 Okay, in the case of multiple solute solutions, for the most part these are usually done following a protocol or a recipe. So we're just going to go over a couple examples of how that protocol might look and the steps you might have to take if you see a protocol that tells you to prepare a multiple solute solution in these ways. One example of how a protocol might look is it might tell you that you want 5 mLs of a one molar magnesium chloride solution, 10 mLs of a .4% thymidine solution, and 25 mLs of a 20% glucose solution. So in order to do that, you would have to make one molar magnesium chloride 5 mLs. You'd have to make .4% thymidine, and you'd have to make 20% glucose. And then you could take 5 mLs of one molar magnesium chloride, 10 mLs of the thymidine, and 25 mLs of the glucose, and then add them together to have your final solution. Your final solution is going to have a total volume of 40 mLs. So that's one example. It might just spell it out for you, but you would have to make the stock solutions to be able to make this combination. Another example is oftentimes you'll have a solution called PBS, Phosphate Buffered Saline. If you look on, if you just Google PBS, Phosphate Buffered Saline, you're going to see a lot of different solutions, a lot of different kind of twists and turns about how people make a PBS solution of it. But if you're given these weights, 7.5 grams of sodium chloride, 1.15 grams of Na2HPO4, 0.2 grams of KH2PO4, and you know that you're supposed to bring to a final volume of one liter, you can add these solids into less than one liter. You're going to make sure that they dissolve because that's going to change the volume before you add that final volume. Another note is that sometimes with PBS, you may be asked for a particular pH of the solution, and so what you'd have to do is make up a partial volume and bring it over to your pH meter and add either acid or base to get it to the right pH. So you don't want to have the volume already at one liter when you do that because you're going to have to add volume by adding acid or base. So it's important if you're going to have to bring a solution to a particular pH that you dissolve the weights that you've been asked to dissolve in a partial volume, not in the final volume. Another example, you may be asked for a final volume or you may be that you're just asked to make a solution that's 0.1 molar tris, 0.01 molar EDTA, and 1% SDS. So if they're not giving you a final volume, you can determine that you'd like to make a liter or half a liter, or if you have a final volume, then obviously you're going to make sure that you understand the concentrations in terms of that final volume. So for this solution, you'd need to determine the molecular weight of tris so that you know how to make a 0.1 molar final volume of tris. You'd have to do the same for EDTA so that you could make the final liter of solution that you have be 0.01 molar EDTA, and you would be able to know that 10 ml is 1% of 1 liter, so you'd need to add 10 ml of SDS. So the thing to remember with something like this is that this concentration, this 0.1 molar tris concentration is independent of the concentrations of the other solutes. So you have to make sure that it's 0.1 moles per liter of tris, so if you're making a liter, you need to add 0.1 moles of tris. So you can kind of ignore what else is going on and deal with each piece separately, and then at the end, you would bring it up to a final volume of 1 liter.