 mG, but 2,000 mG is 2 g, and then you would bring to volume 100 mLs. So that's direct notation. That's just another way that you might be given a concentration that you have to deal with in this lab in solutions.